RPi SPI

rpi_spi.c

    // Mode options: SPI_LOOP, SPI_CPHA, SPI_CPOL, SPI_LSB_FIRST, 
    //               SPI_CS_HIGH, SPI_3WIRE, SPI_NO_CS, SPI_READY
    static uint8_t mode = SPI_CPHA;
    static uint8_t bits = 8;
    static uint32_t speed = 3000000;
    static uint16_t delay = 0;
    
    SPI_RESULT_T SPI_DoTransfer(char * device, uint8_t * p_rx_buf, uint8_t * p_tx_buf, uint32_t len)
    {
      int fd;
      int ret;

      // Open the device
      fd = open(device, O_RDWR);
      if (fd < 0) return SPI_ERR_OPENING_DEVICE;

      // Set SPI mode
      ret = ioctl(fd, SPI_IOC_WR_MODE, &mode);
      if (ret == -1) return SPI_ERR_CFGING_PERIPH;

      ret = ioctl(fd, SPI_IOC_RD_MODE, &mode);
      if (ret == -1) return SPI_ERR_CFGING_PERIPH;

      // Set the Bits per Word
      ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
      if (ret == -1) return SPI_ERR_CFGING_PERIPH;

      ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
      if (ret == -1) return SPI_ERR_CFGING_PERIPH;

      // Set the max speed
      ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
      if (ret == -1) return SPI_ERR_CFGING_PERIPH;

      ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
      if (ret == -1) return SPI_ERR_CFGING_PERIPH;

      struct spi_ioc_transfer tr = 
      {
        .tx_buf = (unsigned long)p_tx_buf,
        .rx_buf = (unsigned long)p_rx_buf,
        .len = len,
        .delay_usecs = delay,
        .speed_hz = speed,
        .bits_per_word = bits,
      };

      ret = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
      close(fd);
      
      if (ret < 1) 
        return SPI_XFER_ERROR;
      else
        return SPI_SUCCESS;
    }