1 files changed, 36 insertions, 0 deletions
diff --git a/src/rtc.c b/src/rtc.c
new file mode 100644
index 0000000..1ac50c3
--- /dev/null
+++ b/src/rtc.c
@@ -0,0 +1,36 @@
+#include <avr/interrupt.h>
+#include <avr/io.h>
+#include <stdint.h>
+#include <util/delay.h>
+
+#include "rtc.h"
+
+void rtc_setup(void) {
+  // Set prescaler CS12 + CS10 (F_CPU / 1024) + CTC
+  // For 32768Hz -> 32768/1024 = 32Hz
+  TCCR1B = (1 << CS12) | (1 << CS10) | (1 << WGM12) | (1 << WGM13);
+  TCCR1A = (1 << WGM11) | (1 << WGM10);
+
+  TCNT1 = 0;  // Start counting from 0
+  OCR1A = 31; // 0-31 = 32 counts before timer interrupt (1Hz)
+  OCR1B = 0;
+
+  TIFR1 = (1 << OCF1A) | (1 << OCF1B) | (1 << TOV1); // Clear interrupt flags
+  TIMSK1 = (1 << OCIE1A); // Enable timer overflow interrupt
+}
+
+volatile uint8_t seconds = 10;
+volatile uint8_t minutes = 0;
+volatile uint8_t hours = 0;
+
+void rtc_increment(void) {
+  uint8_t s = seconds + 1;
+  seconds = s % 60;
+  if (s >= 60) {
+    uint8_t m = minutes + 1;
+    minutes = m % 60;
+    if (m >= 60) {
+      hours = (hours + 1) % 24;
+    }
+  }
+}