hw-rollerderby-scoreboard/avr.c

45 lines
783 B
C

#include <stdint.h>
#include <stdbool.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include "avr.h"
/* Clock must be a multiple of 2MHz or there will be clock drift */
#define TICK_HZ (CLOCK_HZ / 8 / 64)
#define TICKS_PER_JIFFY (TICK_HZ / 10)
#define cbi(byt, bit) (byt &= ~_BV(bit))
#define sbi(byt, bit) (byt |= _BV(bit))
extern volatile bool tick;
extern volatile uint32_t jiffies;
// Interrupt called every jiffy
ISR(TIM1_COMPA_vect)
{
jiffies += 1;
tick = true;
}
void
init(void)
{
int i;
DDRA = ~(_BV(NESOUT));
DDRB = 0xff;
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0; // reset counter
OCR1A = TICKS_PER_JIFFY - 1;
TCCR1B |= _BV(WGM12);
TCCR1B |= _BV(CS11) | _BV(CS10); // prescale: clk_io / 64
TIMSK1 |= _BV(OCIE1A);
bit(PORTA, _BV(7), true);
sei();
}