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stmhal: Resolve question in comment about timer clock.

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Damien George 2014-08-14 00:30:14 +01:00
parent 2c781eabbd
commit bf133f7737
1 changed files with 5 additions and 2 deletions
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stmhal/timer.c
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@ -274,8 +274,11 @@ STATIC mp_obj_t pyb_timer_init_helper(pyb_timer_obj_t *self, uint n_args, const
tim_clock = HAL_RCC_GetPCLK1Freq();
}
// compute the prescaler value so TIM triggers at freq-Hz
// dpgeorge: I don't understand why we need to multiply tim_clock by 2
// Compute the prescaler value so TIM triggers at freq-Hz
// On STM32F405/407/415/417 there are 2 cases for how the clock freq is set.
// If the APB prescaler is 1, then the timer clock is equal to its respective
// APB clock. Otherwise (APB prescaler > 1) the timer clock is twice its
// respective APB clock. See DM00031020 Rev 4, page 115.
uint32_t period = MAX(1, 2 * tim_clock / vals[0].u_int);
uint32_t prescaler = 1;
while (period > 0xffff) {