runtime/fe310: add support for PLIC interrupts

This commit adds support for software vectoring in the PLIC interrupt.
The interrupt table is created by the compiler, which leads to very
compact code while retaining the flexibility that the interrupt API
provides.

tools/gen-device-svd/gen-device-svd.go

@@ -595,7 +595,7 @@ func parseRegister(groupName string, regEl *SVDRegister, baseAddress uint64, bit
 }
 
 // The Go module for this device.
-func writeGo(outdir string, device *Device) error {
+func writeGo(outdir string, device *Device, interruptSystem string) error {
 	outf, err := os.Create(filepath.Join(outdir, device.metadata["nameLower"]+".go"))
 	if err != nil {
 		return err
@@ -621,7 +621,7 @@ func writeGo(outdir string, device *Device) error {
 package {{.pkgName}}
 
 import (
-	"runtime/interrupt"
+{{if eq .interruptSystem "hardware"}}"runtime/interrupt"{{end}}
 	"runtime/volatile"
 	"unsafe"
 )
@@ -637,11 +637,13 @@ const ({{range .interrupts}}
 	IRQ_max = {{.interruptMax}} // Highest interrupt number on this device.
 )
 
+{{if eq .interruptSystem "hardware"}}
 // Map interrupt numbers to function names.
 // These aren't real calls, they're removed by the compiler.
 var ({{range .interrupts}}
 	_ = interrupt.Register(IRQ_{{.Name}}, "{{.HandlerName}}"){{end}}
 )
+{{end}}
 
 // Peripherals.
 var (
@@ -649,11 +651,12 @@ var (
 {{end}})
 `))
 	err = t.Execute(w, map[string]interface{}{
-		"metadata":     device.metadata,
-		"interrupts":   device.interrupts,
-		"peripherals":  device.peripherals,
-		"pkgName":      filepath.Base(strings.TrimRight(outdir, "/")),
-		"interruptMax": maxInterruptValue,
+		"metadata":        device.metadata,
+		"interrupts":      device.interrupts,
+		"peripherals":     device.peripherals,
+		"pkgName":         filepath.Base(strings.TrimRight(outdir, "/")),
+		"interruptMax":    maxInterruptValue,
+		"interruptSystem": interruptSystem,
 	})
 	if err != nil {
 		return err
@@ -910,7 +913,7 @@ Default_Handler:
 	return w.Flush()
 }
 
-func generate(indir, outdir, sourceURL string) error {
+func generate(indir, outdir, sourceURL, interruptSystem string) error {
 	if _, err := os.Stat(indir); os.IsNotExist(err) {
 		fmt.Fprintln(os.Stderr, "cannot find input directory:", indir)
 		os.Exit(1)
@@ -929,13 +932,20 @@ func generate(indir, outdir, sourceURL string) error {
 		if err != nil {
 			return fmt.Errorf("failed to read: %w", err)
 		}
-		err = writeGo(outdir, device)
+		err = writeGo(outdir, device, interruptSystem)
 		if err != nil {
 			return fmt.Errorf("failed to write Go file: %w", err)
 		}
-		err = writeAsm(outdir, device)
-		if err != nil {
-			return fmt.Errorf("failed to write assembly file: %w", err)
+		switch interruptSystem {
+		case "software":
+			// Nothing to do.
+		case "hardware":
+			err = writeAsm(outdir, device)
+			if err != nil {
+				return fmt.Errorf("failed to write assembly file: %w", err)
+			}
+		default:
+			return fmt.Errorf("unknown interrupt system: %s", interruptSystem)
 		}
 	}
 	return nil
@@ -943,6 +953,7 @@ func generate(indir, outdir, sourceURL string) error {
 
 func main() {
 	sourceURL := flag.String("source", "<unknown>", "source SVD file")
+	interruptSystem := flag.String("interrupts", "hardware", "interrupt system in use (software, hardware)")
 	flag.Parse()
 	if flag.NArg() != 2 {
 		fmt.Fprintln(os.Stderr, "provide exactly two arguments: input directory (with .svd files) and output directory for generated files")
@@ -951,7 +962,7 @@ func main() {
 	}
 	indir := flag.Arg(0)
 	outdir := flag.Arg(1)
-	err := generate(indir, outdir, *sourceURL)
+	err := generate(indir, outdir, *sourceURL, *interruptSystem)
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)