Read and Write TWI Sensor Registers

[CMan1]

Hi there,

I'm developing with the nRF52840 right now.

I'm trying to read some sensordata with TWI. The sensors are BMM150, BMI270 and BMP388.

Unfortunately, I already have problems with the my first sensor (BMM150), reading the Chip ID.

To read it, I have to set the Power Control Bit of the sensor. That seems to be working.

But when I want to read registers again, I only get zeros. Even for reading the Power Control Bit.


This is the function to write Registers:

bool writeRegister(uint8_t regNumber, uint8_t value){
  ret_code_t err_code;

  uint8_t valueBuffer[2];
  valueBuffer[0] = regNumber;
  valueBuffer[1] = value;
  err_code = nrf_drv_twi_tx(&m_twi, 0x10, valueBuffer, sizeof(valueBuffer), false);
  APP_ERROR_CHECK(err_code);
  return 1;
}

Read Registers:

uint8_t readRegister(uint8_t regNumber){
  ret_code_t err_code;

  uint8_t resultsWhoAmI;
  uint8_t whoAmIPointer = regNumber;
  err_code = nrf_drv_twi_tx(&m_twi, 0x10, &whoAmIPointer, 1, true);
  err_code = nrf_drv_twi_rx(&m_twi, 0x10, &resultsWhoAmI, 1);
  APP_ERROR_CHECK(err_code);

  return resultsWhoAmI;
}



Main to test reading the Chip ID. Later on I want to use the Bosch Sensortec API. But first I want this one to work:
int main(void)
{
    ret_code_t err_code;
    uint8_t address = 0x10;
    uint8_t read_data;
    uint8_t write_data;

 
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

    NRF_LOG_INFO("Read Chip ID started");

    NRF_LOG_FLUSH();
    twi_init();

    // Read Power Control Bit
    read_data = readRegister(0x4B);
    uint8_t pwr_bit = read_data & 0b1;
    NRF_LOG_INFO("Read Power Control = %x", pwr_bit);
    NRF_LOG_FLUSH();

    write_data = read_data | 1;
    writeRegister(0x4B, write_data);
    NRF_LOG_INFO("Set Power Control Register to %x", write_data & 0b1);
    NRF_LOG_FLUSH();

    read_data = readRegister(0x4B);
    pwr_bit = read_data & 0b1;
    NRF_LOG_INFO("Read Power Control = %x", pwr_bit);
    NRF_LOG_FLUSH();


    read_data = readRegister(0x4C);
    uint8_t opMode = (read_data | 0b110) >> 1;
    NRF_LOG_INFO("Read MODE = %x", opMode);
    NRF_LOG_FLUSH();

    write_data = read_data | 0b00000110;
    writeRegister(0x4b, write_data);
    NRF_LOG_INFO("Set Mode Register to: %x", (write_data & 0b110)>>1);
    NRF_LOG_FLUSH();

    read_data = readRegister(0x4C);
    opMode = (read_data | 0b110) >> 1;
    NRF_LOG_INFO("Read MODE = %x", opMode);
    NRF_LOG_FLUSH();

    nrf_delay_ms(5000);

    read_data = readRegister(0x4B);
    pwr_bit = read_data & 0b1;
    NRF_LOG_INFO("Read Power Control = %x", pwr_bit);
    NRF_LOG_FLUSH();

    read_data = readRegister(0x40);
    NRF_LOG_INFO("Chip ID = %x", read_data);
    NRF_LOG_FLUSH();

}



This is the Output: 

I've already read a couple of posts where others also had trouble reading on the bus after something was written. However, I couldn't find a solution.

Maybe somethings wrong with my code. I hope you could help me.


Thank you.

[Jørgen Holmefjord]

Hi,

How does your twi_init function look? If you have provided an event handler, you need some synchronization mechanism before starting the next transfer. You are also not checking the return code from the first nrf_drv_twi_tx call in readRegister(), it may report an error code.

I do not have the sensor available, so I'm not able to try to reproduce your issue.

Have you checked the TWI bus with a logic analyzer, to see if the commands are sent/received correctly? Please post logic traces.

Best regards,
Jørgen