atsamd5x: add SPI.TxN()

This makes it possible to assign I2C objects (machine.I2C0,
machine.I2C1, etc.) without needing to take a pointer.

This is important especially in the future when I2C may be driven using
DMA and the machine.I2C type needs to store some state.

Makefile

@@ -107,7 +107,10 @@ fmt-check:
 	@unformatted=$$(gofmt -l $(FMT_PATHS)); [ -z "$$unformatted" ] && exit 0; echo "Unformatted:"; for fn in $$unformatted; do echo "  $$fn"; done; exit 1
 
 
-gen-device: gen-device-avr gen-device-esp gen-device-nrf gen-device-sam gen-device-sifive gen-device-stm32 gen-device-kendryte gen-device-nxp
+gen-device: gen-device-avr gen-device-esp gen-device-nrf gen-device-sam gen-device-sifive gen-device-kendryte gen-device-nxp
+ifneq ($(STM32), 0)
+gen-device: gen-device-stm32
+endif
 
 gen-device-avr:
 	@if [ ! -e lib/avr/README.md ]; then echo "Submodules have not been downloaded. Please download them using:\n  git submodule update --init"; exit 1; fi
@@ -257,8 +260,6 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10031            examples/blinky1
 	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=bluepill            examples/blinky1
-	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=reelboard           examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=reelboard           examples/blinky2
@@ -267,6 +268,10 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10056            examples/blinky2
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pca10059            examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pca10059            examples/blinky2
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=itsybitsy-m0        examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=feather-m0          examples/blinky1
@@ -275,14 +280,6 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=circuitplay-express examples/blinky1
 	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=stm32f4disco        examples/blinky1
-	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=stm32f4disco        examples/blinky2
-	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=stm32f4disco-1      examples/blinky1
-	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=feather-stm32f405   examples/blinky1
-	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=circuitplay-bluefruit examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=circuitplay-express examples/i2s
@@ -307,12 +304,8 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=particle-xenon      examples/blinky1
 	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=nucleo-f103rb       examples/blinky1
-	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pinetime-devkit0    examples/blinky1
 	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=lgt92    examples/blinky1
-	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=x9pro               examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10056-s140v7     examples/blinky1
@@ -339,10 +332,6 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=teensy36            examples/blinky1
 	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=nucleo-f722ze       examples/blinky1
-	@$(MD5SUM) test.hex
-	$(TINYGO) build -size short -o test.hex -target=nucleo-l552ze       examples/blinky1
-	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=p1am-100            examples/blinky1
 	@$(MD5SUM) test.hex
 	# test pwm
@@ -354,6 +343,28 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pyportal            examples/pwm
 	@$(MD5SUM) test.hex
+ifneq ($(STM32), 0)
+	$(TINYGO) build -size short -o test.hex -target=bluepill            examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=feather-stm32f405   examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=lgt92               examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-f103rb       examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-f722ze       examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-l432kc       examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-l552ze       examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=stm32f4disco        examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=stm32f4disco        examples/blinky2
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=stm32f4disco-1      examples/blinky1
+	@$(MD5SUM) test.hex
+endif
 ifneq ($(AVR), 0)
 	$(TINYGO) build -size short -o test.hex -target=atmega1284p         examples/serial
 	@$(MD5SUM) test.hex
@@ -394,6 +405,7 @@ endif
 	$(TINYGO) build -size short -o test.hex -target=pca10040 -opt=0     ./testdata/stdlib.go
 	@$(MD5SUM) test.hex
 
+
 wasmtest:
 	$(GO) test ./tests/wasm
 

compileopts/target.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"reflect"
 	"runtime"
@@ -42,7 +43,7 @@ type TargetSpec struct {
 	ExtraFiles       []string `json:"extra-files"`
 	Emulator         []string `json:"emulator" override:"copy"` // inherited Emulator must not be append
 	FlashCommand     string   `json:"flash-command"`
-	GDB              string   `json:"gdb"`
+	GDB              []string `json:"gdb"`
 	PortReset        string   `json:"flash-1200-bps-reset"`
 	FlashMethod      string   `json:"flash-method"`
 	FlashVolume      string   `json:"msd-volume-name"`
@@ -240,7 +241,7 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 		Compiler:  "clang",
 		Linker:    "cc",
 		CFlags:    []string{"--target=" + triple},
-		GDB:       "gdb",
+		GDB:       []string{"gdb"},
 		PortReset: "false",
 	}
 	if goos == "darwin" {
@@ -253,7 +254,7 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 	}
 	if goarch != runtime.GOARCH {
 		// Some educated guesses as to how to invoke helper programs.
-		spec.GDB = "gdb-multiarch"
+		spec.GDB = []string{"gdb-multiarch"}
 		if goarch == "arm" && goos == "linux" {
 			spec.CFlags = append(spec.CFlags, "--sysroot=/usr/arm-linux-gnueabihf")
 			spec.Linker = "arm-linux-gnueabihf-gcc"
@@ -271,3 +272,17 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 	}
 	return &spec, nil
 }
+
+// LookupGDB looks up a gdb executable.
+func (spec *TargetSpec) LookupGDB() (string, error) {
+	if len(spec.GDB) == 0 {
+		return "", errors.New("gdb not configured in the target specification")
+	}
+	for _, d := range spec.GDB {
+		_, err := exec.LookPath(d)
+		if err == nil {
+			return d, nil
+		}
+	}
+	return "", errors.New("no gdb found configured in the target specification (" + strings.Join(spec.GDB, ", ") + ")")
+}

compiler/asserts.go

@@ -159,6 +159,9 @@ func (b *builder) createNilCheck(inst ssa.Value, ptr llvm.Value, blockPrefix str
 	}
 
 	switch inst := inst.(type) {
+	case *ssa.Alloc:
+		// An alloc is never nil.
+		return
 	case *ssa.IndexAddr:
 		// This pointer is the result of an index operation into a slice or
 		// array. Such slices/arrays are already bounds checked so the pointer

compiler/compiler.go

@@ -23,7 +23,7 @@ import (
 // Version of the compiler pacakge. Must be incremented each time the compiler
 // package changes in a way that affects the generated LLVM module.
 // This version is independent of the TinyGo version number.
-const Version = 1
+const Version = 5 // last change: add method set to interface types
 
 func init() {
 	llvm.InitializeAllTargets()
@@ -781,6 +781,12 @@ func (b *builder) createFunction() {
 		b.llvmFn.SetVisibility(llvm.HiddenVisibility)
 		b.llvmFn.SetUnnamedAddr(true)
 	}
+	if b.info.exported && strings.HasPrefix(b.Triple, "wasm") {
+		// Set the exported name. This is necessary for WebAssembly because
+		// otherwise the function is not exported.
+		functionAttr := b.ctx.CreateStringAttribute("wasm-export-name", b.info.linkName)
+		b.llvmFn.AddFunctionAttr(functionAttr)
+	}
 
 	// Some functions have a pragma controlling the inlining level.
 	switch b.info.inline {

compiler/compiler_test.go

@@ -4,7 +4,6 @@ import (
 	"flag"
 	"go/types"
 	"io/ioutil"
-	"regexp"
 	"strconv"
 	"strings"
 	"testing"
@@ -20,6 +19,19 @@ var flagUpdate = flag.Bool("update", false, "update tests based on test output")
 // Basic tests for the compiler. Build some Go files and compare the output with
 // the expected LLVM IR for regression testing.
 func TestCompiler(t *testing.T) {
+	// Check LLVM version.
+	llvmMajor, err := strconv.Atoi(strings.SplitN(llvm.Version, ".", 2)[0])
+	if err != nil {
+		t.Fatal("could not parse LLVM version:", llvm.Version)
+	}
+	if llvmMajor < 11 {
+		// It is likely this version needs to be bumped in the future.
+		// The goal is to at least test the LLVM version that's used by default
+		// in TinyGo and (if possible without too many workarounds) also some
+		// previous versions.
+		t.Skip("compiler tests require LLVM 11 or above, got LLVM ", llvm.Version)
+	}
+
 	target, err := compileopts.LoadTarget("i686--linux")
 	if err != nil {
 		t.Fatal("failed to load target:", err)
@@ -47,7 +59,9 @@ func TestCompiler(t *testing.T) {
 		"basic.go",
 		"pointer.go",
 		"slice.go",
+		"string.go",
 		"float.go",
+		"interface.go",
 	}
 
 	for _, testCase := range tests {
@@ -108,8 +122,6 @@ func TestCompiler(t *testing.T) {
 	}
 }
 
-var alignRegexp = regexp.MustCompile(", align [0-9]+$")
-
 // fuzzyEqualIR returns true if the two LLVM IR strings passed in are roughly
 // equal. That means, only relevant lines are compared (excluding comments
 // etc.).
@@ -121,15 +133,6 @@ func fuzzyEqualIR(s1, s2 string) bool {
 	}
 	for i, line1 := range lines1 {
 		line2 := lines2[i]
-		match1 := alignRegexp.MatchString(line1)
-		match2 := alignRegexp.MatchString(line2)
-		if match1 != match2 {
-			// Only one of the lines has the align keyword. Remove it.
-			// This is a change to make the test work in both LLVM 10 and LLVM
-			// 11 (LLVM 11 appears to automatically add alignment everywhere).
-			line1 = alignRegexp.ReplaceAllString(line1, "")
-			line2 = alignRegexp.ReplaceAllString(line2, "")
-		}
 		if line1 != line2 {
 			return false
 		}
@@ -143,12 +146,6 @@ func fuzzyEqualIR(s1, s2 string) bool {
 // stripped out.
 func filterIrrelevantIRLines(lines []string) []string {
 	var out []string
-	llvmVersion, err := strconv.Atoi(strings.Split(llvm.Version, ".")[0])
-	if err != nil {
-		// Note: this should never happen and if it does, it will always happen
-		// for a particular build because llvm.Version is a constant.
-		panic(err)
-	}
 	for _, line := range lines {
 		line = strings.Split(line, ";")[0]    // strip out comments/info
 		line = strings.TrimRight(line, "\r ") // drop '\r' on Windows and remove trailing spaces from comments
@@ -158,15 +155,6 @@ func filterIrrelevantIRLines(lines []string) []string {
 		if strings.HasPrefix(line, "source_filename = ") {
 			continue
 		}
-		if llvmVersion < 10 && strings.HasPrefix(line, "attributes ") {
-			// Ignore attribute groups. These may change between LLVM versions.
-			// Right now test outputs are for LLVM 10.
-			continue
-		}
-		if llvmVersion < 10 && strings.HasPrefix(line, "target datalayout ") {
-			// Ignore the target layout. This may change between LLVM versions.
-			continue
-		}
 		out = append(out, line)
 	}
 	return out

compiler/interface.go

@@ -24,16 +24,7 @@ import (
 func (b *builder) createMakeInterface(val llvm.Value, typ types.Type, pos token.Pos) llvm.Value {
 	itfValue := b.emitPointerPack([]llvm.Value{val})
 	itfTypeCodeGlobal := b.getTypeCode(typ)
-	itfMethodSetGlobal := b.getTypeMethodSet(typ)
-	itfConcreteTypeGlobal := b.mod.NamedGlobal("typeInInterface:" + itfTypeCodeGlobal.Name())
-	if itfConcreteTypeGlobal.IsNil() {
-		typeInInterface := b.getLLVMRuntimeType("typeInInterface")
-		itfConcreteTypeGlobal = llvm.AddGlobal(b.mod, typeInInterface, "typeInInterface:"+itfTypeCodeGlobal.Name())
-		itfConcreteTypeGlobal.SetInitializer(llvm.ConstNamedStruct(typeInInterface, []llvm.Value{itfTypeCodeGlobal, itfMethodSetGlobal}))
-		itfConcreteTypeGlobal.SetGlobalConstant(true)
-		itfConcreteTypeGlobal.SetLinkage(llvm.LinkOnceODRLinkage)
-	}
-	itfTypeCode := b.CreatePtrToInt(itfConcreteTypeGlobal, b.uintptrType, "")
+	itfTypeCode := b.CreatePtrToInt(itfTypeCodeGlobal, b.uintptrType, "")
 	itf := llvm.Undef(b.getLLVMRuntimeType("_interface"))
 	itf = b.CreateInsertValue(itf, itfTypeCode, 0, "")
 	itf = b.CreateInsertValue(itf, itfValue, 1, "")
@@ -54,6 +45,7 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 		// reflect lowering simpler.
 		var references llvm.Value
 		var length int64
+		var methodSet llvm.Value
 		switch typ := typ.(type) {
 		case *types.Named:
 			references = c.getTypeCode(typ.Underlying())
@@ -70,15 +62,26 @@ func (c *compilerContext) getTypeCode(typ types.Type) llvm.Value {
 			// Take a pointer to the typecodeID of the first field (if it exists).
 			structGlobal := c.makeStructTypeFields(typ)
 			references = llvm.ConstBitCast(structGlobal, global.Type())
+		case *types.Interface:
+			methodSetGlobal := c.getInterfaceMethodSet(typ)
+			references = llvm.ConstBitCast(methodSetGlobal, global.Type())
 		}
-		if !references.IsNil() {
+		if _, ok := typ.Underlying().(*types.Interface); !ok {
+			methodSet = c.getTypeMethodSet(typ)
+		}
+		if !references.IsNil() || length != 0 || !methodSet.IsNil() {
 			// Set the 'references' field of the runtime.typecodeID struct.
 			globalValue := llvm.ConstNull(global.Type().ElementType())
-			globalValue = llvm.ConstInsertValue(globalValue, references, []uint32{0})
+			if !references.IsNil() {
+				globalValue = llvm.ConstInsertValue(globalValue, references, []uint32{0})
+			}
 			if length != 0 {
 				lengthValue := llvm.ConstInt(c.uintptrType, uint64(length), false)
 				globalValue = llvm.ConstInsertValue(globalValue, lengthValue, []uint32{1})
 			}
+			if !methodSet.IsNil() {
+				globalValue = llvm.ConstInsertValue(globalValue, methodSet, []uint32{2})
+			}
 			global.SetInitializer(globalValue)
 			global.SetLinkage(llvm.LinkOnceODRLinkage)
 		}
@@ -103,8 +106,8 @@ func (c *compilerContext) makeStructTypeFields(typ *types.Struct) llvm.Value {
 		fieldName.SetLinkage(llvm.PrivateLinkage)
 		fieldName.SetUnnamedAddr(true)
 		fieldName = llvm.ConstGEP(fieldName, []llvm.Value{
-			llvm.ConstInt(llvm.Int32Type(), 0, false),
-			llvm.ConstInt(llvm.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+			llvm.ConstInt(c.ctx.Int32Type(), 0, false),
 		})
 		fieldGlobalValue = llvm.ConstInsertValue(fieldGlobalValue, fieldName, []uint32{1})
 		if typ.Tag(i) != "" {
@@ -112,8 +115,8 @@ func (c *compilerContext) makeStructTypeFields(typ *types.Struct) llvm.Value {
 			fieldTag.SetLinkage(llvm.PrivateLinkage)
 			fieldTag.SetUnnamedAddr(true)
 			fieldTag = llvm.ConstGEP(fieldTag, []llvm.Value{
-				llvm.ConstInt(llvm.Int32Type(), 0, false),
-				llvm.ConstInt(llvm.Int32Type(), 0, false),
+				llvm.ConstInt(c.ctx.Int32Type(), 0, false),
+				llvm.ConstInt(c.ctx.Int32Type(), 0, false),
 			})
 			fieldGlobalValue = llvm.ConstInsertValue(fieldGlobalValue, fieldTag, []uint32{2})
 		}
@@ -186,7 +189,7 @@ func getTypeCodeName(t types.Type) string {
 	case *types.Interface:
 		methods := make([]string, t.NumMethods())
 		for i := 0; i < t.NumMethods(); i++ {
-			methods[i] = getTypeCodeName(t.Method(i).Type())
+			methods[i] = t.Method(i).Name() + ":" + getTypeCodeName(t.Method(i).Type())
 		}
 		return "interface:" + "{" + strings.Join(methods, ",") + "}"
 	case *types.Map:
@@ -338,10 +341,16 @@ func (b *builder) createTypeAssert(expr *ssa.TypeAssert) llvm.Value {
 		commaOk = b.createRuntimeCall("interfaceImplements", []llvm.Value{actualTypeNum, methodSet}, "")
 
 	} else {
+		globalName := "reflect/types.type:" + getTypeCodeName(expr.AssertedType) + "$id"
+		assertedTypeCodeGlobal := b.mod.NamedGlobal(globalName)
+		if assertedTypeCodeGlobal.IsNil() {
+			// Create a new typecode global.
+			assertedTypeCodeGlobal = llvm.AddGlobal(b.mod, b.ctx.Int8Type(), globalName)
+			assertedTypeCodeGlobal.SetGlobalConstant(true)
+		}
 		// Type assert on concrete type.
 		// Call runtime.typeAssert, which will be lowered to a simple icmp or
 		// const false in the interface lowering pass.
-		assertedTypeCodeGlobal := b.getTypeCode(expr.AssertedType)
 		commaOk = b.createRuntimeCall("typeAssert", []llvm.Value{actualTypeNum, assertedTypeCodeGlobal}, "typecode")
 	}
 

compiler/sizes.go

@@ -150,6 +150,9 @@ func (s *stdSizes) Sizeof(T types.Type) int64 {
 		return s.PtrSize * 2
 	case *types.Pointer:
 		return s.PtrSize
+	case *types.Signature:
+		// Func values in TinyGo are two words in size.
+		return s.PtrSize * 2
 	default:
 		panic("unknown type: " + t.String())
 	}

compiler/testdata/interface.go

@@ -0,0 +1,54 @@
+// This file tests interface types and interface builtins.
+
+package main
+
+// Test interface construction.
+
+func simpleType() interface{} {
+	return 0
+}
+
+func pointerType() interface{} {
+	// Pointers have an element type, in this case int.
+	var v *int
+	return v
+}
+
+func interfaceType() interface{} {
+	// Interfaces can exist in interfaces, but only indirectly (through
+	// pointers).
+	var v *error
+	return v
+}
+
+func anonymousInterfaceType() interface{} {
+	var v *interface {
+		String() string
+	}
+	return v
+}
+
+// Test interface builtins.
+
+func isInt(itf interface{}) bool {
+	_, ok := itf.(int)
+	return ok
+}
+
+func isError(itf interface{}) bool {
+	// Interface assert on (builtin) named interface type.
+	_, ok := itf.(error)
+	return ok
+}
+
+func isStringer(itf interface{}) bool {
+	// Interface assert on anonymous interface type.
+	_, ok := itf.(interface {
+		String() string
+	})
+	return ok
+}
+
+func callErrorMethod(itf error) string {
+	return itf.Error()
+}

compiler/testdata/interface.ll

@@ -0,0 +1,100 @@
+; ModuleID = 'interface.go'
+source_filename = "interface.go"
+target datalayout = "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i686--linux"
+
+%runtime.typecodeID = type { %runtime.typecodeID*, i32, %runtime.interfaceMethodInfo* }
+%runtime.interfaceMethodInfo = type { i8*, i32 }
+%runtime._interface = type { i32, i8* }
+%runtime._string = type { i8*, i32 }
+
+@"reflect/types.type:basic:int" = linkonce_odr constant %runtime.typecodeID zeroinitializer
+@"reflect/types.type:pointer:basic:int" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:basic:int", i32 0, %runtime.interfaceMethodInfo* null }
+@"reflect/types.type:pointer:named:error" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:named:error", i32 0, %runtime.interfaceMethodInfo* null }
+@"reflect/types.type:named:error" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:interface:{Error:func:{}{basic:string}}", i32 0, %runtime.interfaceMethodInfo* null }
+@"reflect/types.type:interface:{Error:func:{}{basic:string}}" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* bitcast ([1 x i8*]* @"reflect/types.interface:interface{Error() string}$interface" to %runtime.typecodeID*), i32 0, %runtime.interfaceMethodInfo* null }
+@"func Error() string" = external constant i8
+@"reflect/types.interface:interface{Error() string}$interface" = linkonce_odr constant [1 x i8*] [i8* @"func Error() string"]
+@"reflect/types.type:pointer:interface:{String:func:{}{basic:string}}" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:interface:{String:func:{}{basic:string}}", i32 0, %runtime.interfaceMethodInfo* null }
+@"reflect/types.type:interface:{String:func:{}{basic:string}}" = linkonce_odr constant %runtime.typecodeID { %runtime.typecodeID* bitcast ([1 x i8*]* @"reflect/types.interface:interface{String() string}$interface" to %runtime.typecodeID*), i32 0, %runtime.interfaceMethodInfo* null }
+@"func String() string" = external constant i8
+@"reflect/types.interface:interface{String() string}$interface" = linkonce_odr constant [1 x i8*] [i8* @"func String() string"]
+@"reflect/types.type:basic:int$id" = external constant i8
+@"error$interface" = linkonce_odr constant [1 x i8*] [i8* @"func Error() string"]
+
+declare noalias nonnull i8* @runtime.alloc(i32, i8*, i8*)
+
+define hidden void @main.init(i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret void
+}
+
+define hidden %runtime._interface @main.simpleType(i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret %runtime._interface { i32 ptrtoint (%runtime.typecodeID* @"reflect/types.type:basic:int" to i32), i8* null }
+}
+
+define hidden %runtime._interface @main.pointerType(i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret %runtime._interface { i32 ptrtoint (%runtime.typecodeID* @"reflect/types.type:pointer:basic:int" to i32), i8* null }
+}
+
+define hidden %runtime._interface @main.interfaceType(i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret %runtime._interface { i32 ptrtoint (%runtime.typecodeID* @"reflect/types.type:pointer:named:error" to i32), i8* null }
+}
+
+define hidden %runtime._interface @main.anonymousInterfaceType(i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret %runtime._interface { i32 ptrtoint (%runtime.typecodeID* @"reflect/types.type:pointer:interface:{String:func:{}{basic:string}}" to i32), i8* null }
+}
+
+define hidden i1 @main.isInt(i32 %itf.typecode, i8* %itf.value, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %typecode = call i1 @runtime.typeAssert(i32 %itf.typecode, i8* nonnull @"reflect/types.type:basic:int$id", i8* undef, i8* null)
+  br i1 %typecode, label %typeassert.ok, label %typeassert.next
+
+typeassert.ok:                                    ; preds = %entry
+  br label %typeassert.next
+
+typeassert.next:                                  ; preds = %typeassert.ok, %entry
+  ret i1 %typecode
+}
+
+declare i1 @runtime.typeAssert(i32, i8* dereferenceable_or_null(1), i8*, i8*)
+
+define hidden i1 @main.isError(i32 %itf.typecode, i8* %itf.value, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %0 = call i1 @runtime.interfaceImplements(i32 %itf.typecode, i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"error$interface", i32 0, i32 0), i8* undef, i8* null)
+  br i1 %0, label %typeassert.ok, label %typeassert.next
+
+typeassert.ok:                                    ; preds = %entry
+  br label %typeassert.next
+
+typeassert.next:                                  ; preds = %typeassert.ok, %entry
+  ret i1 %0
+}
+
+declare i1 @runtime.interfaceImplements(i32, i8** dereferenceable_or_null(4), i8*, i8*)
+
+define hidden i1 @main.isStringer(i32 %itf.typecode, i8* %itf.value, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %0 = call i1 @runtime.interfaceImplements(i32 %itf.typecode, i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"reflect/types.interface:interface{String() string}$interface", i32 0, i32 0), i8* undef, i8* null)
+  br i1 %0, label %typeassert.ok, label %typeassert.next
+
+typeassert.ok:                                    ; preds = %entry
+  br label %typeassert.next
+
+typeassert.next:                                  ; preds = %typeassert.ok, %entry
+  ret i1 %0
+}
+
+define hidden %runtime._string @main.callErrorMethod(i32 %itf.typecode, i8* %itf.value, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %invoke.func = call i32 @runtime.interfaceMethod(i32 %itf.typecode, i8** getelementptr inbounds ([1 x i8*], [1 x i8*]* @"error$interface", i32 0, i32 0), i8* nonnull @"func Error() string", i8* undef, i8* null)
+  %invoke.func.cast = inttoptr i32 %invoke.func to %runtime._string (i8*, i8*, i8*)*
+  %0 = call %runtime._string %invoke.func.cast(i8* %itf.value, i8* undef, i8* undef)
+  ret %runtime._string %0
+}
+
+declare i32 @runtime.interfaceMethod(i32, i8** dereferenceable_or_null(4), i8* dereferenceable_or_null(1), i8*, i8*)

