interrupt stuff

lib/7segment_4digits.c

@@ -39,6 +39,13 @@ float update_display() {
 }
 
 void show_float(float value) {
+    if (value >= 10000 || value < 0) {
+        for (int i = 0; i < 4; i++) {
+            set_display_value(i, 0b01000000); // minus character
+        }
+        return;
+    }
+
     int digits = num_digits((int)value);
     int full_number = value * (int)roundf(powf(10, 4 - digits));
 

main.c

@@ -5,14 +5,41 @@
 #include <avr/io.h>
 #include <util/delay.h>
 #include <stdbool.h>
+#include <avr/interrupt.h>
 #include "lib/util.h"
 #include "lib/7segment.h"
 #include "lib/7segment_4digits.h"
 
+volatile int ticks = 0;
+
+// https://gist.github.com/Wollw/2381139
+void start_timer() {
+    // Sets the Clock Select. See table on page 157 the Atmel datasheet.
+    TCCR1B |= _BV(CS10) | _BV(CS12);
+
+    // Set the TOIE (Timer Overflow Interrupt Enable) bit
+    // on TIMSK1 (Timer 1 Interrupt Mask Register).
+    TIMSK1 |= _BV(TOIE1);
+
+    // Sets the current timer value
+    TCNT1 = 63974;
+
+    // Enable interrupts
+    sei();
+}
+
 void main() {
+    start_timer();
     prog_7segment_4digit();
 }
 
+// ISR is used to handle interrupts. TIMER1_OVF_vect
+// is triggered whenever timer 1 (16 bit) overflows.
+ISR(TIMER1_OVF_vect) {
+    TCNT1 = 63974; // TODO figure out how to get the correct number
+    ticks++;
+}
+
 void prog_7segment() {
     DDRF  = 0b11111111;
     DDRK  = 0b00000000;
@@ -49,7 +76,7 @@ void prog_7segment_4digit() {
     bool pressed = false;
 
     while(1) {
-        show_float(num);
+        show_float(ticks);
         float sleep_time = update_display();
 
         if (!pressed && bit_is_clear(PINK, PINK7)) {