Fix timer interrupt priority + refactor

5 files changed, 90 insertions, 98 deletions

diff --git a/src/display.c b/src/display.c
index 5fccd50..8de5043 100644
--- a/src/display.c
+++ b/src/display.c
@@ -4,6 +4,7 @@
 #include <util/delay.h>
 
 #include "display.h"
+#include "rtc.h"
 
 // "_gfedcba"
 // Reversed because a-g is mapped to pa0-6. (pa7 is decimal)
@@ -13,20 +14,18 @@ const uint32_t digit_masks[] = {
     0b00010010, 0b00000010, 0b01111000, 0b00000000, 0b00010000,
 };
 
-void setup_display() {
-  TIMSK1 = 0;
-
-  // Set prescaler (Timer clock = F_CPU / 64)
+void display_setup() {
+  // Set prescaler CS01 + CS00 (F_CPU / 64) + CTC
   // For 32768Hz -> 32768/64 = 512Hz
-  TCCR1B = (1 << CS11) | (1 << CS10) | (1 << WGM12) | (1 << WGM13);
-  TCCR1A = (1 << WGM11) | (1 << WGM10);
+  TCCR0B = (1 << CS01) | (1 << CS00) | (1 << WGM02);
+  TCCR0A = (1 << WGM01) | (1 << WGM00);
 
-  TCNT1 = 0; // Start counting from 0
-  OCR1A = 1; // 0-1 = 2 counts before timer interrupt (512/2 = 256Hz)
-  OCR1B = 0;
+  TCNT0 = 0; // Start counting from 0
+  OCR0A = 1; // 0-1 = 2 counts before timer interrupt (512/2 = 256Hz)
+  OCR0B = 0;
 
-  TIFR1 = (1 << OCF1A) | (1 << OCF1B) | (1 << TOV1); // Clear interrupt flags
-  TIMSK1 = (1 << OCIE1A); // Enable timer overflow interrupt
+  TIFR0 = (1 << OCF0A) | (1 << OCF0B) | (1 << TOV0); // Clear interrupt flags
+  TIMSK0 = (1 << OCIE0A); // Enable timer overflow interrupt
 
   // Draw startup state
   DDRA |= 0b11111111;
@@ -35,6 +34,19 @@ void setup_display() {
   PORTB = (1 << PB2);
 }
 
+volatile uint8_t current_digit = 0;
+
+// Render current digit
+void display_render(void) {
+  DDRA |= 0b11111111;
+  DDRB |= 0b11111111;
+
+  write_time(minutes, seconds, current_digit);
+
+  // Next digit
+  current_digit = (current_digit + 1) % 4;
+}
+
 void write_digit(uint8_t digit) {
   if (digit > 9 || digit < 0)
     return;
@@ -47,25 +59,23 @@ void write_time(uint16_t hour, uint16_t minute, uint8_t mask) {
   // unsigned short hour_digit1 = hour % 10;
   // unsigned short hour_digit2 = (hour / 10) % 10;
 
-  // _delay_ms(4);
   // Reset digit control pins
   PORTA &= ~(1 << PA7); // minute digit 1
   PORTB &= ~(1 << PB2); // minute digit 2
-  // _delay_ms(4);
 
   // cli();
-  if (mask & 0b0001 || mask & 0b0100) {
+  if (mask == 0 || mask == 2) {
 #ifdef STUBBED
-    printf(":: %d\n", minute_digit1);
+    printf(" %d\n", minute_digit1);
     fflush(stdout);
 #endif
     write_digit(minute_digit1);
     PORTA |= (1 << PA7);
   }
 
-  if (mask & 0b0010 || mask & 0b1000) {
+  if (mask == 1 || mask == 3) {
 #ifdef STUBBED
-    printf(":: %d\n", minute_digit2);
+    printf(":: %d", minute_digit2);
     fflush(stdout);
 #endif
     write_digit(minute_digit2);
diff --git a/src/display.h b/src/display.h
index 167374a..34a065d 100644
--- a/src/display.h
+++ b/src/display.h
@@ -2,10 +2,14 @@
 #define _LOADED_DISPLAY
 #include <stdint.h>
 
-void setup_display();
+volatile extern uint8_t current_digit;
+
+void display_setup(void);
 
 void write_digit(uint8_t digit);
 
 void write_time(uint16_t hour, uint16_t minute, uint8_t digit_mask);
 
-#endif
+void display_render(void);
+
+#endif
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index b3fa431..cf6f7a8 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,10 +1,10 @@
 #include <avr/interrupt.h>
 #include <avr/io.h>
 #include <stdbool.h>
-#include <stdint.h>
 #include <util/delay.h>
 