compiler/testdata/slice.go

@@ -7,3 +7,19 @@ func sliceLen(ints []int) int {
 func sliceCap(ints []int) int {
 	return cap(ints)
 }
+
+func sliceElement(ints []int, index int) int {
+	return ints[index]
+}
+
+func sliceAppendValues(ints []int) []int {
+	return append(ints, 1, 2, 3)
+}
+
+func sliceAppendSlice(ints, added []int) []int {
+	return append(ints, added...)
+}
+
+func sliceCopy(dst, src []int) int {
+	return copy(dst, src)
+}

compiler/testdata/slice.ll

@@ -19,3 +19,70 @@ define hidden i32 @main.sliceCap(i32* %ints.data, i32 %ints.len, i32 %ints.cap,
 entry:
   ret i32 %ints.cap
 }
+
+define hidden i32 @main.sliceElement(i32* %ints.data, i32 %ints.len, i32 %ints.cap, i32 %index, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %.not = icmp ult i32 %index, %ints.len
+  br i1 %.not, label %lookup.next, label %lookup.throw
+
+lookup.throw:                                     ; preds = %entry
+  call void @runtime.lookupPanic(i8* undef, i8* null)
+  unreachable
+
+lookup.next:                                      ; preds = %entry
+  %0 = getelementptr inbounds i32, i32* %ints.data, i32 %index
+  %1 = load i32, i32* %0, align 4
+  ret i32 %1
+}
+
+declare void @runtime.lookupPanic(i8*, i8*)
+
+define hidden { i32*, i32, i32 } @main.sliceAppendValues(i32* %ints.data, i32 %ints.len, i32 %ints.cap, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %varargs = call i8* @runtime.alloc(i32 12, i8* undef, i8* null)
+  %0 = bitcast i8* %varargs to i32*
+  store i32 1, i32* %0, align 4
+  %1 = getelementptr inbounds i8, i8* %varargs, i32 4
+  %2 = bitcast i8* %1 to i32*
+  store i32 2, i32* %2, align 4
+  %3 = getelementptr inbounds i8, i8* %varargs, i32 8
+  %4 = bitcast i8* %3 to i32*
+  store i32 3, i32* %4, align 4
+  %append.srcPtr = bitcast i32* %ints.data to i8*
+  %append.new = call { i8*, i32, i32 } @runtime.sliceAppend(i8* %append.srcPtr, i8* nonnull %varargs, i32 %ints.len, i32 %ints.cap, i32 3, i32 4, i8* undef, i8* null)
+  %append.newPtr = extractvalue { i8*, i32, i32 } %append.new, 0
+  %append.newBuf = bitcast i8* %append.newPtr to i32*
+  %append.newLen = extractvalue { i8*, i32, i32 } %append.new, 1
+  %append.newCap = extractvalue { i8*, i32, i32 } %append.new, 2
+  %5 = insertvalue { i32*, i32, i32 } undef, i32* %append.newBuf, 0
+  %6 = insertvalue { i32*, i32, i32 } %5, i32 %append.newLen, 1
+  %7 = insertvalue { i32*, i32, i32 } %6, i32 %append.newCap, 2
+  ret { i32*, i32, i32 } %7
+}
+
+declare { i8*, i32, i32 } @runtime.sliceAppend(i8*, i8*, i32, i32, i32, i32, i8*, i8*)
+
+define hidden { i32*, i32, i32 } @main.sliceAppendSlice(i32* %ints.data, i32 %ints.len, i32 %ints.cap, i32* %added.data, i32 %added.len, i32 %added.cap, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %append.srcPtr = bitcast i32* %ints.data to i8*
+  %append.srcPtr1 = bitcast i32* %added.data to i8*
+  %append.new = call { i8*, i32, i32 } @runtime.sliceAppend(i8* %append.srcPtr, i8* %append.srcPtr1, i32 %ints.len, i32 %ints.cap, i32 %added.len, i32 4, i8* undef, i8* null)
+  %append.newPtr = extractvalue { i8*, i32, i32 } %append.new, 0
+  %append.newBuf = bitcast i8* %append.newPtr to i32*
+  %append.newLen = extractvalue { i8*, i32, i32 } %append.new, 1
+  %append.newCap = extractvalue { i8*, i32, i32 } %append.new, 2
+  %0 = insertvalue { i32*, i32, i32 } undef, i32* %append.newBuf, 0
+  %1 = insertvalue { i32*, i32, i32 } %0, i32 %append.newLen, 1
+  %2 = insertvalue { i32*, i32, i32 } %1, i32 %append.newCap, 2
+  ret { i32*, i32, i32 } %2
+}
+
+define hidden i32 @main.sliceCopy(i32* %dst.data, i32 %dst.len, i32 %dst.cap, i32* %src.data, i32 %src.len, i32 %src.cap, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %copy.dstPtr = bitcast i32* %dst.data to i8*
+  %copy.srcPtr = bitcast i32* %src.data to i8*
+  %copy.n = call i32 @runtime.sliceCopy(i8* %copy.dstPtr, i8* %copy.srcPtr, i32 %dst.len, i32 %src.len, i32 4, i8* undef, i8* null)
+  ret i32 %copy.n
+}
+
+declare i32 @runtime.sliceCopy(i8*, i8*, i32, i32, i32, i8*, i8*)

compiler/testdata/string.go

@@ -0,0 +1,21 @@
+package main
+
+func stringLen(s string) int {
+	return len(s)
+}
+
+func stringIndex(s string, index int) byte {
+	return s[index]
+}
+
+func stringCompareEqual(s1, s2 string) bool {
+	return s1 == s2
+}
+
+func stringCompareUnequal(s1, s2 string) bool {
+	return s1 != s2
+}
+
+func stringCompareLarger(s1, s2 string) bool {
+	return s1 > s2
+}

compiler/testdata/string.ll

@@ -0,0 +1,57 @@
+; ModuleID = 'string.go'
+source_filename = "string.go"
+target datalayout = "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-f64:32:64-f80:32-n8:16:32-S128"
+target triple = "i686--linux"
+
+declare noalias nonnull i8* @runtime.alloc(i32, i8*, i8*)
+
+define hidden void @main.init(i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret void
+}
+
+define hidden i32 @main.stringLen(i8* %s.data, i32 %s.len, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  ret i32 %s.len
+}
+
+define hidden i8 @main.stringIndex(i8* %s.data, i32 %s.len, i32 %index, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %.not = icmp ult i32 %index, %s.len
+  br i1 %.not, label %lookup.next, label %lookup.throw
+
+lookup.throw:                                     ; preds = %entry
+  call void @runtime.lookupPanic(i8* undef, i8* null)
+  unreachable
+
+lookup.next:                                      ; preds = %entry
+  %0 = getelementptr inbounds i8, i8* %s.data, i32 %index
+  %1 = load i8, i8* %0, align 1
+  ret i8 %1
+}
+
+declare void @runtime.lookupPanic(i8*, i8*)
+
+define hidden i1 @main.stringCompareEqual(i8* %s1.data, i32 %s1.len, i8* %s2.data, i32 %s2.len, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %0 = call i1 @runtime.stringEqual(i8* %s1.data, i32 %s1.len, i8* %s2.data, i32 %s2.len, i8* undef, i8* null)
+  ret i1 %0
+}
+
+declare i1 @runtime.stringEqual(i8*, i32, i8*, i32, i8*, i8*)
+
+define hidden i1 @main.stringCompareUnequal(i8* %s1.data, i32 %s1.len, i8* %s2.data, i32 %s2.len, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %0 = call i1 @runtime.stringEqual(i8* %s1.data, i32 %s1.len, i8* %s2.data, i32 %s2.len, i8* undef, i8* null)
+  %1 = xor i1 %0, true
+  ret i1 %1
+}
+
+define hidden i1 @main.stringCompareLarger(i8* %s1.data, i32 %s1.len, i8* %s2.data, i32 %s2.len, i8* %context, i8* %parentHandle) unnamed_addr {
+entry:
+  %0 = call i1 @runtime.stringLess(i8* %s1.data, i32 %s1.len, i8* %s2.data, i32 %s2.len, i8* undef, i8* null)
+  %1 = xor i1 %0, true
+  ret i1 %1
+}
+
+declare i1 @runtime.stringLess(i8*, i32, i8*, i32, i8*, i8*)

interp/interpreter.go

@@ -155,11 +155,8 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				// which case this call won't even get to this point but will
 				// already be emitted in initAll.
 				continue
-			case callFn.name == "(reflect.Type).Elem" || strings.HasPrefix(callFn.name, "runtime.print") || callFn.name == "runtime._panic" || callFn.name == "runtime.hashmapGet":
+			case strings.HasPrefix(callFn.name, "runtime.print") || callFn.name == "runtime._panic" || callFn.name == "runtime.hashmapGet":
 				// These functions should be run at runtime. Specifically:
-				//   * (reflect.Type).Elem is a special function. It should
-				//     eventually be interpreted, but fall back to a runtime call
-				//     for now.
 				//   * Print and panic functions are best emitted directly without
 				//     interpreting them, otherwise we get a ton of putchar (etc.)
 				//     calls.
@@ -280,26 +277,48 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				copy(dstBuf.buf[dst.offset():dst.offset()+nBytes], srcBuf.buf[src.offset():])
 				dstObj.buffer = dstBuf
 				mem.put(dst.index(), dstObj)
+			case callFn.name == "(reflect.rawType).elem":
+				if r.debug {
+					fmt.Fprintln(os.Stderr, indent+"call (reflect.rawType).elem:", operands[1:])
+				}
+				// Extract the type code global from the first parameter.
+				typecodeID := operands[1].toLLVMValue(inst.llvmInst.Operand(0).Type(), &mem).Operand(0)
+
+				// Get the type class.
+				// See also: getClassAndValueFromTypeCode in transform/reflect.go.
+				typecodeName := typecodeID.Name()
+				const prefix = "reflect/types.type:"
+				if !strings.HasPrefix(typecodeName, prefix) {
+					panic("unexpected typecode name: " + typecodeName)
+				}
+				id := typecodeName[len(prefix):]
+				class := id[:strings.IndexByte(id, ':')]
+				value := id[len(class)+1:]
+				if class == "named" {
+					// Get the underlying type.
+					class = value[:strings.IndexByte(value, ':')]
+					value = value[len(class)+1:]
+				}
+
+				// Elem() is only valid for certain type classes.
+				switch class {
+				case "chan", "pointer", "slice", "array":
+					elementType := llvm.ConstExtractValue(typecodeID.Initializer(), []uint32{0})
+					uintptrType := r.mod.Context().IntType(int(mem.r.pointerSize) * 8)
+					locals[inst.localIndex] = r.getValue(llvm.ConstPtrToInt(elementType, uintptrType))
+				default:
+					return nil, mem, r.errorAt(inst, fmt.Errorf("(reflect.Type).Elem() called on %s type", class))
+				}
 			case callFn.name == "runtime.typeAssert":
 				// This function must be implemented manually as it is normally
 				// implemented by the interface lowering pass.
 				if r.debug {
 					fmt.Fprintln(os.Stderr, indent+"typeassert:", operands[1:])
 				}
-				typeInInterfacePtr, err := operands[1].asPointer(r)
-				if err != nil {
-					return nil, mem, r.errorAt(inst, err)
-				}
-				actualType, err := mem.load(typeInInterfacePtr, r.pointerSize).asPointer(r)
-				if err != nil {
-					return nil, mem, r.errorAt(inst, err)
-				}
-				assertedType, err := operands[2].asPointer(r)
-				if err != nil {
-					return nil, mem, r.errorAt(inst, err)
-				}
-				result := assertedType.asRawValue(r).equal(actualType.asRawValue(r))
-				if result {
+				assertedType := operands[2].toLLVMValue(inst.llvmInst.Operand(1).Type(), &mem)
+				actualTypePtrToInt := operands[1].toLLVMValue(inst.llvmInst.Operand(0).Type(), &mem)
+				actualType := actualTypePtrToInt.Operand(0)
+				if actualType.Name()+"$id" == assertedType.Name() {
 					locals[inst.localIndex] = literalValue{uint8(1)}
 				} else {
 					locals[inst.localIndex] = literalValue{uint8(0)}
@@ -310,11 +329,11 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				}
 
 				// Load various values for the interface implements check below.
-				typeInInterfacePtr, err := operands[1].asPointer(r)
+				typecodePtr, err := operands[1].asPointer(r)
 				if err != nil {
 					return nil, mem, r.errorAt(inst, err)
 				}
-				methodSetPtr, err := mem.load(typeInInterfacePtr.addOffset(r.pointerSize), r.pointerSize).asPointer(r)
+				methodSetPtr, err := mem.load(typecodePtr.addOffset(r.pointerSize*2), r.pointerSize).asPointer(r)
 				if err != nil {
 					return nil, mem, r.errorAt(inst, err)
 				}
@@ -349,6 +368,39 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 				}
 				// If assertOk is still 1, the assertion succeeded.
 				locals[inst.localIndex] = literalValue{assertOk}
+			case callFn.name == "runtime.interfaceMethod":
+				// This builtin returns the function (which may be a thunk) to
+				// invoke a method on an interface. It does not call the method.
+				if r.debug {
+					fmt.Fprintln(os.Stderr, indent+"interface method:", operands[1:])
+				}
+
+				// Load the first param, which is the type code (ptrtoint of the
+				// type code global).
+				typecodeID := operands[1].toLLVMValue(inst.llvmInst.Operand(0).Type(), &mem).Operand(0).Initializer()
+
+				// Load the method set, which is part of the typecodeID object.
+				methodSet := llvm.ConstExtractValue(typecodeID, []uint32{2}).Operand(0).Initializer()
+
+				// We don't need to load the interface method set.
+
+				// Load the signature of the to-be-called function.
+				signature := inst.llvmInst.Operand(2)
+
+				// Iterate through all methods, looking for the one method that
+				// should be returned.
+				numMethods := methodSet.Type().ArrayLength()
+				var method llvm.Value
+				for i := 0; i < numMethods; i++ {
+					methodSignature := llvm.ConstExtractValue(methodSet, []uint32{uint32(i), 0})
+					if methodSignature == signature {
+						method = llvm.ConstExtractValue(methodSet, []uint32{uint32(i), 1}).Operand(0)
+					}
+				}
+				if method.IsNil() {
+					return nil, mem, r.errorAt(inst, errors.New("could not find method: "+signature.Name()))
+				}
+				locals[inst.localIndex] = r.getValue(method)
 			case callFn.name == "runtime.hashmapMake":
 				// Create a new map.
 				hashmapPointerType := inst.llvmInst.Type()

interp/memory.go

@@ -1048,7 +1048,7 @@ func (v rawValue) rawLLVMValue(mem *memoryView) llvm.Value {
 				// There are some special pointer types that should be used as a
 				// ptrtoint, so that they can be used in certain optimizations.
 				name := elementType.StructName()
-				if name == "runtime.typeInInterface" || name == "runtime.funcValueWithSignature" {
+				if name == "runtime.typecodeID" || name == "runtime.funcValueWithSignature" {
 					uintptrType := ctx.IntType(int(mem.r.pointerSize) * 8)
 					field = llvm.ConstPtrToInt(field, uintptrType)
 				}

interp/testdata/interface.ll

@@ -1,17 +1,16 @@
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64--linux"
 
-%runtime.typecodeID = type { %runtime.typecodeID*, i64 }
+%runtime.typecodeID = type { %runtime.typecodeID*, i64, %runtime.interfaceMethodInfo* }
 %runtime.interfaceMethodInfo = type { i8*, i64 }
-%runtime.typeInInterface = type { %runtime.typecodeID*, %runtime.interfaceMethodInfo* }
 
 @main.v1 = global i1 0
-@"reflect/types.type:named:main.foo" = private constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:basic:int", i64 0 }
+@"reflect/types.type:named:main.foo" = private constant %runtime.typecodeID { %runtime.typecodeID* @"reflect/types.type:basic:int", i64 0, %runtime.interfaceMethodInfo* null }
+@"reflect/types.type:named:main.foo$id" = external constant i8
 @"reflect/types.type:basic:int" = external constant %runtime.typecodeID
-@"typeInInterface:reflect/types.type:named:main.foo" = private constant %runtime.typeInInterface { %runtime.typecodeID* @"reflect/types.type:named:main.foo", %runtime.interfaceMethodInfo* null }
 
 
-declare i1 @runtime.typeAssert(i64, %runtime.typecodeID*, i8*, i8*)
+declare i1 @runtime.typeAssert(i64, i8*, i8*, i8*)
 
 define void @runtime.initAll() unnamed_addr {
 entry:
@@ -22,7 +21,7 @@ entry:
 define internal void @main.init() unnamed_addr {
 entry:
   ; Test type asserts.
-  %typecode = call i1 @runtime.typeAssert(i64 ptrtoint (%runtime.typeInInterface* @"typeInInterface:reflect/types.type:named:main.foo" to i64), %runtime.typecodeID* @"reflect/types.type:named:main.foo", i8* undef, i8* null)
+  %typecode = call i1 @runtime.typeAssert(i64 ptrtoint (%runtime.typecodeID* @"reflect/types.type:named:main.foo" to i64), i8* @"reflect/types.type:named:main.foo$id", i8* undef, i8* null)
   store i1 %typecode, i1* @main.v1
   ret void
 }

main.go

@@ -344,8 +344,9 @@ func FlashGDB(pkgName string, ocdOutput bool, options *compileopts.Options) erro
 	if err != nil {
 		return err
 	}
-	if config.Target.GDB == "" {
-		return errors.New("gdb not configured in the target specification")
+	gdb, err := config.Target.LookupGDB()
+	if err != nil {
+		return err
 	}
 
 	return builder.Build(pkgName, "", config, func(result builder.BuildResult) error {
@@ -490,7 +491,7 @@ func FlashGDB(pkgName string, ocdOutput bool, options *compileopts.Options) erro
 		for _, cmd := range gdbCommands {
 			params = append(params, "-ex", cmd)
 		}
-		cmd := executeCommand(config.Options, config.Target.GDB, params...)
+		cmd := executeCommand(config.Options, gdb, params...)
 		cmd.Stdin = os.Stdin
 		cmd.Stdout = os.Stdout
 		cmd.Stderr = os.Stderr

main_test.go

@@ -59,7 +59,10 @@ func TestCompiler(t *testing.T) {
 		t.Run("Host", func(t *testing.T) {
 			runPlatTests("", matches, t)
 			if runtime.GOOS == "darwin" {
-				runTest("testdata/libc/env.go", "", t, []string{"ENV1=VALUE1", "ENV2=VALUE2"}...)
+				runTest("testdata/libc/filesystem.go", "", t,
+					nil, nil)
+				runTest("testdata/libc/env.go", "", t,
+					[]string{"ENV1=VALUE1", "ENV2=VALUE2"}, nil)
 			}
 		})
 	}
@@ -107,7 +110,9 @@ func TestCompiler(t *testing.T) {
 
 		t.Run("WASI", func(t *testing.T) {
 			runPlatTests("wasi", matches, t)
-			runTest("testdata/libc/env.go", "wasi", t, []string{"ENV1=VALUE1", "ENV2=VALUE2"}...)
+			runTest("testdata/libc/env.go", "wasi", t,
+				[]string{"--env", "ENV1=VALUE1", "--env", "ENV2=VALUE2"}, nil)
+			runTest("testdata/libc/filesystem.go", "wasi", t, nil, []string{"--dir=."})
 		})
 	}
 }
@@ -119,7 +124,7 @@ func runPlatTests(target string, matches []string, t *testing.T) {
 		path := path // redefine to avoid race condition
 		t.Run(filepath.Base(path), func(t *testing.T) {
 			t.Parallel()
-			runTest(path, target, t)
+			runTest(path, target, t, nil, nil)
 		})
 	}
 }
@@ -136,7 +141,7 @@ func runBuild(src, out string, opts *compileopts.Options) error {
 	return Build(src, out, opts)
 }
 
-func runTest(path, target string, t *testing.T, environmentVars ...string) {
+func runTest(path, target string, t *testing.T, environmentVars []string, additionalArgs []string) {
 	// Get the expected output for this test.
 	txtpath := path[:len(path)-3] + ".txt"
 	if path[len(path)-1] == os.PathSeparator {
@@ -195,7 +200,7 @@ func runTest(path, target string, t *testing.T, environmentVars ...string) {
 			cmd = exec.Command(binary)
 		} else {
 			args := append(spec.Emulator[1:], binary)
-			cmd = exec.Command(spec.Emulator[0], args...)
+			cmd = exec.Command(spec.Emulator[0], append(args, additionalArgs...)...)
 		}
 
 		if len(spec.Emulator) != 0 && spec.Emulator[0] == "wasmtime" {

src/internal/task/task_coroutine.go

@@ -11,7 +11,7 @@ import (
 type rawState uint8
 
 //export llvm.coro.resume
-func (s *rawState) resume()
+func coroResume(*rawState)
 
 type state struct{ *rawState }
 
@@ -20,7 +20,7 @@ func noopState() *rawState
 
 // Resume the task until it pauses or completes.
 func (t *Task) Resume() {
-	t.state.resume()
+	coroResume(t.state.rawState)
 }
 
