i2c: implement target mode for rp2040 and nrf

src/examples/i2c-target/main.go

@@ -0,0 +1,130 @@
+// Example demonstrating I2C controller / target comms.
+//
+// To use this example, physically connect I2C0 and I2C1.
+// I2C0 will be used as the controller and I2C1 used as
+// the target.
+//
+// In this example, the target implements a simple memory
+// map, with the controller able to read and write the
+// memory.
+
+package main
+
+import (
+	"machine"
+	"time"
+)
+
+const (
+	targetAddress = 0x11
+	maxTxSize     = 16
+)
+
+func main() {
+	// Delay to enable USB monitor time to attach
+	time.Sleep(3 * time.Second)
+
+	// Controller uses default I2C pins and controller
+	// mode is default
+	err := controller.Configure(machine.I2CConfig{})
+	if err != nil {
+		panic("failed to config I2C0 as controller")
+	}
+
+	// Target uses alternate pins and target mode is
+	// explicit
+	err = target.Configure(machine.I2CConfig{
+		Mode: machine.I2CModeTarget,
+		SCL:  TARGET_SCL,
+		SDA:  TARGET_SDA,
+	})
+	if err != nil {
+		panic("failed to config I2C1 as target")
+	}
+
+	// Put welcome message directly into target memory
+	copy(mem[0:], []byte("Hello World!"))
+	err = target.Listen(targetAddress)
+	if err != nil {
+		panic("failed to listen as I2C target")
+	}
+
+	// Start the target
+	go targetMain()
+
+	// Read welcome message from target over I2C
+	buf := make([]byte, 12)
+	err = controller.Tx(targetAddress, []byte{0}, buf)
+	if err != nil {
+		println("failed to read welcome message over I2C")
+		panic(err)
+	}
+	println("message from target:", string(buf))
+
+	// Write (1,2,3) to the target starting at memory address 3
+	println("writing (1,2,3) @ 0x3")
+	err = controller.Tx(targetAddress, []byte{3, 1, 2, 3}, nil)
+	if err != nil {
+		println("failed to write to I2C target")
+		panic(err)
+	}
+
+	time.Sleep(100 * time.Millisecond) // Wait for target to process write
+	println("mem:", mem[0], mem[1], mem[2], mem[3], mem[4], mem[5])
+
+	// Read memory address 4 from target, which should be the value 2
+	buf = make([]byte, 1)
+	err = controller.Tx(targetAddress, []byte{4}, buf[:1])
+	if err != nil {
+		println("failed to read from I2C target")
+		panic(err)
+	}
+
+	if buf[0] != 2 {
+		panic("read incorrect value from I2C target")
+	}
+
+	println("all done!")
+	for {
+		time.Sleep(1 * time.Second)
+	}
+}
+
+// -- target ---
+
+var (
+	mem [256]byte
+)
+
+// targetMain implements the 'main loop' for an I2C target
+func targetMain() {
+	buf := make([]byte, maxTxSize)
+	var ptr uint8
+
+	for {
+		evt, n, err := target.WaitForEvent(buf)
+		if err != nil {
+			panic(err)
+		}
+
+		switch evt {
+		case machine.I2CReceive:
+			if n > 0 {
+				ptr = buf[0]
+			}
+
+			for o := 1; o < n; o++ {
+				mem[ptr] = buf[o]
+				ptr++
+			}
+
+		case machine.I2CRequest:
+			target.Reply(mem[ptr:256])
+
+		case machine.I2CFinish:
+			// nothing to do
+
+		default:
+		}
+	}
+}

src/examples/i2c-target/main_feather_nrf52840.go

@@ -0,0 +1,15 @@
+//go:build feather_nrf52840
+
+package main
+
+import "machine"
+
+const (
+	TARGET_SCL = machine.A5
+	TARGET_SDA = machine.A4
+)
+
+var (
+	controller = machine.I2C0
+	target     = machine.I2C1
+)

src/examples/i2c-target/main_feather_rp2040.go

@@ -0,0 +1,15 @@
+//go:build rp2040
+
+package main
+
+import "machine"
+
+const (
+	TARGET_SCL = machine.GPIO25
+	TARGET_SDA = machine.GPIO24
+)
+
+var (
+	controller = machine.I2C1
+	target     = machine.I2C0
+)