diff options
| -rw-r--r-- | stmhal/timer.c | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/stmhal/timer.c b/stmhal/timer.c index 3465003135..1a4fd66ea1 100644 --- a/stmhal/timer.c +++ b/stmhal/timer.c @@ -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; |