WHO_AM_I with MPU9250

[techteam1]

Hi,

I was trying nrf5-mpu-simple example with MPU9250 - SDK 14.2.0, it is giving me x, y & z axis values.

When I try WHO_AM_I with it, I am unable to do so. I have added the following code in nrf_drv_mpu_twi.c file.

static void read_whoAmIdata()
{
	#define MPU_REG_WHO_AM_I           0x75
	static volatile bool m_xfer_done = false;
		ret_code_t err_code;
		uint8_t addr8 = MPU_REG_WHO_AM_I;
	
		printf("WHO_AM_I Tx\r\n");

    m_xfer_done = false;
		err_code = nrf_drv_twi_tx(&m_twi_instance, MPU_ADDRESS, &addr8, 1, false);
		while (m_xfer_done == false);	

		printf("WHO_AM_I Tx\r\n");
	
		m_xfer_done = false;
		err_code = nrf_drv_twi_rx(&m_twi_instance, MPU_ADDRESS, &addr8, 1);
		APP_ERROR_CHECK(err_code);

		printf("read_data() done\r\n");
}

Please let me know where I am committing mistake.

[MartinBL]

Hi,

1. What do you mean "I am unable to do so."? What happens?
2. Is it so that you are able to read the x, y, and z value registers, but not the WHO_AM_I register?

[techteam1]

Could you please show me how to display WHO_AM_I  with that example?

[MartinBL]

If you are using the drivers and libraries provided in the github repository you can simply use:

nrf_drv_mpu_read_registers(MPU_REG_WHO_AM_I, who_am_i, 1);

Then use printf, or whatever method you have to print data to a terminal, and print the returned value. 

I noticed that in your code, you have this line:

static volatile bool m_xfer_done = false;

Is this variable ever set to true in an event handler? Otherwise your code would never get past the first while(m_xfer_done == false);.

[techteam1]

I have cleared that function and did a fresh start.

Could you please tell me where to add

nrf_drv_mpu_read_registers(MPU_REG_WHO_AM_I, who_am_i, 1);

Thanks

[MartinBL]

Wherever you need it? 

Remember to include nrf_drv_mpu.h in the file where you intend to use it. 

[techteam1]

Thank you

I got WHO AM I running, was making simple mistake.

Below is the simple function which reads WHO_AM_I.

void mpu_read_whoAmI()
	{
		SEGGER_RTT_printf(0, "WHO AM I\n");
		uint32_t err_code;
		uint8_t who_am_i;
		err_code=nrf_drv_mpu_read_registers(MPU_REG_WHO_AM_I, &who_am_i, 1);
		SEGGER_RTT_printf(0, "err_code: %d\t", err_code);
		
		SEGGER_RTT_printf(0, "WHO_AM_I value: 0x%02x\n", who_am_i);
	}

[MartinBL]

Great! I'm glad you got it up and running