TWI Confusion-Receiving NACK on example code

RE: TWI Confusion-Receiving NACK on example code

RishS — Thu, 25 Feb 2021 01:46:46 GMT

Thank you for looking into this! That is a good point that I didn't think about. I never questioned my source but maybe the sensor I got was a knock off- will investigate this.

Thanks for your help Edvin. I will leave this as verified for now and may make a new thread if my attempts to solve this still don't work.

RE: TWI Confusion-Receiving NACK on example code

Edvin — Mon, 08 Feb 2021 09:40:04 GMT

Hello,

I found an MPU6050 laying around, and I tested the WHO_AM_I register, and it worked for me.

Can you try the unmodified example from Martin's repo and use SDK14.2.0:

Use the project nrf5-ble-mpu-simple\pca10056

I needed to change the memory settings, according to the log output. I don't remember what it was, but I changed the RAM start address to 0x20002A18 and the size to 0x3D5E8. Then you need to replace the preprocessor definition "MPU9150" to "MPU60x0" (keep the 'x'), and then add these lines to the top of app_mpu.c:

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

Then I modified the app_mpu_init() function:

uint32_t app_mpu_init(void)
{
    uint32_t err_code;
	
		uint8_t buffer;
	
	// Initate TWI or SPI driver dependent on what is defined from the project
	err_code = nrf_drv_mpu_init();
    if(err_code != NRF_SUCCESS) return err_code;

    uint8_t reset_value = 7; // Resets gyro, accelerometer and temperature sensor signal paths.
    err_code = nrf_drv_mpu_write_single_register(MPU_REG_SIGNAL_PATH_RESET, reset_value);
    if(err_code != NRF_SUCCESS) return err_code;

    // Chose  PLL with X axis gyroscope reference as clock source
    err_code = nrf_drv_mpu_write_single_register(MPU_REG_PWR_MGMT_1, 1);
    if(err_code != NRF_SUCCESS) return err_code;
	
		err_code = nrf_drv_mpu_read_registers(MPU_REG_WHO_AM_I, &buffer, 1);
		NRF_LOG_INFO("read err_code = %d", err_code);
		NRF_LOG_INFO("buffer: 0b%d%d%d%d%d%d", (1 && (buffer & 1<<1)),
                                               (1 && (buffer & 1<<2)),
                                               (1 && (buffer & 1<<3)),
                                               (1 && (buffer & 1<<4)),
                                               (1 && (buffer & 1<<5)),
                                               (1 && (buffer & 1<<6)));
        NRF_LOG_INFO("buffer hex value: %02x", buffer);

    return NRF_SUCCESS;
}

When I run this, the log prints the WHO_AM_I register value 0x68, which according to this document is the default value:

https://invensense.tdk.com/wp-content/uploads/2015/02/MPU-6000-Register-Map1.pdf

(page 45)

Best regards,

Edvin

I am not sure why it doesn't reply as it should. It could be a knock off copy of the sensor for all I know. You may try to contact the manufacturer and ask why it doesn't reply to that register.

RE: TWI Confusion-Receiving NACK on example code

RishS — Fri, 05 Feb 2021 17:17:22 GMT

It doesn't reply. It is the correct register-Martin had it in a header file and it matches the data sheet, so it's confusing why this is happening. It seems to only be an issue with this register (either that or I just haven't called his "read_registers" function properly- which doesnt make sense because I copied his example where he read data in another function).

RE: TWI Confusion-Receiving NACK on example code

Edvin — Fri, 05 Feb 2021 14:44:56 GMT

Hello,

I don't have the sensor, so I can't check, but are you saying that the example (from Martin) doesn't check the WHO_AM_I register, or that the sensor doesn't reply to the WHO_AM_I register?

If it is the last case, are you sure it is the correct register? Does it match the datasheet on the sensor?

Best regards,

Edvin

RE: TWI Confusion-Receiving NACK on example code

RishS — Thu, 04 Feb 2021 23:21:24 GMT

Hi Edvin! Thank you for your response. This was very helpful the example worked out of the box which was amazing. One problem I noticed however was that Martin's code doesn't verify the productID at the beginning to ensure it is communicating with the right device. I'm starting to suspect this was why I was receiving a Nack with my code because once I added that functionality in it performed exactly as my own code did. I was wondering if you had any thoughts on why this wouldn't work, the function I added can be seen here, the register is 0x75 which matches my datasheet:

uint32_t app_mpu_read_who_am_i(uint8_t * product_id)
{
return nrf_drv_mpu_read_registers(MPU_REG_WHO_AM_I, product_id, 1);
}

Everything else in my code matches the github you linked me- I'm running the nrf5-mpu-simple example. The accelerometer itself works its just this readProductID() function giving me trouble

RE: TWI Confusion-Receiving NACK on example code

Edvin — Wed, 27 Jan 2021 15:02:15 GMT

Hello,

I have not tried to follow the youtube tutorial that you linked to, but I know that a former colleague of mine created an example project for this sensor. Perhaps you can try it:

https://github.com/Martinsbl/nrf5-mpu-examples

Read the readme on that repository, and run it on SDK14.2.0 and check that it is working before you run it in SDK17.0.2.

BR,

Edvin