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avr: Fix bug causing timer_read_time() to not be in sync with scheduler 

Commit 16e3dbb1 changed the avr implementation of timer_read_time().
Unfortunately, it raised the possibility for timer_read_time() to be
out of sync with the scheduler's understanding of the current time.
In particular, it was common for the timer irq to overflow the 16bit
hardware counter once at startup, and this would lead to
timer_read_time() always returning a time ~4ms ahead of the scheduler
on 16Mhz chips.  This resulted in "Move queue empty" errors.

To resolve this issue, only increment timer_high from timer_periodic()
and make sure the timer irqs start immediately after timer_init().

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-03-31 14:26:29 -04:00
parent aa0f1aaeb2
commit a1c61563a0
1 changed files with 19 additions and 10 deletions
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29
src/avr/timer.c
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@ -70,6 +70,17 @@ timer_repeat_set(uint16_t next)
TIFR1 = 1<<OCF1B; TIFR1 = 1<<OCF1B;
} }
// Reset the timer - clear settings and dispatch next timer immediately
static void
timer_reset(void)
{
uint16_t now = timer_get();
timer_set(now + 50);
TIFR1 = 1<<OCF1A;
timer_repeat_set(now + 50);
}
DECL_SHUTDOWN(timer_reset);
static void static void
timer_init(void) timer_init(void)
{ {
@ -85,8 +96,13 @@ timer_init(void)
TCCR1A = 0; TCCR1A = 0;
// Normal Mode // Normal Mode
TCCR1B = 1<<CS10; TCCR1B = 1<<CS10;
// Setup for first irq
irqstatus_t flag = irq_save();
timer_reset();
TIFR1 = 1<<TOV1;
// enable interrupt // enable interrupt
TIMSK1 = 1<<OCIE1A; TIMSK1 = 1<<OCIE1A;
irq_restore(flag);
} }
DECL_INIT(timer_init); DECL_INIT(timer_init);
@ -105,16 +121,9 @@ timer_read_time(void)
union u32_u calc; union u32_u calc;
calc.val = timer_get(); calc.val = timer_get();
calc.hi = timer_high; calc.hi = timer_high;
if (likely(!(TIFR1 & (1<<TOV1)))) { if (TIFR1 & (1<<TOV1) && calc.lo < 0x8000)
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++;
irq_restore(flag);
return calc.val; return calc.val;
} }
@ -122,7 +131,7 @@ timer_read_time(void)
void void
timer_periodic(void) timer_periodic(void)
{ {
if (unlikely(TIFR1 & (1<<TOV1))) { if (TIFR1 & (1<<TOV1)) {
// Hardware timer has overflowed - update overflow counter // Hardware timer has overflowed - update overflow counter
TIFR1 = 1<<TOV1; TIFR1 = 1<<TOV1;
timer_high++; timer_high++;