avr: i2c implementation with BlinkM example

Signed-off-by: Ron Evans <ron@hybridgroup.com>

src/examples/blinkm/blinkm.go

@@ -0,0 +1,42 @@
+// Connects to an BlinkM I2C RGB LED.
+// http://thingm.com/fileadmin/thingm/downloads/BlinkM_datasheet.pdf
+package main
+
+import (
+	"machine"
+	"time"
+)
+
+func main() {
+	machine.I2C0.Configure(machine.I2CConfig{})
+
+	// Init BlinkM
+	machine.I2C0.WriteTo(0x09, []byte("o"))
+
+	version := []byte{0, 0}
+	machine.I2C0.WriteTo(0x09, []byte("Z"))
+	machine.I2C0.ReadFrom(0x09, version)
+	println("Firmware version:", string(version[0]), string(version[1]))
+
+	count := 0
+	for {
+		machine.I2C0.WriteTo(0x09, []byte("n"))
+
+		switch count {
+		case 0:
+			// Crimson
+			machine.I2C0.WriteTo(0x09, []byte{0xdc, 0x14, 0x3c})
+			count = 1
+		case 1:
+			// MediumPurple
+			machine.I2C0.WriteTo(0x09, []byte{0x93, 0x70, 0xdb})
+			count = 2
+		case 2:
+			// MediumSeaGreen
+			machine.I2C0.WriteTo(0x09, []byte{0x3c, 0xb3, 0x71})
+			count = 0
+		}
+
+		time.Sleep(100 * time.Millisecond)
+	}
+}