 #include "display.h"
+#include "rtc.h"
 
 // Config for attiny84a + external 32KHz crystal osc taken from
 // https://github.com/ingepnet/breadboardwatch/blob/master/Makefile#L26
@@ -15,68 +15,13 @@ FUSES = {
     .extended = 0xff,
 };
 
-void set_all_pins_output(void) {
-  DDRA |= 0b11111111;
-  DDRB |= 0b11111111;
-}
-
-void setup_rtc() {
-  // Set prescaler (Timer clock = F_CPU / 1024)
-  // For 32768Hz -> 32768/1024 = 32Hz
-  TCCR0B = (1 << CS02) | (1 << CS00) | (1 << WGM02);
-  TCCR0A = (1 << WGM01) | (1 << WGM00);
-
-  TCNT0 = 0;  // Start counting from 0
-  OCR0A = 31; // 0-31 = 32 counts before timer interrupt (1Hz)
-  OCR0B = 0;
-
-  // TIFR0 = (1 << TOV0);  // Clear interrupt flags
-  TIFR0 = (1 << OCF0A) | (1 << OCF0B) | (1 << TOV0); // Clear interrupt flags
-  // TIMSK0 = (1 << TOIE0); // Enable timer overflow interrupt
-  TIMSK0 = (1 << OCIE0A); // Enable timer overflow interrupt
-}
-
-volatile uint8_t seconds = 10;
-volatile uint8_t minutes = 0;
-volatile uint8_t hours = 0;
-// Clock
-ISR(TIM0_COMPA_vect, ISR_FLATTEN) {
-  // if (true) {
-  //   OCR0A = 32;
-  // } else if (true) {
-  //   OCR0A = 31;
-  // } else {
-  //   OCR0A = 30;
-  // }
-
-  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;
-    }
-  }
-}
-
-volatile static uint8_t digit_mask = 0b0001;
 // Display
-ISR(TIM1_COMPA_vect, ISR_FLATTEN) {
-  set_all_pins_output();
-  write_time(minutes, seconds, digit_mask);
-  if (seconds % 2) {
-    PORTA &= ~(1 << PA5);
-    PORTB &= ~(1 << PB3);
-  } else {
-    PORTA |= (1 << PA5);
-    PORTB |= (1 << PB3);
-  }
+// timer 0 has lower priority than timer 1, so some ticks could get skipped due
+// to interrupt starvation
+ISR(TIM0_COMPA_vect, ISR_FLATTEN) { display_render(); }
 
-  digit_mask = digit_mask << 1;
-  if (digit_mask > 0b1000)
-    digit_mask = 0b0001;
-}
+// RTC interrupt
+ISR(TIM1_COMPA_vect, ISR_FLATTEN) { rtc_increment(); }
 
 #define IS_BUTTON_ON() ((PINA & (1 << PA0)) == 0)
 #define ENABLE_BUTTON() (DDRA &= ~(1 << PA0))
@@ -84,28 +29,12 @@ ISR(TIM1_COMPA_vect, ISR_FLATTEN) {
 int main(void) {
   PRR = 0b0011; // Power reduction register. Shut down USI and ADC
 
-  setup_rtc();
-  setup_display();
+  display_setup();
+  rtc_setup();
 
   sei();
 
-  set_all_pins_output();
-
   while (1) {
-    // cli();
-    // set_all_pins_output();
-    // write_time(minutes, seconds, digit_mask);
-    // if (seconds % 2) {
-    //   PORTA &= ~(1 << PA5);
-    //   PORTB &= ~(1 << PB3);
-    // } else {
-    //   PORTA |= (1 << PA5);
-    //   PORTB |= (1 << PB3);
-    // }
-    // digit_mask = digit_mask << 1;
-    // if (digit_mask > 0b1000)
-    //   digit_mask = 0b0001;
-
     // ENABLE_BUTTON();
     // if (IS_BUTTON_ON()) {
     //   cli();
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;
+    }
+  }
+}
diff --git a/src/rtc.h b/src/rtc.h
new file mode 100644
index 0000000..f3f8f9c
--- /dev/null
+++ b/src/rtc.h
@@ -0,0 +1,13 @@
+#ifndef _LOADED_RTC
+#define _LOADED_RTC
+#include <stdint.h>
+
+volatile extern uint8_t seconds;
+volatile extern uint8_t minutes;
+volatile extern uint8_t hours;
+
+void rtc_setup(void);
+
+void rtc_increment(void);
+
+#endif