Update for 0.6.0 release

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

CHANGELOG.md

@@ -1,3 +1,8 @@
+0.6.0
+---
+- **new devices**
+    - Support software SPI for APA102 (Itsy Bitsy M0 on-board "Dotstar" LED as example)
+
 0.5.0
 ---
 - **new devices**

Makefile

@@ -11,6 +11,7 @@ smoke-test:
 	@mkdir -p build
 	tinygo build -size short -o ./build/test.elf -target=itsybitsy-m0 ./examples/adxl345/main.go
 	tinygo build -size short -o ./build/test.elf -target=itsybitsy-m0 ./examples/apa102/main.go
+	tinygo build -size short -o ./build/test.elf -target=itsybitsy-m0 ./examples/apa102/itsybitsy-m0/main.go
 	tinygo build -size short -o ./build/test.elf -target=microbit ./examples/at24cx/main.go
 	tinygo build -size short -o ./build/test.elf -target=itsybitsy-m0 ./examples/bh1750/main.go
 	tinygo build -size short -o ./build/test.elf -target=itsybitsy-m0 ./examples/blinkm/main.go

apa102/apa102.go

@@ -21,15 +21,28 @@ const (
 
 // Device wraps APA102 SPI LEDs.
 type Device struct {
-	bus   machine.SPI
+	bus   SPI
 	Order int
 }
 
+// The SPI interface specifies the minimum functionality that a bus
+// implementation needs to provide for use by the APA102 driver.  Hardware
+// SPI from the TinyGo "machine" package implements this already.
+type SPI interface {
+	Tx(w, r []byte) error
+}
+
 // New returns a new APA102 driver. Pass in a fully configured SPI bus.
-func New(b machine.SPI) Device {
+func New(b SPI) Device {
 	return Device{bus: b, Order: BGR}
 }
 
+// NewSoftwareSPI returns a new APA102 driver that will use a software based
+// implementation of the SPI protocol.
+func NewSoftwareSPI(sckPin, mosiPin machine.Pin, delay uint32) Device {
+	return New(&bbSPI{SCK: sckPin, MOSI: mosiPin, Delay: delay})
+}
+
 // WriteColors writes the given RGBA color slice out using the APA102 protocol.
 // The A value (Alpha channel) is used for brightness, set to 0xff (255) for maximum.
 func (d Device) WriteColors(cs []color.RGBA) (n int, err error) {

apa102/softspi.go

@@ -0,0 +1,68 @@
+package apa102
+
+import "machine"
+
+// bbSPI is a dumb bit-bang implementation of SPI protocol that is hardcoded
+// to mode 0 and ignores trying to receive data. Just enough for the APA102.
+// Note: making this unexported for now because it is probable not suitable
+// most purposes other than the APA102 package. It might be desirable to make
+// this more generic and include it in the TinyGo "machine" package instead.
+type bbSPI struct {
+	SCK   machine.Pin
+	MOSI  machine.Pin
+	Delay uint32
+}
+
+// Configure sets up the SCK and MOSI pins as outputs and sets them low
+func (s *bbSPI) Configure() {
+	s.SCK.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	s.MOSI.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	s.SCK.Low()
+	s.MOSI.Low()
+	if s.Delay == 0 {
+		s.Delay = 1
+	}
+}
+
+// Tx matches signature of machine.SPI.Tx() and is used to send multiple bytes.
+// The r slice is ignored and no error will ever be returned.
+func (s *bbSPI) Tx(w []byte, r []byte) error {
+	s.Configure()
+	for _, b := range w {
+		s.Transfer(b)
+	}
+	return nil
+}
+
+// delay represents a quarter of the clock cycle
+func (s *bbSPI) delay() {
+	for i := uint32(0); i < s.Delay; {
+		i++
+	}
+}
+
+// Transfer is used to send a single byte.
+func (s *bbSPI) Transfer(b byte) {
+	for i := uint8(0); i < 8; i++ {
+
+		// half clock cycle high to start
+		s.SCK.High()
+		s.delay()
+
+		// write the value to MOSI (MSB first)
+		if b&(1<<(7-i)) == 0 {
+			s.MOSI.Low()
+		} else {
+			s.MOSI.High()
+		}
+		s.delay()
+
+		// half clock cycle low
+		s.SCK.Low()
+		s.delay()
+
+		// for actual SPI would try to read the MISO value here
+		s.delay()
+
+	}
+}

examples/apa102/itsybitsy-m0/main.go

@@ -0,0 +1,84 @@
+// This example demostrates how to control the "Dotstar" (APA102) LED included
+// on the Adafruit Itsy Bitsy M0 board.  It implements a "rainbow effect" based
+// on the following example:
+// https://github.com/adafruit/Adafruit_Learning_System_Guides/blob/master/CircuitPython_Essentials/CircuitPython_Internal_RGB_LED_rainbow.py
+package main
+
+import (
+	"image/color"
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/apa102"
+)
+
+var (
+	apa apa102.Device
+
+	led   = machine.PWM{machine.LED}
+	leds  = make([]color.RGBA, 1)
+	wheel = &Wheel{Brightness: 0x10}
+)
+
+func init() {
+
+	// APA102 on Itsy Bitsy is connected to pins that require a software-based
+	// SPI implementation.
+	apa = apa102.NewSoftwareSPI(machine.PA00, machine.PA01, 1)
+
+	// Configure the regular on-board LED for PWM fading
+	machine.InitPWM()
+	led.Configure()
+
+}
+
+func main() {
+
+	// We'll fade the on-board LED in a goroutine to show/ensure that the APA102
+	// works fine with the scheduler enabled.  Comment this out to test this code
+	// with the scheduler disabled.
+	go func() {
+		for i, brightening := uint8(0), false; ; i++ {
+			if i == 0 {
+				brightening = !brightening
+				continue
+			}
+			var brightness uint16 = uint16(i) << 8
+			if !brightening {
+				brightness = 0xFFFF - brightness
+			}
+			led.Set(brightness)
+			time.Sleep(5 * time.Millisecond)
+		}
+	}()
+
+	// Use the "wheel" function from Adafruit's example to cycle the APA102
+	for {
+		leds[0] = wheel.Next()
+		apa.WriteColors(leds)
+		time.Sleep(25 * time.Millisecond)
+	}
+
+}
+
+// Wheel is a port of Adafruit's Circuit Python example referenced above.
+type Wheel struct {
+	Brightness uint8
+	pos        uint8
+}
+
+// Next increments the internal state of the color and returns the new RGBA
+func (w *Wheel) Next() (c color.RGBA) {
+	pos := w.pos
+	if w.pos < 85 {
+		c = color.RGBA{R: 0xFF - pos*3, G: pos * 3, B: 0x0, A: w.Brightness}
+	} else if w.pos < 170 {
+		pos -= 85
+		c = color.RGBA{R: 0x0, G: 0xFF - pos*3, B: pos * 3, A: w.Brightness}
+	} else {
+		pos -= 170
+		c = color.RGBA{R: pos * 3, G: 0x0, B: 0xFF - pos*3, A: w.Brightness}
+	}
+	w.pos++
+	return
+}