Reading Data from Sensor by TWIM

[simon1516]

Hi,

I would like to read data from sensor and send it over BLE to nRF connect. Unfortunaly, something went wrong while reading the data by TWIM.

I´m using SDK16.

I would like to read 12 Bytes from a Sensor and store this in a Puffer. After this, I send the Puffer ober BLE to nRF connect. So the procedure should be:

- determine Sensor

- determine start register

- read 12 Bytes, starting at start register

- send 12 Bytes ober Bluetooth Low Energy

I think someting goes wrong by collecting the data over TWIM. For doing this, I use the following functions to determine the correct Sensor:

void ICM20948_set_mode(void)
{


      
ret_code_t err_code;

    /* Sensor on */
    uint8_t reg3[2] = {0x06, 0x01};
    nrfx_twim_xfer_desc_t normal_mode_config = NRFX_TWIM_XFER_DESC_TX(ICM20948_ADDR, reg3, sizeof(reg3));
    err_code = nrfx_twim_xfer(&m_twim, &normal_mode_config, NULL);
    while (m_xfer_done == false);

    /* Register choose */
    uint8_t reg4[1] = {0x2D}; // Since this register there are 12 Bytes we would have to read
    m_xfer_done = false;
    nrfx_twim_xfer_desc_t temp_reg_write = NRFX_TWIM_XFER_DESC_TX(ICM20948_ADDR, reg4, sizeof(reg4));
    err_code = nrfx_twim_xfer(&m_twim, &normal_mode_config, NULL);    APP_ERROR_CHECK(err_code);
    while (m_xfer_done == false);


}

After determine the correct sensor and correct register, I would like to read 12 Bytes from the register and send it by bluetooth.:

static void read_sensor_data()
{


    m_xfer_done = false;
    nrfx_twim_xfer_desc_t lm75b_reading = NRFX_TWIM_XFER_DESC_RX(ICM20948_ADDR, &m_sample[0], sizeof(m_sample));
 

    /* Read 12 bytes from the specified address - skip 3 bits dedicated for fractional part of temperature. */
    ret_code_t err_code = nrfx_twim_xfer(&m_twim, &lm75b_reading, NULL);
    APP_ERROR_CHECK(err_code);


// Send data over Bluetooth 
                     
//nrf_delay_ms(100); 
uint32_t err_code2; 
uint16_t length = (uint16_t)12;

err_code2 = ble_nus_data_send(&m_nus, m_sample, &length, m_conn_handle);
if ((err_code2 != NRF_ERROR_INVALID_STATE) &&
(err_code2 != NRF_ERROR_RESOURCES) &&
(err_code2 != NRF_ERROR_NOT_FOUND))
{
APP_ERROR_CHECK(err_code2);
}

}

Unfortunaly, there are not the correct sensor values on nRF connect app. For analyzing, I attached the hole project for you too.

It would be great, if someone could have a look to my functions I use.

Thanks in advance.

Simon

ble_app_uart_with_twim v0.1.zip

[haakonsh]

Have you verified that you are able to read the sensor correctly, before sending it over BLE?

[simon1516]

I´m sorry for late reply.

No, I didn´t checked it. Could you please help me with that?

The values from sensor a stores in uint8_t puffer "m_sample". I would like to see the actual values of this array of bytes.

For this, I press "build and debug" (debug is the active buld configuration). After that, I make a right click to m_sample --> quick watch. Unfortunaly, there is not the actual value shown.

Do I have to activate something in for debugging? Is there somewhere explained, how to see actual values stored in variables in general?

Thanks in advance

Simon

[haakonsh]

 You need to halt the cpu in order for the watched states to update. Use a breakpoint or manually halt the CPU with the halt button/command

If the Watch window does not work, then you need to find the address in Memory where the buffer is stored and go to the Memory view. You still need to halt the cpu. 

[simon1516]

Okay, I´m now able for debugging. I can take a watch to my relevant variables.

Could you please help me with a TWIM read function? I have initialized the TWIM and Sensor successfully. In my read function, I just read one byte by TWIM. The value I would like to read is a known constance, stored in register "0". Sometimes, the watch shows the correct value in the watch window. So it seems that a part of my code is working. But not always. The value is changing all the time (I update the variable two times a second). Because in this register is just stored a constance, I have to read always the same value. Could you please have a look to a few lines code of my read function?

static void read_sensor_data()
{

static uint8_t m_sample;

        /* Sensor Register 0 write to Sensor */
        uint8_t reg5 = {0x00};
        nrfx_twim_xfer_desc_t test = NRFX_TWIM_XFER_DESC_TX(ICM20948_ADDR, &reg5, sizeof(reg5));


        /* Read 1 byte from the specified address. */
        m_xfer_done = false;
        nrfx_twim_xfer_desc_t lm75b_reading = NRFX_TWIM_XFER_DESC_RX(ICM20948_ADDR, &m_sample, sizeof(m_sample));

        ret_code_t err_code = nrfx_twim_xfer(&m_twim, &lm75b_reading, NULL);
        APP_ERROR_CHECK(err_code);

}

Like I said, sometimes the correct value of register "0" is stored in my buffer "m_sample".

Is there something I´m doing wrong? Is the way I try to read a value by TWIM correct (send register to I2C address - read from I2C adrdess)?

Thanks in advance

Simon

[haakonsh]

What does the sensor's datasheet say you need to do to read a register?

[simon1516]

I am working with ICM20948 sensor:

https://invensense.tdk.com/wp-content/uploads/2016/06/DS-000189-ICM-20948-v1.3.pdf

1. Sensor has to powered up

2. correct user bank/map has to be selected

3. correct register has to be selected.

How I am doing sep 3 I sent in my last post. Steps 1 and 2 I´m doing like the following:

void ICM20948_set_mode(void)
{

ret_code_t err_code;

    /* Sensor on , Step 1*/
    uint8_t reg3[2] = {0x06, 0x01};
    nrfx_twim_xfer_desc_t normal_mode_config = NRFX_TWIM_XFER_DESC_TX(ICM20948_ADDR, reg3, sizeof(reg3));
    err_code = nrfx_twim_xfer(&m_twim, &normal_mode_config, NULL);
    while (m_xfer_done == false);

        /* USER BANK selection, Step 2 */
    uint8_t reg4[2] = {0x7F, 0x00};
    nrfx_twim_xfer_desc_t reg_usr_bank      = NRFX_TWIM_XFER_DESC_TX(ICM20948_ADDR, reg4, sizeof(reg4));
    err_code = nrfx_twim_xfer(&m_twim, &reg_usr_bank, NULL);  
    while (m_xfer_done == false);
}

Thanks in advance for your help.

Simon

[haakonsh]

I suggest you scope you serial communication with a logic analyzer and compare that with the read/write descriptions in chapter 6.3 of the invensense datasheet. 

[simon1516]

Hi haakonsh,

could you please help me a bit more, in special with my code? I already used TWI sensor example of SDK and get it working. So there are no hardware or wrong voltage level faults. The change toTWIM is not working, so I think there are errors in my code. Unfortunaly, there are no examples for TWIM in SDK 16 or is there anywhere some stuff, showing the TWIM communication?

Regards

Simon