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stmhal, timer: Improve accuracy of freq computation.

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This commit is contained in:
Damien George 2014-10-04 14:59:35 +01:00
parent 97ef94df83
commit 55f68b3ce8
1 changed files with 19 additions and 4 deletions
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23
stmhal/timer.c
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@ -307,7 +307,11 @@ STATIC uint32_t compute_prescaler_period_from_freq(pyb_timer_obj_t *self, mp_obj
if (freq <= 0) {
goto bad_freq;
}
period = MAX(1, source_freq / freq);
while (freq < 1 && prescaler < 6553) {
prescaler *= 10;
freq *= 10;
}
period = (float)source_freq / freq;
#endif
} else {
mp_int_t freq = mp_obj_get_int(freq_in);
@ -316,11 +320,22 @@ STATIC uint32_t compute_prescaler_period_from_freq(pyb_timer_obj_t *self, mp_obj
bad_freq:
nlr_raise(mp_obj_new_exception_msg(&mp_type_ValueError, "must have positive freq"));
}
period = MAX(1, source_freq / freq);
period = source_freq / freq;
}
period = MAX(1, period);
while (period > TIMER_CNT_MASK(self)) {
prescaler <<= 1;
period >>= 1;
// if we can divide exactly, do that first
if (period % 5 == 0) {
prescaler *= 5;
period /= 5;
} else if (period % 3 == 0) {
prescaler *= 3;
period /= 3;
} else {
// may not divide exactly, but loses minimal precision
prescaler <<= 1;
period >>= 1;
}
}
*period_out = (period - 1) & TIMER_CNT_MASK(self);
return (prescaler - 1) & 0xffff;