succd: add pirani failsafe

succbone/succd/process.go

@@ -17,6 +17,8 @@ type daemon struct {
 	// Pirani gauge.
 	adcPirani adc
 
+	failsafe bool
+
 	gpioDiffusionPump gpio
 	gpioRoughingPump  gpio
 	gpioBtnPumpDown   gpio
@@ -120,6 +122,24 @@ func (d *daemon) processOnce(_ context.Context) error {
 	d.aboveRough.process(float64(mbar))
 	d.aboveHigh.process(float64(mbar))
 
+	if mbar < 4e-6 {
+		// Unrealistic result, Pirani probe probably disconnected. Failsafe mode.
+		if !d.failsafe {
+			d.failsafe = true
+			klog.Errorf("Pirani probe seems disconnected; enabling failsafe mode")
+		}
+	} else {
+		if d.failsafe {
+			d.failsafe = false
+			klog.Infof("Pirani probe has been reconnected; quitting failsafe mode")
+		}
+	}
+
+	if d.failsafe {
+		d.aboveRough.output = true
+		d.aboveHigh.output = true
+	}
+
 	// Update relay outputs.
 	for _, rel := range []struct {
 		name string