ESP32 Forum

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        portBASE_TYPE evt_res = xQueueReceive(p_i2c->cmd_evt_queue, &evt, wait_time);
        if (evt_res == pdTRUE) {
            if (evt.type == I2C_CMD_EVT_DONE) {
                if (p_i2c->status == I2C_STATUS_TIMEOUT) {
                    // If the I2C slave are powered off or the SDA/SCL are connected to ground, for example,
                    // I2C hw FSM would get stuck in wrong state, we have to reset the I2C module in this case.
                    ESP_LOGE(I2C_TAG,"Timeout after xQueueReceive");  // AD: this is the timeout i get
                    i2c_hw_fsm_reset(i2c_num);
                    clear_bus_cnt = 0;
                    ret = ESP_ERR_TIMEOUT;

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static esp_err_t i2c_master_clear_bus(i2c_port_t i2c_num)
{
    I2C_CHECK(i2c_num < I2C_NUM_MAX, I2C_NUM_ERROR_STR, ESP_ERR_INVALID_ARG);
    int sda_in_sig = 0, scl_in_sig = 0;
    if (i2c_num == I2C_NUM_0) {
        sda_in_sig = I2CEXT0_SDA_IN_IDX;
        scl_in_sig = I2CEXT0_SCL_IN_IDX;
    } else if (i2c_num == I2C_NUM_1) {
        sda_in_sig = I2CEXT1_SDA_IN_IDX;
        scl_in_sig = I2CEXT1_SCL_IN_IDX;
    }
    int scl_io = GPIO.func_in_sel_cfg[scl_in_sig].func_sel;
    int sda_io = GPIO.func_in_sel_cfg[sda_in_sig].func_sel;
    I2C_CHECK((GPIO_IS_VALID_OUTPUT_GPIO(scl_io)), I2C_SCL_IO_ERR_STR, ESP_ERR_INVALID_ARG);
    I2C_CHECK((GPIO_IS_VALID_GPIO(sda_io)), I2C_SDA_IO_ERR_STR, ESP_ERR_INVALID_ARG);
    // We do not check whether the SDA line is low
    // because after some serious interference, the bus may keep high all the time and the i2c bus is out of service.
    gpio_set_direction(scl_io, GPIO_MODE_OUTPUT_OD);
    gpio_set_direction(sda_io, GPIO_MODE_OUTPUT_OD);
    gpio_set_level(scl_io, 0);
    gpio_set_level(sda_io, 1);
    gpio_set_level(scl_io, 1); //clock transition
    gpio_set_level(sda_io, 0); //start condition
    for (int i = 0; i < 9; i++) { //9 clocks
        gpio_set_level(scl_io, 0);
        gpio_set_level(scl_io, 1);
        gpio_set_level(scl_io, 1); //allow for rise time
    }
    gpio_set_level(scl_io, 0);
    gpio_set_level(sda_io, 1);
    gpio_set_level(scl_io, 1); //clock transition
    gpio_set_level(sda_io, 0); //another start condition
    gpio_set_level(scl_io, 0);
    gpio_set_level(scl_io, 1); //clock transition
    gpio_set_level(sda_io, 1); //stop condition
    
    i2c_set_pin(i2c_num, sda_io, scl_io, 1, 1, I2C_MODE_MASTER);
    return ESP_OK;
}