circuitpython/shared-module/bitbangio/I2C.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2016 Damien P. George, Scott Shawcroft
 *
 * 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 "shared-bindings/bitbangio/I2C.h"

#include "py/obj.h"

#include "common-hal/microcontroller/types.h"
#include "shared-bindings/microcontroller/__init__.h"
#include "shared-bindings/nativeio/DigitalInOut.h"
#include "shared-module/bitbangio/types.h"

#define I2C_STRETCH_LIMIT 255

STATIC void delay(bitbangio_i2c_obj_t *self) {
    // We need to use an accurate delay to get acceptable I2C
    // speeds (eg 1us should be not much more than 1us).
    common_hal_mcu_delay_us(self->us_delay);
}

STATIC void scl_low(bitbangio_i2c_obj_t *self) {
    common_hal_nativeio_digitalinout_set_value(&self->scl, false);
}

STATIC void scl_release(bitbangio_i2c_obj_t *self) {
    common_hal_nativeio_digitalinout_set_value(&self->scl, true);
    delay(self);
    // For clock stretching, wait for the SCL pin to be released, with timeout.
    for (int count = I2C_STRETCH_LIMIT; !common_hal_nativeio_digitalinout_get_value(&self->scl) && count; --count) {
        common_hal_mcu_delay_us(1);
    }
}

STATIC void sda_low(bitbangio_i2c_obj_t *self) {
    common_hal_nativeio_digitalinout_set_value(&self->sda, false);
}

STATIC void sda_release(bitbangio_i2c_obj_t *self) {
    common_hal_nativeio_digitalinout_set_value(&self->sda, true);
}

STATIC bool sda_read(bitbangio_i2c_obj_t *self) {
    common_hal_nativeio_digitalinout_switch_to_input(&self->sda, PULL_UP);
    bool value = common_hal_nativeio_digitalinout_get_value(&self->sda);
    common_hal_nativeio_digitalinout_switch_to_output(&self->sda, true, DRIVE_MODE_OPEN_DRAIN);
    return value;
}

STATIC void start(bitbangio_i2c_obj_t *self) {
    sda_release(self);
    delay(self);
    scl_release(self);
    sda_low(self);
    delay(self);
}

STATIC void stop(bitbangio_i2c_obj_t *self) {
    delay(self);
    sda_low(self);
    delay(self);
    scl_release(self);
    sda_release(self);
    delay(self);
}

STATIC int write_byte(bitbangio_i2c_obj_t *self, uint8_t val) {
    delay(self);
    scl_low(self);

    for (int i = 7; i >= 0; i--) {
        if ((val >> i) & 1) {
            sda_release(self);
        } else {
            sda_low(self);
        }
        delay(self);
        scl_release(self);
        scl_low(self);
    }

    sda_release(self);
    delay(self);
    scl_release(self);

    int ret = sda_read(self);
    delay(self);
    scl_low(self);

    return !ret;
}

STATIC bool read_byte(bitbangio_i2c_obj_t *self, uint8_t *val, bool ack) {
    delay(self);
    scl_low(self);
    delay(self);

    uint8_t data = 0;
    for (int i = 7; i >= 0; i--) {
        scl_release(self);
        data = (data << 1) | sda_read(self);
        scl_low(self);
        delay(self);
    }
    *val = data;

    // send ack/nack bit
    if (ack) {
        sda_low(self);
    }
    delay(self);
    scl_release(self);
    scl_low(self);
    sda_release(self);

    return true;
}

void shared_module_bitbangio_i2c_construct(bitbangio_i2c_obj_t *self,
                                           const mcu_pin_obj_t * scl,
                                           const mcu_pin_obj_t * sda,
                                           uint32_t freq) {
    self->us_delay = 500000 / freq;
    if (self->us_delay == 0) {
        self->us_delay = 1;
    }
    digitalinout_result_t result = common_hal_nativeio_digitalinout_construct(&self->scl, scl);
    if (result != DIGITALINOUT_OK) {
        return;
    }
    result = common_hal_nativeio_digitalinout_construct(&self->sda, sda);
    if (result != DIGITALINOUT_OK) {
        common_hal_nativeio_digitalinout_deinit(&self->scl);
        return;
    }
    common_hal_nativeio_digitalinout_switch_to_output(&self->scl, true, DRIVE_MODE_OPEN_DRAIN);
    common_hal_nativeio_digitalinout_switch_to_output(&self->sda, true, DRIVE_MODE_OPEN_DRAIN);

    stop(self);
}

void shared_module_bitbangio_i2c_deinit(bitbangio_i2c_obj_t *self) {
    common_hal_nativeio_digitalinout_deinit(&self->scl);
    common_hal_nativeio_digitalinout_deinit(&self->sda);
}

bool shared_module_bitbangio_i2c_probe(bitbangio_i2c_obj_t *self, uint8_t addr) {
    start(self);
    bool ok = write_byte(self, addr << 1);
    stop(self);
    return ok;
}

bool shared_module_bitbangio_i2c_write(bitbangio_i2c_obj_t *self, uint16_t addr,
                                       const uint8_t *data, size_t len, bool transmit_stop_bit) {
    // start the I2C transaction
    start(self);
    bool ok = write_byte(self, addr << 1);

    for (uint32_t i = 0; i < len; i++) {
        ok = ok && write_byte(self, data[i]);
        if (!ok) {
            break;
        }
    }

    if (transmit_stop_bit) {
        stop(self);
    }
    return ok;
}

bool shared_module_bitbangio_i2c_read(bitbangio_i2c_obj_t *self, uint16_t addr,
                                      uint8_t * data, size_t len) {
    // start the I2C transaction
    start(self);
    bool ok = write_byte(self, (addr << 1) | 1);

    for (uint32_t i = 0; i < len; i++) {
        ok = ok && read_byte(self, data + i, i < len - 1);
        if (!ok) {
            break;
        }
    }

    stop(self);
    return ok;
}