BeagleBone Green Wireless SPI only reads least Significant Nibble and spreads in a byte.

[sque...@gmail.com]

I have the SPI working for full duplex, but for a half-duplex device. 

The issue is the receive array does not return the correct values. 

The O-Scope shows the device is returning the correct values but they are recorded as the least significant nibble...doubled.

If 0x01 is returned I have 0x03 stored in the array. If 0x0A is returned I have 0xCC stored in the array. It's as if the "read" only works for the final 4 bits and at double the speed. Any data in the high nibble is lost.

Has anyone experienced this before or know of something I can do to have the correct values stored?

This is the code I used. 

int fd, i=0;                   //file handle and loop counter

unsigned char value, null=0x00;         //sending only a single char

uint8_t bits = 8, mode = 0;             //8-bits per word, SPI mode 3

uint32_t speed = 4000000;               //Speed is 4 MHz  (Not Really due to clock, but it works)

unsigned char send_buffer[3];

unsigned char receive_buffer[3];

int transfer(int fd, unsigned char send[], unsigned char receive[], int length){

   struct spi_ioc_transfer transfer[3];           //the transfer structure

   memset(&transfer, 0, sizeof(transfer));

   

   transfer[0].cs_change = 0;

   transfer[0].tx_buf = (unsigned long) send;     //the buffer for sending data

   transfer[0].rx_buf = (unsigned long) receive;  //the buffer for receiving data

   transfer[0].len = length;                      //the length of buffer

   transfer[0].speed_hz = speed;                //the speed in Hz

   transfer[0].bits_per_word = bits;                 //bits per word

   transfer[0].delay_usecs = 0;                   //delay in us

   transfer[0].pad = 0;                   //delay in us

   transfer[0].rx_nbits = 8;                   //delay in us

   // send the SPI message (all of the above fields, inc. buffers)

   int status = ioctl(fd, SPI_IOC_MESSAGE(1), &transfer);

   if (status < 0) {

      printf("SPI: SPI_IOC_MESSAGE Failed:\t%i", status);

      return -1;

   }

}

int main(){

   // The following calls set up the SPI bus properties

   if ((fd = open(SPI_PATH, O_RDWR))<0){

      perror("SPI Error: Can't open device.");

      return -1;

   }

   if (ioctl(fd, SPI_IOC_WR_MODE, &mode)==-1){

      perror("SPI: Can't set SPI mode.");

      return -1;

   }

   if (ioctl(fd, SPI_IOC_RD_MODE, &mode)==-1){

      perror("SPI: Can't get SPI mode.");

      return -1;

   }

   if (ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits)==-1){

      perror("SPI: Can't set bits per word.");

      return -1;

   }

   if (ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits)==-1){

      perror("SPI: Can't get bits per word.");

      return -1;

   }

   if (ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed)==-1){

      perror("SPI: Can't set max speed HZ");

      return -1;

   }

   if (ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed)==-1){

      perror("SPI: Can't get max speed HZ.");

      return -1;

   }

   // Check that the properties have been set

   printf("SPI Mode is: %d\n", mode);

   printf("SPI Bits is: %d\n", bits);

   printf("SPI Speed is: %d\n", speed);

   printf("Attempting to right IDLE to CC1101:\n");

   transfer(fd, send_buffer, receive_buffer, 2);

}