Issues reading virtual registers via I2C

RE: Issues reading virtual registers via I2C

ovrebekk — Tue, 25 Jun 2019 06:54:10 GMT

Hi Bennett

You welcome!

I'm glad you were able to solve the issue 🙂

Best regards
Torbjørn

RE: Issues reading virtual registers via I2C

bsas — Fri, 21 Jun 2019 18:44:04 GMT

Hi Torbjørn,

So I'm not sure exactly why, but this issue seems to have solved itself when I tried it again yesterday morning. I don't know what change fixed it, I'm thinking it may have just been resetting the DK/rebuilding the project, though I did try that initially as well.

Thank you for all your help,

Bennett

RE: Issues reading virtual registers via I2C

ovrebekk — Fri, 21 Jun 2019 08:54:24 GMT

Hi Bennett

I am having a hard time understanding why this happens by looking at the code alone.

Are you able to provide another scope plot, similar to the one you provided before?

Ideally one showing the entire communication sequence (assuming the code doesn't have to check the status register over and over).

Best regards
Torbjørn

RE: Issues reading virtual registers via I2C

bsas — Wed, 19 Jun 2019 23:53:07 GMT

Hi Torbjørn,

Thank you again for your help. I have resolved this issue by adding some extra read/writes. It looks like the main fix was changing the p_data argument in nrf_drv_twi_tx from just the virtual register address to an array holding both the HW write register and the virtual address.

However, I'm running into a new issue now. When I read all the values from these registers, the registers seem to be "offset" by 1. For example, the value I should get for R0 is instead returned for R1, the value I should get for R1 is returned for R2, etc. My code is below, do you know why this may be happening?

void read_sensor(uint16_t values[], const uint8_t registers[]) {
  uint8_t reg = 0;
  uint8_t read_addy = I2C_AS72XX_SLAVE_READ_REG;
  uint8_t stat_addy = I2C_AS72XX_SLAVE_STATUS_REG;
  uint8_t reg_addr[2] = {I2C_AS72XX_SLAVE_WRITE_REG, registers[0]}; //first virtual register to read
  uint8_t end_reg = registers[1];
  uint8_t buf;
  ret_code_t status;
  int counter = 0;
  FILE *fp;
  fp = fopen("./test.txt", "w");

  while (reg_addr[1] <= end_reg) {
    buf = 0;

    //Check status
    while (true) {
      nrf_drv_twi_tx(&m_twi, AS72XX_ADDR, &stat_addy, sizeof(stat_addy), true);
      status = nrf_drv_twi_rx(&m_twi, AS72XX_ADDR, &buf, sizeof(buf));
      if ((buf & I2C_AS72XX_SLAVE_TX_VALID) == 0)
        break;
    }
    buf = 0;

    //Write virtual address
    while(true) {
      status = nrf_drv_twi_tx(&m_twi, AS72XX_ADDR, reg_addr, sizeof(reg_addr), true);
      if (status == NRF_SUCCESS)
        break;
    }

    //Check status
    while(true) {
      nrf_drv_twi_tx(&m_twi, AS72XX_ADDR, &stat_addy, sizeof(stat_addy), true);
      status = nrf_drv_twi_rx(&m_twi, AS72XX_ADDR, &buf, sizeof(buf));
      if ((buf & I2C_AS72XX_SLAVE_RX_VALID) != 0)
        break;
    }
    buf = 0;

    //Read virtual register
    while(true) {
      status = nrf_drv_twi_tx(&m_twi, AS72XX_ADDR, &read_addy, 1, true);
      if (status == NRF_SUCCESS)
        break;
    }

    while(true) {
      status = nrf_drv_twi_rx(&m_twi, AS72XX_ADDR, &buf, sizeof(buf));
      if (status == NRF_SUCCESS)
        break;
    }

    printf("Value at register %#x: %#x\r\n", reg_addr[1], buf);
    fprintf(fp, "Value at register %#x: %#x\r\n", reg_addr[1], buf);
    reg_addr[1]++;
  }
  fclose(fp);
}

...

int main() {
...
    uint16_t values[6];
    const uint8_t regs[2] = {0x00, 0x13};
    read_sensor(values, regs);
...
}

Thank you again for your help,

Bennett Sasaki

RE: Issues reading virtual registers via I2C

ovrebekk — Thu, 13 Jun 2019 12:12:03 GMT

Hi Bennett

Thanks for sharing the data sheet.

Reading through the sample code for reading and writing the virtual registers this seems considerably more complicated than similar sensors I have worked with, and I am not sure the code you sent me is equivalent to the code they provided.

For one thing their virtual register read example starts with a read loop, to wait for the read buffer to be ready, while your code starts with a write.

Secondly, it is important to note that the nrf_drv_twi_rx function returns any error code returned by the TWI driver, it doesn't return the data read. The data read is stored in the buffer that you pass into the function.

In other words you have to implement the while(1) loops in the virtual register write/read procedures a bit different from what they do in the data sheet in order to properly check the status data returned from the sensor.

Best regards
Torbjørn

RE: Issues reading virtual registers via I2C

bsas — Wed, 12 Jun 2019 16:53:49 GMT

Hi Torbjørn,

Thank you for your detailed respone. The data sheet is available here.

Thanks,

Bennett

RE: Issues reading virtual registers via I2C

awneil — Wed, 12 Jun 2019 13:43:56 GMT

[quote userid="2116" url="~/f/nordic-q-a/48300/issues-reading-virtual-registers-via-i2c/192410"] I also think it's normal for the sensor to send a NACK after the last byte of information has been sent[/quote]

Yes - it is.

RE: Issues reading virtual registers via I2C

ovrebekk — Wed, 12 Jun 2019 13:35:30 GMT

Hi Bennett

Thanks for the traces.

To me they look pretty normal. I tried running some comparable code on a nRF52DK which reads an LM75BD temperature sensor and an MMA7660 accelerometer over I2C, and the results are comparable.

Granted it's running on a nRF52 device and not a nRF51, but the driver is the same, and I also see the 'missing' gap in the RX calls which is not there when sending data.

I also think it's normal for the sensor to send a NACK after the last byte of information has been sent, to signal that no more data is coming. I see similar behavior from the LM75BD and MMA7660 devices.

Do you have a data sheet for the sensor that I could have a look at?

Best regards
Torbjørn

RE: Issues reading virtual registers via I2C

bsas — Tue, 11 Jun 2019 23:48:11 GMT

I'm using SDK 12.03.

I'm now noticing a few oddities when I use the scope. After doing a write (with nrf_drv_twi_tx), it mostly looks fine but SCL does not return to high at the end of the call. When I call the subsequent read, it looks like there's a NACK, but nrf_drv_twi_rx returns NRF_SUCCESS. I'll attach the scope captures below:

Write:

Read:

I'm kind of new to this stuff so I'm not sure where the issue may lie, I'm thinking it's in the sensor, I've tried contacting the manufacturer. I also noticed that on the read, there isn't the "break" in the clock line between the end of the address and the start of the data like there is in the write screenshot, not sure if that's an issue or not.

Thank you for your help,

Bennett

RE: Issues reading virtual registers via I2C

ovrebekk — Tue, 11 Jun 2019 06:45:41 GMT

Hi Bennett

Could there be some init/configuration sequence that you have to run before accessing these registers?

Are there any registers in the sensor that hold a fixed value, that you could use to debug the communication?
Many sensors have some kind of device ID register that will never change.

Have you tried to scope the lines to see what happens on the bus?

Assuming the nrf_drv_twi_tx/rx calls are blocking I can't see any issues with the code. Can you let me know which SDK version you are using?

Best regards
Torbjørn