/* Sample SPI Example Program to read the Device ID of the ADXL345 on the
*  SPI bus. Written by Derek Molloy (derekmolloy.ie) for the book Exploring
*  Beaglebone.
*
*  To read to the ADXL345 the leading bit of the address must be
*  high. The Device ID of the ADXL345 is 0xE5, which is 229 in decimal, so
*  this should be the value returned. This code is based on the code at:
*  https://www.kernel.org/doc/Documentation/spi/
*
* Written by Derek Molloy for the book "Exploring BeagleBone: Tools and
* Techniques for Building with Embedded Linux" by John Wiley & Sons, 2014
* ISBN 9781118935125. Please see the file README.md in the repository root
* directory for copyright and GNU GPLv3 license information.            */

#include<stdio.h>
#include<fcntl.h>
#include<string.h>
#include<stdint.h>
#include<unistd.h>
#include<sys/ioctl.h>
#include<linux/spi/spidev.h>

// You need to correctly identify the SPI device bus and number
static const char *device = "/dev/spidev1.0";

int main(){
   unsigned char send[2], receive[2];
   send[0]= (0x80|0x00);  //want to read address 0x00 on the ADXL345
   uint8_t mode=3, bits=8;
   uint32_t speed=500000;
   int file;
   struct spi_ioc_transfer transfer = {
      .tx_buf = (unsigned long) send,
      .rx_buf = (unsigned long) receive,
      .len = 2,
   };
   if ((file = open(device, O_RDWR))<0){
      perror("SPI: Can't open device.");
      return -1;
   }
   if (ioctl(file, SPI_IOC_WR_MODE, &mode)==-1){
      perror("SPI: Can't set SPI mode.");
      return -1;
   }
   if (ioctl(file, SPI_IOC_RD_MODE, &mode)==-1){
      perror("SPI: Can't get SPI mode.");
      return -1;
   }
   if (ioctl(file, SPI_IOC_WR_BITS_PER_WORD, &bits)==-1){
      perror("SPI: Can't set bits per word.");
      return -1;
   }
   if (ioctl(file, SPI_IOC_RD_BITS_PER_WORD, &bits)==-1){
      perror("SPI: Can't get bits per word.");
      return -1;
   }
   if (ioctl(file, SPI_IOC_WR_MAX_SPEED_HZ, &speed)==-1){
      perror("SPI: Can't set max speed HZ");
      return -1;
   }
   if (ioctl(file, SPI_IOC_RD_MAX_SPEED_HZ, &speed)==-1){
      perror("SPI: Can't get max speed HZ.");
      return -1;
   }
   printf("spi mode: 0x%x\n", mode);
   printf("bits per word: %d\n", bits);
   printf("max speed: %d Hz (%d KHz)\n", speed, speed/1000);

   if (ioctl(file, SPI_IOC_MESSAGE(1), &transfer)<0){
      perror("Failed to send SPI message");
      return -1;
   }
   printf("Return value: %d\n",receive[1]);
   close(file);
   return 0;
}