 // setState is used by the compiler to set the state of the function at the beginning of a function call.

src/machine/board_arduino_nano33_baremetal.go

@@ -32,7 +32,7 @@ func init() {
 
 // I2C on the Arduino Nano 33.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM4_I2CM,
 		SERCOM: 4,
 	}

src/machine/board_circuitplay_express_baremetal.go

@@ -23,12 +23,12 @@ func init() {
 // I2C on the Circuit Playground Express.
 var (
 	// external device
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM5_I2CM,
 		SERCOM: 5,
 	}
 	// internal device
-	I2C1 = I2C{
+	I2C1 = &I2C{
 		Bus:    sam.SERCOM1_I2CM,
 		SERCOM: 1,
 	}

src/machine/board_feather-m0.go

@@ -75,7 +75,7 @@ const (
 
 // I2C on the Feather M0.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM3_I2CM,
 		SERCOM: 3,
 	}

src/machine/board_feather-m4_baremetal.go

@@ -28,7 +28,7 @@ func init() {
 
 // I2C on the Feather M4.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/board_feather-stm32f405.go

@@ -120,19 +120,22 @@ const (
 
 var (
 	UART1 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART3,
-		AltFuncSelector: AF7_USART1_2_3,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART3,
+		TxAltFuncSelector: AF7_USART1_2_3,
+		RxAltFuncSelector: AF7_USART1_2_3,
 	}
 	UART2 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART6,
-		AltFuncSelector: AF8_USART4_5_6,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART6,
+		TxAltFuncSelector: AF8_USART4_5_6,
+		RxAltFuncSelector: AF8_USART4_5_6,
 	}
 	UART3 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART1,
-		AltFuncSelector: AF7_USART1_2_3,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART1,
+		TxAltFuncSelector: AF7_USART1_2_3,
+		RxAltFuncSelector: AF7_USART1_2_3,
 	}
 	UART0 = UART1
 )
@@ -227,15 +230,15 @@ const (
 )
 
 var (
-	I2C1 = I2C{
+	I2C1 = &I2C{
 		Bus:             stm32.I2C1,
 		AltFuncSelector: AF4_I2C1_2_3,
 	}
-	I2C2 = I2C{
+	I2C2 = &I2C{
 		Bus:             stm32.I2C2,
 		AltFuncSelector: AF4_I2C1_2_3,
 	}
-	I2C3 = I2C{
+	I2C3 = &I2C{
 		Bus:             stm32.I2C1,
 		AltFuncSelector: AF4_I2C1_2_3,
 	}

src/machine/board_grandcentral-m4_baremetal.go

@@ -40,11 +40,11 @@ var (
 
 // I2C on the Grand Central M4
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM3_I2CM,
 		SERCOM: 3,
 	}
-	I2C1 = I2C{
+	I2C1 = &I2C{
 		Bus:    sam.SERCOM6_I2CM,
 		SERCOM: 6,
 	}

src/machine/board_hifive1b_baremetal.go

@@ -10,10 +10,3 @@ var (
 		Bus: sifive.QSPI1,
 	}
 )
-
-// I2C on the HiFive1 rev B.
-var (
-	I2C0 = I2C{
-		Bus: sifive.I2C0,
-	}
-)

src/machine/board_itsybitsy-m0.go

@@ -75,7 +75,7 @@ const (
 
 // I2C on the ItsyBitsy M0.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM3_I2CM,
 		SERCOM: 3,
 	}

src/machine/board_itsybitsy-m4_baremetal.go

@@ -28,7 +28,7 @@ func init() {
 
 // I2C on the ItsyBitsy M4.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/board_lgt92.go

@@ -54,16 +54,18 @@ var (
 
 	// Console UART (LPUSART1)
 	UART0 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.LPUART1,
-		AltFuncSelector: 6,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.LPUART1,
+		TxAltFuncSelector: 6,
+		RxAltFuncSelector: 6,
 	}
 
 	// Gps UART
 	UART1 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART1,
-		AltFuncSelector: 0,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART1,
+		TxAltFuncSelector: 0,
+		RxAltFuncSelector: 0,
 	}
 
 	// SPI

src/machine/board_maixbit_baremetal.go

@@ -13,16 +13,3 @@ var (
 		Bus: kendryte.SPI1,
 	}
 )
-
-// I2C on the MAix Bit.
-var (
-	I2C0 = I2C{
-		Bus: kendryte.I2C0,
-	}
-	I2C1 = I2C{
-		Bus: kendryte.I2C1,
-	}
-	I2C2 = I2C{
-		Bus: kendryte.I2C2,
-	}
-)

src/machine/board_matrixportal-m4_baremetal.go

@@ -29,7 +29,7 @@ func init() {
 
 // I2C on the MatrixPortal M4
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM5_I2CM,
 		SERCOM: 5,
 	}

src/machine/board_metro-m4-airlift_baremetal.go

@@ -28,7 +28,7 @@ func init() {
 
 // I2C on the Metro M4.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM5_I2CM,
 		SERCOM: 5,
 	}

src/machine/board_nrf52840-mdk-usb-dongle.go

@@ -44,7 +44,7 @@ const (
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Makerdiary nRF52840 MDK USB Dongle"
-	usb_STRING_MANUFACTURER = "Makerdiary"
+	usb_STRING_MANUFACTURER = "Nordic Semiconductor ASA"
 )
 
 var (

src/machine/board_nrf52840-mdk.go

@@ -39,7 +39,7 @@ const (
 // USB CDC identifiers
 const (
 	usb_STRING_PRODUCT      = "Makerdiary nRF52840 MDK"
-	usb_STRING_MANUFACTURER = "Makerdiary"
+	usb_STRING_MANUFACTURER = "Nordic Semiconductor ASA"
 )
 
 var (

src/machine/board_nucleof722ze.go

@@ -33,9 +33,10 @@ var (
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to USART2.
 	UART0 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART3,
-		AltFuncSelector: UART_ALT_FN,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART3,
+		TxAltFuncSelector: UART_ALT_FN,
+		RxAltFuncSelector: UART_ALT_FN,
 	}
 	UART1 = &UART0
 )
@@ -53,6 +54,15 @@ const (
 
 // I2C pins
 const (
-	SCL_PIN = PB6
-	SDA_PIN = PB7
+	I2C0_SCL_PIN = PB8
+	I2C0_SDA_PIN = PB9
+)
+
+var (
+	// I2C1 is documented, alias to I2C0 as well
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: 4,
+	}
+	I2C0 = I2C1
 )

src/machine/board_nucleol432kc.go

@@ -0,0 +1,56 @@
+// +build nucleol432kc
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
+const (
+	LED         = LED_BUILTIN
+	LED_BUILTIN = LED_GREEN
+	LED_GREEN   = PB3
+)
+
+// UART pins
+const (
+	// PA2 and PA15 are connected to the ST-Link Virtual Com Port (VCP)
+	UART_TX_PIN = PA2
+	UART_RX_PIN = PA15
+)
+
+// I2C pins
+const (
+	// With default solder bridge settings:
+	//    PB6 / Arduino D5 / CN3 Pin 8 is SCL
+	//    PB7 / Arduino D4 / CN3 Pin 7 is SDA
+	I2C0_SCL_PIN = PB6
+	I2C0_SDA_PIN = PB7
+)
+
+var (
+	// USART2 is the hardware serial port connected to the onboard ST-LINK
+	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
+	// Both UART0 and UART1 refer to USART2.
+	UART0 = UART{
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART2,
+		TxAltFuncSelector: 7,
+		RxAltFuncSelector: 3,
+	}
+	UART1 = &UART0
+)
+
+var (
+	// I2C1 is documented, alias to I2C0 as well
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: 4,
+	}
+	I2C0 = I2C1
+)
+
+func init() {
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+}

src/machine/board_nucleol552ze.go

@@ -33,13 +33,28 @@ var (
 	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
 	// Both UART0 and UART1 refer to LPUART1.
 	UART0 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.LPUART1,
-		AltFuncSelector: UART_ALT_FN,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.LPUART1,
+		TxAltFuncSelector: UART_ALT_FN,
+		RxAltFuncSelector: UART_ALT_FN,
 	}
 	UART1 = &UART0
 )
 
+const (
+	I2C0_SCL_PIN = PB8
+	I2C0_SDA_PIN = PB9
+)
+
+var (
+	// I2C1 is documented, alias to I2C0 as well
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: 4,
+	}
+	I2C0 = I2C1
+)
+
 func init() {
 	UART0.Interrupt = interrupt.New(stm32.IRQ_LPUART1, UART0.handleInterrupt)
 }

src/machine/board_p1am-100_baremetal.go

@@ -22,7 +22,7 @@ func init() {
 
 // I2C on the P1AM-100.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM0_I2CM,
 		SERCOM: 0,
 	}

src/machine/board_pca10059.go

@@ -0,0 +1,64 @@
+// +build pca10059
+
+package machine
+
+// The PCA10040 has a low-frequency (32kHz) crystal oscillator on board.
+const HasLowFrequencyCrystal = true
+
+// LEDs on the PCA10059 (nRF52840 dongle)
+const (
+	LED  Pin = LED1
+	LED1 Pin = 6
+	LED2 Pin = 8
+	LED3 Pin = (1 << 5) | 9
+	LED4 Pin = 12
+)
+
+// Buttons on the PCA10059 (nRF52840 dongle)
+const (
+	BUTTON  Pin = BUTTON1
+	BUTTON1 Pin = (1 << 5) | 6
+)
+
+// ADC pins
+const (
+	ADC1 Pin = 2
+	ADC2 Pin = 4
+	ADC3 Pin = 29
+	ADC4 Pin = 31
+)
+
+// UART pins
+const (
+	UART_TX_PIN Pin = NoPin
+	UART_RX_PIN Pin = NoPin
+)
+
+// UART0 is the USB device
+var (
+	UART0 = USB
+)
+
+// I2C pins (unused)
+const (
+	SDA_PIN = NoPin
+	SCL_PIN = NoPin
+)
+
+// SPI pins (unused)
+const (
+	SPI0_SCK_PIN = NoPin
+	SPI0_SDO_PIN = NoPin
+	SPI0_SDI_PIN = NoPin
+)
+
+// USB CDC identifiers
+const (
+	usb_STRING_PRODUCT      = "nRF52840 Dongle"
+	usb_STRING_MANUFACTURER = "Nordic Semiconductor ASA"
+)
+
+var (
+	usb_VID uint16 = 0x1915
+	usb_PID uint16 = 0xCAFE
+)

src/machine/board_pybadge_baremetal.go

@@ -28,7 +28,7 @@ func init() {
 
 // I2C on the ItsyBitsy M4.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/board_pygamer.go

@@ -99,7 +99,7 @@ const (
 
 // I2C on the PyGamer.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/board_pyportal_baremetal.go

@@ -21,7 +21,7 @@ func init() {
 
 // I2C on the PyPortal.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM5_I2CM,
 		SERCOM: 5,
 	}

src/machine/board_qtpy.go

@@ -93,7 +93,7 @@ const (
 
 // I2C on the QT Py M0.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/board_stm32f4disco.go

@@ -28,9 +28,10 @@ const (
 
 var (
 	UART0 = UART{
-		Buffer:          NewRingBuffer(),
-		Bus:             stm32.USART2,
-		AltFuncSelector: AF7_USART1_2_3,
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART2,
+		TxAltFuncSelector: AF7_USART1_2_3,
+		RxAltFuncSelector: AF7_USART1_2_3,
 	}
 	UART1 = &UART0
 )
@@ -73,7 +74,7 @@ const (
 )
 
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:             stm32.I2C1,
 		AltFuncSelector: AF4_I2C1_2_3,
 	}

src/machine/board_trinket.go

@@ -81,7 +81,7 @@ const (
 
 // I2C on the Trinket M0.
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/board_wioterminal_baremetal.go

@@ -29,12 +29,12 @@ func init() {
 
 // I2C on the Wio Terminal
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM4_I2CM,
 		SERCOM: 4,
 	}
 
-	I2C1 = I2C{
+	I2C1 = &I2C{
 		Bus:    sam.SERCOM4_I2CM,
 		SERCOM: 4,
 	}

src/machine/board_xiao.go

@@ -81,7 +81,7 @@ const (
 
 // I2C on the Xiao
 var (
-	I2C0 = I2C{
+	I2C0 = &I2C{
 		Bus:    sam.SERCOM2_I2CM,
 		SERCOM: 2,
 	}

src/machine/i2c.go

@@ -1,4 +1,4 @@
-// +build avr nrf sam stm32,!stm32f7x2,!stm32l5x2,!stm32l0 fe310 k210
+// +build atmega nrf sam stm32,!stm32l0 fe310 k210
 
 package machine
 
@@ -29,7 +29,7 @@ var (
 // Many I2C-compatible devices are organized in terms of registers. This method
 // is a shortcut to easily write to such registers. Also, it only works for
 // devices with 7-bit addresses, which is the vast majority.
-func (i2c I2C) WriteRegister(address uint8, register uint8, data []byte) error {
+func (i2c *I2C) WriteRegister(address uint8, register uint8, data []byte) error {
 	buf := make([]uint8, len(data)+1)
 	buf[0] = register
 	copy(buf[1:], data)
@@ -42,6 +42,6 @@ func (i2c I2C) WriteRegister(address uint8, register uint8, data []byte) error {
 // Many I2C-compatible devices are organized in terms of registers. This method
 // is a shortcut to easily read such registers. Also, it only works for devices
 // with 7-bit addresses, which is the vast majority.
-func (i2c I2C) ReadRegister(address uint8, register uint8, data []byte) error {
+func (i2c *I2C) ReadRegister(address uint8, register uint8, data []byte) error {
 	return i2c.Tx(uint16(address), []byte{register}, data)
 }

src/machine/machine_atmega.go

@@ -9,13 +9,20 @@ import (
 	"unsafe"
 )
 
+// I2C on AVR.
+type I2C struct {
+}
+
+// I2C0 is the only I2C interface on most AVRs.
+var I2C0 *I2C = nil
+
 // I2CConfig is used to store config info for I2C.
 type I2CConfig struct {
 	Frequency uint32
 }
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
@@ -42,7 +49,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 // Tx does a single I2C transaction at the specified address.
 // It clocks out the given address, writes the bytes in w, reads back len(r)
 // bytes and stores them in r, and generates a stop condition on the bus.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 	if len(w) != 0 {
 		i2c.start(uint8(addr), true) // start transmission for writing
 		for _, b := range w {
@@ -63,7 +70,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 }
 
 // start starts an I2C communication session.
-func (i2c I2C) start(address uint8, write bool) {
+func (i2c *I2C) start(address uint8, write bool) {
 	// Clear TWI interrupt flag, put start condition on SDA, and enable TWI.
 	avr.TWCR.Set((avr.TWCR_TWINT | avr.TWCR_TWSTA | avr.TWCR_TWEN))
 
@@ -80,7 +87,7 @@ func (i2c I2C) start(address uint8, write bool) {
 }
 
 // stop ends an I2C communication session.
-func (i2c I2C) stop() {
+func (i2c *I2C) stop() {
 	// Send stop condition.
 	avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWSTO)
 
@@ -90,7 +97,7 @@ func (i2c I2C) stop() {
 }
 
 // writeByte writes a single byte to the I2C bus.
-func (i2c I2C) writeByte(data byte) {
+func (i2c *I2C) writeByte(data byte) {
 	// Write data to register.
 	avr.TWDR.Set(data)
 
@@ -103,7 +110,7 @@ func (i2c I2C) writeByte(data byte) {
 }
 
 // readByte reads a single byte from the I2C bus.
-func (i2c I2C) readByte() byte {
+func (i2c *I2C) readByte() byte {
 	// Clear TWI interrupt flag and enable TWI.
 	avr.TWCR.Set(avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWEA)
 

src/machine/machine_atsamd21.go

@@ -669,7 +669,7 @@ const (
 const i2cTimeout = 1000
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
@@ -725,7 +725,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 }
 
 // SetBaudRate sets the communication speed for the I2C.
-func (i2c I2C) SetBaudRate(br uint32) {
+func (i2c *I2C) SetBaudRate(br uint32) {
 	// Synchronous arithmetic baudrate, via Arduino SAMD implementation:
 	// SystemCoreClock / ( 2 * baudrate) - 5 - (((SystemCoreClock / 1000000) * WIRE_RISE_TIME_NANOSECONDS) / (2 * 1000));
 	baud := CPUFrequency()/(2*br) - 5 - (((CPUFrequency() / 1000000) * riseTimeNanoseconds) / (2 * 1000))
@@ -735,7 +735,7 @@ func (i2c I2C) SetBaudRate(br uint32) {
 // Tx does a single I2C transaction at the specified address.
 // It clocks out the given address, writes the bytes in w, reads back len(r)
 // bytes and stores them in r, and generates a stop condition on the bus.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 	var err error
 	if len(w) != 0 {
 		// send start/address for write
@@ -812,7 +812,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 }
 
 // WriteByte writes a single byte to the I2C bus.
-func (i2c I2C) WriteByte(data byte) error {
+func (i2c *I2C) WriteByte(data byte) error {
 	// Send data byte
 	i2c.Bus.DATA.Set(data)
 
@@ -837,7 +837,7 @@ func (i2c I2C) WriteByte(data byte) error {
 }
 
 // sendAddress sends the address and start signal
-func (i2c I2C) sendAddress(address uint16, write bool) error {
+func (i2c *I2C) sendAddress(address uint16, write bool) error {
 	data := (address << 1)
 	if !write {
 		data |= 1 // set read flag
@@ -857,7 +857,7 @@ func (i2c I2C) sendAddress(address uint16, write bool) error {
 	return nil
 }
 
-func (i2c I2C) signalStop() error {
+func (i2c *I2C) signalStop() error {
 	i2c.Bus.CTRLB.SetBits(wireCmdStop << sam.SERCOM_I2CM_CTRLB_CMD_Pos) // Stop command
 	timeout := i2cTimeout
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
@@ -869,7 +869,7 @@ func (i2c I2C) signalStop() error {
 	return nil
 }
 
-func (i2c I2C) signalRead() error {
+func (i2c *I2C) signalRead() error {
 	i2c.Bus.CTRLB.SetBits(wireCmdRead << sam.SERCOM_I2CM_CTRLB_CMD_Pos) // Read command
 	timeout := i2cTimeout
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
@@ -881,7 +881,7 @@ func (i2c I2C) signalRead() error {
 	return nil
 }
 
-func (i2c I2C) readByte() byte {
+func (i2c *I2C) readByte() byte {
 	for !i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_SB) {
 	}
 	return byte(i2c.Bus.DATA.Get())

src/machine/machine_atsamd51.go

@@ -1104,7 +1104,7 @@ const (
 const i2cTimeout = 1000
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
@@ -1163,7 +1163,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 }
 
 // SetBaudRate sets the communication speed for the I2C.
-func (i2c I2C) SetBaudRate(br uint32) {
+func (i2c *I2C) SetBaudRate(br uint32) {
 	// Synchronous arithmetic baudrate, via Adafruit SAMD51 implementation:
 	// sercom->I2CM.BAUD.bit.BAUD = SERCOM_FREQ_REF / ( 2 * baudrate) - 1 ;
 	baud := SERCOM_FREQ_REF/(2*br) - 1
@@ -1173,7 +1173,7 @@ func (i2c I2C) SetBaudRate(br uint32) {
 // Tx does a single I2C transaction at the specified address.
 // It clocks out the given address, writes the bytes in w, reads back len(r)
 // bytes and stores them in r, and generates a stop condition on the bus.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 	var err error
 	if len(w) != 0 {
 		// send start/address for write
@@ -1250,7 +1250,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 }
 
 // WriteByte writes a single byte to the I2C bus.
-func (i2c I2C) WriteByte(data byte) error {
+func (i2c *I2C) WriteByte(data byte) error {
 	// Send data byte
 	i2c.Bus.DATA.Set(data)
 
@@ -1275,7 +1275,7 @@ func (i2c I2C) WriteByte(data byte) error {
 }
 
 // sendAddress sends the address and start signal
-func (i2c I2C) sendAddress(address uint16, write bool) error {
+func (i2c *I2C) sendAddress(address uint16, write bool) error {
 	data := (address << 1)
 	if !write {
 		data |= 1 // set read flag
@@ -1295,7 +1295,7 @@ func (i2c I2C) sendAddress(address uint16, write bool) error {
 	return nil
 }
 
-func (i2c I2C) signalStop() error {
+func (i2c *I2C) signalStop() error {
 	i2c.Bus.CTRLB.SetBits(wireCmdStop << sam.SERCOM_I2CM_CTRLB_CMD_Pos) // Stop command
 	timeout := i2cTimeout
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
@@ -1307,7 +1307,7 @@ func (i2c I2C) signalStop() error {
 	return nil
 }
 
-func (i2c I2C) signalRead() error {
+func (i2c *I2C) signalRead() error {
 	i2c.Bus.CTRLB.SetBits(wireCmdRead << sam.SERCOM_I2CM_CTRLB_CMD_Pos) // Read command
 	timeout := i2cTimeout
 	for i2c.Bus.SYNCBUSY.HasBits(sam.SERCOM_I2CM_SYNCBUSY_SYSOP) {
@@ -1319,7 +1319,7 @@ func (i2c I2C) signalRead() error {
 	return nil
 }
 
-func (i2c I2C) readByte() byte {
+func (i2c *I2C) readByte() byte {
 	for !i2c.Bus.INTFLAG.HasBits(sam.SERCOM_I2CM_INTFLAG_SB) {
 	}
 	return byte(i2c.Bus.DATA.Get())
@@ -1560,6 +1560,76 @@ func (spi SPI) txrx(tx, rx []byte) {
 	rx[len(rx)-1] = byte(spi.Bus.DATA.Get())
 }
 
