diff options
| -rw-r--r-- | ports/stm32/timer.c | 42 |
1 files changed, 40 insertions, 2 deletions
diff --git a/ports/stm32/timer.c b/ports/stm32/timer.c index 8e3a00cb5..0aa3c47b6 100644 --- a/ports/stm32/timer.c +++ b/ports/stm32/timer.c @@ -314,6 +314,40 @@ STATIC uint32_t compute_prescaler_period_from_freq(pyb_timer_obj_t *self, mp_obj return (prescaler - 1) & 0xffff; } +// computes prescaler and period so TIM triggers with a period of t_num/t_den seconds +STATIC uint32_t compute_prescaler_period_from_t(pyb_timer_obj_t *self, int32_t t_num, int32_t t_den, uint32_t *period_out) { + uint32_t source_freq = timer_get_source_freq(self->tim_id); + if (t_num <= 0 || t_den <= 0) { + mp_raise_ValueError("must have positive freq"); + } + uint64_t period = (uint64_t)source_freq * (uint64_t)t_num / (uint64_t)t_den; + uint32_t prescaler = 1; + while (period > TIMER_CNT_MASK(self)) { + // if we can divide exactly, and without prescaler overflow, do that first + if (prescaler <= 13107 && period % 5 == 0) { + prescaler *= 5; + period /= 5; + } else if (prescaler <= 21845 && period % 3 == 0) { + prescaler *= 3; + period /= 3; + } else { + // may not divide exactly, but loses minimal precision + uint32_t period_lsb = period & 1; + prescaler <<= 1; + period >>= 1; + if (period < prescaler) { + // round division up + prescaler |= period_lsb; + } + if (prescaler > 0x10000) { + mp_raise_ValueError("period too large"); + } + } + } + *period_out = (period - 1) & TIMER_CNT_MASK(self); + return (prescaler - 1) & 0xffff; +} + // Helper function for determining the period used for calculating percent STATIC uint32_t compute_period(pyb_timer_obj_t *self) { // In center mode, compare == period corresponds to 100% @@ -529,11 +563,12 @@ STATIC void pyb_timer_print(const mp_print_t *print, mp_obj_t self_in, mp_print_ /// /// You must either specify freq or both of period and prescaler. STATIC mp_obj_t pyb_timer_init_helper(pyb_timer_obj_t *self, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) { - enum { ARG_freq, ARG_prescaler, ARG_period, ARG_mode, ARG_div, ARG_callback, ARG_deadtime }; + enum { ARG_freq, ARG_prescaler, ARG_period, ARG_tick_hz, ARG_mode, ARG_div, ARG_callback, ARG_deadtime }; static const mp_arg_t allowed_args[] = { { MP_QSTR_freq, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} }, { MP_QSTR_prescaler, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0xffffffff} }, { MP_QSTR_period, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0xffffffff} }, + { MP_QSTR_tick_hz, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1000} }, { MP_QSTR_mode, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = TIM_COUNTERMODE_UP} }, { MP_QSTR_div, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1} }, { MP_QSTR_callback, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} }, @@ -554,8 +589,11 @@ STATIC mp_obj_t pyb_timer_init_helper(pyb_timer_obj_t *self, size_t n_args, cons // set prescaler and period directly init->Prescaler = args[ARG_prescaler].u_int; init->Period = args[ARG_period].u_int; + } else if (args[ARG_period].u_int != 0xffffffff) { + // set prescaler and period from desired period and tick_hz scale + init->Prescaler = compute_prescaler_period_from_t(self, args[ARG_period].u_int, args[ARG_tick_hz].u_int, &init->Period); } else { - mp_raise_TypeError("must specify either freq, or prescaler and period"); + mp_raise_TypeError("must specify either freq, period, or prescaler and period"); } init->CounterMode = args[ARG_mode].u_int; |