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nrf51: Fix a race condition in hwtimer.c

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The check for overflow was originally in __hw_clock_source_read()

If it got interrupted, it would frequently see an overflow, because
"prev_read" would be less than "now".

1 - Use the comparator to check for overflow.
2 - Only check for overflow in the interrupt handler.

BUG=chrome-os-partner:35312
BRANCH=none
TEST=make buildall -j
use the keyboard code to type
use a console command "forcetime", to force the system time to overflow soon.

Signed-off-by: Myles Watson <mylesgw@chromium.org>

Change-Id: I7005724222289ba967e89af0ce8b9ef8f90a4ae4
Reviewed-on: https://chromium-review.googlesource.com/239967
Reviewed-by: Alec Berg <alecaberg@chromium.org>
Tested-by: Myles Watson <mylesgw@chromium.org>
Commit-Queue: Myles Watson <mylesgw@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
This commit is contained in:
Myles Watson
2015-01-09 11:43:33 -08:00
committed by ChromeOS Commit Bot
parent 4ee50837a0
commit 16eaf5cfde
1 changed files with 9 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
chip/nrf51/hwtimer.c
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@@ -56,8 +56,6 @@ static uint32_t last_deadline; /* cache of event set */
*
*/
static uint32_t shift;
static uint32_t overflow;
static uint32_t prev_read;
void __hw_clock_event_set(uint32_t deadline)
{
@@ -81,50 +79,44 @@ void __hw_clock_event_clear(void)
uint32_t __hw_clock_source_read(void)
{
uint32_t now;
/* to capture the current value */
NRF51_TIMER0_CAPTURE1 = 1;
now = NRF51_TIMER0_CC1 + shift;
/* detect if a wrap happened */
if (now < prev_read)
overflow++;
prev_read = now;
return now;
return NRF51_TIMER0_CC1 + shift;
}
void __hw_clock_source_set(uint32_t ts)
{
shift = prev_read = ts;
shift = ts;
/* reset counter to zero */
NRF51_TIMER0_STOP = 1;
NRF51_TIMER0_CLEAR = 1;
NRF51_TIMER0_START = 1;
/* So that no interrupt until next __hw_clock_event_set() */
NRF51_TIMER0_CC0 = ts - 1;
/* Update the overflow point */
NRF51_TIMER0_CC2 = 0 - shift;
/* Start the timer again */
NRF51_TIMER0_START = 1;
}
/* Interrupt handler for timer */
void timer_irq(void)
{
int overflow = 0;
/* clear status */
NRF51_TIMER0_COMPARE0 = 0;
if (NRF51_TIMER0_COMPARE2) {
/* Invoke a read to update overflow variable */
__hw_clock_source_read();
NRF51_TIMER0_COMPARE2 = 0;
overflow = 1;
}
process_timers(overflow);
overflow = 0;
}
DECLARE_IRQ(NRF51_PERID_TIMER0, timer_irq, 1);