improved bluetooth loop

cmd/bridge/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/binary"
 	"fmt"
+	"math"
 	"os/exec"
 	"time"
 
@@ -53,31 +54,41 @@ func main() {
 	}))
 	must(adapter.DefaultAdvertisement().Start())
 	fmt.Println("BLE advertising...")
-	var crankRevs uint16
-	var lastCrankEventTime uint16
 
+	var totalRevs float64
+	var lastCompletedRev float64 // time in 1/1024s of last completed revolution
+	lastUpdate := time.Now()
+	var elapsedTicks float64
 	for {
-		sec := time.Now().Second()
+		now := time.Now()
+		deltaT := now.Sub(lastUpdate).Seconds()
+		lastUpdate = now
+
+		sec := now.Second()
 		watts := uint16(100 + sec)
-		rpm := uint16(50 + sec)
+		rpm := float64(50 + sec)
 
-		// advance crank event time based on rpm
-		// time between crank events = 1024*60/rpm ticks
-		crankEventInterval := uint16(1024 * 60 / rpm)
-		lastCrankEventTime += crankEventInterval
-		crankRevs++
+		totalRevs += rpm / 60.0 * deltaT
+		elapsedTicks += deltaT * 1024.0
+
+		completedRevs := math.Floor(totalRevs)
+		// 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
 
-		// flags: bit 5 = crank revolution data present
 		payload := make([]byte, 8)
 		binary.LittleEndian.PutUint16(payload[0:], 0x20)
 		binary.LittleEndian.PutUint16(payload[2:], watts)
-		binary.LittleEndian.PutUint16(payload[4:], crankRevs)
-		binary.LittleEndian.PutUint16(payload[6:], lastCrankEventTime)
+		binary.LittleEndian.PutUint16(payload[4:], uint16(completedRevs))
+		binary.LittleEndian.PutUint16(payload[6:], uint16(lastCompletedRev))
 
 		powerChar.Write(payload)
-		fmt.Printf("watts: %d  rpm: %d  crankRevs: %d  eventTime: %d\n", watts, rpm, crankRevs, lastCrankEventTime)
+		fmt.Printf("watts: %d  rpm: %.0f  completedRevs: %.0f  lastRevTime: %.0f\n",
+			watts, rpm, completedRevs, lastCompletedRev)
 
-		time.Sleep(time.Second)
+		time.Sleep(250 * time.Millisecond)
 	}
 }