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LP ticker workaround 

There is an errata in LPTIM specification that explains that CMP Flag
condition is not an exact match (COUNTER = MATCH) but rather a
comparison (COUNTER >= MATCH).

As a consequence the interrupt is firing early than expected when
programing a timestamp after the 0xFFFF wrap-around.

In order to
work-around this issue, we implement the below work-around.
In case timestamp is after the work-around, let's decide to program the
CMP value to 0xFFFF, which is the wrap-around value. There would anyway be
a wake-up at the time of wrap-around to let the OS update the system time.
When the wrap-around interrupt happen, OS will check the current time and
program again the timestamp to the proper value.
pull/10701/head
Laurent Meunier 2019-03-29 14:51:14 +01:00
parent 85c477c1dc
commit 6452eb3172
1 changed files with 9 additions and 2 deletions
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11
targets/TARGET_STM/lp_ticker.c
View File

@ -226,8 +226,15 @@ void lp_ticker_set_interrupt(timestamp_t timestamp)
/* Any successive write before the CMPOK flag be set, will lead to unpredictable results */
/* LPTICKER_DELAY_TICKS value prevents OS to call this set interrupt function before CMPOK */
MBED_ASSERT(__HAL_LPTIM_GET_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK) == SET);
__HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
__HAL_LPTIM_COMPARE_SET(&LptimHandle, timestamp);
if(timestamp < lp_ticker_read()) {
/* Workaround, because limitation */
__HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
__HAL_LPTIM_COMPARE_SET(&LptimHandle, ~0);
} else {
__HAL_LPTIM_CLEAR_FLAG(&LptimHandle, LPTIM_FLAG_CMPOK);
__HAL_LPTIM_COMPARE_SET(&LptimHandle, timestamp);
}
lp_ticker_clear_interrupt();