succd: Add hysteresis feature to thresholdOutput blocks

Add a hysteresis value that can be optionally configured for
thresholdOutput blocks.  This will hopefully help to prevent jumping
outputs from feedback that is caused by the thresholdOutput itself.

succbone/succd/process_blocks.go

@@ -30,13 +30,20 @@ type thresholdOutput struct {
 	debounce time.Time
 	// threshold is the setpoint of the block.
 	threshold float64
+	// hysteresis around the process setpoint (min/max is threshold +- hysteresis)
+	hysteresis float64
 }
 
 func (t *thresholdOutput) process(value float64) {
 	if time.Now().Before(t.debounce) {
 		return
 	}
-	new := value > t.threshold
+	new := t.output
+	if t.output {
+		new = value > (t.threshold - t.hysteresis)
+	} else {
+		new = value > (t.threshold + t.hysteresis)
+	}
 	if new != t.output {
 		t.output = new
 		t.debounce = time.Now().Add(time.Second * 5)

succbone/succd/process_blocks_test.go

@@ -26,20 +26,37 @@ func TestMomentaryOutput(t *testing.T) {
 
 func TestThresholdOutput(t *testing.T) {
 	to := thresholdOutput{
-		threshold: 1,
+		threshold:  1,
+		hysteresis: 0.2,
 	}
-	to.process(0)
+	to.process(0.7)
 	if to.output {
 		t.Fatalf("output shouldn't have triggered")
 	}
-	to.process(2)
+	to.process(1)
+	if to.output {
+		t.Fatalf("output shouldn't have triggered")
+	}
+	to.process(1.3)
 	if !to.output {
 		t.Fatalf("output should have triggered")
 	}
-	to.process(0)
+	to.process(1)
+	if !to.output {
+		t.Fatalf("output should have triggered")
+	}
+	to.process(0.7)
 	if !to.output {
 		t.Fatalf("output should have triggered (in debounce)")
 	}
+
+	// let debounce timeout pass
+	time.Sleep(time.Second * 6)
+
+	to.process(0.7)
+	if to.output {
+		t.Fatalf("output shouldn't have triggered")
+	}
 }
 
 func TestRingbufferInput(t *testing.T) {