exp/sensor: initiate the darwin/{arm,arm64} backend

The CL provides accelerometer events only, upcoming CLs will add
support for gyroscope and magnetometer.

Change-Id: Ib5629ca7c49c9dfc8ca533fe7acde371efc102b2
Reviewed-on: https://go-review.googlesource.com/14036
Reviewed-by: Nigel Tao <nigeltao@golang.org>

exp/sensor/darwin_armx.go

@@ -7,29 +7,113 @@
 
 package sensor
 
+/*
+#cgo CFLAGS: -x objective-c
+#cgo LDFLAGS: -framework CoreMotion
+
+#import <stdlib.h>
+
+void GoIOS_createManager();
+
+void GoIOS_startAccelerometer();
+void GoIOS_stopAccelerometer();
+void GoIOS_readAccelerometer(int64_t* timestamp, float* vector);
+
+void GoIOS_destroyManager();
+
+*/
+import "C"
 import (
-	"errors"
+	"fmt"
+	"sync"
 	"time"
+	"unsafe"
 )
 
+var channels struct {
+	sync.Mutex
+	acceleroDone chan struct{}
+}
+
 type manager struct {
 }
 
 func (m *manager) initialize() {
+	C.GoIOS_createManager()
 }
 
 func (m *manager) enable(s Sender, t Type, delay time.Duration) error {
-	return errors.New("sensor: no sensors available")
+	// TODO(jbd): If delay is smaller than 10 milliseconds, set it to
+	// 10 milliseconds. It is highest frequency iOS SDK suppports and
+	// we don't want to have time.Tick durations smaller than this value.
+	channels.Lock()
+	defer channels.Unlock()
+
+	switch t {
+	case Accelerometer:
+		if channels.acceleroDone != nil {
+			return fmt.Errorf("sensor: cannot enable; %v sensor is already enabled", t)
+		}
+		// TODO(jbd): Check if accelerometer is available.
+		C.GoIOS_startAccelerometer()
+		channels.acceleroDone = make(chan struct{})
+		go m.runAccelerometer(s, delay, channels.acceleroDone)
+	case Gyroscope:
+	case Magnetometer:
+	default:
+		return fmt.Errorf("sensor: unknown sensor type: %v", t)
+	}
+	return nil
 }
 
 func (m *manager) disable(t Type) error {
-	return errors.New("sensor: no sensors available")
-}
+	channels.Lock()
+	defer channels.Unlock()
 
-func (m *manager) read(e []Event) (n int, err error) {
-	return 0, errors.New("sensor: no sensor data available")
-}
-
-func (m *manager) close() error {
+	switch t {
+	case Accelerometer:
+		if channels.acceleroDone == nil {
+			return fmt.Errorf("sensor: cannot disable; %v sensor is not enabled", t)
+		}
+		close(channels.acceleroDone)
+		channels.acceleroDone = nil
+		C.GoIOS_stopAccelerometer()
+	case Gyroscope:
+	case Magnetometer:
+	default:
+		return fmt.Errorf("sensor: unknown sensor type: %v", t)
+	}
+	return nil
+}
+
+func (m *manager) runAccelerometer(s Sender, d time.Duration, done chan struct{}) {
+	var timestamp C.int64_t
+	var ev [3]C.float
+	var lastTimestamp int64
+	for {
+		select {
+		case <-done:
+			return
+		default:
+			C.GoIOS_readAccelerometer((*C.int64_t)(unsafe.Pointer(&timestamp)), (*C.float)(unsafe.Pointer(&ev[0])))
+			t := int64(timestamp)
+			if t > lastTimestamp {
+				// TODO(jbd): Do we need to convert the values to another unit?
+				// How does iOS units compare to the Android units.
+				s.Send(Event{
+					Sensor:    Accelerometer,
+					Timestamp: t,
+					Data:      []float64{float64(ev[0]), float64(ev[1]), float64(ev[2])},
+				})
+				lastTimestamp = t
+				time.Sleep(d / 2)
+			}
+		}
+	}
+}
+
+// TODO(jbd): Remove close?
+func (m *manager) close() error {
+	C.GoIOS_destroyManager()
 	return nil
 }

exp/sensor/darwin_armx.m

@@ -0,0 +1,35 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin
+// +build arm arm64
+
+#import <CoreMotion/CoreMotion.h>
+
+CMMotionManager* manager = nil;
+
+void GoIOS_createManager() {
+  manager = [[CMMotionManager alloc] init];
+}
+
+void GoIOS_startAccelerometer() {
+  [manager startAccelerometerUpdates];
+}
+
+void GoIOS_stopAccelerometer() {
+  [manager stopAccelerometerUpdates];
+}
+
+void GoIOS_readAccelerometer(int64_t* timestamp, float* v) {
+  CMAccelerometerData* data = manager.accelerometerData;
+  *timestamp = (int64_t)(data.timestamp * 1000 * 1000);
+  v[0] = data.acceleration.x;
+  v[1] = data.acceleration.y;
+  v[2] = data.acceleration.z;
+}
+
+void GoIOS_destroyManager() {
+  [manager release];
+  manager = nil;
+}