add timer_counter module

src/timer_counter.c

@@ -0,0 +1,43 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include "timer_counter.h"
+
+volatile uint16_t counter = 0;
+
+void timer0_init(void)
+{
+    // Mode CTC: WGM01 = 1, WGM00 = 0
+    TCCR0A = (1 << WGM01);
+
+    // Prescaler 64: CS01 = 1, CS00 = 1 (CS02 = 0)
+    // TCCR0B = (1 << CS01) | (1 << CS00);
+    // Prescaler 8: CS01 = 1, (CS00 = 0, CS02 = 0)
+    TCCR0B = (1 << CS01);
+
+    // Setting OCR0A to 124 gives 1 ms with 8 MHz and prescaler of 64
+    // OCR0A = 124;
+    // Setting OCR0A to 99 gives 100 us with 8 MHz and prescaler of 8
+    OCR0A = 99;
+
+    // Enable Timer/Counter0 Output Compare Match A interrupt
+    TIMSK0 = (1 << OCIE0A);
+}
+
+ISR(TIM0_COMPA_vect)
+{
+    counter++;
+}
+
+uint16_t ticks100us(void)
+{
+    uint16_t value1, value2;
+
+    // Double-checked locking to ensure atomic read of counter
+    do
+    {
+        value1 = counter;
+        value2 = counter;
+    } while (value1 != value2);
+
+    return value1;
+}

src/timer_counter.h

@@ -0,0 +1,4 @@
+#pragma once
+
+void timer0_init(void);
+uint16_t ticks100us(void);