succd: calcuate change rate for safety interlock directly from adc ringbuffer

succbone/succd/main.go

@@ -31,7 +31,6 @@ func main() {
 	}
 	d.aboveRough.threshold = float64(flagPressureThresholdRough)
 	d.aboveHigh.threshold = float64(flagPressureThresholdHigh)
-  d.lastPressures = newRingbuffer()
 	if flagFake {
 		klog.Infof("Starting with fake peripherals")
 		d.adcPirani = &fakeADC{}

succbone/succd/process.go

@@ -17,8 +17,6 @@ type daemon struct {
 	// Pirani gauge.
 	adcPirani adc
 
-  lastPressures ringbuffer
-
 	failsafe     bool
 	highPressure bool
 
@@ -125,10 +123,8 @@ func (d *daemon) processOnce(_ context.Context) error {
 	d.aboveRough.process(float64(mbar))
 	d.aboveHigh.process(float64(mbar))
 
-  d.lastPressures.AddValue(mbar)
-
   // max rate of 1.0 in 500 ms because ringbuffer holds 5 values
-  if d.lastPressures.MaxMinDiff() > 1.0 {
+  if d.piraniRateOfChange() > 2.0 {
     if !d.failsafe {
       d.failsafe = true
 			klog.Errorf("Pressure changed too fast; entering failsafe mode")
@@ -199,6 +195,25 @@ func (d *daemon) processOnce(_ context.Context) error {
 	return nil
 }
 
+func (d *daemon) piraniRateOfChange() float32 {
+  max := d.adcPiraniVolts[0]
+  min := d.adcPiraniVolts[0]
+  for _, val := range d.adcPiraniVolts {
+    if val < min {
+      min = val
+    }
+    if val > max {
+      max = val
+    }
+  }
+  max_bar := math.Pow(10.0, float64(max)-8.5);
+  max_mbar := float32(max_bar * 1000.0)
+  min_bar := math.Pow(10.0, float64(min)-8.5);
+  min_mbar := float32(min_bar * 1000.0)
+
+  return max_mbar - min_mbar
+}
+
 // pirani returns the Pirani gauge voltage and pressure.
 func (d *daemon) pirani() (volts float32, mbar float32) {
 	d.mu.RLock()

succbone/succd/ringbuffer.go

@@ -1,34 +0,0 @@
-package main
-
-type ringbuffer struct {
-  data  []float32
-  idx   int
-}
-
-func newRingbuffer() ringbuffer {
-  return ringbuffer {
-    data: make([]float32, 5),
-    idx: 0,
-  }
-}
-
-func (rb *ringbuffer) AddValue(value float32) {
-  rb.data[rb.idx] = value;
-  rb.idx = (rb.idx + 1) % len(rb.data)
-}
-
-func (rb *ringbuffer) MaxMinDiff() float32 {
-  min := rb.data[0]
-  max := rb.data[0]
-
-  for _, val := range rb.data {
-    if val < min {
-      min = val
-    }
-    if val > max {
-      max = val
-    }
-  }
-
-  return max - min
-}