nrf52840 MPU9250 Magnetometer Reading

[YooLoo]

Hello, I am using nrf52840 PDK, sdk 13.0.0. I managed to read accel, gyro data from the MPU9250 using MPU library based on this example. However, I got magnetometer reading 0. I've checked this question and this question. Here is the code how I setup the MPU:

void mpu_setup(void)
{
	printf("\r\nMPU setup start... \r\n");

    ret_code_t ret_code;
    // Initiate MPU driver
    ret_code = mpu_init();

	printf("\r\nMPU init complete! \r\n");	

    APP_ERROR_CHECK(ret_code); // Check for errors in return value

    // Setup and configure the MPU with intial values
    mpu_config_t p_mpu_config = MPU_DEFAULT_CONFIG(); // Load default values
    p_mpu_config.smplrt_div = 19;   // Change sampelrate. Sample Rate = Gyroscope Output Rate / (1 + SMPLRT_DIV). 19 gives a sample rate of 50Hz
    p_mpu_config.accel_config.afs_sel = AFS_16G; // Set accelerometer full scale range
    p_mpu_config.gyro_config.fs_sel = GFS_1000DPS; //Set gyroscope full scale range 
    ret_code = mpu_config(&p_mpu_config); // Configure the MPU with above values
    APP_ERROR_CHECK(ret_code); // Check for errors in return value 
}

void magn_setup()
{
	ret_code_t ret_code;
	
	
	//Enable bypass mode
	mpu_int_pin_cfg_t bypass_config;
	bypass_config.i2c_bypass_en = 1;
	ret_code = mpu_int_cfg_pin(&bypass_config); // Set bypass mode
	APP_ERROR_CHECK(ret_code); // Check for errors in return value
	

	// Setup and configure the MPU Magnetometer
	mpu_magn_config_t p_mpu_magn_config;
	p_mpu_magn_config.resolution = OUTPUT_RESOLUTION_16bit; // Set output resolution
	p_mpu_magn_config.mode = CONTINUOUS_MEASUREMENT_100Hz_MODE;	//Set measurement mode
	
	ret_code = mpu_magnetometer_init(&p_mpu_magn_config);
	APP_ERROR_CHECK(ret_code); // Check for errors in return value

}

The full project can be found here. Need some help. Many thanks.

======================================================================

Update 22 Jan 2018:

Code added to magn_setup:

    ret_code = nrf_drv_mpu_write_magnetometer_register(0x0A, 6);	//writing to the control register
	APP_ERROR_CHECK(ret_code);	
	
	uint8_t TempReading;
	ret_code = nrf_drv_mpu_read_magnetometer_registers(0x00, &TempReading, 8);
	APP_ERROR_CHECK(ret_code);
	printf("Device ID: %d \n", TempReading);

	ret_code = nrf_drv_mpu_read_magnetometer_registers(0x0A, &TempReading, 8);
	APP_ERROR_CHECK(ret_code);
	printf("Vaule read from control register: %d \n", TempReading);

Result observed by Termite:

Test1: MPU twi communication 

MPU setup start... 

MPU init complete! 

MPU setup complete! 
Device ID: 72 
Vaule read from control register: 6 
Accel Data: X: 000732 ; Y: -00111 ; Z: -02000 ; 
Gyro Data: X: -00010 ; Y: 000030 ; Z: 000021 ; 
Magn Data: X: 000000 ; Y: 000000 ; Z: 000000 ; 

[MartinBL]

Hi,

It seems like I forgot to add functions for actually starting the magnetometer. Please refer to the MPU 9250 register map and look at Chapter 5.8, CNTL1: Control 1. Write e.g. 6 to this register to start continuous measurement.

A quick and dirty way to do it is to include nrf_drv_mpu.h in main.c and call nrf_drv_mpu_write_magnetometer_register(0x0A, 6) when you initialize your MPU.

Note to MPU 9150 users: There is no continuous mode on the MPU 9150 so a single measurement has to be started before every read. Note that it seems like it takes ~5ms from the measurement is started until valid data is ready to be read.

[MartinBL]

If you write '1' to the control register (CNTL1 at 0x0A) you start a single magnetometer measurement. It could be that you start the measurement, but read the data before the measurement is completed. When I put in a 5ms delay between starting a single mode measurement and reading the data it worked fine (with an MPU 9150 though). If you write '6' to the register instead you will start continuous measurements.