diff options
Diffstat (limited to 'extmod/machine_pulse.c')
| -rw-r--r-- | extmod/machine_pulse.c | 37 |
1 files changed, 26 insertions, 11 deletions
diff --git a/extmod/machine_pulse.c b/extmod/machine_pulse.c index 85dba86d9b..b78a63f182 100644 --- a/extmod/machine_pulse.c +++ b/extmod/machine_pulse.c @@ -30,20 +30,35 @@ #if MICROPY_PY_MACHINE_PULSE -MP_WEAK mp_uint_t machine_time_pulse_us(mp_hal_pin_obj_t pin, int pulse_level, mp_uint_t timeout_us) { +mp_uint_t machine_time_pulse_us(mp_hal_pin_obj_t pin, int pulse_level, mp_uint_t timeout_us) { + mp_uint_t nchanges = 2; mp_uint_t start = mp_hal_ticks_us(); - while (mp_hal_pin_read(pin) != pulse_level) { - if ((mp_uint_t)(mp_hal_ticks_us() - start) >= timeout_us) { - return (mp_uint_t)-2; - } - } - start = mp_hal_ticks_us(); - while (mp_hal_pin_read(pin) == pulse_level) { - if ((mp_uint_t)(mp_hal_ticks_us() - start) >= timeout_us) { - return (mp_uint_t)-1; + for (;;) { + // Sample ticks and pin as close together as possible, and always in the same + // order each time around the loop. This gives the most accurate measurement. + mp_uint_t t = mp_hal_ticks_us(); + int pin_value = mp_hal_pin_read(pin); + + if (pin_value == pulse_level) { + // Pin is at desired value. Flip desired value and see if we are done. + pulse_level = 1 - pulse_level; + if (--nchanges == 0) { + return t - start; + } + start = t; + } else { + // Pin hasn't changed yet, check for timeout. + mp_uint_t dt = t - start; + if (dt >= timeout_us) { + return -nchanges; + } + + // Allow a port to perform background task processing if needed. + #ifdef MICROPY_PY_MACHINE_TIME_PULSE_US_HOOK + MICROPY_PY_MACHINE_TIME_PULSE_US_HOOK(dt); + #endif } } - return mp_hal_ticks_us() - start; } static mp_obj_t machine_time_pulse_us_(size_t n_args, const mp_obj_t *args) { |