+// TxN handles read/write operation for SPI interface. The difference with Tx() is that
+// it repeats the process n times.
+//
+func (spi SPI) TxN(w, r []byte, n int) error {
+	switch {
+	case w == nil:
+		// read only, so write zero and read a result.
+		spi.rxn(r, n)
+	case r == nil:
+		// write only
+		spi.txn(w, n)
+
+	default:
+		// write/read
+		if len(w) != len(r) {
+			return ErrTxInvalidSliceSize
+		}
+
+		spi.txrxn(w, r, n)
+	}
+	return nil
+}
+
+func (spi SPI) txn(tx []byte, n int) {
+	for i := 0; i < len(tx)*n; i++ {
+		for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_DRE) {
+		}
+		spi.Bus.DATA.Set(uint32(tx[i%len(tx)]))
+	}
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_TXC) {
+	}
+
+	// read to clear RXC register
+	for spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+		spi.Bus.DATA.Get()
+	}
+}
+
+func (spi SPI) rxn(rx []byte, n int) {
+	spi.Bus.DATA.Set(0)
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_DRE) {
+	}
+
+	for i := 1; i < len(rx)*n; i++ {
+		spi.Bus.DATA.Set(0)
+		for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+		}
+		rx[(i-1)%len(rx)] = byte(spi.Bus.DATA.Get())
+	}
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+	}
+	rx[len(rx)-1] = byte(spi.Bus.DATA.Get())
+}
+
+func (spi SPI) txrxn(tx, rx []byte, n int) {
+	spi.Bus.DATA.Set(uint32(tx[0]))
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_DRE) {
+	}
+
+	for i := 1; i < len(rx)*n; i++ {
+		spi.Bus.DATA.Set(uint32(tx[i%len(rx)]))
+		for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+		}
+		rx[(i-1)%len(rx)] = byte(spi.Bus.DATA.Get())
+	}
+	for !spi.Bus.INTFLAG.HasBits(sam.SERCOM_SPIM_INTFLAG_RXC) {
+	}
+	rx[len(rx)-1] = byte(spi.Bus.DATA.Get())
+}
+
 // The QSPI peripheral on ATSAMD51 is only available on the following pins
 const (
 	QSPI_SCK   = PB10

src/machine/machine_attiny.go

@@ -1,9 +0,0 @@
-// +build avr,attiny
-
-package machine
-
-// Tx is a dummy implementation. I2C has not been implemented for ATtiny
-// devices.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
-	return nil
-}

src/machine/machine_avr.go

@@ -141,10 +141,3 @@ func (a ADC) Get() uint16 {
 
 	return uint16(avr.ADCL.Get()) | uint16(avr.ADCH.Get())<<8
 }
-
-// I2C on AVR.
-type I2C struct {
-}
-
-// I2C0 is the only I2C interface on most AVRs.
-var I2C0 = I2C{}

src/machine/machine_fe310.go

@@ -5,6 +5,7 @@ package machine
 import (
 	"device/sifive"
 	"runtime/interrupt"
+	"unsafe"
 )
 
 func CPUFrequency() uint32 {
@@ -185,9 +186,13 @@ func (spi SPI) Transfer(w byte) (byte, error) {
 
 // I2C on the FE310-G002.
 type I2C struct {
-	Bus *sifive.I2C_Type
+	Bus sifive.I2C_Type
 }
 
+var (
+	I2C0 = (*I2C)(unsafe.Pointer(sifive.I2C0))
+)
+
 // I2CConfig is used to store config info for I2C.
 type I2CConfig struct {
 	Frequency uint32
@@ -196,7 +201,7 @@ type I2CConfig struct {
 }
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 	var i2cClockFrequency uint32 = 32000000
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
@@ -228,7 +233,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 // Tx does a single I2C transaction at the specified address.
 // It clocks out the given address, writes the bytes in w, reads back len(r)
 // bytes and stores them in r, and generates a stop condition on the bus.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 	var err error
 	if len(w) != 0 {
 		// send start/address for write
@@ -276,7 +281,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 }
 
 // Writes a single byte to the I2C bus.
-func (i2c I2C) writeByte(data byte) error {
+func (i2c *I2C) writeByte(data byte) error {
 	// Send data byte
 	i2c.Bus.TXR_RXR.Set(uint32(data))
 
@@ -295,7 +300,7 @@ func (i2c I2C) writeByte(data byte) error {
 }
 
 // Reads a single byte from the I2C bus.
-func (i2c I2C) readByte() byte {
+func (i2c *I2C) readByte() byte {
 	i2c.Bus.CR_SR.Set(sifive.I2C_CR_RD)
 
 	// wait until transmission complete
@@ -306,7 +311,7 @@ func (i2c I2C) readByte() byte {
 }
 
 // Sends the address and start signal.
-func (i2c I2C) sendAddress(address uint16, write bool) error {
+func (i2c *I2C) sendAddress(address uint16, write bool) error {
 	data := (address << 1)
 	if !write {
 		data |= 1 // set read flag in transmit register

src/machine/machine_generic.go

@@ -6,7 +6,7 @@ package machine
 
 var (
 	SPI0  = SPI{0}
-	I2C0  = I2C{0}
+	I2C0  = &I2C{0}
 	UART0 = UART{0}
 )
 
@@ -115,13 +115,13 @@ type I2CConfig struct {
 }
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 	i2cConfigure(i2c.Bus, config.SCL, config.SDA)
 	return nil
 }
 
 // Tx does a single I2C transaction at the specified address.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 	i2cTransfer(i2c.Bus, &w[0], len(w), &r[0], len(r))
 	// TODO: do something with the returned error code.
 	return nil

src/machine/machine_k210.go

@@ -7,6 +7,7 @@ import (
 	"device/riscv"
 	"errors"
 	"runtime/interrupt"
+	"unsafe"
 )
 
 func CPUFrequency() uint32 {
@@ -493,9 +494,15 @@ func (spi SPI) Transfer(w byte) (byte, error) {
 
 // I2C on the K210.
 type I2C struct {
-	Bus *kendryte.I2C_Type
+	Bus kendryte.I2C_Type
 }
 
+var (
+	I2C0 = (*I2C)(unsafe.Pointer(kendryte.I2C0))
+	I2C1 = (*I2C)(unsafe.Pointer(kendryte.I2C1))
+	I2C2 = (*I2C)(unsafe.Pointer(kendryte.I2C2))
+)
+
 // I2CConfig is used to store config info for I2C.
 type I2CConfig struct {
 	Frequency uint32
@@ -504,7 +511,7 @@ type I2CConfig struct {
 }
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
@@ -518,7 +525,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 	// Enable APB0 clock.
 	kendryte.SYSCTL.CLK_EN_CENT.SetBits(kendryte.SYSCTL_CLK_EN_CENT_APB0_CLK_EN)
 
-	switch i2c.Bus {
+	switch &i2c.Bus {
 	case kendryte.I2C0:
 		// Initialize I2C0 clock.
 		kendryte.SYSCTL.CLK_EN_PERI.SetBits(kendryte.SYSCTL_CLK_EN_PERI_I2C0_CLK_EN)
@@ -567,7 +574,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 // Tx does a single I2C transaction at the specified address.
 // It clocks out the given address, writes the bytes in w, reads back len(r)
 // bytes and stores them in r, and generates a stop condition on the bus.
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 	// Set peripheral address.
 	i2c.Bus.TAR.Set(uint32(addr))
 	// Enable controller.

src/machine/machine_nrf.go

@@ -6,6 +6,7 @@ import (
 	"device/nrf"
 	"errors"
 	"runtime/interrupt"
+	"unsafe"
 )
 
 var (
@@ -203,13 +204,13 @@ func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 
 // I2C on the NRF.
 type I2C struct {
-	Bus *nrf.TWI_Type
+	Bus nrf.TWI_Type
 }
 
 // There are 2 I2C interfaces on the NRF.
 var (
-	I2C0 = I2C{Bus: nrf.TWI0}
-	I2C1 = I2C{Bus: nrf.TWI1}
+	I2C0 = (*I2C)(unsafe.Pointer(nrf.TWI0))
+	I2C1 = (*I2C)(unsafe.Pointer(nrf.TWI1))
 )
 
 // I2CConfig is used to store config info for I2C.
@@ -220,7 +221,7 @@ type I2CConfig struct {
 }
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
@@ -261,7 +262,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 // Tx does a single I2C transaction at the specified address.
 // It clocks out the given address, writes the bytes in w, reads back len(r)
 // bytes and stores them in r, and generates a stop condition on the bus.
-func (i2c I2C) Tx(addr uint16, w, r []byte) (err error) {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) (err error) {
 	i2c.Bus.ADDRESS.Set(uint32(addr))
 
 	if len(w) != 0 {
@@ -299,7 +300,7 @@ cleanUp:
 // signalStop sends a stop signal when writing or tells the I2C peripheral that
 // it must generate a stop condition after the next character is retrieved when
 // reading.
-func (i2c I2C) signalStop() {
+func (i2c *I2C) signalStop() {
 	i2c.Bus.TASKS_STOP.Set(1)
 	for i2c.Bus.EVENTS_STOPPED.Get() == 0 {
 	}
@@ -307,7 +308,7 @@ func (i2c I2C) signalStop() {
 }
 
 // writeByte writes a single byte to the I2C bus.
-func (i2c I2C) writeByte(data byte) error {
+func (i2c *I2C) writeByte(data byte) error {
 	i2c.Bus.TXD.Set(uint32(data))
 	for i2c.Bus.EVENTS_TXDSENT.Get() == 0 {
 		if e := i2c.Bus.EVENTS_ERROR.Get(); e != 0 {
@@ -320,7 +321,7 @@ func (i2c I2C) writeByte(data byte) error {
 }
 
 // readByte reads a single byte from the I2C bus.
-func (i2c I2C) readByte() (byte, error) {
+func (i2c *I2C) readByte() (byte, error) {
 	for i2c.Bus.EVENTS_RXDREADY.Get() == 0 {
 		if e := i2c.Bus.EVENTS_ERROR.Get(); e != 0 {
 			i2c.Bus.EVENTS_ERROR.Set(0)

src/machine/machine_nrf51.go

@@ -24,7 +24,7 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSELRXD.Set(uint32(rx))
 }
 
-func (i2c I2C) setPins(scl, sda Pin) {
+func (i2c *I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSELSCL.Set(uint32(scl))
 	i2c.Bus.PSELSDA.Set(uint32(sda))
 }

src/machine/machine_nrf52.go

@@ -56,7 +56,7 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSELRXD.Set(uint32(rx))
 }
 
-func (i2c I2C) setPins(scl, sda Pin) {
+func (i2c *I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSELSCL.Set(uint32(scl))
 	i2c.Bus.PSELSDA.Set(uint32(sda))
 }

src/machine/machine_nrf52833.go

@@ -76,7 +76,7 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSEL.RXD.Set(uint32(rx))
 }
 
-func (i2c I2C) setPins(scl, sda Pin) {
+func (i2c *I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSEL.SCL.Set(uint32(scl))
 	i2c.Bus.PSEL.SDA.Set(uint32(sda))
 }

src/machine/machine_nrf52840.go

@@ -72,7 +72,7 @@ func (uart UART) setPins(tx, rx Pin) {
 	nrf.UART0.PSEL.RXD.Set(uint32(rx))
 }
 
-func (i2c I2C) setPins(scl, sda Pin) {
+func (i2c *I2C) setPins(scl, sda Pin) {
 	i2c.Bus.PSEL.SCL.Set(uint32(scl))
 	i2c.Bus.PSEL.SDA.Set(uint32(sda))
 }

src/machine/machine_stm32_i2c_reva.go

@@ -1,8 +1,9 @@
-// +build stm32,!stm32f7x2,!stm32l5x2,!stm32l0
+// +build stm32f4 stm32f1
 
 package machine
 
-// Peripheral abstraction layer for I2C on the stm32 family
+// I2C implementation for 'older' STM32 MCUs, including the F1 and F4 series
+// of MCUs.
 
 import (
 	"device/stm32"
@@ -28,7 +29,7 @@ const (
 	flagMSL     = 0x00100001
 )
 
-func (i2c I2C) hasFlag(flag uint32) bool {
+func (i2c *I2C) hasFlag(flag uint32) bool {
 	const mask = 0x0000FFFF
 	if uint8(flag>>16) == 1 {
 		return i2c.Bus.SR1.HasBits(flag & mask)
@@ -37,18 +38,18 @@ func (i2c I2C) hasFlag(flag uint32) bool {
 	}
 }
 
-func (i2c I2C) clearFlag(flag uint32) {
+func (i2c *I2C) clearFlag(flag uint32) {
 	const mask = 0x0000FFFF
 	i2c.Bus.SR1.Set(^(flag & mask))
 }
 
 // clearFlagADDR reads both status registers to clear any pending ADDR flags.
-func (i2c I2C) clearFlagADDR() {
+func (i2c *I2C) clearFlagADDR() {
 	i2c.Bus.SR1.Get()
 	i2c.Bus.SR2.Get()
 }
 
-func (i2c I2C) waitForFlag(flag uint32, set bool) bool {
+func (i2c *I2C) waitForFlag(flag uint32, set bool) bool {
 	const tryMax = 10000
 	hasFlag := false
 	for i := 0; !hasFlag && i < tryMax; i++ {
@@ -57,7 +58,7 @@ func (i2c I2C) waitForFlag(flag uint32, set bool) bool {
 	return hasFlag
 }
 
-func (i2c I2C) waitForFlagOrError(flag uint32, set bool) bool {
+func (i2c *I2C) waitForFlagOrError(flag uint32, set bool) bool {
 	const tryMax = 10000
 	hasFlag := false
 	for i := 0; !hasFlag && i < tryMax; i++ {
@@ -106,7 +107,7 @@ type I2CConfig struct {
 }
 
 // Configure is intended to setup the STM32 I2C interface.
-func (i2c I2C) Configure(config I2CConfig) error {
+func (i2c *I2C) Configure(config I2CConfig) error {
 
 	// The following is the required sequence in controller mode.
 	// 1. Program the peripheral input clock in I2C_CR2 Register in order to
@@ -156,7 +157,7 @@ func (i2c I2C) Configure(config I2CConfig) error {
 	return nil
 }
 
-func (i2c I2C) Tx(addr uint16, w, r []byte) error {
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 
 	if err := i2c.controllerTransmit(addr, w); nil != err {
 		return err
@@ -171,7 +172,7 @@ func (i2c I2C) Tx(addr uint16, w, r []byte) error {
 	return nil
 }
 
-func (i2c I2C) controllerTransmit(addr uint16, w []byte) error {
+func (i2c *I2C) controllerTransmit(addr uint16, w []byte) error {
 
 	if !i2c.waitForFlag(flagBUSY, false) {
 		return errI2CBusReadyTimeout
@@ -223,7 +224,7 @@ func (i2c I2C) controllerTransmit(addr uint16, w []byte) error {
 	return nil
 }
 
-func (i2c I2C) controllerRequestWrite(addr uint16, option transferOption) error {
+func (i2c *I2C) controllerRequestWrite(addr uint16, option transferOption) error {
 
 	if frameFirstAndLast == option || frameFirst == option || frameNoOption == option {
 		// generate start condition
@@ -249,7 +250,7 @@ func (i2c I2C) controllerRequestWrite(addr uint16, option transferOption) error
 	return nil
 }
 
-func (i2c I2C) controllerReceive(addr uint16, r []byte) error {
+func (i2c *I2C) controllerReceive(addr uint16, r []byte) error {
 
 	if !i2c.waitForFlag(flagBUSY, false) {
 		return errI2CBusReadyTimeout
@@ -399,7 +400,7 @@ func (i2c I2C) controllerReceive(addr uint16, r []byte) error {
 	return nil
 }
 
-func (i2c I2C) controllerRequestRead(addr uint16, option transferOption) error {
+func (i2c *I2C) controllerRequestRead(addr uint16, option transferOption) error {
 
 	// enable ACK
 	i2c.Bus.CR1.SetBits(stm32.I2C_CR1_ACK)

src/machine/machine_stm32_i2c_revb.go

@@ -0,0 +1,347 @@
+// +build stm32l5 stm32f7 stm32l4
+
+package machine
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+//go:linkname ticks runtime.ticks
+func ticks() int64
+
+// I2C implementation for 'newer' STM32 MCUs, including the F7, L5 and L4
+// series of MCUs.
+//
+// Currently, only 100KHz mode is supported
+
+const (
+	flagBUSY  = stm32.I2C_ISR_BUSY
+	flagTCR   = stm32.I2C_ISR_TCR
+	flagRXNE  = stm32.I2C_ISR_RXNE
+	flagSTOPF = stm32.I2C_ISR_STOPF
+	flagAF    = stm32.I2C_ISR_NACKF
+	flagTXIS  = stm32.I2C_ISR_TXIS
+	flagTXE   = stm32.I2C_ISR_TXE
+)
+
+const (
+	MAX_NBYTE_SIZE = 255
+	TIMEOUT_TICKS  = 100 // 100ms
+
+	I2C_NO_STARTSTOP         = 0x0
+	I2C_GENERATE_START_WRITE = 0x80000000 | stm32.I2C_CR2_START
+	I2C_GENERATE_START_READ  = 0x80000000 | stm32.I2C_CR2_START | stm32.I2C_CR2_RD_WRN
+	I2C_GENERATE_STOP        = 0x80000000 | stm32.I2C_CR2_STOP
+)
+
+type I2C struct {
+	Bus             *stm32.I2C_Type
+	AltFuncSelector uint8
+}
+
+// I2CConfig is used to store config info for I2C.
+type I2CConfig struct {
+	SCL Pin
+	SDA Pin
+}
+
+func (i2c *I2C) Configure(config I2CConfig) error {
+	// disable I2C interface before any configuration changes
+	i2c.Bus.CR1.ClearBits(stm32.I2C_CR1_PE)
+
+	// enable clock for I2C
+	enableAltFuncClock(unsafe.Pointer(i2c.Bus))
+
+	// init pins
+	if config.SCL == 0 && config.SDA == 0 {
+		config.SCL = I2C0_SCL_PIN
+		config.SDA = I2C0_SDA_PIN
+	}
+	i2c.configurePins(config)
+
+	// Frequency range
+	i2c.Bus.TIMINGR.Set(i2c.getFreqRange())
+
+	// Disable Own Address1 before set the Own Address1 configuration
+	i2c.Bus.OAR1.ClearBits(stm32.I2C_OAR1_OA1EN)
+
+	// 7 bit addressing, no self address
+	i2c.Bus.OAR1.Set(stm32.I2C_OAR1_OA1EN)
+
+	// Enable the AUTOEND by default, and enable NACK (should be disable only during Slave process
+	i2c.Bus.CR2.Set(stm32.I2C_CR2_AUTOEND | stm32.I2C_CR2_NACK)
+
+	// Disable Own Address2 / Dual Addressing
+	i2c.Bus.OAR2.Set(0)
+
+	// Disable Generalcall and NoStretch, Enable peripheral
+	i2c.Bus.CR1.Set(stm32.I2C_CR1_PE)
+
+	return nil
+}
+
+func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
+	if len(w) > 0 {
+		if err := i2c.controllerTransmit(addr, w); nil != err {
+			return err
+		}
+	}
+
+	if len(r) > 0 {
+		if err := i2c.controllerReceive(addr, r); nil != err {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (i2c *I2C) configurePins(config I2CConfig) {
+	config.SCL.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSCL}, i2c.AltFuncSelector)
+	config.SDA.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSDA}, i2c.AltFuncSelector)
+}
+
+func (i2c *I2C) controllerTransmit(addr uint16, w []byte) error {
+	start := ticks()
+
+	if !i2c.waitOnFlagUntilTimeout(flagBUSY, false, start) {
+		return errI2CBusReadyTimeout
+	}
+
+	pos := 0
+	xferCount := len(w)
+	xferSize := uint8(xferCount)
+	if xferCount > MAX_NBYTE_SIZE {
+		// Large write, indicate reload
+		xferSize = MAX_NBYTE_SIZE
+		i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_RELOAD, I2C_GENERATE_START_WRITE)
+	} else {
+		// Small write, auto-end
+		i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_AUTOEND, I2C_GENERATE_START_WRITE)
+	}
+
+	for xferCount > 0 {
+		if !i2c.waitOnTXISFlagUntilTimeout(start) {
+			return errI2CWriteTimeout
+		}
+
+		i2c.Bus.TXDR.Set(uint32(w[pos]))
+		pos++
+		xferCount--
+		xferSize--
+
+		// If we've written the last byte of this chunk
+		if xferCount != 0 && xferSize == 0 {
+			// Wait for Transfer Complete Reload to be flagged
+			if !i2c.waitOnFlagUntilTimeout(flagTCR, true, start) {
+				return errI2CWriteTimeout
+			}
+
+			if xferCount > MAX_NBYTE_SIZE {
+				// Large write remaining, indicate reload
+				xferSize = MAX_NBYTE_SIZE
+				i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_RELOAD, I2C_NO_STARTSTOP)
+			} else {
+				// Small write, auto-end
+				xferSize = uint8(xferCount)
+				i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_AUTOEND, I2C_NO_STARTSTOP)
+			}
+		}
+	}
+
+	if !i2c.waitOnStopFlagUntilTimeout(start) {
+		return errI2CWriteTimeout
+	}
+
+	i2c.clearFlag(stm32.I2C_ISR_STOPF)
+
+	i2c.resetCR2()
+
+	return nil
+}
+
+func (i2c *I2C) controllerReceive(addr uint16, r []byte) error {
+	start := ticks()
+
+	if !i2c.waitOnFlagUntilTimeout(flagBUSY, false, start) {
+		return errI2CBusReadyTimeout
+	}
+
+	pos := 0
+	xferCount := len(r)
+	xferSize := uint8(xferCount)
+	if xferCount > MAX_NBYTE_SIZE {
+		// Large read, indicate reload
+		xferSize = MAX_NBYTE_SIZE
+		i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_RELOAD, I2C_GENERATE_START_READ)
+	} else {
+		// Small read, auto-end
+		i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_AUTOEND, I2C_GENERATE_START_READ)
+	}
+
+	for xferCount > 0 {
+		if !i2c.waitOnRXNEFlagUntilTimeout(start) {
+			return errI2CWriteTimeout
+		}
+
+		r[pos] = uint8(i2c.Bus.RXDR.Get())
+		pos++
+		xferCount--
+		xferSize--
+
+		// If we've read the last byte of this chunk
+		if xferCount != 0 && xferSize == 0 {
+			// Wait for Transfer Complete Reload to be flagged
+			if !i2c.waitOnFlagUntilTimeout(flagTCR, true, start) {
+				return errI2CWriteTimeout
+			}
+
+			if xferCount > MAX_NBYTE_SIZE {
+				// Large read remaining, indicate reload
+				xferSize = MAX_NBYTE_SIZE
+				i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_RELOAD, I2C_NO_STARTSTOP)
+			} else {
+				// Small read, auto-end
+				xferSize = uint8(xferCount)
+				i2c.transferConfig(addr, xferSize, stm32.I2C_CR2_AUTOEND, I2C_NO_STARTSTOP)
+			}
+		}
+	}
+
+	if !i2c.waitOnStopFlagUntilTimeout(start) {
+		return errI2CWriteTimeout
+	}
+
+	i2c.clearFlag(stm32.I2C_ISR_STOPF)
+
+	i2c.resetCR2()
+
+	return nil
+}
+
+func (i2c *I2C) waitOnFlagUntilTimeout(flag uint32, set bool, startTicks int64) bool {
+	for i2c.hasFlag(flag) != set {
+		if (ticks() - startTicks) > TIMEOUT_TICKS {
+			return false
+		}
+	}
+	return true
+}
+
+func (i2c *I2C) waitOnRXNEFlagUntilTimeout(startTicks int64) bool {
+	for !i2c.hasFlag(flagRXNE) {
+		if i2c.isAcknowledgeFailed(startTicks) {
+			return false
+		}
+
+		if i2c.hasFlag(flagSTOPF) {
+			i2c.clearFlag(flagSTOPF)
+			i2c.resetCR2()
+			return false
+		}
+
+		if (ticks() - startTicks) > TIMEOUT_TICKS {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (i2c *I2C) waitOnTXISFlagUntilTimeout(startTicks int64) bool {
+	for !i2c.hasFlag(flagTXIS) {
+		if i2c.isAcknowledgeFailed(startTicks) {
+			return false
+		}
+
+		if (ticks() - startTicks) > TIMEOUT_TICKS {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (i2c *I2C) waitOnStopFlagUntilTimeout(startTicks int64) bool {
+	for !i2c.hasFlag(flagSTOPF) {
+		if i2c.isAcknowledgeFailed(startTicks) {
+			return false
+		}
+
+		if (ticks() - startTicks) > TIMEOUT_TICKS {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (i2c *I2C) isAcknowledgeFailed(startTicks int64) bool {
+	if i2c.hasFlag(flagAF) {
+		// Wait until STOP Flag is reset
+		// AutoEnd should be initiate after AF
+		for !i2c.hasFlag(flagSTOPF) {
+			if (ticks() - startTicks) > TIMEOUT_TICKS {
+				return true
+			}
+		}
+
+		i2c.clearFlag(flagAF)
+		i2c.clearFlag(flagSTOPF)
+		i2c.flushTXDR()
+		i2c.resetCR2()
+
+		return true
+	}
+
+	return false
+}
+
+func (i2c *I2C) flushTXDR() {
+	// If a pending TXIS flag is set, write a dummy data in TXDR to clear it
+	if i2c.hasFlag(flagTXIS) {
+		i2c.Bus.TXDR.Set(0)
+	}
+
+	// Flush TX register if not empty
+	if !i2c.hasFlag(flagTXE) {
+		i2c.clearFlag(flagTXE)
+	}
+}
+
+func (i2c *I2C) resetCR2() {
+	i2c.Bus.CR2.ClearBits(stm32.I2C_CR2_SADD_Msk |
+		stm32.I2C_CR2_HEAD10R_Msk |
+		stm32.I2C_CR2_NBYTES_Msk |
+		stm32.I2C_CR2_RELOAD_Msk |
+		stm32.I2C_CR2_RD_WRN_Msk)
+}
+
+func (i2c *I2C) transferConfig(addr uint16, size uint8, mode uint32, request uint32) {
+	mask := uint32(stm32.I2C_CR2_SADD_Msk |
+		stm32.I2C_CR2_NBYTES_Msk |
+		stm32.I2C_CR2_RELOAD_Msk |
+		stm32.I2C_CR2_AUTOEND_Msk |
+		(stm32.I2C_CR2_RD_WRN & uint32(request>>(31-stm32.I2C_CR2_RD_WRN_Pos))) |
+		stm32.I2C_CR2_START_Msk |
+		stm32.I2C_CR2_STOP_Msk)
+
+	value := (uint32(addr<<1) & stm32.I2C_CR2_SADD_Msk) |
+		((uint32(size) << stm32.I2C_CR2_NBYTES_Pos) & stm32.I2C_CR2_NBYTES_Msk) |
+		mode | request
+
+	i2c.Bus.CR2.ReplaceBits(value, mask, 0)
+}
+
+func (i2c *I2C) hasFlag(flag uint32) bool {
+	return i2c.Bus.ISR.HasBits(flag)
+}
+
+func (i2c *I2C) clearFlag(flag uint32) {
+	if flag == stm32.I2C_ISR_TXE {
+		i2c.Bus.ISR.SetBits(flag)
+	} else {
+		i2c.Bus.ICR.SetBits(flag)
+	}
+}

