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#include "common.h"
#include <avr/io.h>
#include <avr/interrupt.h>
#include "timer.h"
/* useconds per clock tick */
#define US_PER_TICK 128
/* max useconds with max OCRA1 */
#define MAX_US ((uint32_t) 8388480)
/* max/current timer hits */
volatile uint8_t maxhits, hits;
/* compare value for n-1, last hits */
uint16_t count, lastcount;
/* accumulated time since last timeout/call to timerHit (us) */
uint32_t time;
ISR(TIMER1_COMPA_vect) {
++hits;
time += (uint32_t) OCR1A * (uint32_t) US_PER_TICK;
if (hits == maxhits-1) {
OCR1A = lastcount;
} else if (hits >= maxhits) {
enableWakeup (WAKE_TIMER);
}
}
/* Check if timer was hit, return time since last restart or 0 if not hit yet
*/
uint32_t timerHit () {
if (shouldWakeup (WAKE_TIMER)) {
disableWakeup (WAKE_TIMER);
const uint32_t ret = time;
/* reset timer, start again */
hits = 0;
time = 0;
OCR1A = count;
TCNT1 = 0;
return ret;
} else {
return 0;
}
}
/* Start a timer that fires every t us
*/
void timerStart (const uint32_t t) {
hits = 0;
time = 0;
/* reset timer value */
TCNT1 = 0;
/* set ctc (compare timer and clear) mode (part 1) */
TCCR1A = 0;
/* enable compare match interrupt */
TIMSK1 = (1 << OCIE1A);
/* set compare value */
#if F_CPU == 8000000
/* with divider 1024 each clock tick is 128us with a rounding error of 64us
* per second/4ms per minute, since it’s a 16 bit timer we support up to
* 2**16-1 ticks, which is 8388480us (8s) */
if (t >= MAX_US) {
maxhits = t/MAX_US+1;
count = UINT16_MAX;
lastcount = (t % MAX_US) / US_PER_TICK;
OCR1A = UINT16_MAX;
} else {
maxhits = 1;
const uint16_t tdiv = t / US_PER_TICK;
count = tdiv;
lastcount = tdiv;
OCR1A = tdiv;
}
#else
#error "cpu speed not supported"
#endif
/* io clock with 1024 prescaler; ctc (part 2) */
TCCR1B = (1 << CS12) | (1 << CS10) | (1 << WGM12);
}
void timerStop () {
/* zero clock source */
TCCR1B = 0;
}
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