nrf: add support for pin change interrupts

src/examples/pininterrupt/pca10040.go

@@ -0,0 +1,10 @@
+// +build pca10040
+
+package main
+
+import "machine"
+
+const (
+	buttonMode      = machine.PinInputPullup
+	buttonPinChange = machine.PinRising
+)

src/examples/pininterrupt/pininterrupt.go

@@ -0,0 +1,52 @@
+package main
+
+// This example demonstrates how to use pin change interrupts.
+//
+// This is only an example and should not be copied directly in any serious
+// circuit, because it lacks an important feature: debouncing.
+// See: https://en.wikipedia.org/wiki/Switch#Contact_bounce
+
+import (
+	"machine"
+	"runtime/volatile"
+	"time"
+)
+
+const (
+	button = machine.BUTTON
+	led    = machine.LED
+)
+
+func main() {
+	var lightLed volatile.Register8
+	lightLed.Set(0)
+
+	// Configure the LED, defaulting to on (usually setting the pin to low will
+	// turn the LED on).
+	led.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	led.Low()
+
+	// Make sure the pin is configured as a pullup to avoid floating inputs.
+	// Pullup works for most buttons, as most buttons short to ground when
+	// pressed.
+	button.Configure(machine.PinConfig{Mode: buttonMode})
+
+	// Set an interrupt on this pin.
+	err := button.SetInterrupt(buttonPinChange, func(machine.Pin) {
+		if lightLed.Get() != 0 {
+			lightLed.Set(0)
+			led.Low()
+		} else {
+			lightLed.Set(1)
+			led.High()
+		}
+	})
+	if err != nil {
+		println("could not configure pin interrupt:", err.Error())
+	}
+
+	// Make sure the program won't exit.
+	for {
+		time.Sleep(time.Hour)
+	}
+}