Can't write/read 16 bit register addresses on npm1300 through i2c

[kruenheck]

I'm trying to demonstrate that I can write a value to a Nordic npm1300 register and read the same value back. Using the code below, I write 0x5a but read 0x0a, so the msb 5 is getting lost:

    uint8_t pmic_config[] = {0x06, 0x01, 0x5a};                                 //register followed by value

    ret = i2c_write_dt(&dev_i2c_pmic, pmic_config, 2);                              

    if (ret != 0)

    {

        printk("Failed to write pmic register %x \n", pmic_config[0]);

        return -1;

    }

    //read something from the pmic

    int myVal = 0;                                                                      //this will be returned

    uint8_t regsy[] = {0x06, 0x01};            

    ret = i2c_write_read_dt(&dev_i2c_pmic, regsy, 2, &myVal, 1);

    if (ret != 0)

    {

        printk("Failed to read pmic register %x%x \n", regsy[0], regsy[1]);

        return -1;

    }

    else

    {

        printk("pmic Register 0x%x%x is 0x%x \n", regsy[0], regsy[1], myVal);

    }

Result:

pmic Register 0x61 is 0xa 

All the solutions I saw posted here used nrf_drv_twi_tx and nrf_drv_twi_rx which seem more complex than i2c_write_read_dt(), so it would be nice if there's a simple solution involving the code I shared above.

[kruenheck]

Note: I'm sure the i2c comm is working somewhat because when I change the write value, the read value also changes. For instance, changing 0x5a to 0x52 give 0x02 as a response. 

[Kenneth]

    uint8_t pmic_config[] = {0x06, 0x01, 0x5a};                                 //register followed by value

    ret = i2c_write_dt(&dev_i2c_pmic, pmic_config, 2);        

Shouldn't it be 3 bytes in total? Not 2.

Also, what register you are writing to, and are both values 8bit? I can see many registers are less than 8bit.

Kenneth

[SergeiOv]

If you look at the description of the register you are attempting to write (address 0x0601 corresponds to https://docs.nordicsemi.com/bundle/ps_npm1300/page/chapters/core_components/gpio/doc/frontpage.html#ariaid-title6), you can see that it uses only the lower 4 bits, so the msb 5 in your case is simply ignored. And yes, the number of bytes to write in the `i2c_write_dt` should be equal to the array size.

To get an idea of how to communicate with the PMIC through I2C it is worth taking a look at how the mfd_npm13xx driver implements this: github.com/.../mfd_npm13xx.c

[kruenheck]

Yes, it should have been three bytes. But as you pointed out, the underlying problem was that the register I was writing to was only four bits.

[kruenheck]

Thank you, the problem was that I was writing/reading a four bit register.