Timer: set up a 62.5kHz timer

firmware/src/timer.cpp

@@ -1,16 +1,26 @@
 #include <Arduino.h>
 
-#define DEMO_TRIGGER_MS 1500
+#define DEMO_TRIGGER_MS 1000
+
+#if F_CPU != 16000000
+  #error "Unsupported F_CPU"
+#endif
 
 void setupTimer() {
-  // Set up Timer 0 to trigger interrupt every 1ms
-  // Timer 0 is already used and configured by Arduino for millis()
-  // however it uses TOIE0 (overflow interrupt), so we'll use OCIE0A:
-  //   When this bit is written to one, and the I-flag in the Status Register is set
-  //   (interrupts globally enabled), the Timer/Counter0 Output Compare A Match interrupt is enabled
-  //   The corresponding Interrupt Vector is executed when the OCF0A Flag, located in TIFR0, is set.
-  OCR0A = 0xAF; // any number is OK, it will trigger at some point during the counter
-  TIMSK0 |= _BV(OCIE0A);
+  noInterrupts();
+  // reset timer settings
+  TCCR1A = 0;
+  TCCR1B = 0;
+  TCNT1 = 0;
+  // 256 prescaler (16MHz / 256 = 62.5kHz)
+  TCCR1B |= (1 << CS12);
+  // CTC mode (Clear Timer on Compare Match)
+  TCCR1B |= (1 << WGM12);
+  // interrupt at 62.5kHz / (OCR1A + 1)
+  OCR1A = 0;
+  // enable timer
+  TIMSK1 |= (1 << OCIE1A);
+  interrupts();
 }
 
 // incremented every DEMO_TRIGGER_MS by interrupt,
@@ -32,11 +42,16 @@ void demoTimer() {
   }
 }
 
+volatile uint16_t timerTicks = 0;
 volatile uint16_t timerMillis = 0;
 
-// triggers every 1ms
-ISR(TIMER0_COMPA_vect) {
-  timerMillis++;
+// triggers at 62.5kHz
+ISR(TIMER1_COMPA_vect) {
+  timerTicks++;
+  if (timerTicks == 625) {
+    timerTicks = 0;
+    timerMillis += 10;
+  }
   if (timerMillis >= DEMO_TRIGGER_MS) {
     timerMillis -= DEMO_TRIGGER_MS;
     timerEvents++;