First pass at Web Bluetooth accelerometer data

lib/accelerometer-service.ts

@@ -0,0 +1,84 @@
+import {
+  Accelerometer,
+  AccelerometerData,
+  AccelerometerDataEvent,
+  AccelerometerEventMap,
+} from "./accelerometer";
+import { profile } from "./bluetooth-profile";
+import { TypedEventTarget } from "./events";
+
+export type CharacteristicDataTarget = EventTarget & {
+  value: DataView;
+};
+
+export class AccelerometerService
+  extends TypedEventTarget<AccelerometerEventMap>
+  implements Accelerometer
+{
+  private static accelerometerInstance: AccelerometerService | undefined;
+
+  constructor(
+    private accelerometerDataCharacteristic: BluetoothRemoteGATTCharacteristic,
+    // @ts-ignore temporarily unused characteristic
+    private accelerometerPeriodCharacteristic: BluetoothRemoteGATTCharacteristic
+  ) {
+    super();
+    this.accelerometerDataCharacteristic.addEventListener(
+      "characteristicvaluechanged",
+      this.dataListener
+    );
+  }
+
+  static async init(gattServer: BluetoothRemoteGATTServer) {
+    if (this.accelerometerInstance) {
+      return this.accelerometerInstance;
+    }
+    const accelerometerService = await gattServer.getPrimaryService(
+      profile.accelerometer.id
+    );
+    const accelerometerDataCharacteristic =
+      await accelerometerService.getCharacteristic(
+        profile.accelerometer.characteristics.data.id
+      );
+    const accelerometerPeriodCharacteristic =
+      await accelerometerService.getCharacteristic(
+        profile.accelerometer.characteristics.period.id
+      );
+    this.accelerometerInstance = new AccelerometerService(
+      accelerometerDataCharacteristic,
+      accelerometerPeriodCharacteristic
+    );
+    return this.accelerometerInstance;
+  }
+
+  async getData(): Promise<AccelerometerData> {
+    const dataView = await this.accelerometerDataCharacteristic.readValue();
+    const data = this.dataViewToData(dataView);
+    return data;
+  }
+
+  private dataViewToData(dataView: DataView): AccelerometerData {
+    return {
+      x: dataView.getInt16(0, true),
+      y: dataView.getInt16(2, true),
+      z: dataView.getInt16(4, true),
+    };
+  }
+
+  private dataListener = (event: Event) => {
+    const target = event.target as CharacteristicDataTarget;
+    const data = this.dataViewToData(target.value);
+    this.dispatchTypedEvent(
+      "accelerometerdatachanged",
+      new AccelerometerDataEvent(data)
+    );
+  };
+
+  startNotifications() {
+    this.accelerometerDataCharacteristic.startNotifications();
+  }
+
+  stopNotifications() {
+    this.accelerometerDataCharacteristic.stopNotifications();
+  }
+}

lib/accelerometer.ts

@@ -0,0 +1,23 @@
+import { TypedEventTarget } from "./events";
+
+export interface Accelerometer extends TypedEventTarget<AccelerometerEventMap> {
+  getData: () => Promise<AccelerometerData>;
+  startNotifications: () => void;
+  stopNotifications: () => void;
+}
+
+export class AccelerometerDataEvent extends Event {
+  constructor(public readonly data: AccelerometerData) {
+    super("accelerometerdatachanged");
+  }
+}
+
+export class AccelerometerEventMap {
+  "accelerometerdatachanged": AccelerometerDataEvent;
+}
+
+export interface AccelerometerData {
+  x: number;
+  y: number;
+  z: number;
+}

lib/bluetooth-device-wrapper.ts

@@ -4,6 +4,8 @@
  * SPDX-License-Identifier: MIT
  */
 
+import { Accelerometer } from "./accelerometer";
+import { AccelerometerService } from "./accelerometer-service";
 import { profile } from "./bluetooth-profile";
 import { BoardVersion } from "./device";
 import { Logging, NullLogging } from "./logging";
@@ -48,11 +50,11 @@ export class BluetoothDeviceWrapper {
 
   constructor(
     public readonly device: BluetoothDevice,
-    private logging: Logging = new NullLogging(),
+    private logging: Logging = new NullLogging()
   ) {
     device.addEventListener(
       "gattserverdisconnected",
-      this.handleDisconnectEvent,
+      this.handleDisconnectEvent
     );
   }
 
@@ -63,7 +65,7 @@ export class BluetoothDeviceWrapper {
     });
     if (this.duringExplicitConnectDisconnect) {
       this.logging.log(
-        "Skipping connect attempt when one is already in progress",
+        "Skipping connect attempt when one is already in progress"
       );
       // Wait for the gattConnectPromise while showing a "connecting" dialog.
       // If the user clicks disconnect while the automatic reconnect is in progress,
@@ -74,7 +76,7 @@ export class BluetoothDeviceWrapper {
     this.duringExplicitConnectDisconnect++;
     if (this.device.gatt === undefined) {
       throw new Error(
-        "BluetoothRemoteGATTServer for micro:bit device is undefined",
+        "BluetoothRemoteGATTServer for micro:bit device is undefined"
       );
     }
     try {
@@ -93,15 +95,15 @@ export class BluetoothDeviceWrapper {
             // Do we still want to be connected?
             if (!this.connecting) {
               this.logging.log(
-                "Bluetooth GATT server connect after timeout, triggering disconnect",
+                "Bluetooth GATT server connect after timeout, triggering disconnect"
               );
               this.disconnectPromise = (async () => {
                 await this.disconnectInternal(false);
                 this.disconnectPromise = undefined;
               })();
             } else {
               this.logging.log(
-                "Bluetooth GATT server connected when connecting",
+                "Bluetooth GATT server connected when connecting"
               );
             }
           })
@@ -112,7 +114,7 @@ export class BluetoothDeviceWrapper {
             } else {
               this.logging.error(
                 "Bluetooth GATT server connect error after our timeout",
-                e,
+                e
               );
               return undefined;
             }
@@ -127,7 +129,7 @@ export class BluetoothDeviceWrapper {
         const gattConnectResult = await Promise.race([
           this.gattConnectPromise,
           new Promise<"timeout">((resolve) =>
-            setTimeout(() => resolve("timeout"), connectTimeoutDuration),
+            setTimeout(() => resolve("timeout"), connectTimeoutDuration)
           ),
         ]);
         if (gattConnectResult === "timeout") {
@@ -161,7 +163,7 @@ export class BluetoothDeviceWrapper {
 
