From 840777b2fdb4cb8c12d716ffe94e3c3dca0d5cad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=B8ren=20Rasmussen?= <sr@jondahl.net>
Date: Tue, 15 Mar 2022 17:09:53 +0100
Subject: [PATCH] Wait on slaves for w1 bus master bulk read

---
 cmd/fermentord/main.go     |  2 --
 pkg/temperature/ds18b20.go | 44 +++++++++++++++++++++++++++++++++++---
 2 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/cmd/fermentord/main.go b/cmd/fermentord/main.go
index d2ea191..e8e9c5d 100644
--- a/cmd/fermentord/main.go
+++ b/cmd/fermentord/main.go
@@ -28,8 +28,6 @@ func mainLoop(ctx context.Context, wg *sync.WaitGroup, js nats.JetStream, config
 	defer hub.Flush(10 * time.Second)
 	defer wg.Done()
 
-	temperature.Initialize()
-
 	// Controller
 	chCtrlTemp := make(chan temperature.TemperatureReading, 10)
 	defer close(chCtrlTemp)
diff --git a/pkg/temperature/ds18b20.go b/pkg/temperature/ds18b20.go
index 873f5a8..5bd6521 100644
--- a/pkg/temperature/ds18b20.go
+++ b/pkg/temperature/ds18b20.go
@@ -18,8 +18,15 @@ import (
 	"github.com/getsentry/sentry-go"
 )
 
+type BulkReadBusState int
+
 const (
+	BulkReadIdle  BulkReadBusState = 0
+	BulkReadBusy  BulkReadBusState = -1
+	BulkReadReady BulkReadBusState = 1
+
 	sensorConversionTime = 750 * time.Millisecond
+	busPollDelay         = 10 * time.Millisecond
 )
 
 var (
@@ -39,7 +46,7 @@ var (
 	filters       map[string]*EWMAFilter
 )
 
-func Initialize() {
+func init() {
 	sensors = make([]string, 0)
 	filters = make(map[string]*EWMAFilter)
 	C = make(chan TemperatureReading, 30)
@@ -60,6 +67,7 @@ func PollSensors(ctx context.Context, wg *sync.WaitGroup, readingInterval time.D
 	defer ticker.Stop()
 
 	for {
+	work_loop:
 		select {
 		case <-ticker.C:
 			start := time.Now()
@@ -91,8 +99,24 @@ func PollSensors(ctx context.Context, wg *sync.WaitGroup, readingInterval time.D
 				time.Sleep(deltaSleep)
 			}
 
-			// Read all sensors.
-			readSensors(hub)
+			// Poll bus state
+		poll_bus:
+			state, err := pollBusState()
+			if err != nil {
+				accErrTrigger++
+				hub.CaptureException(err)
+				log.Print(err)
+				break work_loop
+			}
+
+			switch state {
+			case BulkReadBusy:
+				time.Sleep(busPollDelay)
+				goto poll_bus
+
+			case BulkReadIdle, BulkReadReady:
+				readSensors(hub)
+			}
 
 		case c := <-ConfigUpdates:
 			sensors = c
@@ -153,6 +177,20 @@ func triggerBulkRead() error {
 	return err
 }
 
+func pollBusState() (BulkReadBusState, error) {
+	b, err := ioutil.ReadFile("/sys/bus/w1/devices/w1_bus_master1/therm_bulk_read")
+	if err != nil {
+		return BulkReadIdle, err
+	}
+
+	i, err := strconv.Atoi(string(b))
+	if err != nil {
+		return BulkReadIdle, err
+	}
+
+	return BulkReadBusState(i), nil
+}
+
 // read returns the temperature of the specified sensor in millidegrees celcius.
 func read(sensor string) (int64, error) {
 	path := filepath.Join("/sys/bus/w1/devices", sensor, "w1_slave")