machine/samd51: add DAC support (#1198)

* machine/samd51: add DAC support

src/examples/dac/circuitplay_express.go

@@ -0,0 +1,13 @@
+// +build circuitplay_express
+
+package main
+
+import (
+	"machine"
+)
+
+func init() {
+	enable := machine.PA30
+	enable.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	enable.Set(true)
+}

src/examples/dac/dac.go

@@ -10,16 +10,12 @@ import (
 )
 
 func main() {
-	enable := machine.PA30
-	enable.Configure(machine.PinConfig{Mode: machine.PinOutput})
-	enable.Set(true)
-
 	speaker := machine.A0
 	speaker.Configure(machine.PinConfig{Mode: machine.PinOutput})
 
 	machine.DAC0.Configure(machine.DACConfig{})
 
-	data := []uint16{32768, 8192, 2048, 512, 0}
+	data := []uint16{0xFFFF, 0x8000, 0x4000, 0x2000, 0x1000, 0x0000}
 
 	for {
 		for _, val := range data {

src/examples/dac/pyportal.go

@@ -0,0 +1,13 @@
+// +build pyportal
+
+package main
+
+import (
+	"machine"
+)
+
+func init() {
+	enable := machine.SPK_SD
+	enable.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	enable.Set(true)
+}