107 lines
3.3 KiB
Go
107 lines
3.3 KiB
Go
package main
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import (
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"encoding/binary"
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"math"
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"time"
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"tinygo.org/x/bluetooth"
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)
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const (
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bleCyclingPowerServiceUUID = 0x1818 // BLE Cycling Power Service UUID
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bleCyclingPowerFeatureCharacteristic = 0x2A65 // BLE Cycling Power Feature characteristic
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bleCyclingPowerMeasurementCharacteristic = 0x2A63 // BLE Cycling Power Measurement characteristic
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bleSignalDetectedFlag = 0x20 // Signal Detected bit in BLE payload header
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bleCyclingPowerFeatureCumulativeTorque = 0x01 // Cumulative Torque feature bit
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bleCyclingPowerFeaturePowerOutput = 0x02 // Power Output feature bit
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)
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var adapter = bluetooth.DefaultAdapter
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func must(err error) {
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if err != nil {
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panic(err)
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}
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}
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func ExposeBluetooth(events <-chan Event) {
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must(adapter.Enable())
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var powerChar bluetooth.Characteristic
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must(adapter.AddService(&bluetooth.Service{
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UUID: bluetooth.New16BitUUID(bleCyclingPowerServiceUUID),
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Characteristics: []bluetooth.CharacteristicConfig{
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{
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UUID: bluetooth.New16BitUUID(bleCyclingPowerFeatureCharacteristic),
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Flags: bluetooth.CharacteristicReadPermission,
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Value: []byte{bleCyclingPowerFeatureCumulativeTorque | bleCyclingPowerFeaturePowerOutput, 0, 0, 0},
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},
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{
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UUID: bluetooth.New16BitUUID(bleCyclingPowerMeasurementCharacteristic),
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Flags: bluetooth.CharacteristicNotifyPermission,
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Handle: &powerChar,
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},
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},
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}))
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must(adapter.DefaultAdvertisement().Configure(bluetooth.AdvertisementOptions{
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LocalName: "LinuxAntBtBridge",
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ServiceUUIDs: []bluetooth.UUID{bluetooth.New16BitUUID(bleCyclingPowerServiceUUID)},
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}))
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must(adapter.DefaultAdvertisement().Start())
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logMsg("bt: BLE advertising...")
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var totalRevs float64 = 0.0
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var elapsedTicks float64 = 0.0
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// initial event.
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event := <-events
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lastUpdateTime := event.Now
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var lastCompletedRevs float64 = 0.0
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var lastRevTicks float64 = 0.0 // time in 1/1024s of last completed revolution
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for event := range events {
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now := event.Now
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deltaT := now.Sub(lastUpdateTime).Seconds()
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lastUpdateTime = now
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watts := event.Power
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rpm := float64(event.Cadence)
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totalRevs += rpm / 60.0 * deltaT
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elapsedTicks += deltaT * 1024.0
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completedRevs := math.Floor(totalRevs)
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if completedRevs > lastCompletedRevs {
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// we crossed a new full RPM so comput the last time of that rotation
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// time at which the last completed revolution occurred
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// = current time - fractional part of revolution * time per revolution
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fracRev := totalRevs - completedRevs
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ticksPerRev := 1024.0 * 60.0 / rpm
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lastRevTicks = elapsedTicks - fracRev*ticksPerRev
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lastCompletedRevs = completedRevs
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} else {
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// No change we need to emit the same data ss before.
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}
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payload := make([]byte, 8)
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binary.LittleEndian.PutUint16(payload[0:], bleSignalDetectedFlag)
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binary.LittleEndian.PutUint16(payload[2:], watts)
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binary.LittleEndian.PutUint16(payload[4:], uint16(lastCompletedRevs))
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binary.LittleEndian.PutUint16(payload[6:], uint16(lastRevTicks))
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if _, err := powerChar.Write(payload); err != nil {
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logPrintf("bt: failed to write power characteristic: %v\n", err)
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}
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logPrintf("bt: watts: %d rpm: %.0f completedRevs: %.0f lastRevTime: %.0f processingDelay: %v\n",
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watts, rpm, completedRevs, lastRevTicks, time.Now().Sub(now))
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}
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logMsg("bt: BLE advertising stopped")
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}
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