ws2812: add support for the Arduino

ws2812/ws2812_avr_16m.go

@@ -0,0 +1,41 @@
+// +build arduino
+
+package ws2812
+
+// This file implements the WS2812 protocol for 16MHz AVR microcontrollers.
+
+import (
+	"device/avr"
+)
+
+// Send a single byte using the WS2812 protocol.
+func (d Device) WriteByte(c byte) {
+	// For the AVR at 16MHz
+	portSet, maskSet := d.Pin.PortMaskSet()
+	portClear, maskClear := d.Pin.PortMaskClear()
+
+	avr.AsmFull(`
+	send_bit:
+		st    {portSet}, {maskSet}     ; [2]   set output high
+		lsl   {value}                  ; [1]   shift off the next bit, store it in C
+		brcs  skip_store               ; [1/2] branch if this bit is high (long pulse)
+		st    {portClear}, {maskClear} ; [2]   set output low (short pulse)
+	skip_store:
+		nop                            ; [6]   wait before changing the output again
+		nop
+		nop
+		nop
+		nop
+		nop
+		st    {portClear}, {maskClear} ; [2]   set output low (end of pulse)
+		subi  {i}, 1                   ; [1]   subtract one (for the loop)
+		brne  send_bit                 ; [1/2] send the next bit, if not at the end of the loop
+	`, map[string]interface{}{
+		"value":     c,
+		"i":         8,
+		"maskSet":   maskSet,
+		"portSet":   portSet,
+		"maskClear": maskClear,
+		"portClear": portClear,
+	})
+}