nRF52832 SPI function

Question

Hi, 
 I am trying to make a simple function for writing via SPI. I am using the SPI example and it works fine. Now I would just like to make two SPI functions that I can use in my project: 
 
 - initSPI() 
 - ReadWriteSPI() 
 
 I have made the following so far and the event handler and initSPI seems to work fine if I keep the original example code for the spi transfer. It is just the ReadWriteSPI function which doesn't work. I am sure it has something to do with my function arguments. I am not too familiar with using pointers. The code below compiles without errors, but the LED does not flash as it is the case with the original sample code. See my code below. 
 
 Any help is appreciated. 
 
 Regards, 
 Jan 
 
 Here is my code so far 
 
 void spi_event_handler(nrf_drv_spi_evt_t const * p_event) { spi_xfer_done = true; NRF_LOG_INFO("Transfer completed.
"); SEGGER_RTT_WriteString(0, "SPI transfer completed!
"); if (m_rx_buf[0] != 0) { NRF_LOG_INFO(" Received: 
"); SEGGER_RTT_WriteString(0, "SPI received!
"); NRF_LOG_HEXDUMP_INFO(m_rx_buf, strlen((const char *)m_rx_buf)); } } 
 static void initSPI(void) { nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG; spi_config.ss_pin = SPI_SS_PIN; // Slave Select pin spi_config.miso_pin = SPI_MISO_PIN; // Output spi_config.mosi_pin = SPI_MOSI_PIN; // Input spi_config.sck_pin = SPI_SCK_PIN; // Clock pin APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler)); } 
 
 void ReadWriteSPI(nrf_drv_spi_t spi, uint8_t m_tx_buf, uint8_t m_rx_buf, uint8_t m_length) { // Reset rx buffer and transfer done flag memset(m_rx_buf, 0, m_length); spi_xfer_done = false; APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, m_tx_buf, m_length, m_rx_buf, m_length)); 
 while (!spi_xfer_done) { __WFE(); // Wait For Event } NRF_LOG_FLUSH(); 
 bsp_board_led_invert(BSP_BOARD_LED_0); nrf_delay_ms(1000); }

int main(void) 
 { 
 initSPI(); 
 while (1) 
 { 
 ReadWriteSPI(spi, m_tx_buf, m_rx_buf, m_length); 
 } 
 
 }

hmolesworth · Answer

There is a bug in the code you list above, but due to the way the c compiler works you can fool the code into working. Look at the definition of nrf_drv_spi_transfer() , it requires pointers to the buffers 
 ret_code_t nrf_drv_spi_transfer(nrf_drv_spi_t const * const p_instance,
 uint8_t const * p_tx_buffer,
 uint8_t tx_buffer_length,
 uint8_t * p_rx_buffer,
 uint8_t rx_buffer_length)
 
 The buffers mTxBuf[] and mRxBuf[] are pointers as they are defined as arrays, and are used as pointers by nrf_drv_spi_transfer() : 
 uint8_t mTxBuf[] = {ADS_CMND_RREG, NUMBER_OF_ADS_REGISTERS-1, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
uint8_t mRxBuf[sizeof(mTxBuf)];

APP_ERROR_CHECK(nrf_drv_spi_transfer(&mAfeSpiInstance, mTxBuf, mRxTxBufLength, mRxBuf, mRxTxBufLength));
 
 Your function definition omits the pointer definition, and so expects uint8_t values, which in practice probably passes as 32-bit values which you have been able to force to pointers (also 32-bit values) 
 void ReadWriteSPI(nrf_drv_spi_t spi, uint8_t m_tx_buf, uint8_t m_rx_buf, uint8_t m_length)
 
 Change function definition to use pointers to correct this issue: 
 void ReadWriteSPI(nrf_drv_spi_t spi, uint8_t *m_tx_buf, uint8_t *m_rx_buf, uint8_t m_length)