src/machine/machine_stm32_spi.go

@@ -1,4 +1,4 @@
-// +build stm32,!stm32f7x2,!stm32l5x2
+// +build stm32,!stm32f7x2,!stm32l5x2,!stm32l4x2
 
 package machine
 

src/machine/machine_stm32_uart.go

@@ -13,10 +13,11 @@ import (
 
 // UART representation
 type UART struct {
-	Buffer          *RingBuffer
-	Bus             *stm32.USART_Type
-	Interrupt       interrupt.Interrupt
-	AltFuncSelector uint8
+	Buffer            *RingBuffer
+	Bus               *stm32.USART_Type
+	Interrupt         interrupt.Interrupt
+	TxAltFuncSelector uint8
+	RxAltFuncSelector uint8
 
 	// Registers specific to the chip
 	rxReg       *volatile.Register32

src/machine/machine_stm32f103.go

@@ -201,7 +201,7 @@ func (spi SPI) configurePins(config SPIConfig) {
 // Since the first interface is named I2C1, both I2C0 and I2C1 refer to I2C1.
 // TODO: implement I2C2.
 var (
-	I2C1 = I2C{Bus: stm32.I2C1}
+	I2C1 = (*I2C)(unsafe.Pointer(stm32.I2C1))
 	I2C0 = I2C1
 )
 
@@ -209,7 +209,7 @@ type I2C struct {
 	Bus *stm32.I2C_Type
 }
 
-func (i2c I2C) configurePins(config I2CConfig) {
+func (i2c *I2C) configurePins(config I2CConfig) {
 	if config.SDA == PB9 {
 		// use alternate I2C1 pins PB8/PB9 via AFIO mapping
 		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_AFIOEN)
@@ -220,7 +220,7 @@ func (i2c I2C) configurePins(config I2CConfig) {
 	config.SCL.Configure(PinConfig{Mode: PinOutput50MHz + PinOutputModeAltOpenDrain})
 }
 
-func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
+func (i2c *I2C) getFreqRange(config I2CConfig) uint32 {
 	// pclk1 clock speed is main frequency divided by PCLK1 prescaler (div 2)
 	pclk1 := CPUFrequency() / 2
 
@@ -229,7 +229,7 @@ func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
 	return pclk1 / 1000000
 }
 
-func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
+func (i2c *I2C) getRiseTime(config I2CConfig) uint32 {
 	// These bits must be programmed with the maximum SCL rise time given in the
 	// I2C bus specification, incremented by 1.
 	// For instance: in Sm mode, the maximum allowed SCL rise time is 1000 ns.
@@ -245,7 +245,7 @@ func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
 	return (freqRange + 1) << stm32.I2C_TRISE_TRISE_Pos
 }
 
-func (i2c I2C) getSpeed(config I2CConfig) uint32 {
+func (i2c *I2C) getSpeed(config I2CConfig) uint32 {
 	ccr := func(pclk uint32, freq uint32, coeff uint32) uint32 {
 		return (((pclk - 1) / (freq * coeff)) + 1) & stm32.I2C_CCR_CCR_Msk
 	}

src/machine/machine_stm32f405.go

@@ -37,8 +37,8 @@ const (
 
 func (uart *UART) configurePins(config UARTConfig) {
 	// enable the alternate functions on the TX and RX pins
-	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
-	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
 }
 
 func (uart *UART) getBaudRateDivisor(baudRate uint32) uint32 {
@@ -116,12 +116,12 @@ type I2C struct {
 	AltFuncSelector uint8
 }
 
-func (i2c I2C) configurePins(config I2CConfig) {
+func (i2c *I2C) configurePins(config I2CConfig) {
 	config.SCL.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSCL}, i2c.AltFuncSelector)
 	config.SDA.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSDA}, i2c.AltFuncSelector)
 }
 
-func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
+func (i2c *I2C) getFreqRange(config I2CConfig) uint32 {
 	// all I2C interfaces are on APB1 (42 MHz)
 	clock := CPUFrequency() / 4
 	// convert to MHz
@@ -139,7 +139,7 @@ func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
 	return clock << stm32.I2C_CR2_FREQ_Pos
 }
 
-func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
+func (i2c *I2C) getRiseTime(config I2CConfig) uint32 {
 	// These bits must be programmed with the maximum SCL rise time given in the
 	// I2C bus specification, incremented by 1.
 	// For instance: in Sm mode, the maximum allowed SCL rise time is 1000 ns.
@@ -155,7 +155,7 @@ func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
 	return (freqRange + 1) << stm32.I2C_TRISE_TRISE_Pos
 }
 
-func (i2c I2C) getSpeed(config I2CConfig) uint32 {
+func (i2c *I2C) getSpeed(config I2CConfig) uint32 {
 	ccr := func(pclk uint32, freq uint32, coeff uint32) uint32 {
 		return (((pclk - 1) / (freq * coeff)) + 1) & stm32.I2C_CCR_CCR_Msk
 	}

src/machine/machine_stm32f407.go

@@ -37,8 +37,8 @@ const (
 // Configure the UART.
 func (uart *UART) configurePins(config UARTConfig) {
 	// enable the alternate functions on the TX and RX pins
-	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
-	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
 }
 
 // UART baudrate calc based on the bus and clockspeed
@@ -128,12 +128,12 @@ type I2C struct {
 	AltFuncSelector uint8
 }
 
-func (i2c I2C) configurePins(config I2CConfig) {
+func (i2c *I2C) configurePins(config I2CConfig) {
 	config.SCL.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSCL}, i2c.AltFuncSelector)
 	config.SDA.ConfigureAltFunc(PinConfig{Mode: PinModeI2CSDA}, i2c.AltFuncSelector)
 }
 
-func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
+func (i2c *I2C) getFreqRange(config I2CConfig) uint32 {
 	// all I2C interfaces are on APB1 (42 MHz)
 	clock := CPUFrequency() / 4
 	// convert to MHz
@@ -151,7 +151,7 @@ func (i2c I2C) getFreqRange(config I2CConfig) uint32 {
 	return clock << stm32.I2C_CR2_FREQ_Pos
 }
 
-func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
+func (i2c *I2C) getRiseTime(config I2CConfig) uint32 {
 	// These bits must be programmed with the maximum SCL rise time given in the
 	// I2C bus specification, incremented by 1.
 	// For instance: in Sm mode, the maximum allowed SCL rise time is 1000 ns.
@@ -167,7 +167,7 @@ func (i2c I2C) getRiseTime(config I2CConfig) uint32 {
 	return (freqRange + 1) << stm32.I2C_TRISE_TRISE_Pos
 }
 
-func (i2c I2C) getSpeed(config I2CConfig) uint32 {
+func (i2c *I2C) getSpeed(config I2CConfig) uint32 {
 	ccr := func(pclk uint32, freq uint32, coeff uint32) uint32 {
 		return (((pclk - 1) / (freq * coeff)) + 1) & stm32.I2C_CCR_CCR_Msk
 	}

src/machine/machine_stm32f7x2.go

@@ -17,8 +17,8 @@ func CPUFrequency() uint32 {
 // Configure the UART.
 func (uart *UART) configurePins(config UARTConfig) {
 	// enable the alternate functions on the TX and RX pins
-	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
-	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
 }
 
 // UART baudrate calc based on the bus and clockspeed
@@ -41,3 +41,13 @@ func (uart *UART) setRegisters() {
 	uart.statusReg = &uart.Bus.ISR
 	uart.txEmptyFlag = stm32.USART_ISR_TXE
 }
+
+//---------- I2C related code
+
+// Gets the value for TIMINGR register
+func (i2c *I2C) getFreqRange() uint32 {
+	// This is a 'magic' value calculated by STM32CubeMX
+	// for 27MHz PCLK1 (216MHz CPU Freq / 8).
+	// TODO: Do calculations based on PCLK1
+	return 0x00606A9B
+}

src/machine/machine_stm32l0.go

@@ -191,8 +191,8 @@ func enableAltFuncClock(bus unsafe.Pointer) {
 // Configure the UART.
 func (uart UART) configurePins(config UARTConfig) {
 	// enable the alternate functions on the TX and RX pins
-	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
-	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
 }
 
 // UART baudrate calc based on the bus and clockspeed

src/machine/machine_stm32l4.go

@@ -0,0 +1,184 @@
+// +build stm32l4
+
+package machine
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+// Peripheral abstraction layer for the stm32l4
+
+const (
+	PA0  = portA + 0
+	PA1  = portA + 1
+	PA2  = portA + 2
+	PA3  = portA + 3
+	PA4  = portA + 4
+	PA5  = portA + 5
+	PA6  = portA + 6
+	PA7  = portA + 7
+	PA8  = portA + 8
+	PA9  = portA + 9
+	PA10 = portA + 10
+	PA11 = portA + 11
+	PA12 = portA + 12
+	PA13 = portA + 13
+	PA14 = portA + 14
+	PA15 = portA + 15
+
+	PB0  = portB + 0
+	PB1  = portB + 1
+	PB2  = portB + 2
+	PB3  = portB + 3
+	PB4  = portB + 4
+	PB5  = portB + 5
+	PB6  = portB + 6
+	PB7  = portB + 7
+	PB8  = portB + 8
+	PB9  = portB + 9
+	PB10 = portB + 10
+	PB11 = portB + 11
+	PB12 = portB + 12
+	PB13 = portB + 13
+	PB14 = portB + 14
+	PB15 = portB + 15
+
+	PC0  = portC + 0
+	PC1  = portC + 1
+	PC2  = portC + 2
+	PC3  = portC + 3
+	PC4  = portC + 4
+	PC5  = portC + 5
+	PC6  = portC + 6
+	PC7  = portC + 7
+	PC8  = portC + 8
+	PC9  = portC + 9
+	PC10 = portC + 10
+	PC11 = portC + 11
+	PC12 = portC + 12
+	PC13 = portC + 13
+	PC14 = portC + 14
+	PC15 = portC + 15
+
+	PD0  = portD + 0
+	PD1  = portD + 1
+	PD2  = portD + 2
+	PD3  = portD + 3
+	PD4  = portD + 4
+	PD5  = portD + 5
+	PD6  = portD + 6
+	PD7  = portD + 7
+	PD8  = portD + 8
+	PD9  = portD + 9
+	PD10 = portD + 10
+	PD11 = portD + 11
+	PD12 = portD + 12
+	PD13 = portD + 13
+	PD14 = portD + 14
+	PD15 = portD + 15
+
+	PE0  = portE + 0
+	PE1  = portE + 1
+	PE2  = portE + 2
+	PE3  = portE + 3
+	PE4  = portE + 4
+	PE5  = portE + 5
+	PE6  = portE + 6
+	PE7  = portE + 7
+	PE8  = portE + 8
+	PE9  = portE + 9
+	PE10 = portE + 10
+	PE11 = portE + 11
+	PE12 = portE + 12
+	PE13 = portE + 13
+	PE14 = portE + 14
+	PE15 = portE + 15
+)
+
+func (p Pin) getPort() *stm32.GPIO_Type {
+	switch p / 16 {
+	case 0:
+		return stm32.GPIOA
+	case 1:
+		return stm32.GPIOB
+	case 2:
+		return stm32.GPIOC
+	case 3:
+		return stm32.GPIOD
+	case 4:
+		return stm32.GPIOE
+	default:
+		panic("machine: unknown port")
+	}
+}
+
+// enableClock enables the clock for this desired GPIO port.
+func (p Pin) enableClock() {
+	switch p / 16 {
+	case 0:
+		stm32.RCC.AHB2ENR.SetBits(stm32.RCC_AHB2ENR_GPIOAEN)
+	case 1:
+		stm32.RCC.AHB2ENR.SetBits(stm32.RCC_AHB2ENR_GPIOBEN)
+	case 2:
+		stm32.RCC.AHB2ENR.SetBits(stm32.RCC_AHB2ENR_GPIOCEN)
+	case 3:
+		stm32.RCC.AHB2ENR.SetBits(stm32.RCC_AHB2ENR_GPIODEN)
+	case 4:
+		stm32.RCC.AHB2ENR.SetBits(stm32.RCC_AHB2ENR_GPIOEEN)
+	default:
+		panic("machine: unknown port")
+	}
+}
+
+// Enable peripheral clock
+func enableAltFuncClock(bus unsafe.Pointer) {
+	switch bus {
+	case unsafe.Pointer(stm32.PWR): // Power interface clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_PWREN)
+	case unsafe.Pointer(stm32.I2C3): // I2C3 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_I2C3EN)
+	case unsafe.Pointer(stm32.I2C2): // I2C2 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_I2C2EN)
+	case unsafe.Pointer(stm32.I2C1): // I2C1 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_I2C1EN)
+	case unsafe.Pointer(stm32.UART4): // UART4 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_UART4EN)
+	case unsafe.Pointer(stm32.USART3): // USART3 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_USART3EN)
+	case unsafe.Pointer(stm32.USART2): // USART2 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_USART2EN)
+	case unsafe.Pointer(stm32.SPI3): // SPI3 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_SPI3EN)
+	case unsafe.Pointer(stm32.SPI2): // SPI2 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_SPI2EN)
+	case unsafe.Pointer(stm32.WWDG): // Window watchdog clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_WWDGEN)
+	case unsafe.Pointer(stm32.TIM7): // TIM7 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_TIM7EN)
+	case unsafe.Pointer(stm32.TIM6): // TIM6 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_TIM6EN)
+	case unsafe.Pointer(stm32.TIM3): // TIM3 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_TIM3EN)
+	case unsafe.Pointer(stm32.TIM2): // TIM2 clock enable
+		stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_TIM2EN)
+	case unsafe.Pointer(stm32.LPTIM2): // LPTIM2 clock enable
+		stm32.RCC.APB1ENR2.SetBits(stm32.RCC_APB1ENR2_LPTIM2EN)
+	case unsafe.Pointer(stm32.I2C4): // I2C4 clock enable
+		stm32.RCC.APB1ENR2.SetBits(stm32.RCC_APB1ENR2_I2C4EN)
+	case unsafe.Pointer(stm32.LPUART1): // LPUART1 clock enable
+		stm32.RCC.APB1ENR2.SetBits(stm32.RCC_APB1ENR2_LPUART1EN)
+	case unsafe.Pointer(stm32.TIM16): // TIM16 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_TIM16EN)
+	case unsafe.Pointer(stm32.TIM15): // TIM15 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_TIM15EN)
+	case unsafe.Pointer(stm32.SYSCFG): // System configuration controller clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SYSCFGEN)
+	case unsafe.Pointer(stm32.SPI1): // SPI1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI1EN)
+	case unsafe.Pointer(stm32.USART1): // USART1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_USART1EN)
+	case unsafe.Pointer(stm32.TIM1): // TIM1 clock enable
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_TIM1EN)
+	}
+}

src/machine/machine_stm32l4x2.go

@@ -0,0 +1,46 @@
+// +build stm32l4x2
+
+package machine
+
+// Peripheral abstraction layer for the stm32l4x2
+
+import (
+	"device/stm32"
+)
+
+func CPUFrequency() uint32 {
+	return 80000000
+}
+
+//---------- UART related code
+
+// Configure the UART.
+func (uart *UART) configurePins(config UARTConfig) {
+	// enable the alternate functions on the TX and RX pins
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
+}
+
+// UART baudrate calc based on the bus and clockspeed
+// NOTE: keep this in sync with the runtime/runtime_stm32l5x2.go clock init code
+func (uart *UART) getBaudRateDivisor(baudRate uint32) uint32 {
+	return (CPUFrequency() / baudRate)
+}
+
+// Register names vary by ST processor, these are for STM L5
+func (uart *UART) setRegisters() {
+	uart.rxReg = &uart.Bus.RDR
+	uart.txReg = &uart.Bus.TDR
+	uart.statusReg = &uart.Bus.ISR
+	uart.txEmptyFlag = stm32.USART_ISR_TXE
+}
+
+//---------- I2C related code
+
+// Gets the value for TIMINGR register
+func (i2c *I2C) getFreqRange() uint32 {
+	// This is a 'magic' value calculated by STM32CubeMX
+	// for 80MHz PCLK1.
+	// TODO: Do calculations based on PCLK1
+	return 0x10909CEC
+}

src/machine/machine_stm32l5x2.go

@@ -22,8 +22,8 @@ func (uart *UART) configurePins(config UARTConfig) {
 	}
 
 	// enable the alternate functions on the TX and RX pins
-	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.AltFuncSelector)
-	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.AltFuncSelector)
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
 }
 
 // UART baudrate calc based on the bus and clockspeed
@@ -39,3 +39,13 @@ func (uart *UART) setRegisters() {
 	uart.statusReg = &uart.Bus.ISR
 	uart.txEmptyFlag = stm32.USART_ISR_TXE
 }
+
+//---------- I2C related code
+
+// Gets the value for TIMINGR register
+func (i2c *I2C) getFreqRange() uint32 {
+	// This is a 'magic' value calculated by STM32CubeMX
+	// for 110MHz PCLK1.
+	// TODO: Do calculations based on PCLK1
+	return 0x40505681
+}

src/machine/spi.go

@@ -1,4 +1,4 @@
-// +build !baremetal stm32,!stm32f7x2,!stm32l5x2 fe310 k210 atmega
+// +build !baremetal stm32,!stm32f7x2,!stm32l5x2,!stm32l4x2 fe310 k210 atmega
 
 package machine
 

src/os/errors.go

@@ -2,6 +2,7 @@ package os
 
 import (
 	"errors"
+	"syscall"
 )
 
 var (
@@ -17,9 +18,8 @@ var (
 	ErrExist          = errors.New("file exists")
 )
 
-func IsPermission(err error) bool {
-	return err == ErrPermission
-}
+// The following code is copied from the official implementation.
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/error.go#L65-L104
 
 func NewSyscallError(syscall string, err error) error {
 	if err == nil {
@@ -37,3 +37,39 @@ type SyscallError struct {
 func (e *SyscallError) Error() string { return e.Syscall + ": " + e.Err.Error() }
 
 func (e *SyscallError) Unwrap() error { return e.Err }
+
+func IsExist(err error) bool {
+	return underlyingErrorIs(err, ErrExist)
+}
+
+func IsNotExist(err error) bool {
+	return underlyingErrorIs(err, ErrNotExist)
+}
+
+func IsPermission(err error) bool {
+	return underlyingErrorIs(err, ErrPermission)
+}
+
+func underlyingErrorIs(err, target error) bool {
+	// Note that this function is not errors.Is:
+	// underlyingError only unwraps the specific error-wrapping types
+	// that it historically did, not all errors implementing Unwrap().
+	err = underlyingError(err)
+	if err == target {
+		return true
+	}
+	// To preserve prior behavior, only examine syscall errors.
+	e, ok := err.(syscall.Errno)
+	return ok && e.Is(target)
+}
+
+// underlyingError returns the underlying error for known os error types.
+func underlyingError(err error) error {
+	switch err := err.(type) {
+	case *PathError:
+		return err.Err
+	case *SyscallError:
+		return err.Err
+	}
+	return err
+}

src/os/file.go

@@ -6,6 +6,7 @@
 package os
 
 import (
+	"io"
 	"syscall"
 )
 
