more stable computation of lastRevtime

Only computing lastRevtime when we have made a new full rev.
This leads to more consistency in RPMs, especially when accelerating or
decellerating.

cmd/bridge/bluetooth.go

@@ -51,14 +51,19 @@ func ExposeBluetooth(events <-chan Event) {
 	must(adapter.DefaultAdvertisement().Start())
 	logMsg("bt: BLE advertising...")
 
-	var totalRevs float64
-	var lastCompletedRev float64 // time in 1/1024s of last completed revolution
-	lastUpdate := time.Now()
-	var elapsedTicks float64
+	var totalRevs float64 = 0.0
+	var elapsedTicks float64 = 0.0
+
+	// initial event.
+	event := <-events
+	lastUpdateTime := event.Now
+	var lastCompletedRevs float64 = 0.0
+	var lastRevTicks float64 = 0.0 // time in 1/1024s of last completed revolution
+
 	for event := range events {
 		now := event.Now
-		deltaT := now.Sub(lastUpdate).Seconds()
-		lastUpdate = now
+		deltaT := now.Sub(lastUpdateTime).Seconds()
+		lastUpdateTime = now
 
 		watts := event.Power
 		rpm := float64(event.Cadence)
@@ -67,23 +72,33 @@ func ExposeBluetooth(events <-chan Event) {
 		elapsedTicks += deltaT * 1024.0
 
 		completedRevs := math.Floor(totalRevs)
+
+		if completedRevs > lastCompletedRevs {
+			// we crossed a new full RPM so comput the last time of that rotation
+
 			// time at which the last completed revolution occurred
 			// = current time - fractional part of revolution * time per revolution
 			fracRev := totalRevs - completedRevs
-		timePerRev := 1024.0 * 60.0 / rpm
-		lastCompletedRev = elapsedTicks - fracRev*timePerRev
+			ticksPerRev := 1024.0 * 60.0 / rpm
+
+			lastRevTicks = elapsedTicks - fracRev*ticksPerRev
+			lastCompletedRevs = completedRevs
+
+		} else {
+			// No change we need to emit the same data ss before.
+		}
 
 		payload := make([]byte, 8)
 		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))
+		binary.LittleEndian.PutUint16(payload[4:], uint16(lastCompletedRevs))
+		binary.LittleEndian.PutUint16(payload[6:], uint16(lastRevTicks))
 
 		if _, err := powerChar.Write(payload); err != nil {
 			logPrintf("bt: failed to write power characteristic: %v\n", err)
 		}
 		logPrintf("bt: watts: %d  rpm: %.0f  completedRevs: %.0f  lastRevTime: %.0f processingDelay: %v\n",
-			watts, rpm, completedRevs, lastCompletedRev, time.Now().Sub(now))
+			watts, rpm, completedRevs, lastRevTicks, time.Now().Sub(now))
 	}
 	logMsg("bt: BLE advertising stopped")
 }

run.sh

@@ -1,3 +1,13 @@
 #!/bin/bash
 
-systemd-inhibit --what=idle:sleep --why="Do not interrupt cycling" $( dirname $0 )/bin/bridge
+
+
+while :
+do
+  systemd-inhibit --what=idle:sleep --why="Do not interrupt cycling" $( dirname $0 )/bin/bridge "$@"
+  if [[ $? -ne 0 ]]
+  then
+    echo "ERROR: bridge exited with ERROR" 1>&2
+  fi
+  sleep 1 
+done