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drivers: timer: lptim timer clock on stm32u5 has a prescaler

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The stm32 devices shows a x2 factor on the LPTIM1,3,4
clock source but it acts as a prescaler.
The max lptim counter (timebase) is counting 4 sec
In that case, the LPTIM count unit is double.

Signed-off-by: Francois Ramu <francois.ramu@st.com>
This commit is contained in:
Francois Ramu 2022-12-14 11:08:21 +01:00 committed by Fabio Baltieri
parent 572b286010
commit c14670abea
1 changed files with 14 additions and 3 deletions
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17
drivers/timer/stm32_lptim_timer.c
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@ -348,9 +348,7 @@ static int sys_clock_driver_init(const struct device *dev)
}
#endif
/* Set LPTIM time base based on clck source freq
* Time base = (2s * freq) - 1
*/
/* Set LPTIM time base based on clock source freq */
if (lptim_clock_freq == KHZ(32)) {
lptim_time_base = 0xF9FF;
} else if (lptim_clock_freq == 32768) {
@ -359,6 +357,19 @@ static int sys_clock_driver_init(const struct device *dev)
return -EIO;
}
if (IS_ENABLED(DT_PROP(DT_DRV_INST(0), st_static_prescaler))) {
/*
* LPTIM of the stm32, like stm32U5, which has a clock source x2.
* A full 16bit LPTIM counter is counting 4s at 2 * 1/32768 (with LSE)
* Time base = (4s * freq) - 1
*/
lptim_clock_freq = lptim_clock_freq / 2;
}
/*
* Else, a full 16bit LPTIM counter is counting 2s at 1/32768 (with LSE)
* Time base = (2s * freq) - 1
*/
/* Clear the event flag and possible pending interrupt */
IRQ_CONNECT(DT_INST_IRQN(0),
DT_INST_IRQ(0, priority),