zwack/lib/cps/cycling-power-measurement-characteristic.js

Simulate an indoor bicycle trainer with BLE (Bluetooth Low Energy)

var debugCSP = require('debug')('zwack:csp');
const Bleno = require('@abandonware/bleno');

// Spec
//https://developer.bluetooth.org/gatt/characteristics/Pages/CharacteristicViewer.aspx?u=org.bluetooth.characteristic.cycling_power_measurement.xml

class CyclingPowerMeasurementCharacteristic extends Bleno.Characteristic {
    constructor() {
        super({
            uuid: '2A63',
            value: null,
            properties: ['notify'],
            descriptors: [
                new Bleno.Descriptor({
                    uuid: '2901',
                    value: 'Cycling Power Measurement',
                }),
                new Bleno.Descriptor({
                    // Client Characteristic Configuration
                    uuid: '2902',
                    value: Buffer.alloc(2),
                }),
                new Bleno.Descriptor({
                    // Server Characteristic Configuration
                    uuid: '2903',
                    value: Buffer.alloc(2),
                }),
            ],
        });
        this._updateValueCallback = null;
    }

    onSubscribe(maxValueSize, updateValueCallback) {
        debugCSP('[CyclingPowerMeasurementCharacteristic] client subscribed to PM');
        this._updateValueCallback = updateValueCallback;
        return this.RESULT_SUCCESS;
    }

    onUnsubscribe() {
        debugCSP('[CyclingPowerMeasurementCharacteristic] client unsubscribed from PM');
        this._updateValueCallback = null;
        return this.RESULT_UNLIKELY_ERROR;
    }

    notify(event) {
        if (!('watts' in event) && !('rev_count' in event)) {
            // ignore events with no power and no crank data
            return this.RESULT_SUCCESS;
        }
        var buffer = new Buffer(8);
        // flags
        // 00000001 - 1   - 0x001 - Pedal Power Balance Present
        // 00000010 - 2   - 0x002 - Pedal Power Balance Reference
        // 00000100 - 4   - 0x004 - Accumulated Torque Present
        // 00001000 - 8   - 0x008 - Accumulated Torque Source
        // 00010000 - 16  - 0x010 - Wheel Revolution Data Present
        // 00100000 - 32  - 0x020 - Crank Revolution Data Present
        // 01000000 - 64  - 0x040 - Extreme Force Magnitudes Present
        // 10000000 - 128 - 0x080 - Extreme Torque Magnitudes Present
        if ('rev_count' in event) {
            buffer.writeUInt16LE(0x020, 0);
        } else {
            buffer.writeUInt16LE(0x00, 0);
        }

        if ('watts' in event) {
            var watts = event.watts;
            debugCSP('power: ' + watts);
            buffer.writeInt16LE(watts, 2);
        }

        if ('rev_count' in event) {
            event.rev_count = event.rev_count % 65536;
            //debugCSP("rev_count: " + event.rev_count);

            buffer.writeUInt16LE(event.rev_count, 4);

            var now = Date.now();
            var now_1024 = Math.floor((now * 1e3) / 1024);
            var event_time = now_1024 % 65536; // rolls over every 64 seconds
            debugCSP('event time: ' + event_time);
            buffer.writeUInt16LE(event_time, 6);
        }

        if (this._updateValueCallback) {
            this._updateValueCallback(buffer);
        }
        return this.RESULT_SUCCESS;
    }
}

module.exports = CyclingPowerMeasurementCharacteristic;