@@ -76,7 +77,7 @@ func Create(name string) (*File, error) {
 // read and any error encountered. At end of file, Read returns 0, io.EOF.
 func (f *File) Read(b []byte) (n int, err error) {
 	n, err = f.handle.Read(b)
-	if err != nil {
+	if err != nil && err != io.EOF {
 		err = &PathError{"read", f.name, err}
 	}
 	return
@@ -155,59 +156,17 @@ func (e *PathError) Error() string {
 	return e.Op + " " + e.Path + ": " + e.Err.Error()
 }
 
-type FileMode uint32
-
-// Mode constants, copied from the mainline Go source
-// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
 const (
-	// The single letters are the abbreviations used by the String method's formatting.
-	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
-	ModeAppend                                     // a: append-only
-	ModeExclusive                                  // l: exclusive use
-	ModeTemporary                                  // T: temporary file; Plan 9 only
-	ModeSymlink                                    // L: symbolic link
-	ModeDevice                                     // D: device file
-	ModeNamedPipe                                  // p: named pipe (FIFO)
-	ModeSocket                                     // S: Unix domain socket
-	ModeSetuid                                     // u: setuid
-	ModeSetgid                                     // g: setgid
-	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
-	ModeSticky                                     // t: sticky
-	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
-
-	// Mask for the type bits. For regular files, none will be set.
-	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
-
-	ModePerm FileMode = 0777 // Unix permission bits
+	O_RDONLY int = syscall.O_RDONLY
+	O_WRONLY int = syscall.O_WRONLY
+	O_RDWR   int = syscall.O_RDWR
+	O_APPEND int = syscall.O_APPEND
+	O_CREATE int = syscall.O_CREAT
+	O_EXCL   int = syscall.O_EXCL
+	O_SYNC   int = syscall.O_SYNC
+	O_TRUNC  int = syscall.O_TRUNC
 )
 
-// IsDir is a stub, always returning false
-func (m FileMode) IsDir() bool {
-	return false
-}
-
-// Stub constants
-const (
-	O_RDONLY int = 1
-	O_WRONLY int = 2
-	O_RDWR   int = 4
-	O_APPEND int = 8
-	O_CREATE int = 16
-	O_EXCL   int = 32
-	O_SYNC   int = 64
-	O_TRUNC  int = 128
-)
-
-// A FileInfo describes a file and is returned by Stat and Lstat.
-type FileInfo interface {
-	Name() string   // base name of the file
-	Size() int64    // length in bytes for regular files; system-dependent for others
-	Mode() FileMode // file mode bits
-	// TODO ModTime() time.Time // modification time
-	IsDir() bool      // abbreviation for Mode().IsDir()
-	Sys() interface{} // underlying data source (can return nil)
-}
-
 // Stat is a stub, not yet implemented
 func Stat(name string) (FileInfo, error) {
 	return nil, &PathError{"stat", name, ErrNotImplemented}
@@ -233,16 +192,6 @@ func TempDir() string {
 	return "/tmp"
 }
 
-// IsExist is a stub (for now), always returning false
-func IsExist(err error) bool {
-	return false
-}
-
-// IsNotExist is a stub (for now), always returning false
-func IsNotExist(err error) bool {
-	return false
-}
-
 // Getpid is a stub (for now), always returning 1
 func Getpid() int {
 	return 1

src/os/file_go_116.go

@@ -0,0 +1,81 @@
+// +build go1.16
+
+package os
+
+import (
+	"io"
+	"io/fs"
+)
+
+type (
+	DirEntry = fs.DirEntry
+	FileMode = fs.FileMode
+	FileInfo = fs.FileInfo
+)
+
+func (f *File) ReadDir(n int) ([]DirEntry, error) {
+	return nil, &PathError{"ReadDir", f.name, ErrNotImplemented}
+}
+
+// The followings are copied from Go 1.16 official implementation:
+// https://github.com/golang/go/blob/go1.16/src/os/file.go
+
+// ReadFile reads the named file and returns the contents.
+// A successful call returns err == nil, not err == EOF.
+// Because ReadFile reads the whole file, it does not treat an EOF from Read
+// as an error to be reported.
+func ReadFile(name string) ([]byte, error) {
+	f, err := Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var size int
+	if info, err := f.Stat(); err == nil {
+		size64 := info.Size()
+		if int64(int(size64)) == size64 {
+			size = int(size64)
+		}
+	}
+	size++ // one byte for final read at EOF
+
+	// If a file claims a small size, read at least 512 bytes.
+	// In particular, files in Linux's /proc claim size 0 but
+	// then do not work right if read in small pieces,
+	// so an initial read of 1 byte would not work correctly.
+	if size < 512 {
+		size = 512
+	}
+
+	data := make([]byte, 0, size)
+	for {
+		if len(data) >= cap(data) {
+			d := append(data[:cap(data)], 0)
+			data = d[:len(data)]
+		}
+		n, err := f.Read(data[len(data):cap(data)])
+		data = data[:len(data)+n]
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			return data, err
+		}
+	}
+}
+
+// WriteFile writes data to the named file, creating it if necessary.
+// If the file does not exist, WriteFile creates it with permissions perm (before umask);
+// otherwise WriteFile truncates it before writing, without changing permissions.
+func WriteFile(name string, data []byte, perm FileMode) error {
+	f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm)
+	if err != nil {
+		return err
+	}
+	_, err = f.Write(data)
+	if err1 := f.Close(); err1 != nil && err == nil {
+		err = err1
+	}
+	return err
+}

src/os/file_go_other.go

@@ -0,0 +1,46 @@
+// +build !go1.16
+
+package os
+
+import "time"
+
+// A FileInfo describes a file and is returned by Stat and Lstat.
+type FileInfo interface {
+	Name() string       // base name of the file
+	Size() int64        // length in bytes for regular files; system-dependent for others
+	Mode() FileMode     // file mode bits
+	ModTime() time.Time // modification time
+	IsDir() bool        // abbreviation for Mode().IsDir()
+	Sys() interface{}   // underlying data source (can return nil)
+}
+
+type FileMode uint32
+
+// Mode constants, copied from the mainline Go source
+// https://github.com/golang/go/blob/4ce6a8e89668b87dce67e2f55802903d6eb9110a/src/os/types.go#L35-L63
+const (
+	// The single letters are the abbreviations used by the String method's formatting.
+	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
+	ModeAppend                                     // a: append-only
+	ModeExclusive                                  // l: exclusive use
+	ModeTemporary                                  // T: temporary file; Plan 9 only
+	ModeSymlink                                    // L: symbolic link
+	ModeDevice                                     // D: device file
+	ModeNamedPipe                                  // p: named pipe (FIFO)
+	ModeSocket                                     // S: Unix domain socket
+	ModeSetuid                                     // u: setuid
+	ModeSetgid                                     // g: setgid
+	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
+	ModeSticky                                     // t: sticky
+	ModeIrregular                                  // ?: non-regular file; nothing else is known about this file
+
+	// Mask for the type bits. For regular files, none will be set.
+	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice | ModeCharDevice | ModeIrregular
+
+	ModePerm FileMode = 0777 // Unix permission bits
+)
+
+// IsDir is a stub, always returning false
+func (m FileMode) IsDir() bool {
+	return false
+}

src/os/file_other.go

@@ -1,4 +1,4 @@
-// +build baremetal wasm
+// +build baremetal wasm,!wasi
 
 package os
 

src/os/file_unix.go

@@ -1,8 +1,9 @@
-// +build darwin linux,!baremetal,!wasi freebsd,!baremetal
+// +build darwin linux,!baremetal freebsd,!baremetal
 
 package os
 
 import (
+	"io"
 	"syscall"
 )
 
@@ -77,6 +78,9 @@ type unixFileHandle uintptr
 func (f unixFileHandle) Read(b []byte) (n int, err error) {
 	n, err = syscall.Read(int(f), b)
 	err = handleSyscallError(err)
+	if n == 0 && err == nil {
+		err = io.EOF
+	}
 	return
 }
 

src/reflect/swapper.go

@@ -21,7 +21,7 @@ func Swapper(slice interface{}) func(i, j int) {
 		return func(i, j int) {}
 	}
 
-	typ := v.Type().Elem()
+	typ := v.typecode.Elem()
 	size := typ.Size()
 
 	header := (*SliceHeader)(v.value)

src/reflect/type.go

@@ -122,30 +122,218 @@ func (k Kind) String() string {
 }
 
 // basicType returns a new Type for this kind if Kind is a basic type.
-func (k Kind) basicType() Type {
-	return Type(k << 1)
+func (k Kind) basicType() rawType {
+	return rawType(k << 1)
+}
+
+// The following Type type has been copied almost entirely from
+// https://github.com/golang/go/blob/go1.15/src/reflect/type.go#L27-L212.
+// Some methods have been commented out as they haven't yet been implemented.
+
+// Type is the representation of a Go type.
+//
+// Not all methods apply to all kinds of types. Restrictions,
+// if any, are noted in the documentation for each method.
+// Use the Kind method to find out the kind of type before
+// calling kind-specific methods. Calling a method
+// inappropriate to the kind of type causes a run-time panic.
+//
+// Type values are comparable, such as with the == operator,
+// so they can be used as map keys.
+// Two Type values are equal if they represent identical types.
+type Type interface {
+	// Methods applicable to all types.
+
+	// Align returns the alignment in bytes of a value of
+	// this type when allocated in memory.
+	Align() int
+
+	// FieldAlign returns the alignment in bytes of a value of
+	// this type when used as a field in a struct.
+	FieldAlign() int
+
+	// Method returns the i'th method in the type's method set.
+	// It panics if i is not in the range [0, NumMethod()).
+	//
+	// For a non-interface type T or *T, the returned Method's Type and Func
+	// fields describe a function whose first argument is the receiver.
+	//
+	// For an interface type, the returned Method's Type field gives the
+	// method signature, without a receiver, and the Func field is nil.
+	//
+	// Only exported methods are accessible and they are sorted in
+	// lexicographic order.
+	//Method(int) Method
+
+	// MethodByName returns the method with that name in the type's
+	// method set and a boolean indicating if the method was found.
+	//
+	// For a non-interface type T or *T, the returned Method's Type and Func
+	// fields describe a function whose first argument is the receiver.
+	//
+	// For an interface type, the returned Method's Type field gives the
+	// method signature, without a receiver, and the Func field is nil.
+	//MethodByName(string) (Method, bool)
+
+	// NumMethod returns the number of exported methods in the type's method set.
+	NumMethod() int
+
+	// Name returns the type's name within its package for a defined type.
+	// For other (non-defined) types it returns the empty string.
+	Name() string
+
+	// PkgPath returns a defined type's package path, that is, the import path
+	// that uniquely identifies the package, such as "encoding/base64".
+	// If the type was predeclared (string, error) or not defined (*T, struct{},
+	// []int, or A where A is an alias for a non-defined type), the package path
+	// will be the empty string.
+	//PkgPath() string
+
+	// Size returns the number of bytes needed to store
+	// a value of the given type; it is analogous to unsafe.Sizeof.
+	Size() uintptr
+
+	// String returns a string representation of the type.
+	// The string representation may use shortened package names
+	// (e.g., base64 instead of "encoding/base64") and is not
+	// guaranteed to be unique among types. To test for type identity,
+	// compare the Types directly.
+	String() string
+
+	// Kind returns the specific kind of this type.
+	Kind() Kind
+
+	// Implements reports whether the type implements the interface type u.
+	Implements(u Type) bool
+
+	// AssignableTo reports whether a value of the type is assignable to type u.
+	AssignableTo(u Type) bool
+
+	// ConvertibleTo reports whether a value of the type is convertible to type u.
+	ConvertibleTo(u Type) bool
+
+	// Comparable reports whether values of this type are comparable.
+	Comparable() bool
+
+	// Methods applicable only to some types, depending on Kind.
+	// The methods allowed for each kind are:
+	//
+	//	Int*, Uint*, Float*, Complex*: Bits
+	//	Array: Elem, Len
+	//	Chan: ChanDir, Elem
+	//	Func: In, NumIn, Out, NumOut, IsVariadic.
+	//	Map: Key, Elem
+	//	Ptr: Elem
+	//	Slice: Elem
+	//	Struct: Field, FieldByIndex, FieldByName, FieldByNameFunc, NumField
+
+	// Bits returns the size of the type in bits.
+	// It panics if the type's Kind is not one of the
+	// sized or unsized Int, Uint, Float, or Complex kinds.
+	Bits() int
+
+	// ChanDir returns a channel type's direction.
+	// It panics if the type's Kind is not Chan.
+	//ChanDir() ChanDir
+
+	// IsVariadic reports whether a function type's final input parameter
+	// is a "..." parameter. If so, t.In(t.NumIn() - 1) returns the parameter's
+	// implicit actual type []T.
+	//
+	// For concreteness, if t represents func(x int, y ... float64), then
+	//
+	//	t.NumIn() == 2
+	//	t.In(0) is the reflect.Type for "int"
+	//	t.In(1) is the reflect.Type for "[]float64"
+	//	t.IsVariadic() == true
+	//
+	// IsVariadic panics if the type's Kind is not Func.
+	//IsVariadic() bool
+
+	// Elem returns a type's element type.
+	// It panics if the type's Kind is not Array, Chan, Map, Ptr, or Slice.
+	Elem() Type
+
+	// Field returns a struct type's i'th field.
+	// It panics if the type's Kind is not Struct.
+	// It panics if i is not in the range [0, NumField()).
+	Field(i int) StructField
+
+	// FieldByIndex returns the nested field corresponding
+	// to the index sequence. It is equivalent to calling Field
+	// successively for each index i.
+	// It panics if the type's Kind is not Struct.
+	//FieldByIndex(index []int) StructField
+
+	// FieldByName returns the struct field with the given name
+	// and a boolean indicating if the field was found.
+	//FieldByName(name string) (StructField, bool)
+
+	// FieldByNameFunc returns the struct field with a name
+	// that satisfies the match function and a boolean indicating if
+	// the field was found.
+	//
+	// FieldByNameFunc considers the fields in the struct itself
+	// and then the fields in any embedded structs, in breadth first order,
+	// stopping at the shallowest nesting depth containing one or more
+	// fields satisfying the match function. If multiple fields at that depth
+	// satisfy the match function, they cancel each other
+	// and FieldByNameFunc returns no match.
+	// This behavior mirrors Go's handling of name lookup in
+	// structs containing embedded fields.
+	//FieldByNameFunc(match func(string) bool) (StructField, bool)
+
+	// In returns the type of a function type's i'th input parameter.
+	// It panics if the type's Kind is not Func.
+	// It panics if i is not in the range [0, NumIn()).
+	//In(i int) Type
+
+	// Key returns a map type's key type.
+	// It panics if the type's Kind is not Map.
+	Key() Type
+
+	// Len returns an array type's length.
+	// It panics if the type's Kind is not Array.
+	Len() int
+
+	// NumField returns a struct type's field count.
+	// It panics if the type's Kind is not Struct.
+	NumField() int
+
+	// NumIn returns a function type's input parameter count.
+	// It panics if the type's Kind is not Func.
+	//NumIn() int
+
+	// NumOut returns a function type's output parameter count.
+	// It panics if the type's Kind is not Func.
+	//NumOut() int
+
+	// Out returns the type of a function type's i'th output parameter.
+	// It panics if the type's Kind is not Func.
+	// It panics if i is not in the range [0, NumOut()).
+	//Out(i int) Type
 }
 
 // The typecode as used in an interface{}.
-type Type uintptr
+type rawType uintptr
 
 func TypeOf(i interface{}) Type {
 	return ValueOf(i).typecode
 }
 
 func PtrTo(t Type) Type {
-	ptrType := t<<5 | 5 // 0b0101 == 5
+	ptrType := t.(rawType)<<5 | 5 // 0b0101 == 5
 	if ptrType>>5 != t {
 		panic("reflect: PtrTo type does not fit")
 	}
 	return ptrType
 }
 
-func (t Type) String() string {
+func (t rawType) String() string {
 	return "T"
 }
 
-func (t Type) Kind() Kind {
+func (t rawType) Kind() Kind {
 	if t%2 == 0 {
 		// basic type
 		return Kind((t >> 1) % 32)
@@ -156,14 +344,18 @@ func (t Type) Kind() Kind {
 
 // Elem returns the element type for channel, slice and array types, the
 // pointed-to value for pointer types, and the key type for map types.
-func (t Type) Elem() Type {
+func (t rawType) Elem() Type {
+	return t.elem()
+}
+
+func (t rawType) elem() rawType {
 	switch t.Kind() {
 	case Chan, Ptr, Slice:
 		return t.stripPrefix()
 	case Array:
 		index := t.stripPrefix()
 		elem, _ := readVarint(unsafe.Pointer(uintptr(unsafe.Pointer(&arrayTypesSidetable)) + uintptr(index)))
-		return Type(elem)
+		return rawType(elem)
 	default: // not implemented: Map
 		panic("unimplemented: (reflect.Type).Elem()")
 	}
@@ -175,14 +367,14 @@ func (t Type) Elem() Type {
 // simply shifted off.
 //
 // The behavior is only defined for non-basic types.
-func (t Type) stripPrefix() Type {
+func (t rawType) stripPrefix() rawType {
 	// Look at the 'n' bit in the type code (see the top of this file) to see
 	// whether this is a named type.
 	if (t>>4)%2 != 0 {
 		// This is a named type. The data is stored in a sidetable.
 		namedTypeNum := t >> 5
 		n := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&namedNonBasicTypesSidetable)) + uintptr(namedTypeNum)*unsafe.Sizeof(uintptr(0))))
-		return Type(n)
+		return rawType(n)
 	}
 	// Not a named type, so the value is stored directly in the type code.
 	return t >> 5
@@ -190,7 +382,23 @@ func (t Type) stripPrefix() Type {
 
 // Field returns the type of the i'th field of this struct type. It panics if t
 // is not a struct type.
-func (t Type) Field(i int) StructField {
+func (t rawType) Field(i int) StructField {
+	field := t.rawField(i)
+	return StructField{
+		Name:      field.Name,
+		PkgPath:   field.PkgPath,
+		Type:      field.Type, // note: converts rawType to Type
+		Tag:       field.Tag,
+		Anonymous: field.Anonymous,
+		Offset:    field.Offset,
+	}
+}
+
+// rawField returns nearly the same value as Field but without converting the
+// Type member to an interface.
+//
+// For internal use only.
+func (t rawType) rawField(i int) rawStructField {
 	if t.Kind() != Struct {
 		panic(&TypeError{"Field"})
 	}
@@ -206,7 +414,7 @@ func (t Type) Field(i int) StructField {
 	// efficient, but it is easy to implement.
 	// Adding a jump table at the start to jump to the field directly would
 	// make this much faster, but that would also impact code size.
-	field := StructField{}
+	field := rawStructField{}
 	offset := uintptr(0)
 	for fieldNum := 0; fieldNum <= i; fieldNum++ {
 		// Read some flags of this field, like whether the field is an
@@ -215,15 +423,16 @@ func (t Type) Field(i int) StructField {
 		p = unsafe.Pointer(uintptr(p) + 1)
 
 		// Read the type of this struct field.
-		var fieldType uintptr
-		fieldType, p = readVarint(p)
-		field.Type = Type(fieldType)
+		var fieldTypeVal uintptr
+		fieldTypeVal, p = readVarint(p)
+		fieldType := rawType(fieldTypeVal)
+		field.Type = fieldType
 
 		// Move Offset forward to align it to this field's alignment.
 		// Assume alignment is a power of two.
-		offset = align(offset, uintptr(field.Type.Align()))
+		offset = align(offset, uintptr(fieldType.Align()))
 		field.Offset = offset
-		offset += field.Type.Size() // starting (unaligned) offset for next field
+		offset += fieldType.Size() // starting (unaligned) offset for next field
 
 		// Read the field name.
 		var nameNum uintptr
@@ -264,7 +473,7 @@ func (t Type) Field(i int) StructField {
 // Bits returns the number of bits that this type uses. It is only valid for
 // arithmetic types (integers, floats, and complex numbers). For other types, it
 // will panic.
-func (t Type) Bits() int {
+func (t rawType) Bits() int {
 	kind := t.Kind()
 	if kind >= Int && kind <= Complex128 {
 		return int(t.Size()) * 8
@@ -274,7 +483,7 @@ func (t Type) Bits() int {
 
 // Len returns the number of elements in this array. It panics of the type kind
 // is not Array.
-func (t Type) Len() int {
+func (t rawType) Len() int {
 	if t.Kind() != Array {
 		panic(TypeError{"Len"})
 	}
@@ -290,7 +499,7 @@ func (t Type) Len() int {
 
 // NumField returns the number of fields of a struct type. It panics for other
 // type kinds.
-func (t Type) NumField() int {
+func (t rawType) NumField() int {
 	if t.Kind() != Struct {
 		panic(&TypeError{"NumField"})
 	}
@@ -301,7 +510,7 @@ func (t Type) NumField() int {
 
 // Size returns the size in bytes of a given type. It is similar to
 // unsafe.Sizeof.
-func (t Type) Size() uintptr {
+func (t rawType) Size() uintptr {
 	switch t.Kind() {
 	case Bool, Int8, Uint8:
 		return 1
@@ -324,21 +533,24 @@ func (t Type) Size() uintptr {
 	case Complex128:
 		return 16
 	case String:
-		return unsafe.Sizeof(StringHeader{})
+		return unsafe.Sizeof("")
 	case UnsafePointer, Chan, Map, Ptr:
 		return unsafe.Sizeof(uintptr(0))
 	case Slice:
-		return unsafe.Sizeof(SliceHeader{})
+		return unsafe.Sizeof([]int{})
 	case Interface:
 		return unsafe.Sizeof(interface{}(nil))
+	case Func:
+		var f func()
+		return unsafe.Sizeof(f)
 	case Array:
-		return t.Elem().Size() * uintptr(t.Len())
+		return t.elem().Size() * uintptr(t.Len())
 	case Struct:
 		numField := t.NumField()
 		if numField == 0 {
 			return 0
 		}
-		lastField := t.Field(numField - 1)
+		lastField := t.rawField(numField - 1)
 		return lastField.Offset + lastField.Type.Size()
 	default:
 		panic("unimplemented: size of type")
@@ -347,7 +559,7 @@ func (t Type) Size() uintptr {
 
