machine: make I2C usable in the simulator

This fixes/improves a few issues with I2C support:

  * Validate I2C pins, so only pins that are supported by the hardware
    can be used (similar to how it's done with PWM).
  * Add address to Tx API (without it, the simulator can't really
    simulate I2C).
  * Add frequency when configuring. Not currently used, but might be
    useful in the future and adding it now avoids possibly breaking
    changes.

This is a breaking change, but since the simulator doesn't support I2C
yet that seems fine to me. (It does in my local changes, but those need
to be cleaned up before I can push them).

src/machine/i2c.go

@@ -37,6 +37,9 @@ var (
 	errI2COverflow           = errors.New("I2C receive buffer overflow")
 	errI2COverread           = errors.New("I2C transmit buffer overflow")
 	errI2CNotImplemented     = errors.New("I2C operation not yet implemented")
+	errI2CNoDevices          = errors.New("i2c: bus has no devices")                         // simulator only
+	errI2CMultipleDevices    = errors.New("i2c: bus has address conflict")                   // simulator only
+	errI2CWrongAddress       = errors.New("i2c: bus has devices but none with this address") // simulator only
 )
 
 // I2CTargetEvent reflects events on the I2C bus

src/machine/machine_atmega328p_simulator.go

@@ -0,0 +1,5 @@
+//go:build !baremetal && (arduino || arduino_nano)
+
+package machine
+
+var I2C0 = &I2C{Bus: 0, PinsSDA: []Pin{PC4}, PinsSCL: []Pin{PC5}}

src/machine/machine_atsamd21_simulator.go

@@ -43,3 +43,21 @@ var TCC2 = &timerType{
 		{PA01, PA13, PA17}, // channel 1
 	},
 }
+
+var (
+	// According to the datasheet, only some pins have I2C support. However it
+	// looks like many boards just use any SERCOM I2C instance, even if the
+	// datasheet says those don't support I2C. I guess they do work in practice,
+	// then.
+	// These are:
+	//   * PA00/PA01 for the Adafruit Circuit Playground Express (I2C1, SERCOM1).
+	//   * PB02/PB03 for the Adafruit Circuit Playground Express (I2C0, SERCOM5).
+	//   * PB08/PB09 for the Arduino Nano 33 IoT (I2C0, SERCOM4).
+	// https://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/Atmel-42181-SAM-D21_Datasheet.pdf
+	sercomI2CM0 = &I2C{Bus: 0, PinsSDA: []Pin{PA08}, PinsSCL: []Pin{PA09}}
+	sercomI2CM1 = &I2C{Bus: 1, PinsSDA: []Pin{PA00, PA16}, PinsSCL: []Pin{PA01, PA17}}
+	sercomI2CM2 = &I2C{Bus: 2, PinsSDA: []Pin{PA08, PA12}, PinsSCL: []Pin{PA09, PA13}}
+	sercomI2CM3 = &I2C{Bus: 3, PinsSDA: []Pin{PA16, PA22}, PinsSCL: []Pin{PA17, PA23}}
+	sercomI2CM4 = &I2C{Bus: 4, PinsSDA: []Pin{PA12, PB08, PB12}, PinsSCL: []Pin{PA13, PB09, PB13}}
+	sercomI2CM5 = &I2C{Bus: 5, PinsSDA: []Pin{PA22, PB02, PB16, PB30}, PinsSCL: []Pin{PA23, PB03, PB17, PB31}}
+)

src/machine/machine_fe310_simulator.go

@@ -0,0 +1,5 @@
+//go:build !baremetal && hifive1b
+
+package machine
+
+var I2C0 = &I2C{Bus: 0, PinsSDA: []Pin{P12}, PinsSCL: []Pin{P13}}

src/machine/machine_generic.go

@@ -4,6 +4,8 @@ package machine
 
 import (
 	"crypto/rand"
+	"errors"
+	"slices"
 )
 
 // Dummy machine package that calls out to external functions.
@@ -227,7 +229,9 @@ func adcRead(pin Pin) uint16
 
 // I2C is a generic implementation of the Inter-IC communication protocol.
 type I2C struct {
-	Bus uint8
+	Bus     uint8
+	PinsSCL []Pin
+	PinsSDA []Pin
 }
 
 // I2CConfig is used to store config info for I2C.
@@ -239,7 +243,21 @@ type I2CConfig struct {
 
