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Sensors Component

27.04.2020 23:52 by chris

The sensors component controls the barometric sensors. It has the functions in it’s export interface:

• Init sensors at the start:
  void init_sensors()
• Start a measurement on the first sensor and write results to pointer parameters:@param temp: pointer to the memory region for the resulting temp
@param press: pointer to the memory region for the resulting pressure
@param humid: pointer to the memory region for the resulting humidity
void read_sensor(int32_t* temp, uint32_t* press, uint32_t* humid);
• Equivalent for the second sensor: read_sensor2(...)

The component uses the provided Bosch library. It implements all device specific commands and measurement correction, but needs an interface for communication being implemented on the platform it runs on. The functions of the interface are:

I²C Delay

void user_delay_ms(uint32_t period)
{
    /*
     * Return control or wait,
     * for a period amount of milliseconds
     */
}

Implementation:

void i2c_delay(uint32_t period) {
    vTaskDelay(period / portTICK_PERIOD_MS);
} 

I²C Read

int8_t user_i2c_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */
    /*
     * The parameter dev_id can be used as a variable to store the I2C address of the device
     * Data on the bus should be like
     * |------------+---------------------|
     * | I2C action | Data                |
     * |------------+---------------------|
     * | Start      | -                   |
     * | Write      | (reg_addr)          |
     * | Stop       | -                   |
     * | Start      | -                   |
     * | Read       | (reg_data[0])       |
     * | Read       | (....)              |
     * | Read       | (reg_data[len - 1]) |
     * | Stop       | -                   |
     * |------------+---------------------|
     */
    return rslt;
}

Implementation:

int8_t i2c_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *data, uint16_t len) {
	i2c_cmd_handle_t cmd = i2c_cmd_link_create();
	i2c_master_start(cmd);
	i2c_master_write_byte(cmd, dev_id << 1 | I2C_MASTER_WRITE, 1);
	i2c_master_write_byte(cmd, reg_addr, 1);
	i2c_master_start(cmd);
	i2c_master_write_byte(cmd, dev_id << 1 | I2C_MASTER_READ, 1);
	if (len > 1) {
		i2c_master_read(cmd, data, len - 1, I2C_MASTER_ACK);
	}
	i2c_master_read_byte(cmd, data + len - 1, I2C_MASTER_NACK);
	i2c_master_stop(cmd);
	i2c_master_cmd_begin(I2C_NUM_0, cmd, 500 / portTICK_RATE_MS);
	i2c_cmd_link_delete(cmd);
	return 0;
}

I²C Write

int8_t user_i2c_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */
    /*
     * The parameter dev_id can be used as a variable to store the I2C address of the device
     * Data on the bus should be like
     * |------------+---------------------|
     * | I2C action | Data                |
     * |------------+---------------------|
     * | Start      | -                   |
     * | Write      | (reg_addr)          |
     * | Write      | (reg_data[0])       |
     * | Write      | (....)              |
     * | Write      | (reg_data[len - 1]) |
     * | Stop       | -                   |
     * |------------+---------------------|
     */
    return rslt;
}

Implementation:

int8_t i2c_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *data, uint16_t len) {
	i2c_cmd_handle_t cmd = i2c_cmd_link_create();
	i2c_master_start(cmd);
	i2c_master_write_byte(cmd, (dev_id << 1) | I2C_MASTER_WRITE, 1);
	i2c_master_write_byte(cmd, reg_addr, 1);
	i2c_master_write(cmd, data, len, 1);
	i2c_master_stop(cmd);
	i2c_master_cmd_begin(I2C_NUM_0, cmd, 500 / portTICK_RATE_MS);
	i2c_cmd_link_delete(cmd);
	return 0;
}

After implementing these interface functions, you can use the library functionality to read from the sensors.

The I²C driver from the ESP-IDF needs to be initialized first:

void i2c_setup()
{
	printf("Setting up I2C driver on port 1... ");
	i2c_config_t config;
	config.mode = I2C_MODE_MASTER;
	config.sda_io_num = 33;
	config.sda_pullup_en = GPIO_PULLUP_ENABLE;
	config.scl_io_num = 32;
	config.scl_pullup_en = GPIO_PULLUP_ENABLE;
	config.master.clk_speed = 100000;
	i2c_param_config(I2C_NUM_0, &config);
	printf("Set driver parameters... ");
	esp_err_t err = i2c_driver_install(I2C_NUM_0, I2C_MODE_MASTER, 0, 0, 0);
	if (err == ESP_OK)
		printf("Driver installed!\n");
	else if (err == ESP_ERR_INVALID_ARG)
		printf("Driver install failed, invalid arguments!\n");
	else
		printf("Driver install failed!\n");
}

Above is just ESP-IDF functions, the Bosch libs are not used until know.

Then you need to fill a config struct for a sensor:

dev = malloc(sizeof(struct bme280_dev));
dev->dev_id = 0x76;
dev->intf = BME280_I2C_INTF;
dev->read = i2c_read;
dev->write = i2c_write;
dev->delay_ms = i2c_delay;
bme280_init(dev);

And finally there can a measurement be started:

void read_sensor(int32_t* temp, uint32_t* pressure, uint32_t* humidity) {
	uint8_t settings_sel;
	uint32_t req_delay;
	struct bme280_data comp_data;
	dev->settings.osr_h = BME280_OVERSAMPLING_16X;
	dev->settings.osr_p = BME280_OVERSAMPLING_16X;
	dev->settings.osr_t = BME280_OVERSAMPLING_16X;
	dev->settings.filter = BME280_FILTER_COEFF_16;

	settings_sel = BME280_OSR_PRESS_SEL | BME280_OSR_TEMP_SEL | BME280_OSR_HUM_SEL | BME280_FILTER_SEL;
	bme280_set_sensor_settings(settings_sel, dev);

	req_delay = 12*bme280_cal_meas_delay(&(dev->settings));

	bme280_set_sensor_mode(BME280_FORCED_MODE, dev);
	dev->delay_ms(req_delay / portTICK_PERIOD_MS);
	bme280_get_sensor_data(BME280_ALL, &comp_data, dev);
	*temp = comp_data.temperature;
	*pressure = comp_data.pressure;
	*humidity = comp_data.humidity;
}

Here a measurement with maximum oversampling is started in forced mode (the sensor immediatly takes the measurement and goes back to sleep afterwards). The compensation data is calibration data in the sensor and is used to correct the readings. After the measurement is taken, the results are stored in the memory regions of the corresponding pointers.

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