 // Align returns the alignment of this type. It is similar to calling
 // unsafe.Alignof.
-func (t Type) Align() int {
+func (t rawType) Align() int {
 	switch t.Kind() {
 	case Bool, Int8, Uint8:
 		return int(unsafe.Alignof(int8(0)))
@@ -370,25 +582,28 @@ func (t Type) Align() int {
 	case Complex128:
 		return int(unsafe.Alignof(complex128(0)))
 	case String:
-		return int(unsafe.Alignof(StringHeader{}))
+		return int(unsafe.Alignof(""))
 	case UnsafePointer, Chan, Map, Ptr:
 		return int(unsafe.Alignof(uintptr(0)))
 	case Slice:
-		return int(unsafe.Alignof(SliceHeader{}))
+		return int(unsafe.Alignof([]int(nil)))
 	case Interface:
 		return int(unsafe.Alignof(interface{}(nil)))
+	case Func:
+		var f func()
+		return int(unsafe.Alignof(f))
 	case Struct:
 		numField := t.NumField()
 		alignment := 1
 		for i := 0; i < numField; i++ {
-			fieldAlignment := t.Field(i).Type.Align()
+			fieldAlignment := t.rawField(i).Type.Align()
 			if fieldAlignment > alignment {
 				alignment = fieldAlignment
 			}
 		}
 		return alignment
 	case Array:
-		return t.Elem().Align()
+		return t.elem().Align()
 	default:
 		panic("unimplemented: alignment of type")
 	}
@@ -396,31 +611,31 @@ func (t Type) Align() int {
 
 // FieldAlign returns the alignment if this type is used in a struct field. It
 // is currently an alias for Align() but this might change in the future.
-func (t Type) FieldAlign() int {
+func (t rawType) FieldAlign() int {
 	return t.Align()
 }
 
-// AssignableTo returns whether a value of type u can be assigned to a variable
-// of type t.
-func (t Type) AssignableTo(u Type) bool {
-	if t == u {
+// AssignableTo returns whether a value of type t can be assigned to a variable
+// of type u.
+func (t rawType) AssignableTo(u Type) bool {
+	if t == u.(rawType) {
 		return true
 	}
-	if t.Kind() == Interface {
-		panic("reflect: unimplemented: assigning to interface of different type")
+	if u.Kind() == Interface {
+		panic("reflect: unimplemented: AssignableTo with interface")
 	}
 	return false
 }
 
-func (t Type) Implements(u Type) bool {
-	if t.Kind() != Interface {
+func (t rawType) Implements(u Type) bool {
+	if u.Kind() != Interface {
 		panic("reflect: non-interface type passed to Type.Implements")
 	}
-	return u.AssignableTo(t)
+	return t.AssignableTo(u)
 }
 
 // Comparable returns whether values of this type can be compared to each other.
-func (t Type) Comparable() bool {
+func (t rawType) Comparable() bool {
 	switch t.Kind() {
 	case Bool, Int, Int8, Int16, Int32, Int64, Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
 		return true
@@ -439,7 +654,7 @@ func (t Type) Comparable() bool {
 	case Slice:
 		return false
 	case Array:
-		return t.Elem().Comparable()
+		return t.elem().Comparable()
 	case Func:
 		return false
 	case Map:
@@ -447,7 +662,7 @@ func (t Type) Comparable() bool {
 	case Struct:
 		numField := t.NumField()
 		for i := 0; i < numField; i++ {
-			if !t.Field(i).Type.Comparable() {
+			if !t.rawField(i).Type.Comparable() {
 				return false
 			}
 		}
@@ -457,19 +672,19 @@ func (t Type) Comparable() bool {
 	}
 }
 
-func (t Type) ConvertibleTo(u Type) bool {
+func (t rawType) ConvertibleTo(u Type) bool {
 	panic("unimplemented: (reflect.Type).ConvertibleTo()")
 }
 
-func (t Type) NumMethod() int {
+func (t rawType) NumMethod() int {
 	panic("unimplemented: (reflect.Type).NumMethod()")
 }
 
-func (t Type) Name() string {
+func (t rawType) Name() string {
 	panic("unimplemented: (reflect.Type).Name()")
 }
 
-func (t Type) Key() Type {
+func (t rawType) Key() Type {
 	panic("unimplemented: (reflect.Type).Key()")
 }
 
@@ -488,6 +703,18 @@ type StructField struct {
 	Offset    uintptr
 }
 
+// rawStructField is the same as StructField but with the Type member replaced
+// with rawType. For internal use only. Avoiding this conversion to the Type
+// interface improves code size in many cases.
+type rawStructField struct {
+	Name      string
+	PkgPath   string
+	Type      rawType
+	Tag       StructTag
+	Anonymous bool
+	Offset    uintptr
+}
+
 // A StructTag is the tag string in a struct field.
 type StructTag string
 

src/reflect/value.go

@@ -16,7 +16,7 @@ const (
 )
 
 type Value struct {
-	typecode Type
+	typecode rawType
 	value    unsafe.Pointer
 	flags    valueFlags
 }
@@ -28,6 +28,13 @@ func (v Value) isIndirect() bool {
 	return v.flags&valueFlagIndirect != 0
 }
 
+// isExported returns whether the value represented by this Value could be
+// accessed without violating type system constraints. For example, it is not
+// set for unexported struct fields.
+func (v Value) isExported() bool {
+	return v.flags&valueFlagExported != 0
+}
+
 func Indirect(v Value) Value {
 	if v.Kind() != Ptr {
 		return v
@@ -36,10 +43,10 @@ func Indirect(v Value) Value {
 }
 
 //go:linkname composeInterface runtime.composeInterface
-func composeInterface(Type, unsafe.Pointer) interface{}
+func composeInterface(rawType, unsafe.Pointer) interface{}
 
 //go:linkname decomposeInterface runtime.decomposeInterface
-func decomposeInterface(i interface{}) (Type, unsafe.Pointer)
+func decomposeInterface(i interface{}) (rawType, unsafe.Pointer)
 
 func ValueOf(i interface{}) Value {
 	typecode, value := decomposeInterface(i)
@@ -51,11 +58,20 @@ func ValueOf(i interface{}) Value {
 }
 
 func (v Value) Interface() interface{} {
-	if v.isIndirect() && v.Type().Size() <= unsafe.Sizeof(uintptr(0)) {
+	if !v.isExported() {
+		panic("(reflect.Value).Interface: unexported")
+	}
+	return valueInterfaceUnsafe(v)
+}
+
+// valueInterfaceUnsafe is used by the runtime to hash map keys. It should not
+// be subject to the isExported check.
+func valueInterfaceUnsafe(v Value) interface{} {
+	if v.isIndirect() && v.typecode.Size() <= unsafe.Sizeof(uintptr(0)) {
 		// Value was indirect but must be put back directly in the interface
 		// value.
 		var value uintptr
-		for j := v.Type().Size(); j != 0; j-- {
+		for j := v.typecode.Size(); j != 0; j-- {
 			value = (value << 8) | uintptr(*(*uint8)(unsafe.Pointer(uintptr(v.value) + j - 1)))
 		}
 		v.value = unsafe.Pointer(value)
@@ -67,8 +83,16 @@ func (v Value) Type() Type {
 	return v.typecode
 }
 
+// Internal function only, do not use.
+//
+// RawType returns the raw, underlying type code. It is used in the runtime
+// package and needs to be exported for the runtime package to access it.
+func (v Value) RawType() rawType {
+	return v.typecode
+}
+
 func (v Value) Kind() Kind {
-	return v.Type().Kind()
+	return v.typecode.Kind()
 }
 
 // IsNil returns whether the value is the nil value. It panics if the value Kind
@@ -132,7 +156,7 @@ func (v Value) CanInterface() bool {
 }
 
 func (v Value) CanAddr() bool {
-	panic("unimplemented: (reflect.Value).CanAddr()")
+	return v.flags&(valueFlagIndirect) == valueFlagIndirect
 }
 
 func (v Value) Addr() Value {
@@ -313,10 +337,9 @@ func chanlen(p unsafe.Pointer) int
 // Len returns the length of this value for slices, strings, arrays, channels,
 // and maps. For other types, it panics.
 func (v Value) Len() int {
-	t := v.Type()
-	switch t.Kind() {
+	switch v.typecode.Kind() {
 	case Array:
-		return v.Type().Len()
+		return v.typecode.Len()
 	case Chan:
 		return chanlen(v.value)
 	case Map:
@@ -336,10 +359,9 @@ func chancap(p unsafe.Pointer) int
 // Cap returns the capacity of this value for arrays, channels and slices.
 // For other types, it panics.
 func (v Value) Cap() int {
-	t := v.Type()
-	switch t.Kind() {
+	switch v.typecode.Kind() {
 	case Array:
-		return v.Type().Len()
+		return v.typecode.Len()
 	case Chan:
 		return chancap(v.value)
 	case Slice:
@@ -352,7 +374,7 @@ func (v Value) Cap() int {
 // NumField returns the number of fields of this struct. It panics for other
 // value types.
 func (v Value) NumField() int {
-	return v.Type().NumField()
+	return v.typecode.NumField()
 }
 
 func (v Value) Elem() Value {
@@ -366,7 +388,7 @@ func (v Value) Elem() Value {
 			return Value{}
 		}
 		return Value{
-			typecode: v.Type().Elem(),
+			typecode: v.typecode.elem(),
 			value:    ptr,
 			flags:    v.flags | valueFlagIndirect,
 		}
@@ -377,7 +399,7 @@ func (v Value) Elem() Value {
 
 // Field returns the value of the i'th field of this struct.
 func (v Value) Field(i int) Value {
-	structField := v.Type().Field(i)
+	structField := v.typecode.rawField(i)
 	flags := v.flags
 	if structField.PkgPath != "" {
 		// The fact that PkgPath is present means that this field is not
@@ -385,14 +407,15 @@ func (v Value) Field(i int) Value {
 		flags &^= valueFlagExported
 	}
 
-	size := v.Type().Size()
-	fieldSize := structField.Type.Size()
+	size := v.typecode.Size()
+	fieldType := structField.Type
+	fieldSize := fieldType.Size()
 	if v.isIndirect() || fieldSize > unsafe.Sizeof(uintptr(0)) {
 		// v.value was already a pointer to the value and it should stay that
 		// way.
 		return Value{
 			flags:    flags,
-			typecode: structField.Type,
+			typecode: fieldType,
 			value:    unsafe.Pointer(uintptr(v.value) + structField.Offset),
 		}
 	}
@@ -407,7 +430,7 @@ func (v Value) Field(i int) Value {
 		// situation explicitly.
 		return Value{
 			flags:    flags,
-			typecode: structField.Type,
+			typecode: fieldType,
 			value:    unsafe.Pointer(uintptr(0)),
 		}
 	}
@@ -420,7 +443,7 @@ func (v Value) Field(i int) Value {
 		value := unsafe.Pointer(loadValue(ptr, fieldSize))
 		return Value{
 			flags:    0,
-			typecode: structField.Type,
+			typecode: fieldType,
 			value:    value,
 		}
 	}
@@ -430,7 +453,7 @@ func (v Value) Field(i int) Value {
 	value := maskAndShift(uintptr(v.value), structField.Offset, fieldSize)
 	return Value{
 		flags:    flags,
-		typecode: structField.Type,
+		typecode: fieldType,
 		value:    unsafe.Pointer(value),
 	}
 }
@@ -444,10 +467,10 @@ func (v Value) Index(i int) Value {
 			panic("reflect: slice index out of range")
 		}
 		elem := Value{
-			typecode: v.Type().Elem(),
+			typecode: v.typecode.elem(),
 			flags:    v.flags | valueFlagIndirect,
 		}
-		addr := uintptr(slice.Data) + elem.Type().Size()*uintptr(i) // pointer to new value
+		addr := uintptr(slice.Data) + elem.typecode.Size()*uintptr(i) // pointer to new value
 		elem.value = unsafe.Pointer(addr)
 		return elem
 	case String:
@@ -464,13 +487,13 @@ func (v Value) Index(i int) Value {
 		}
 	case Array:
 		// Extract an element from the array.
-		elemType := v.Type().Elem()
+		elemType := v.typecode.elem()
 		elemSize := elemType.Size()
-		size := v.Type().Size()
+		size := v.typecode.Size()
 		if size == 0 {
 			// The element size is 0 and/or the length of the array is 0.
 			return Value{
-				typecode: v.Type().Elem(),
+				typecode: v.typecode.elem(),
 				flags:    v.flags,
 			}
 		}
@@ -481,7 +504,7 @@ func (v Value) Index(i int) Value {
 			// elemSize.
 			addr := uintptr(v.value) + elemSize*uintptr(i) // pointer to new value
 			return Value{
-				typecode: v.Type().Elem(),
+				typecode: v.typecode.elem(),
 				flags:    v.flags,
 				value:    unsafe.Pointer(addr),
 			}
@@ -492,7 +515,7 @@ func (v Value) Index(i int) Value {
 			// Load the value from the pointer.
 			addr := uintptr(v.value) + elemSize*uintptr(i) // pointer to new value
 			return Value{
-				typecode: v.Type().Elem(),
+				typecode: v.typecode.elem(),
 				flags:    v.flags,
 				value:    unsafe.Pointer(loadValue(unsafe.Pointer(addr), elemSize)),
 			}
@@ -503,7 +526,7 @@ func (v Value) Index(i int) Value {
 		offset := elemSize * uintptr(i)
 		value := maskAndShift(uintptr(v.value), offset, elemSize)
 		return Value{
-			typecode: v.Type().Elem(),
+			typecode: v.typecode.elem(),
 			flags:    v.flags,
 			value:    unsafe.Pointer(value),
 		}
@@ -532,6 +555,14 @@ func maskAndShift(value, offset, size uintptr) uintptr {
 	return (uintptr(value) >> (offset * 8)) & mask
 }
 
+func (v Value) NumMethod() int {
+	return v.typecode.NumMethod()
+}
+
+func (v Value) OverflowFloat(x float64) bool {
+	panic("unimplemented: (reflect.Value).OverflowFloat()")
+}
+
 func (v Value) MapKeys() []Value {
 	panic("unimplemented: (reflect.Value).MapKeys()")
 }
@@ -561,10 +592,10 @@ func (it *MapIter) Next() bool {
 
 func (v Value) Set(x Value) {
 	v.checkAddressable()
-	if !v.Type().AssignableTo(x.Type()) {
+	if !v.typecode.AssignableTo(x.typecode) {
 		panic("reflect: cannot set")
 	}
-	size := v.Type().Size()
+	size := v.typecode.Size()
 	xptr := x.value
 	if size <= unsafe.Sizeof(uintptr(0)) && !x.isIndirect() {
 		value := x.value
@@ -655,6 +686,18 @@ func (v Value) SetString(x string) {
 	}
 }
 
+func (v Value) SetBytes(x []byte) {
+	panic("unimplemented: (reflect.Value).SetBytes()")
+}
+
+func (v Value) SetCap(n int) {
+	panic("unimplemented: (reflect.Value).SetCap()")
+}
+
+func (v Value) SetLen(n int) {
+	panic("unimplemented: (reflect.Value).SetLen()")
+}
+
 func (v Value) checkAddressable() {
 	if !v.isIndirect() {
 		panic("reflect: value is not addressable")

src/runtime/hashmap.go

@@ -349,48 +349,55 @@ func hashmapStringDelete(m *hashmap, key string) {
 
 // Hashmap with interface keys (for everything else).
 
+// This is a method that is intentionally unexported in the reflect package. It
+// is identical to the Interface() method call, except it doesn't check whether
+// a field is exported and thus allows circumventing the type system.
+// The hash function needs it as it also needs to hash unexported struct fields.
+//go:linkname valueInterfaceUnsafe reflect.valueInterfaceUnsafe
+func valueInterfaceUnsafe(v reflect.Value) interface{}
+
 func hashmapInterfaceHash(itf interface{}) uint32 {
 	x := reflect.ValueOf(itf)
-	if x.Type() == 0 {
+	if x.RawType() == 0 {
 		return 0 // nil interface
 	}
 
 	value := (*_interface)(unsafe.Pointer(&itf)).value
 	ptr := value
-	if x.Type().Size() <= unsafe.Sizeof(uintptr(0)) {
+	if x.RawType().Size() <= unsafe.Sizeof(uintptr(0)) {
 		// Value fits in pointer, so it's directly stored in the pointer.
 		ptr = unsafe.Pointer(&value)
 	}
 
-	switch x.Type().Kind() {
+	switch x.RawType().Kind() {
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-		return hashmapHash(ptr, x.Type().Size())
+		return hashmapHash(ptr, x.RawType().Size())
 	case reflect.Bool, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
-		return hashmapHash(ptr, x.Type().Size())
+		return hashmapHash(ptr, x.RawType().Size())
 	case reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
 		// It should be possible to just has the contents. However, NaN != NaN
 		// so if you're using lots of NaNs as map keys (you shouldn't) then hash
 		// time may become exponential. To fix that, it would be better to
 		// return a random number instead:
 		// https://research.swtch.com/randhash
-		return hashmapHash(ptr, x.Type().Size())
+		return hashmapHash(ptr, x.RawType().Size())
 	case reflect.String:
 		return hashmapStringHash(x.String())
 	case reflect.Chan, reflect.Ptr, reflect.UnsafePointer:
 		// It might seem better to just return the pointer, but that won't
 		// result in an evenly distributed hashmap. Instead, hash the pointer
 		// like most other types.
-		return hashmapHash(ptr, x.Type().Size())
+		return hashmapHash(ptr, x.RawType().Size())
 	case reflect.Array:
 		var hash uint32
 		for i := 0; i < x.Len(); i++ {
-			hash |= hashmapInterfaceHash(x.Index(i).Interface())
+			hash |= hashmapInterfaceHash(valueInterfaceUnsafe(x.Index(i)))
 		}
 		return hash
 	case reflect.Struct:
 		var hash uint32
 		for i := 0; i < x.NumField(); i++ {
-			hash |= hashmapInterfaceHash(x.Field(i).Interface())
+			hash |= hashmapInterfaceHash(valueInterfaceUnsafe(x.Field(i)))
 		}
 		return hash
 	default:

src/runtime/interface.go

@@ -31,18 +31,21 @@ func interfaceEqual(x, y interface{}) bool {
 }
 
 func reflectValueEqual(x, y reflect.Value) bool {
-	if x.Type() == 0 || y.Type() == 0 {
+	// Note: doing a x.Type() == y.Type() comparison would not work here as that
+	// would introduce an infinite recursion: comparing two reflect.Type values
+	// is done with this reflectValueEqual runtime call.
+	if x.RawType() == 0 || y.RawType() == 0 {
 		// One of them is nil.
-		return x.Type() == y.Type()
+		return x.RawType() == y.RawType()
 	}
 
-	if x.Type() != y.Type() {
+	if x.RawType() != y.RawType() {
 		// The type is not the same, which means the interfaces are definitely
 		// not the same.
 		return false
 	}
 
-	switch x.Type().Kind() {
+	switch x.RawType().Kind() {
 	case reflect.Bool:
 		return x.Bool() == y.Bool()
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
@@ -107,6 +110,8 @@ type typecodeID struct {
 
 	// The array length, for array types.
 	length uintptr
+
+	methodSet *interfaceMethodInfo // nil or a GEP of an array
 }
 
 // structField is used by the compiler to pass information to the interface
@@ -118,20 +123,11 @@ type structField struct {
 	embedded bool
 }
 
-// Pseudo type used before interface lowering. By using a struct instead of a
-// function call, this is simpler to reason about during init interpretation
-// than a function call. Also, by keeping the method set around it is easier to
-// implement interfaceImplements in the interp package.
-type typeInInterface struct {
-	typecode  *typecodeID          // element type, underlying type, or reference to struct fields
-	methodSet *interfaceMethodInfo // nil or a GEP of an array
-}
-
 // Pseudo function call used during a type assert. It is used during interface
 // lowering, to assign the lowest type numbers to the types with the most type
 // asserts. Also, it is replaced with const false if this type assert can never
 // happen.
-func typeAssert(actualType uintptr, assertedType *typecodeID) bool
+func typeAssert(actualType uintptr, assertedType *uint8) bool
 
 // Pseudo function call that returns whether a given type implements all methods
 // of the given interface.

