machine/nrf52xxx: add I2S support

make/smoketest.mk

@@ -72,6 +72,8 @@ smoketest-examples: | build/smoke
 	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=circuitplay-express examples/i2s
 	@$(MD5SUM) $(SMOKE_OUT).hex
+	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=pca10040            examples/i2s-tone
+	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=pca10040            examples/mcp3008
 	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=pca10040            examples/memstats
@@ -142,6 +144,8 @@ smoketest-nrf: | build/smoke
 	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=microbit-v2         examples/microbit-blink
 	@$(MD5SUM) $(SMOKE_OUT).hex
+	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=microbit-v2         examples/i2s-tone
+	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=microbit-v2-s113v7  examples/microbit-blink
 	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=microbit-v2-s140v7  examples/microbit-blink
@@ -237,6 +241,8 @@ smoketest-samd: | build/smoke
 	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=itsybitsy-nrf52840  examples/blinky1
 	@$(MD5SUM) $(SMOKE_OUT).hex
+	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=itsybitsy-nrf52840  examples/i2s-tone
+	@$(MD5SUM) $(SMOKE_OUT).hex
 	$(TINYGO) build -size short -o $(SMOKE_OUT).hex -target=qtpy                examples/machinetest
 	@$(MD5SUM) $(SMOKE_OUT).hex
 

src/examples/i2s-tone/itsybitsy-nrf52840.go

@@ -0,0 +1,11 @@
+//go:build itsybitsy_nrf52840
+
+package main
+
+import "machine"
+
+const (
+	pinSCK = machine.D9
+	pinWS  = machine.D7
+	pinSDO = machine.D5
+)

src/examples/i2s-tone/main.go

@@ -0,0 +1,48 @@
+// Plays 440 Hz on the left channel and 880 Hz on the right channel on an I2S
+// DAC such as the PCM5102.
+package main
+
+import (
+	"machine"
+	"math"
+)
+
+const sampleRate = 44100
+
+var sine [256]int16
+
+func main() {
+	for i := range sine {
+		sine[i] = int16(math.Sin(2*math.Pi*float64(i)/float64(len(sine))) * 8000)
+	}
+
+	err := machine.I2S0.Configure(machine.I2SConfig{
+		SCK:            pinSCK,
+		WS:             pinWS,
+		SDO:            pinSDO,
+		SDI:            machine.NoPin,
+		Mode:           machine.I2SModeSource,
+		AudioFrequency: sampleRate,
+		Stereo:         true,
+	})
+	if err != nil {
+		println("could not configure I2S:", err.Error())
+		return
+	}
+
+	// Phase steps in 8.24 fixed point, one table entry per 1<<24.
+	left := uint32(440 * uint64(len(sine)) << 24 / sampleRate)
+	right := 2 * left
+	var phaseL, phaseR uint32
+	buf := make([]uint32, 64)
+	for {
+		for i := range buf {
+			l := uint16(sine[(phaseL>>24)%uint32(len(sine))])
+			r := uint16(sine[(phaseR>>24)%uint32(len(sine))])
+			buf[i] = uint32(l) | uint32(r)<<16
+			phaseL += left
+			phaseR += right
+		}
+		machine.I2S0.WriteStereo(buf)
+	}
+}

src/examples/i2s-tone/nrf52.go

@@ -0,0 +1,11 @@
+//go:build nrf52 || nrf52833 || (nrf52840 && !itsybitsy_nrf52840)
+
+package main
+
+import "machine"
+
+const (
+	pinSCK = machine.P0_03
+	pinWS  = machine.P0_04
+	pinSDO = machine.P0_28
+)

src/machine/i2s.go

@@ -1,4 +1,4 @@
-//go:build sam && atsamd21
+//go:build (sam && atsamd21) || nrf52 || nrf52833 || nrf52840
 
 // This is the definition for I2S bus functions.
 // Actual implementations if available for any given hardware