Fix dot flickering when cycling

Nixie_Firmware_Rust/src/nixie.rs

@@ -635,7 +635,14 @@ impl Clock {
             }
         }
 
-        update_digit(&mut self.dot);
+        // The dot is somewhat sensitive to changes to PWM signal, so for the sake
+        // of consistency, keep the signal on time at the end of the PWM period.
+        // Otherwise the distribution algorithm will sometimes place the on time at
+        // the end of the PWM period in one cycle and at the start of the period for
+        // the next, which results in visual flickers.
+        // update_digit(&mut self.dot);
+        self.dot.pwm_start = DIGIT_MAX_BRIGHTNESS - self.dot.value;
+        self.dot.pwm_end = DIGIT_MAX_BRIGHTNESS;
 
         #[cfg(test)]
         println!(
@@ -761,6 +768,48 @@ mod test {
                 println!("Refresh halted");
                 break;
             }
+            clock.tubes.iter_mut().for_each(|tube| {
+                tube.digits.iter_mut().for_each(|digit| {
+                    digit.updated = false;
+                });
+            });
+            clock.dot.updated = false;
+        }
+    }
+
+    #[test]
+    fn cycle_test() {
+        let mut clock: Clock = Clock::default();
+
+        clock.tubes[0].cycle = Some(CycleSettings {
+            last_digit: clock.tubes[0].last_digit,
+            next_digit: 0,
+            iteration: CYCLE_ITERATIONS,
+            last_fade_duration: DIGIT_FADE_DURATION_MS,
+        });
+
+        clock.rtc_tick(10, 23, 12);
+
+        for cycle in 0..1000 {
+            println!("\nCycle tick: {}", cycle);
+            if clock.cycle_tick() {
+                println!("Cycle halted");
+                break;
+            }
+
+            for tick in 0..1005 {
+                println!("\nRefresh tick: {}", tick);
+                if !clock.fps_tick() {
+                    println!("Refresh halted");
+                    break;
+                }
+                clock.tubes.iter_mut().for_each(|tube| {
+                    tube.digits.iter_mut().for_each(|digit| {
+                        digit.updated = false;
+                    });
+                });
+                clock.dot.updated = false;
+            }
         }
     }
 }