ws2812: provide proper file-like interface in Device

* Return len and errors in the Write method, to implement io.Writer.
* Return a nil error in WriteByte, for compatibility with bufio.

ws2812/ws2812.go

@@ -17,10 +17,11 @@ func New(pin machine.GPIO) Device {
 }
 
 // Write the raw bitstring out using the WS2812 protocol.
-func (d Device) Write(buf []byte) {
+func (d Device) Write(buf []byte) (n int, err error) {
 	for _, c := range buf {
 		d.WriteByte(c)
 	}
+	return len(buf), nil
 }
 
 // Write the given color slice out using the WS2812 protocol.

ws2812/ws2812_avr_16m.go

@@ -9,7 +9,7 @@ import (
 )
 
 // Send a single byte using the WS2812 protocol.
-func (d Device) WriteByte(c byte) {
+func (d Device) WriteByte(c byte) error {
 	// For the AVR at 16MHz
 	portSet, maskSet := d.Pin.PortMaskSet()
 	portClear, maskClear := d.Pin.PortMaskClear()
@@ -38,4 +38,5 @@ func (d Device) WriteByte(c byte) {
 		"maskClear": maskClear,
 		"portClear": portClear,
 	})
+	return nil
 }

ws2812/ws2812_m0_16m.go

@@ -10,7 +10,7 @@ import (
 )
 
 // Send a single byte using the WS2812 protocol.
-func (d Device) WriteByte(c byte) {
+func (d Device) WriteByte(c byte) error {
 	// For the Cortex-M0 at 16MHz
 	portSet, maskSet := d.Pin.PortMaskSet()
 	portClear, maskClear := d.Pin.PortMaskClear()
@@ -40,4 +40,5 @@ func (d Device) WriteByte(c byte) {
 		"maskClear": maskClear,
 		"portClear": portClear,
 	})
+	return nil
 }