 // Configure is intended to setup the I2C interface.
 func (i2c *I2C) Configure(config I2CConfig) error {
-	i2cConfigure(i2c.Bus, config.SCL, config.SDA)
+	if i2c.PinsSCL != nil {
+		matchSCL := slices.Index(i2c.PinsSCL, config.SCL) >= 0
+		matchSDA := slices.Index(i2c.PinsSDA, config.SDA) >= 0
+		if !matchSCL && !matchSDA {
+			return errors.New("i2c: SCL and SDA pins are incorrect for this I2C instance")
+		} else if !matchSCL {
+			return errors.New("i2c: SCL pin is incorrect for this I2C instance")
+		} else if !matchSDA {
+			return errors.New("i2c: SDA pin is incorrect for this I2C instance")
+		}
+	}
+	if config.Frequency == 0 {
+		config.Frequency = 100 * KHz
+	}
+	i2cConfigure(i2c.Bus, config.SCL, config.SDA, config.Frequency)
 	return nil
 }
 
@@ -261,19 +279,29 @@ func (i2c *I2C) Tx(addr uint16, w, r []byte) error {
 		rptr = &r[0]
 		rlen = len(r)
 	}
-	i2cTransfer(i2c.Bus, wptr, wlen, rptr, rlen)
-	// TODO: do something with the returned error code.
-	return nil
+	errCode := i2cTransfer(i2c.Bus, addr, wptr, wlen, rptr, rlen)
+	switch errCode {
+	case 0:
+		return nil
+	case 1:
+		return errI2CNoDevices
+	case 2:
+		return errI2CMultipleDevices
+	case 3:
+		return errI2CWrongAddress
+	default:
+		return errI2CBusError // unknown error code
+	}
 }
 
 //export __tinygo_i2c_configure
-func i2cConfigure(bus uint8, scl Pin, sda Pin)
+func i2cConfigure(bus uint8, scl Pin, sda Pin, frequency uint32)
 
 //export __tinygo_i2c_set_baud_rate
 func i2cSetBaudRate(bus uint8, br uint32)
 
 //export __tinygo_i2c_transfer
-func i2cTransfer(bus uint8, w *byte, wlen int, r *byte, rlen int) int
+func i2cTransfer(bus uint8, addr uint16, w *byte, wlen int, r *byte, rlen int) int
 
 type UART struct {
 	Bus uint8
@@ -336,15 +364,6 @@ var (
 	sercomUSART4 = UART{4}
 	sercomUSART5 = UART{5}
 
-	sercomI2CM0 = &I2C{0}
-	sercomI2CM1 = &I2C{1}
-	sercomI2CM2 = &I2C{2}
-	sercomI2CM3 = &I2C{3}
-	sercomI2CM4 = &I2C{4}
-	sercomI2CM5 = &I2C{5}
-	sercomI2CM6 = &I2C{6}
-	sercomI2CM7 = &I2C{7}
-
 	sercomSPIM0 = &SPI{0}
 	sercomSPIM1 = &SPI{1}
 	sercomSPIM2 = &SPI{2}

src/machine/machine_generic_peripherals.go

@@ -10,5 +10,4 @@ var (
 	UART1 = hardwareUART1
 	SPI0  = &SPI{0}
 	SPI1  = &SPI{1}
-	I2C0  = &I2C{0}
 )

src/machine/machine_nrf51_simulator.go

@@ -0,0 +1,6 @@
+//go:build !baremetal && (microbit || pca10031 || hw_651)
+
+package machine
+
+var I2C0 = &I2C{Bus: 0}
+var I2C1 = &I2C{Bus: 1}

src/machine/machine_nrf52840_simulator.go

@@ -58,3 +58,6 @@ var PWM3 = &timerType{
 		nil, // channel 3
 	},
 }
+
+var I2C0 = &I2C{Bus: 0}
+var I2C1 = &I2C{Bus: 1}

src/machine/machine_rp2040_simulator.go

@@ -94,3 +94,15 @@ var PWM7 = &timerType{
 		{GPIO15}, // channel B (1)
 	},
 }
+
+var I2C0 = &I2C{
+	Bus:     0,
+	PinsSCL: []Pin{GPIO1, GPIO5, GPIO9, GPIO13, GPIO17, GPIO21},
+	PinsSDA: []Pin{GPIO0, GPIO4, GPIO8, GPIO12, GPIO16, GPIO20},
+}
+
+var I2C1 = &I2C{
+	Bus:     0,
+	PinsSCL: []Pin{GPIO3, GPIO7, GPIO11, GPIO15, GPIO19, GPIO27},
+	PinsSDA: []Pin{GPIO2, GPIO6, GPIO10, GPIO14, GPIO18, GPIO26},
+}