Erik Brakkee
7ee776ba1a
revolution by using the average RPM over the last interval instead of using the last RPM.
110 lines
3.4 KiB
Go
110 lines
3.4 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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prevRpm := float64(event.Cadence)
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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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avgRpm := (rpm + prevRpm) / 2
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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 / avgRpm
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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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prevRpm = rpm
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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.Little\Endian.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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