src/runtime/runtime_stm32_timers.go

@@ -56,6 +56,7 @@ func nanosecondsToTicks(ns int64) timeUnit {
 }
 
 // number of ticks (microseconds) since start.
+//go:linkname ticks runtime.ticks
 func ticks() timeUnit {
 	return timeUnit(tickCount.Get())
 }

src/runtime/runtime_stm32l4x2.go

@@ -0,0 +1,262 @@
+// +build stm32,stm32l4x2
+
+package runtime
+
+import (
+	"device/stm32"
+	"machine"
+)
+
+/*
+   clock settings
+   +-------------+-----------+
+   | LSE         | 32.768khz |
+   | SYSCLK      | 80mhz     |
+   | HCLK        | 80mhz     |
+   | APB1(PCLK1) | 80mhz     |
+   | APB2(PCLK2) | 80mhz     |
+   +-------------+-----------+
+*/
+const (
+	HSE_STARTUP_TIMEOUT = 0x0500
+	PLL_M               = 1
+	PLL_N               = 40
+	PLL_P               = RCC_PLLP_DIV7
+	PLL_Q               = RCC_PLLQ_DIV2
+	PLL_R               = RCC_PLLR_DIV2
+
+	MSIRANGE = stm32.RCC_CR_MSIRANGE_Range4M
+
+	PWR_CR1_VOS_0                = 1 << stm32.PWR_CR1_VOS_Pos
+	PWR_CR1_VOS_1                = 2 << stm32.PWR_CR1_VOS_Pos
+	PWR_REGULATOR_VOLTAGE_SCALE1 = PWR_CR1_VOS_0
+	PWR_REGULATOR_VOLTAGE_SCALE2 = PWR_CR1_VOS_1
+
+	FLASH_LATENCY_0 = 0
+	FLASH_LATENCY_1 = 1
+	FLASH_LATENCY_2 = 2
+	FLASH_LATENCY_3 = 3
+	FLASH_LATENCY_4 = 4
+
+	RCC_PLLP_DIV7 = 7
+	RCC_PLLQ_DIV2 = 2
+	RCC_PLLR_DIV2 = 2
+
+	RCC_CFGR_SWS_MSI = 0x0
+	RCC_CFGR_SWS_PLL = 0xC
+
+	RCC_PLLSOURCE_MSI = 1
+
+	RCC_PLL_SYSCLK = stm32.RCC_PLLCFGR_PLLREN
+)
+
+/*
+   timer settings used for tick and sleep.
+
+   note: TICK_TIMER_FREQ and SLEEP_TIMER_FREQ are controlled by PLL / clock
+   settings above, so must be kept in sync if the clock settings are changed.
+*/
+const (
+	TICK_RATE        = 1000 // 1 KHz
+	TICK_TIMER_IRQ   = stm32.IRQ_TIM1_UP_TIM16
+	TICK_TIMER_FREQ  = 80000000 // 80 MHz
+	SLEEP_TIMER_IRQ  = stm32.IRQ_TIM1_BRK_TIM15
+	SLEEP_TIMER_FREQ = 80000000 // 84 MHz
+)
+
+type arrtype = uint32
+
+const asyncScheduler = false
+
+func init() {
+	initCLK()
+
+	initSleepTimer(&timerInfo{
+		EnableRegister: &stm32.RCC.APB2ENR,
+		EnableFlag:     stm32.RCC_APB2ENR_TIM15EN,
+		Device:         stm32.TIM15,
+	})
+
+	machine.UART0.Configure(machine.UARTConfig{})
+
+	initTickTimer(&timerInfo{
+		EnableRegister: &stm32.RCC.APB2ENR,
+		EnableFlag:     stm32.RCC_APB2ENR_TIM16EN,
+		Device:         stm32.TIM16,
+	})
+}
+
+func putchar(c byte) {
+	machine.UART0.WriteByte(c)
+}
+
+func initCLK() {
+	// PWR_CLK_ENABLE
+	stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_PWREN)
+	_ = stm32.RCC.APB1ENR1.Get()
+
+	// Disable Backup domain protection
+	if !stm32.PWR.CR1.HasBits(stm32.PWR_CR1_DBP) {
+		stm32.PWR.CR1.SetBits(stm32.PWR_CR1_DBP)
+		for !stm32.PWR.CR1.HasBits(stm32.PWR_CR1_DBP) {
+		}
+	}
+
+	// Set LSE Drive to LOW
+	stm32.RCC.BDCR.ReplaceBits(0, stm32.RCC_BDCR_LSEDRV_Msk, 0)
+
+	// Initialize the High-Speed External Oscillator
+	initOsc()
+
+	// PWR_VOLTAGESCALING_CONFIG
+	stm32.PWR.CR1.ReplaceBits(0, stm32.PWR_CR1_VOS_Msk, 0)
+	_ = stm32.PWR.CR1.Get()
+
+	// Set flash wait states (min 5 latency units) based on clock
+	if (stm32.FLASH.ACR.Get() & 0xF) < 5 {
+		stm32.FLASH.ACR.ReplaceBits(5, 0xF, 0)
+	}
+
+	// Ensure HCLK does not exceed max during transition
+	stm32.RCC.CFGR.ReplaceBits(8<<stm32.RCC_CFGR_HPRE_Pos, stm32.RCC_CFGR_HPRE_Msk, 0)
+
+	// Set SYSCLK source and wait
+	// (3 = RCC_SYSCLKSOURCE_PLLCLK, 2=RCC_CFGR_SWS_Pos)
+	stm32.RCC.CFGR.ReplaceBits(3, stm32.RCC_CFGR_SW_Msk, 0)
+	for stm32.RCC.CFGR.Get()&(3<<2) != (3 << 2) {
+	}
+
+	// Set HCLK
+	// (0 = RCC_SYSCLKSOURCE_PLLCLK)
+	stm32.RCC.CFGR.ReplaceBits(0, stm32.RCC_CFGR_HPRE_Msk, 0)
+
+	// Set flash wait states (max 5 latency units) based on clock
+	if (stm32.FLASH.ACR.Get() & 0xF) > 5 {
+		stm32.FLASH.ACR.ReplaceBits(5, 0xF, 0)
+	}
+
+	// Set APB1 and APB2 clocks (0 = DIV1)
+	stm32.RCC.CFGR.ReplaceBits(0, stm32.RCC_CFGR_PPRE1_Msk, 0)
+	stm32.RCC.CFGR.ReplaceBits(0, stm32.RCC_CFGR_PPRE2_Msk, 0)
+}
+
+func initOsc() {
+	sysclkSource := stm32.RCC.CFGR.Get() & stm32.RCC_CFGR_SWS_Msk
+	pllConfig := stm32.RCC.PLLCFGR.Get() & stm32.RCC_PLLCFGR_PLLSRC_Msk
+
+	// Enable MSI, adjusting flash latency
+	if sysclkSource == RCC_CFGR_SWS_MSI ||
+		(sysclkSource == RCC_CFGR_SWS_PLL && pllConfig == RCC_PLLSOURCE_MSI) {
+		if MSIRANGE > getMSIRange() {
+			setFlashLatencyFromMSIRange(MSIRANGE)
+
+			setMSIFreq(MSIRANGE, 0)
+		} else {
+			setMSIFreq(MSIRANGE, 0)
+
+			if sysclkSource == RCC_CFGR_SWS_MSI {
+				setFlashLatencyFromMSIRange(MSIRANGE)
+			}
+		}
+	} else {
+		stm32.RCC.CR.SetBits(stm32.RCC_CR_MSION)
+		for !stm32.RCC.CR.HasBits(stm32.RCC_CR_MSIRDY) {
+		}
+
+		setMSIFreq(MSIRANGE, 0)
+	}
+
+	// Enable LSE, wait until ready
+	stm32.RCC.BDCR.SetBits(stm32.RCC_BDCR_LSEON)
+	for !stm32.RCC.BDCR.HasBits(stm32.RCC_BDCR_LSEON) {
+	}
+
+	// Disable the PLL, wait until disabled
+	stm32.RCC.CR.ClearBits(stm32.RCC_CR_PLLON)
+	for stm32.RCC.CR.HasBits(stm32.RCC_CR_PLLRDY) {
+	}
+
+	// Configure the PLL
+	stm32.RCC.PLLCFGR.ReplaceBits(
+		(1)| // 1 = RCC_PLLSOURCE_MSI
+			(PLL_M-1)<<stm32.RCC_PLLCFGR_PLLM_Pos|
+			(PLL_N<<stm32.RCC_PLLCFGR_PLLN_Pos)|
+			(((PLL_Q>>1)-1)<<stm32.RCC_PLLCFGR_PLLQ_Pos)|
+			(((PLL_R>>1)-1)<<stm32.RCC_PLLCFGR_PLLR_Pos)|
+			(PLL_P<<stm32.RCC_PLLCFGR_PLLPDIV_Pos),
+		stm32.RCC_PLLCFGR_PLLSRC_Msk|stm32.RCC_PLLCFGR_PLLM_Msk|
+			stm32.RCC_PLLCFGR_PLLN_Msk|stm32.RCC_PLLCFGR_PLLP_Msk|
+			stm32.RCC_PLLCFGR_PLLR_Msk|stm32.RCC_PLLCFGR_PLLPDIV_Msk,
+		0)
+
+	// Enable the PLL and PLL System Clock Output, wait until ready
+	stm32.RCC.CR.SetBits(stm32.RCC_CR_PLLON)
+	stm32.RCC.PLLCFGR.SetBits(stm32.RCC_PLLCFGR_PLLREN) // = RCC_PLL_SYSCLK
+	for !stm32.RCC.CR.HasBits(stm32.RCC_CR_PLLRDY) {
+	}
+
+	// Enable system clock output
+	stm32.RCC.PLLCFGR.SetBits(RCC_PLL_SYSCLK)
+}
+
+func getMSIRange() uint32 {
+	if stm32.RCC.CR.HasBits(stm32.RCC_CR_MSIRGSEL) {
+		return (stm32.RCC.CR.Get() & stm32.RCC_CR_MSIRANGE_Msk) >> stm32.RCC_CR_MSIRANGE_Pos
+	}
+
+	return (stm32.RCC.CSR.Get() & stm32.RCC_CSR_MSISRANGE_Msk) >> stm32.RCC_CSR_MSISRANGE_Pos
+}
+
+func setMSIFreq(r uint32, calibration uint32) {
+	stm32.RCC.CR.SetBits(stm32.RCC_CR_MSIRGSEL)
+	stm32.RCC.CR.ReplaceBits(r<<stm32.RCC_CR_MSIRANGE_Pos, stm32.RCC_CR_MSIRANGE_Msk, 0)
+
+	stm32.RCC.ICSCR.ReplaceBits(calibration<<stm32.RCC_ICSCR_MSITRIM_Pos, stm32.RCC_ICSCR_MSITRIM_Msk, 0)
+}
+
+func setFlashLatencyFromMSIRange(r uint32) {
+	var vos uint32
+	if pwrIsClkEnabled() {
+		vos = pwrExGetVoltageRange()
+	} else {
+		pwrClkEnable()
+		vos = pwrExGetVoltageRange()
+		pwrClkDisable()
+	}
+
+	latency := uint32(FLASH_LATENCY_0)
+	if vos == PWR_REGULATOR_VOLTAGE_SCALE1 {
+		if r > stm32.RCC_CR_MSIRANGE_Range16M {
+			if r > stm32.RCC_CR_MSIRANGE_Range32M {
+				latency = FLASH_LATENCY_2
+			} else {
+				latency = FLASH_LATENCY_1
+			}
+		}
+	} else if r > stm32.RCC_CR_MSIRANGE_Range16M {
+		latency = FLASH_LATENCY_3
+	} else {
+		if r == stm32.RCC_CR_MSIRANGE_Range16M {
+			latency = FLASH_LATENCY_2
+		} else if r == stm32.RCC_CR_MSIRANGE_Range8M {
+			latency = FLASH_LATENCY_1
+		}
+	}
+
+	stm32.FLASH.ACR.ReplaceBits(latency, stm32.Flash_ACR_LATENCY_Msk, 0)
+}
+
+func pwrIsClkEnabled() bool {
+	return stm32.RCC.APB1ENR1.HasBits(stm32.RCC_APB1ENR1_PWREN)
+}
+
+func pwrClkEnable() {
+	stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_PWREN)
+}
+func pwrClkDisable() {
+	stm32.RCC.APB1ENR1.ClearBits(stm32.RCC_APB1ENR1_PWREN)
+}
+
+func pwrExGetVoltageRange() uint32 {
+	return stm32.PWR.CR1.Get() & stm32.PWR_CR1_VOS_Msk
+}

src/runtime/runtime_wasm_wasi.go

@@ -8,11 +8,16 @@ import (
 
 type timeUnit int64
 
+// libc constructors
+//export __wasm_call_ctors
+func __wasm_call_ctors()
+
 //export _start
 func _start() {
 	// These need to be initialized early so that the heap can be initialized.
 	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
 	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)
+	__wasm_call_ctors()
 	run()
 }
 

src/syscall/errno_other.go

@@ -0,0 +1,5 @@
+// +build !wasi,!darwin
+
+package syscall
+
+func (e Errno) Is(target error) bool { return false }

src/syscall/syscall_libc.go

@@ -13,12 +13,15 @@ type sliceHeader struct {
 }
 
 func Close(fd int) (err error) {
-	return ENOSYS // TODO
+	if libc_close(fd) < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Write(fd int, p []byte) (n int, err error) {
 	buf, count := splitSlice(p)
-	n = libc_write(int32(fd), buf, uint(count))
+	n = libc_write(fd, buf, uint(count))
 	if n < 0 {
 		err = getErrno()
 	}
@@ -26,15 +29,25 @@ func Write(fd int, p []byte) (n int, err error) {
 }
 
 func Read(fd int, p []byte) (n int, err error) {
-	return 0, ENOSYS // TODO
+	buf, count := splitSlice(p)
+	n = libc_read(fd, buf, uint(count))
+	if n < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Seek(fd int, offset int64, whence int) (off int64, err error) {
 	return 0, ENOSYS // TODO
 }
 
-func Open(path string, mode int, perm uint32) (fd int, err error) {
-	return 0, ENOSYS // TODO
+func Open(path string, flag int, mode uint32) (fd int, err error) {
+	data := append([]byte(path), 0)
+	fd = libc_open(&data[0], flag, mode)
+	if fd < 0 {
+		err = getErrno()
+	}
+	return
 }
 
 func Mkdir(path string, mode uint32) (err error) {
@@ -78,8 +91,20 @@ func splitSlice(p []byte) (buf *byte, len uintptr) {
 
 // ssize_t write(int fd, const void *buf, size_t count)
 //export write
-func libc_write(fd int32, buf *byte, count uint) int
+func libc_write(fd int, buf *byte, count uint) int
 
 // char *getenv(const char *name);
 //export getenv
 func libc_getenv(name *byte) *byte
+
+// ssize_t read(int fd, void *buf, size_t count);
+//export read
+func libc_read(fd int, buf *byte, count uint) int
+
+// int open(const char *pathname, int flags, mode_t mode);
+//export open
+func libc_open(pathname *byte, flags int, mode uint32) int
+
+// int close(int fd)
+//export close
+func libc_close(fd int) int

src/syscall/syscall_libc_darwin.go

@@ -1,3 +1,5 @@
+// +build darwin
+
 package syscall
 
 // This file defines errno and constants to match the darwin libsystem ABI.
@@ -22,10 +24,25 @@ func getErrno() Errno {
 	return Errno(uintptr(*errptr))
 }
 
+func (e Errno) Is(target error) bool {
+	switch target.Error() {
+	case "permission denied":
+		return e == EACCES || e == EPERM
+	case "file already exists":
+		return e == EEXIST
+	case "file does not exist":
+		return e == ENOENT
+	}
+	return false
+}
+
 const (
+	EPERM       Errno = 0x1
 	ENOENT      Errno = 0x2
+	EACCES      Errno = 0xd
 	EEXIST      Errno = 0x11
 	EINTR       Errno = 0x4
+	ENOTDIR     Errno = 0x14
 	EMFILE      Errno = 0x18
 	EAGAIN      Errno = 0x23
 	ETIMEDOUT   Errno = 0x3c

src/syscall/syscall_libc_nintendoswitch.go

@@ -2,8 +2,6 @@
 
 package syscall
 
-import "errors"
-
 // A Signal is a number describing a process signal.
 // It implements the os.Signal interface.
 type Signal int
@@ -32,7 +30,6 @@ const (
 	O_RDWR   = 2
 
 	O_CREAT  = 0100
-	O_CREATE = O_CREAT
 	O_TRUNC  = 01000
 	O_APPEND = 02000
 	O_EXCL   = 0200
@@ -41,8 +38,9 @@ const (
 	O_CLOEXEC = 0
 )
 
-var dummyError = errors.New("unknown syscall error")
+//go:extern errno
+var libcErrno uintptr
 
 func getErrno() error {
-	return dummyError
+	return Errno(libcErrno)
 }

src/syscall/syscall_libc_wasi.go

@@ -33,7 +33,6 @@ const (
 	O_RDWR   = O_RDONLY | O_WRONLY
 
 	O_CREAT  = __WASI_OFLAGS_CREAT << 12
-	O_CREATE = O_CREAT
 	O_TRUNC  = __WASI_OFLAGS_TRUNC << 12
 	O_APPEND = __WASI_FDFLAGS_APPEND
 	O_EXCL   = __WASI_OFLAGS_EXCL << 12
@@ -48,3 +47,95 @@ var libcErrno uintptr
 func getErrno() error {
 	return Errno(libcErrno)
 }
+
+func (e Errno) Is(target error) bool {
+	switch target.Error() {
+	case "permission denied":
+		return e == EACCES || e == EPERM || e == ENOTCAPABLE // ENOTCAPABLE is unique in WASI
+	case "file already exists":
+		return e == EEXIST || e == ENOTEMPTY
+	case "file does not exist":
+		return e == ENOENT
+	}
+	return false
+}
+
+// https://github.com/WebAssembly/wasi-libc/blob/main/libc-bottom-half/headers/public/__errno.h
+const (
+	E2BIG           Errno = 1      /* Argument list too long */
+	EACCES          Errno = 2      /* Permission denied */
+	EADDRINUSE      Errno = 3      /* Address already in use */
+	EADDRNOTAVAIL   Errno = 4      /* Address not available */
+	EAFNOSUPPORT    Errno = 5      /* Address family not supported by protocol family */
+	EAGAIN          Errno = 6      /* Try again */
+	EWOULDBLOCK     Errno = EAGAIN /* Operation would block */
+	EALREADY        Errno = 7      /* Socket already connected */
+	EBADF           Errno = 8      /* Bad file number */
+	EBADMSG         Errno = 9      /* Trying to read unreadable message */
+	EBUSY           Errno = 10     /* Device or resource busy */
+	ECANCELED       Errno = 11     /* Operation canceled. */
+	ECHILD          Errno = 12     /* No child processes */
+	ECONNABORTED    Errno = 13     /* Connection aborted */
+	ECONNREFUSED    Errno = 14     /* Connection refused */
+	ECONNRESET      Errno = 15     /* Connection reset by peer */
+	EDEADLK         Errno = 16     /* Deadlock condition */
+	EDESTADDRREQ    Errno = 17     /* Destination address required */
+	EDOM            Errno = 18     /* Math arg out of domain of func */
+	EDQUOT          Errno = 19     /* Quota exceeded */
+	EEXIST          Errno = 20     /* File exists */
+	EFAULT          Errno = 21     /* Bad address */
+	EFBIG           Errno = 22     /* File too large */
+	EHOSTUNREACH    Errno = 23     /* Host is unreachable */
+	EIDRM           Errno = 24     /* Identifier removed */
+	EILSEQ          Errno = 25
+	EINPROGRESS     Errno = 26 /* Connection already in progress */
+	EINTR           Errno = 27 /* Interrupted system call */
+	EINVAL          Errno = 28 /* Invalid argument */
+	EIO             Errno = 29 /* I/O error */
+	EISCONN         Errno = 30 /* Socket is already connected */
+	EISDIR          Errno = 31 /* Is a directory */
+	ELOOP           Errno = 32 /* Too many symbolic links */
+	EMFILE          Errno = 33 /* Too many open files */
+	EMLINK          Errno = 34 /* Too many links */
+	EMSGSIZE        Errno = 35 /* Message too long */
+	EMULTIHOP       Errno = 36 /* Multihop attempted */
+	ENAMETOOLONG    Errno = 37 /* File name too long */
+	ENETDOWN        Errno = 38 /* Network interface is not configured */
+	ENETRESET       Errno = 39
+	ENETUNREACH     Errno = 40         /* Network is unreachable */
+	ENFILE          Errno = 41         /* File table overflow */
+	ENOBUFS         Errno = 42         /* No buffer space available */
+	ENODEV          Errno = 43         /* No such device */
+	ENOENT          Errno = 44         /* No such file or directory */
+	ENOEXEC         Errno = 45         /* Exec format error */
+	ENOLCK          Errno = 46         /* No record locks available */
+	ENOLINK         Errno = 47         /* The link has been severed */
+	ENOMEM          Errno = 48         /* Out of memory */
+	ENOMSG          Errno = 49         /* No message of desired type */
+	ENOPROTOOPT     Errno = 50         /* Protocol not available */
+	ENOSPC          Errno = 51         /* No space left on device */
+	ENOSYS          Errno = 52         /* Function not implemented */
+	ENOTCONN        Errno = 53         /* Socket is not connected */
+	ENOTDIR         Errno = 54         /* Not a directory */
+	ENOTEMPTY       Errno = 55         /* Directory not empty */
+	ENOTSOCK        Errno = 57         /* Socket operation on non-socket */
+	ESOCKTNOSUPPORT Errno = 58         /* Socket type not supported */
+	EOPNOTSUPP      Errno = 58         /* Operation not supported on transport endpoint */
+	ENOTSUP         Errno = EOPNOTSUPP /* Not supported */
+	ENOTTY          Errno = 59         /* Not a typewriter */
+	ENXIO           Errno = 60         /* No such device or address */
+	EOVERFLOW       Errno = 61         /* Value too large for defined data type */
+	EPERM           Errno = 63         /* Operation not permitted */
+	EPIPE           Errno = 64         /* Broken pipe */
+	EPROTO          Errno = 65         /* Protocol error */
+	EPROTONOSUPPORT Errno = 66         /* Unknown protocol */
+	EPROTOTYPE      Errno = 67         /* Protocol wrong type for socket */
+	ERANGE          Errno = 68         /* Math result not representable */
+	EROFS           Errno = 69         /* Read-only file system */
+	ESPIPE          Errno = 70         /* Illegal seek */
+	ESRCH           Errno = 71         /* No such process */
+	ESTALE          Errno = 72
+	ETIMEDOUT       Errno = 73 /* Connection timed out */
+	EXDEV           Errno = 75 /* Cross-device link */
+	ENOTCAPABLE     Errno = 76 /* Extension: Capabilities insufficient. */
+)

src/syscall/tables_baremetal.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build baremetal nintendoswitch wasi
+// +build baremetal nintendoswitch
 
 package syscall
 

targets/avr.json

@@ -19,5 +19,5 @@
 		"src/internal/task/task_stack_avr.S",
 		"src/runtime/gc_avr.S"
 	],
-	"gdb": "avr-gdb"
+	"gdb": ["avr-gdb"]
 }

targets/bluepill.json

@@ -1,7 +1,7 @@
 {
 	"inherits": ["cortex-m"],
 	"llvm-target": "armv7m-none-eabi",
-	"build-tags": ["bluepill", "stm32f103", "stm32"],
+	"build-tags": ["bluepill", "stm32f103", "stm32f1", "stm32"],
 	"cflags": [
 		"--target=armv7m-none-eabi",
 		"-Qunused-arguments"

targets/cortex-m.json

@@ -28,5 +28,5 @@
 		"src/internal/task/task_stack_cortexm.S",
 		"src/runtime/gc_arm.S"
 	],
-	"gdb": "gdb-multiarch"
+	"gdb": ["gdb-multiarch", "arm-none-eabi-gdb"]
 }

targets/cortex-m4.json

@@ -3,6 +3,7 @@
 	"llvm-target": "armv7em-none-eabi",
 	"cflags": [
 		"--target=armv7em-none-eabi",
-		"-mfloat-abi=soft"
+		"-mfloat-abi=soft",
+		"-Qunused-arguments"
 	]
 }

targets/cortex-m7.json

@@ -4,6 +4,5 @@
 	"cflags": [
 		"--target=armv7em-none-eabi",
 		"-Qunused-arguments"
-	],
-	"gdb": "arm-none-eabi-gdb"
+	]
 }

targets/gameboy-advance.json

@@ -27,6 +27,6 @@
 		"targets/gameboy-advance.s",
 		"src/runtime/gc_arm.S"
 	],
-	"gdb": "gdb-multiarch",
+	"gdb": ["gdb-multiarch"],
 	"emulator": ["mgba", "-3"]
 }