   private async disconnectInternal(userTriggered: boolean): Promise<void> {
     this.logging.log(
-      `Bluetooth disconnect ${userTriggered ? "(user triggered)" : "(programmatic)"}`,
+      `Bluetooth disconnect ${userTriggered ? "(user triggered)" : "(programmatic)"}`
     );
     this.duringExplicitConnectDisconnect++;
     try {
@@ -175,7 +177,7 @@ export class BluetoothDeviceWrapper {
       this.duringExplicitConnectDisconnect--;
     }
     this.reconnectReadyPromise = new Promise((resolve) =>
-      setTimeout(resolve, 3_500),
+      setTimeout(resolve, 3_500)
     );
   }
 
@@ -198,19 +200,19 @@ export class BluetoothDeviceWrapper {
     try {
       if (!this.duringExplicitConnectDisconnect) {
         this.logging.log(
-          "Bluetooth GATT disconnected... automatically trying reconnect",
+          "Bluetooth GATT disconnected... automatically trying reconnect"
         );
         // stateOnReconnectionAttempt();
         await this.reconnect();
       } else {
         this.logging.log(
-          "Bluetooth GATT disconnect ignored during explicit disconnect",
+          "Bluetooth GATT disconnect ignored during explicit disconnect"
         );
       }
     } catch (e) {
       this.logging.error(
         "Bluetooth connect triggered by disconnect listener failed",
-        e,
+        e
       );
     }
   };
@@ -227,10 +229,10 @@ export class BluetoothDeviceWrapper {
     const serviceMeta = profile.deviceInformation;
     try {
       const deviceInfo = await this.assertGattServer().getPrimaryService(
-        serviceMeta.id,
+        serviceMeta.id
       );
       const characteristic = await deviceInfo.getCharacteristic(
-        serviceMeta.characteristics.modelNumber.id,
+        serviceMeta.characteristics.modelNumber.id
       );
       const modelNumberBytes = await characteristic.readValue();
       const modelNumber = new TextDecoder().decode(modelNumberBytes);
@@ -248,11 +250,17 @@ export class BluetoothDeviceWrapper {
       throw new Error("Could not read model number");
     }
   }
+
+  async getAccelerometerService(): Promise<Accelerometer> {
+    const gattServer = this.assertGattServer();
+    const accelerometer = await AccelerometerService.init(gattServer);
+    return accelerometer;
+  }
 }
 
 export const createBluetoothDeviceWrapper = async (
   device: BluetoothDevice,
-  logging: Logging,
+  logging: Logging
 ): Promise<BluetoothDeviceWrapper | undefined> => {
   try {
     // Reuse our connection objects for the same device as they

lib/bluetooth.ts

@@ -3,6 +3,7 @@
  *
  * SPDX-License-Identifier: MIT
  */
+import { Accelerometer } from "./accelerometer";
 import {
   BluetoothDeviceWrapper,
   createBluetoothDeviceWrapper,
@@ -136,6 +137,10 @@ export class MicrobitWebBluetoothConnection
     }
   }
 
+  async getAccelerometer(): Promise<Accelerometer | undefined> {
+    return this.connection?.getAccelerometerService();
+  }
+
   private setStatus(newStatus: ConnectionStatus) {
     this.status = newStatus;
     this.log("Device status " + newStatus);

lib/device.ts

@@ -5,6 +5,7 @@
  */
 import { TypedEventTarget } from "./events";
 import { BoardId } from "./board-id";
+import { Accelerometer } from "./accelerometer";
 
 /**
  * Specific identified error types.
@@ -242,4 +243,6 @@ export interface DeviceConnection
    * Clear device to enable chooseDevice.
    */
   clearDevice(): void;
+
+  getAccelerometer(): Promise<Accelerometer | undefined>;
 }

lib/mock.ts

@@ -16,6 +16,7 @@ import {
   WebUSBError,
   WebUSBErrorCode,
 } from "./device";
+import { Accelerometer } from "./accelerometer";
 
 /**
  * A mock device used during end-to-end testing.
@@ -83,7 +84,7 @@ export class MockDeviceConnection
        * A progress callback. Called with undefined when the process is complete or has failed.
        */
       progress: (percentage: number | undefined) => void;
-    },
+    }
   ): Promise<void> {
     await new Promise((resolve) => setTimeout(resolve, 100));
     options.progress(0.5);
@@ -112,4 +113,8 @@ export class MockDeviceConnection
   mockWebUsbNotSupported(): void {
     this.setStatus(ConnectionStatus.NOT_SUPPORTED);
   }
+
+  getAccelerometer(): Promise<Accelerometer | undefined> {
+    return Promise.resolve(undefined);
+  }
 }