micropython/extmod/machine_pulse.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2016 Damien P. George
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "py/runtime.h"
#include "py/mperrno.h"
#include "extmod/modmachine.h"

#if MICROPY_PY_MACHINE_PULSE

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();
    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
        }
    }
}

static mp_obj_t machine_time_pulse_us_(size_t n_args, const mp_obj_t *args) {
    mp_hal_pin_obj_t pin = mp_hal_get_pin_obj(args[0]);
    int level = 0;
    if (mp_obj_is_true(args[1])) {
        level = 1;
    }
    mp_uint_t timeout_us = 1000000;
    if (n_args > 2) {
        timeout_us = mp_obj_get_int(args[2]);
    }
    mp_uint_t us = machine_time_pulse_us(pin, level, timeout_us);
    // May return -1 or -2 in case of timeout
    return mp_obj_new_int(us);
}
MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_time_pulse_us_obj, 2, 3, machine_time_pulse_us_);

#endif