put display refreshing into an interrupt

.vscode/settings.json

@@ -12,7 +12,7 @@
     "AVR.device.type": "atmega2560",
     "AVR.device.frequency": 16000000,
     "AVR.programmer.type": "wiring",
-    "AVR.programmer.port": "/dev/ttyACM0",
+    "AVR.programmer.port": "/dev/ttyACM1",
     "AVR.programmer.rate": 115200,
     "AVR.programmer.arguments": [
         "-D"

lib/7segment_4digits.c

@@ -6,6 +6,7 @@
 #include "7segment.h"
 
 uint8_t display[4] = { 0, 0, 0, 0 };
+uint8_t current_digit = 0;
 
 /**
  * Display pins should be mapped like this:
@@ -28,8 +29,17 @@ void set_display_value(uint8_t digit, uint8_t data) {
     display[digit] = data;
 }
 
+void update_next_digit() {
+    update_display_digit(current_digit++);
+    if (current_digit >= 4) current_digit = 0;
+}
+
+void update_display_digit(int digit) {
+    display_value(digit, display[digit]);
+}
+
 // Returns the amount of microseconds we blocked for
-float update_display() {
+float update_display_all_sync() {
     int sleep_time = 2000;
     for (int i = 0; i < 4; i++) {
         display_value(i, display[i]);

lib/7segment_4digits.h

@@ -4,6 +4,10 @@ void display_value(uint8_t digit, uint8_t data);
 
 void set_display_value(uint8_t digit, uint8_t data);
 
-float update_display();
+void update_next_digit();
+
+void update_display_digit(int digit);
+
+float update_display_all_sync();
 
 void show_float(float value);

main.c

@@ -10,7 +10,7 @@
 #include "lib/7segment.h"
 #include "lib/7segment_4digits.h"
 
-int timer_start =  0xffff - (F_CPU / 1024 / 1000);
+int tick_timer_start =  0xffff - (F_CPU / 1024 / 1000); // 1ms
 volatile uint32_t ticks = 0;
 volatile bool counting = false;
 volatile bool beeping = false;
@@ -18,13 +18,15 @@ volatile bool beeping = false;
 void start_timer() {
     // Sets the Clock Select. See table on page 157 the Atmel datasheet.
     TCCR1B |= _BV(CS10) | _BV(CS12); // clk/1024
+    TCCR2B |= _BV(CS22); // clk/64
 
     // Set the TOIE (Timer Overflow Interrupt Enable) bit
     // on TIMSK1 (Timer 1 Interrupt Mask Register).
     TIMSK1 |= _BV(TOIE1);
+    TIMSK2 |= _BV(TOIE2);
 
     // Sets the current timer value
-    TCNT1 = timer_start;
+    TCNT1 = tick_timer_start;
 
     // Enable interrupts
     sei();
@@ -38,7 +40,7 @@ void main() {
 // ISR is used to handle interrupts. TIMER1_OVF_vect
 // is triggered whenever timer 1 (16 bit) overflows.
 ISR(TIMER1_OVF_vect) {
-    TCNT1 = timer_start; // TODO figure out how to get the correct number
+    TCNT1 = tick_timer_start;
     if (counting) ticks += 1;
 
     if (bit_is_set(PIND, PIND0)) {
@@ -48,6 +50,10 @@ ISR(TIMER1_OVF_vect) {
     }
 }
 
+ISR(TIMER2_OVF_vect) {
+    update_next_digit();
+}
+
 void prog_7segment() {
     DDRF  = 0b11111111;
     DDRK  = 0b00000000;
@@ -92,7 +98,6 @@ void prog_7segment_4digit() {
 
     while(1) {
         show_float(ticks / 1000.0f);
-        float sleep_time = update_display();
 
         if (!pressed_pause && bit_is_clear(PINK, PINK7)) {
             beep();