Want to send value on a particular register using SPI

[Meera Shah]

void spi_read_write(0x1E,0x00) ==> output 0x10 as return value of register read.

Here I want to send value 0x90 as register value in the argument of spi_read_write(0x1E, 0x90) function, after  sending this it is retaining  0x10 as a rx_data buffer. Here is my code

static spi_rx_data[2] = {0x00,0x00};

void init(void)
{
    spi_read_write(ACCEL_WHO_M_I,0x00);  //this is working perfectly
    spi_read_write(ACCEL_REG_CTRL0,0x00); //return value spi_rx_data = 0xff,0x10
    
    spi_read_write(ACCEL_REG_CTRL0,0x90); //return value spi_rx_data = 0xff,0x10 also returning 0x10 previous value instead of 0x90
}

void spi_read_write(uint8_t register_pointer, uint8_t register_value)
{
    ret_code_t err_code;
    uint8_t data[2] ={0};
    uint8_t rx_buf;
   
    memset(spi_rx_data,0x00,sizeof(spi_rx_data));
    
    register_pointer |= 0x80;
    
    data[0] = register_pointer;
    data[1] = register_value;
    
    
    err_code = nrf_drv_spi_transfer(&spi, data,sizeof(data), spi_rx_data,sizeof(spi_rx_data));
    NRF_LOG_HEXDUMP_INFO(spi_rx_data,sizeof(spi_rx_data));
    APP_ERROR_CHECK(err_code);  
   
} 

[Jørgen Holmefjord]

Hi,

If you have initialized the SPI driver in non-blocking mode (by providing an event handler to nrf_drv_spi_init), you will have to wait for one transfer to complete before starting a new one (by calling spi_read_write_reg()/spi_read_write()). Please reference the SPI master example in the SDK on how to do this.

Best regards,
Jørgen

[Jørgen Holmefjord]

Delays does not guarantee that the transfer is completed. You should wait for the done event in the event handler.

[Meera Shah]

But I am using blocking mode(so no interrupt). spi_rx_data should come up with the updated register value. Please help me with this.

[Jørgen Holmefjord]

Sorry, I missed that part of your comment. What device you are interfacing? Note that the RX buffer will be filled while transferring the TX bytes to the device. If you expect to receive data after TX is completed, you will have to set the RX buffer length to size of TX + RX buffer and discard the first bytes.

[Meera Shah]

I am working with LIS2DH12 connected with nrf51822 taiyo udan board. I did whatever you say but still I am getting output spi_read_write(ACCEL_REG_CTRL0,0x00) (before) : FF 10

after  spi_read_write(ACCEL_REG_CTRL0,0x90) : FF 10

[Jørgen Holmefjord]

Are you sure that the write operation will echo back the value written to the register? What happens if you read/write it once again? Can you post your entire code you used for writing/reading the registers?

[Meera Shah]

Yes .......I found the solution of my problem. I was masking MSB bit of a register for both read and write operation, but it is needed for read operation only. 

void spi_read(uint8_t register_pointer)
{
    ret_code_t err_code;
    uint8_t tx_data;
   
    memset(spi_rx_data,0x00,sizeof(spi_rx_data));
    register_pointer |= 0x80;   //this is needed for reading operation
    tx_data = register_pointer;
   
    err_code = nrf_drv_spi_transfer(&spi, &tx_data,1, spi_rx_data,sizeof(spi_rx_data));
    NRF_LOG_HEXDUMP_INFO(spi_rx_data,sizeof(spi_rx_data));
    APP_ERROR_CHECK(err_code);  
   
}

void spi_write(uint8_t register_pointer, uint8_t register_value)
{
    ret_code_t err_code;
    memset(spi_rx_data,0x00,sizeof(spi_rx_data));
    
    data[0] = register_pointer;    //no need of masking higher bit of register
    data[1] = register_value;
    
    err_code = nrf_drv_spi_transfer(&spi, data,sizeof(data), spi_rx_data,sizeof(spi_rx_data));
    NRF_LOG_HEXDUMP_INFO(spi_rx_data,sizeof(spi_rx_data));
    APP_ERROR_CHECK(err_code);  
}