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Update comments and fix typo

pull/10701/head
Laurent Meunier 2019-06-04 11:26:34 +02:00
parent 501881bf38
commit 8616cd7655
1 changed files with 13 additions and 3 deletions
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16
targets/TARGET_STM/lp_ticker.c
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@ -196,7 +196,7 @@ void lp_ticker_init(void)
__HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
/* Init is called with Interrupts disabled, so the CMPOK interrupt
* will not be handler. Let's mark it is now safe to write to LP counter */
* will not be handled. Let's mark it is now safe to write to LP counter */
lp_cmpok = true;
}
@ -292,8 +292,18 @@ void lp_ticker_set_interrupt(timestamp_t timestamp)
timestamp = LP_TIMER_WRAP(timestamp + LP_TIMER_SAFE_GUARD);
}
}
/* Then check if this target timestamp is not in the past, or close to wrap-around */
if((timestamp < last_read_counter) && (last_read_counter <= (0xFFFF - LP_TIMER_SAFE_GUARD))) {
/* Then check if this target timestamp is not in the past, or close to wrap-around
* Let's assume last_read_counter = 0xFFFC, and we want to program timestamp = 0x100
* The interrupt will not fire before the CMPOK flag is OK, so there are 2 cases:
* in case CMPOK flag is set by HW after or at wrap-around, then this will fire only @0x100
* in case CMPOK flag is set before, it will indeed fire early, as for the wrap-around case.
* But that will take at least 3 cycles and the interrupt fires at the end of a cycle.
* In our case 0xFFFC + 3 => at the transition between 0xFFFF and 0.
* If last_read_counter was 0xFFFB, it should be at the transition between 0xFFFE and 0xFFFF.
* There might be crossing cases where it would also fire @ 0xFFFE, but by the time we read the counter,
* it may already have moved to the next one, so for now we've taken this as margin of error.
*/
if((timestamp < last_read_counter) && (last_read_counter <= (0xFFFF - LP_TIMER_SAFE_GUARD))) {
/* Workaround, because limitation */
__HAL_LPTIM_COMPARE_SET(&LptimHandle, ~0);
} else {