Segger shows error passing pointer to multiple byte array for i2c driver send/receive multiple bytes

[mneber]

Hi,

I have been having trouble getting any read/writes going with my Infineon TLV493D magnetic sensor over i2c. I suspect it may be a cast or syntax thing that I can't get to the bottom of. 

As I understand it, when calling nrf_drv_twi_rx the size of the buffer array is the number of bytes the master tries to read from the slave. However, I always get a warning from the compiler: expected 'uint8_t * {aka unsigned char *}' but argument is of type 'uint8_t (*)[7] {aka unsigned char (*)[7]}' when I try to pass an array of size 7 to read 7 bytes. I then use that information to write 4 bytes to send to the sensor, and same warning arises for nrf_drv_twi_tx. Is that the right function to use for reading/writing multiple bytes? I understand nrfx_ is the new driver version and will replace all when I get this solved... just trying to get off the ground at this point. 

Some things I have noticed trying to diagnose this are that if I try to declare a byte to send as a const I will get error 16 (invalid address). The only thing that works is casting as static, but not static const. Even though the function itself in nrf_drv_twi.h appears to ask for a const* this doesn't seem to work when I try to pass that. 

I attached a code snippet because the whole file is long. Also I built this from the twi example file in SDK 15.2

/* TWI instance ID. */
#define TWI_INSTANCE_ID             0
#define MAG_SDA_PIN                 NRF_GPIO_PIN_MAP(0,26)
#define MAG_SCL_PIN                 NRF_GPIO_PIN_MAP(0,27)

/* Indicates if operation on TWI has ended. */
static volatile bool m_xfer_done = false;

/* TWI instance. */
static const nrf_drv_twi_t m_twi = NRF_DRV_TWI_INSTANCE(TWI_INSTANCE_ID);

/* Buffer for samples read from temperature sensor. *///
static    uint8_t    m_sample[7];                     // sensor data buffer to create application
static    uint8_t    sensorbitmap[10];                // initial register read and store
static    uint8_t    MAG_SENSOR_ADDRESS = 0x3f;
static    uint8_t    sendrecovery = 0xFF;             // startup send recovery bits
static    uint8_t    sendreset = 0x00;                // startup send reset bits

....later on we call the following...

    err_code = nrf_drv_twi_rx(&m_twi, MAG_SENSOR_ADDRESS, &sensorbitmap, sizeof(sensorbitmap));                  //  Read and store sensorbitmap for later use
    APP_ERROR_CHECK(err_code);                                                                                                                     //
    NRF_LOG_INFO(err_code); 

.... and use it to send this...

void mag_sensor_set_mode(void)
{
    ret_code_t err_code;

const uint8_t write_registers[4] =                                                                    
    { 0x00,
      0x00 | MAG_SENSOR_IICADDR | INT_DISABLE | FAST_MODE_DISABLE | LOW_POWER_MODE_ENABLE,
      sensorbitmap[8],
      TEMPERATURE_ENABLE | LOW_POWER_PERIOD_12MS | PARITY_TEST_DISABLE | (sensorbitmap[9] & 0x0F)
    };

    SEGGER_RTT_printf(0, "write_registers: %d\n", write_registers);

    err_code = nrf_drv_twi_tx(&m_twi, MAG_SENSOR_ADDRESS, write_registers, sizeof(write_registers), true);
    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO(err_code);
   
    while (m_xfer_done == false);
}

Any help is greatly appreciated!

[awneil]

err_code = nrf_drv_twi_rx(&m_twi, MAG_SENSOR_ADDRESS, &sensorbitmap, sizeof(sensorbitmap));      

I think you mean either

err_code = nrf_drv_twi_rx(&m_twi, MAG_SENSOR_ADDRESS, &sensorbitmap[0], sizeof(sensorbitmap));      

OR:

err_code = nrf_drv_twi_rx(&m_twi, MAG_SENSOR_ADDRESS, sensorbitmap, sizeof(sensorbitmap));      

http://c-faq.com/aryptr/aryptrequiv.html

[mneber]

Removing the pointer value reference as you suggested gets rid of the error but I can't understand how this would work properly since the function asks for a pointer to the array:

ret_code_t nrf_drv_twi_rx(nrf_drv_twi_t const * p_instance,
                          uint8_t               address,
                          uint8_t *             p_data,
                          uint8_t               length);

Also can anybody explain why trying to declare (with static const):

static const uint8_t sendrecovery = 0xFF; // startup send recovery bits
static const uint8_t sendreset = 0x00; // startup send reset bits

 err_code = nrf_drv_twi_tx(&m_twi, MAG_SENSOR_ADDRESS, write_registers, sizeof(write_registers), true);
 APP_ERROR_CHECK(err_code);
 NRF_LOG_INFO(err_code);

returns the error

ERROR 16 [NRF_ERROR_INVALID_ADDR]

I have tried address as 0x3F and 0x3F >> 1 but that doesn't seem to make a difference. Also which one is correct? I cannot find anywhere if the drivers automatically handle appending read/write into the address or not.

Thanks!

[awneil]

mneber said:

the function asks for a pointer to the array

No - the function asks for a pointer to the data.

In 'C', an array name is a pointer to the start of the array - see the FAQ entry cited earlier.

[Jørgen Holmefjord]

NRF_ERROR_INVALID_ADDR does not refer to the TWI address, but indicate that EasyDMA is used and that the buffer is not located in RAM. You have declared write_registers as const, which cause it to be placed in flash. Remove const and try again.

[mneber]

OK I'll take it!

Thank you!

[mneber]

If I remove const from write_registers I get a compiler error "initializer element is not constant"

It seems that the function nrf_drv_twi_rx takes in a const as the third parameter. 

Also, I was not getting any error with write_registers declared as const, only with the single byte commands sendrecovery and sendreset but those seem to have no issue when I remove const. 

Would this be easier if I try to replace legacy nrf_drv_ with nrfx_?

[awneil]

mneber said:

If I remove const from write_registers I get a compiler error "initializer element is not constant"

Where, exactly, do you get that error?

mneber said:

It seems that the function nrf_drv_twi_rx takes in a const as the third parameter. 

that 'const' simply indicates that the function does not modify the parameter; ie, it is read only.

[mneber]

[Jørgen Holmefjord]

static uint8_t write_registers[4];
write_registers[0] = 0x00;
write_registers[1] = (0x00 | MAG_SENSOR_IICADDR | INT_DISABLE | FAST_MODE_DISABLE | LOW_POWER_MODE_ENABLE);
write_registers[2] = sensorbitmap[8];
write_registers[3] = (TEMPERATURE_ENABLE | LOW_POWER_PERIOD_12MS | PARITY_TEST_DISABLE | (sensorbitmap[9] & 0x0F));

[awneil]

Yes; they are obviously not constants - they are variables!

[mneber]

Thank you Jorgen. 

I want to tell you that from reading your answers to other people and my own questions has made it possible for us to successfully implement SAADC,PWM, and now TWI/I2C on the our own pcb hardware that we built from scratch and the 52DK. 

I am a mechanical engineer not a software engineer and so I really appreciate your patience with my questions!