BMP280 Barometric Pressure and Temperature Sensor C Device Driver (Platform Independent)

• version 5.0
• Reza Ebrahimi

BMP280 is an absolute barometric pressure sensor especially designed by Bosch Sensortec for mobile applications. It consists of a Piezo-resistive pressure sensing element and a mixed-signal ASIC. The ASIC performs A/D conversions and provides the conversion results and sensor specific compensation data through a digital interface. This library is written in portable C, and is platform independent. .

BMP280 C library abstracts away the internals of the hardware, using high level functions (description below). BMP280 is capable of interfacing with SPI and I2C.

This library is based on the 'BMP280 Digital Pressure Sensor Datsheet' V. 1.23.

General Information

BMP280 consists of two sensors on one module: temperature and barometric pressure. The barometric pressure value needs to be calibrated and compensated using temperature data, so a reading of temperature must be done prior to a pressure reading.

The BMP280 has three modes of operation (Normal, Forced and Sleep), an optional IIR filter, optional standby period in normal mode (continuous reading) and optional oversampling.

It can also be used to calculate altitude based on barometric pressure.

Mutual Exclusion

In order to avoid race conditions, shared resources must be protected using mutual exclusion. I2C or SPI bus are shared resources and accessing them must be protected. Mutual exclusion is made possible with lock and unlock hooks (optional).

HOW TO USE

Set the config file first:

#define BMP280_INCLUDE_ALTITUDE	1
#define BMP280_INCLUDE_ADDITIONAL_GETTERS 1
#define BMP280_INCLUDE_EXCLUSION_HOOK 1

Mutex lock and unlock hooks and mutex handle must be provided by application writer if BMP280_INCLUDE_EXCLUSION_HOOK is defined. If BMP280_INCLUDE_ALTITUDE is not defined, the altitude functions are not included. Same goes for BMP280_INCLUDE_ADDITIONAL_GETTERS. Define a handle:

#include "bmp280.h"

bmp280_handle_t BMP280;

Please pay attention to the scope and life cycle of the handle. The next step is to implement all the interface dependencies; As an example:

BMP280.dependency_interface.bmp280_interface_init = implementation_of_interface_init;
BMP280.dependency_interface.bmp280_interface_deinit = implementation_of_interface_deinit;
BMP280.dependency_interface.bmp280_write_array = implementation_of_write_array;
BMP280.dependency_interface.bmp280_read_array = implementation_of_read_array;
BMP280.dependency_interface.bmp280_delay_function = implementation_of_delay_function;
/*the power function is only used when altitude function is included*/
BMP280.dependency_interface.bmp280_power_function = implementation_of_power_function;

Here you are free to implement the interface and set it up to be used with I2C, SPI or even a software mock. These 'int implementation_of_...(...)' functions should be provided by the application writer. All functions of the interface must return 0 in case of no error. the 'address' parameter in the interface is used solely in case of I2C and is not used in other cases. Once set up correctly, the initializer can be called. As an example for I2C interface:

bmp280_error_code_t error = bmp280_init(&BMP280, BMP280_I2C, BMP280_I2C_ADDRESS_1);

  if(error != BMP280_ERROR_OK)
  {
    printf("FAIL");

    error_handler();
  }

  printf("SUCCESS");

All functions return their error status and its application writer's responsibility to check the return values. Errors are of custom type 'bmp280_error_code_t' and include:

typedef enum {
	BMP280_ERROR_OK = 0,			/*no error*/
	BMP280_ERROR_INTERFACE_INIT,		/*error in interface initialization*/
	BMP280_ERROR_INTERFACE_DEINIT,		/*error in interface deinitialization*/
	BMP280_ERROR_INTERFACE_READ,		/*error in interface read function*/
	BMP280_ERROR_INTERFACE_WRITE,		/*error in interface write function*/
	BMP280_ERROR_INTERFACE_DELAY,		/*error in interface delay function*/
	BMP280_ERROR_INTERFACE_MATH_POW,	/*error in interface math power function*/
	BMP280_ERROR_EXCLUSION_LOCK,		/*error in exclusion lock function*/
	BMP280_ERROR_EXCLUSION_UNLOCK,		/*error in exclusion unlock function*/
	BMP280_ERROR_NULL_INTERFACE,		/*error in dependency function pointers*/
	BMP280_ERROR_SENSOR_ID,			/*error in sensor ID*/
	BMP280_ERROR_NULL_HANDLE,		/*error in null handle pointer*/
	BMP280_ERROR_SENSOR_POLL_TIMEOUT,	/*error in polling timeout. please select a higher timeout*/
	BMP280_ERROR_NULL_MUTEX_HANDLE,		/*handle to mutex does not exist*/
	BMP280_ERROR_MODE_UNKNOWN,		/*unknown mode error*/
	BMP280_ERROR_FILTER_COEFF_UNKNOWN	/*error unknwon filter coeff*/
} bmp280_error_code_t;

In which ERROR_OK means no errors. Now you can set the mode of operation, oversampling rate for temperature or pressure etc. In order to read all he data at once:

bmp280_sensors_data_t sensorsData;

error = bmp280_get_all(&BMP280, &sensorsData);

if(error != BMP280_ERROR_OK)
{
  printf("FAIL");

  error_handler();
}

Optionally, you can calculate the altitude using one of 2 functions provided:

float altitudeHypsometric;

error = bmp280_calculate_altitude_hypsometric(&BMP280, &altitudeHypsometric, sensorsData.pressure, sensorsData.temperature);

History

Version 2.0

There are many design changes to the version 1.0, including:

• Device driver handle design pattern for unlimited instances of sensors
• Dependency injection pattern for interface
• Stateless and reentrant
• Possible to be used with baremetal, RTOS or under Linux
• Error handling baked into the driver

Version 3.0

• Doxygen style comments
• config file for configurations
• Altitude calculations and several 'get' functions are now optional

Version 4.0

• Mutual exclusion is baked in using callback functions
• Changes to some naming conventions

Version 5.0

• Linux example is provided
• More elaborate error reports
• Changes to some naming conventions
• Bug fixes