zwack/lib/ftms/treadmill-data-characteristic.js

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

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

// Spec
// https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.characteristic.treadmill_data.xml

class TreadmillDataCharacteristic extends Bleno.Characteristic {
    constructor() {
        super({
            uuid: '2ACD',
            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) {
        debugFTMS('[CyclingPowerMeasurementCharacteristic] client subscribed to PM');
        this._updateValueCallback = updateValueCallback;
        return this.RESULT_SUCCESS;
    }

    onUnsubscribe() {
        debugFTMS('[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
        // 00000000 00000001 - 0x0001 - More Data
        // 00000000 00000010 - 0x0002 - Average Speed Present (Kilometer per hour with a resolution of 0.01)
        // 00000000 00000100 - 0x0004 - Total Distance Present
        // 00000000 00001000 - 0x0008 - Inclination and Ramp Angle Setting present
        // 00000000 00010000 - 0x0010 - Elevation Gain present
        // 00000000 00100000 - 0x0020 - Instantaneous Pace present
        // 00000000 01000000 - 0x0040 - Average Pace present
        // 00000000 10000000 - 0x0080 - Expended Energy present
        // 00000001 00000000 - 0x0100 - Heart Rate present
        // 00000010 00000000 - 0x0200 - Elapsed Time present
        // 00000100 00000000 - 0x0400 - Remaining Time present
        // 00001000 00000000 - 0x0800 - Force on Belt and Power Output present

        const flagEnum = {
            more_data: 0x01,
            avg_speed: 0x02,
            total_distance: 0x04,
            inclination: 0x08,
            elevation: 0x10,
            pace: 0x20,
            avg_pace: 0x40,
            expended_energy: 0x80,
            heart_rate: 0x100,
            elapsed_time: 0x200,
            remaining_time: 0x400,
            force: 0x800,
        };

        let flags = 0;
        for (var property in event) {
            if (flagEnum.hasOwnProperty(property)) {
                flags = flags | flagEnum[property];
            }
        }
        buffer.writeUInt16LE(flags, 0);

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

        if ('rev_count' in event) {
            event.rev_count = event.rev_count % 65536;
            //debugFTMS("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
            debugFTMS('event time: ' + event_time);
            buffer.writeUInt16LE(event_time, 6);
        }

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

module.exports = TreadmillDataCharacteristic;