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avr: Optimize 16bit timer upscaling 

The hardware timer overflow bit can be used to optimize the conversion
from 16bit timers to 32bit timers.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-03-10 11:23:46 -05:00
parent a38437f378
commit 16e3dbb18c
1 changed files with 24 additions and 22 deletions
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46
src/avr/timer.c
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@ -83,20 +83,29 @@ DECL_INIT(timer_init);
* 32bit timer wrappers * 32bit timer wrappers
****************************************************************/ ****************************************************************/
static uint32_t timer_last; static uint16_t timer_high;
// Return the 32bit current time given the 16bit current time. // Return the current time (in absolute clock ticks).
static __always_inline uint32_t uint32_t
calc_time(uint32_t last, uint16_t cur) timer_read_time(void)
{ {
union u32_u16_u { union u32_u16_u {
struct { uint16_t lo, hi; }; struct { uint16_t lo, hi; };
uint32_t val; uint32_t val;
} calc; } calc;
calc.val = last; irqstatus_t flag = irq_save();
if (cur < calc.lo) calc.val = timer_get();
calc.hi = timer_high;
if (!(TIFR1 & (1<<TOV1))) {
irq_restore(flag);
return calc.val;
}
// Hardware timer has overflowed - update overflow counter
TIFR1 = 1<<TOV1;
timer_high = calc.hi + 1;
irq_restore(flag);
if (calc.lo < 0x8000)
calc.hi++; calc.hi++;
calc.lo = cur;
return calc.val; return calc.val;
} }
@ -104,18 +113,11 @@ calc_time(uint32_t last, uint16_t cur)
void void
timer_periodic(void) timer_periodic(void)
{ {
timer_last = calc_time(timer_last, timer_get()); if (TIFR1 & (1<<TOV1)) {
} // Hardware timer has overflowed - update overflow counter
TIFR1 = 1<<TOV1;
// Return the current time (in absolute clock ticks). timer_high++;
uint32_t }
timer_read_time(void)
{
irqstatus_t flag = irq_save();
uint16_t cur = timer_get();
uint32_t last = timer_last;
irq_restore(flag);
return calc_time(last, cur);
} }
#define TIMER_MIN_TICKS 100 #define TIMER_MIN_TICKS 100
@ -126,11 +128,11 @@ timer_read_time(void)
uint8_t uint8_t
timer_set_next(uint32_t next) timer_set_next(uint32_t next)
{ {
uint16_t cur = timer_get(); uint32_t cur = timer_read_time();
if ((int16_t)(OCR1A - cur) < 0 && !(TIFR1 & (1<<OCF1A))) if ((int16_t)(OCR1A - (uint16_t)cur) < 0 && !(TIFR1 & (1<<OCF1A)))
// Already processing timer irqs // Already processing timer irqs
try_shutdown("timer_set_next called during timer dispatch"); try_shutdown("timer_set_next called during timer dispatch");
uint32_t mintime = calc_time(timer_last, cur + TIMER_MIN_TICKS); uint32_t mintime = cur + TIMER_MIN_TICKS;
if (sched_is_before(mintime, next)) { if (sched_is_before(mintime, next)) {
timer_set_clear(next); timer_set_clear(next);
return 0; return 0;