refactor: replace magic hex constants with named constants

- Add BLE spec constants for service/characteristic UUIDs and signal flag
- Add ANT+ spec constants for data page mask and cycling power page
- Add descriptive comments explaining each constant's origin and purpose

cmd/bridge/ant.go

@@ -10,6 +10,11 @@ import (
 	"github.com/half2me/antgo/driver/usb"
 )
 
+const (
+	antDataPageMask         = 0x7F  // Mask for data page number (7 bits, clears toggle bit)
+	antDataPageCyclingPower = 0x10  // Data page 16 = Cycling Power Feature page
+)
+
 func resetAndWait(drv io.ReadWriter) error {
 	if _, err := drv.Write(ant.SystemResetMessage()); err != nil {
 		return err
@@ -61,8 +66,8 @@ func ListenForTrainer(vendorId uint16, productId uint16, deviceNumber uint32,
 		switch msg.DeviceType() {
 		case ant.DEVICE_TYPE_POWER:
 			// Check data page first
-			page := msg[4] & 0x7F // mask toggle bit
+			page := msg[4] & antDataPageMask
-			if page != 0x10 {
+			if page != antDataPageCyclingPower {
 				continue
 			}
 			cur := ant.PowerMessage(msg)

cmd/bridge/bluetooth.go

@@ -8,6 +8,13 @@ import (
 	"tinygo.org/x/bluetooth"
 )
 
+const (
+	bleCyclingPowerServiceUUID               = 0x1818 // BLE Cycling Power Service UUID
+	bleCyclingPowerFeatureCharacteristic     = 0x2A65 // BLE Cycling Power Feature characteristic
+	bleCyclingPowerMeasurementCharacteristic = 0x2A63 // BLE Cycling Power Measurement characteristic
+	bleSignalDetectedFlag                    = 0x20   // Signal Detected bit in BLE payload header
+)
+
 var adapter = bluetooth.DefaultAdapter
 
 func must(err error) {
@@ -22,15 +29,15 @@ func ExposeBluetooth(events <-chan Event) {
 	var powerChar bluetooth.Characteristic
 
 	must(adapter.AddService(&bluetooth.Service{
-		UUID: bluetooth.New16BitUUID(0x1818),
+		UUID: bluetooth.New16BitUUID(bleCyclingPowerServiceUUID),
 		Characteristics: []bluetooth.CharacteristicConfig{
 			{
-				UUID:  bluetooth.New16BitUUID(0x2A65), // Cycling Power Feature
+				UUID:  bluetooth.New16BitUUID(bleCyclingPowerFeatureCharacteristic),
 				Flags: bluetooth.CharacteristicReadPermission,
 				Value: []byte{0, 0, 0, 0},
 			},
 			{
-				UUID:   bluetooth.New16BitUUID(0x2A63), // Cycling Power Measurement
+				UUID:   bluetooth.New16BitUUID(bleCyclingPowerMeasurementCharacteristic),
 				Flags:  bluetooth.CharacteristicNotifyPermission,
 				Handle: &powerChar,
 			},
@@ -39,7 +46,7 @@ func ExposeBluetooth(events <-chan Event) {
 
 	must(adapter.DefaultAdvertisement().Configure(bluetooth.AdvertisementOptions{
 		LocalName:    "LinuxAntBtBridge",
-		ServiceUUIDs: []bluetooth.UUID{bluetooth.New16BitUUID(0x1818)},
+		ServiceUUIDs: []bluetooth.UUID{bluetooth.New16BitUUID(bleCyclingPowerServiceUUID)},
 	}))
 	must(adapter.DefaultAdvertisement().Start())
 	logMsg("BLE advertising...")
@@ -67,7 +74,7 @@ func ExposeBluetooth(events <-chan Event) {
 		lastCompletedRev = elapsedTicks - fracRev*timePerRev
 
 		payload := make([]byte, 8)
-		binary.LittleEndian.PutUint16(payload[0:], 0x20)
+		binary.LittleEndian.PutUint16(payload[0:], bleSignalDetectedFlag)
 		binary.LittleEndian.PutUint16(payload[2:], watts)
 		binary.LittleEndian.PutUint16(payload[4:], uint16(completedRevs))
 		binary.LittleEndian.PutUint16(payload[6:], uint16(lastCompletedRev))