/* 
    PIC_i2c_one_ADnumber_only_a.c
    Read value of A to D input
    ------------------------------
 
      1) send the i2c address
      2) send x value - this determines which byte-pairs are sent from the PIC
      3) send 6 bytes for buf[0-6]

  usage :-  type with spaces but without the < >
<PIC_i2c_one_value.c>  <i2c address as decimal(80)> <x> <display command> <5 bytes>
use x = 0, 2, 4
to read A to D lines 0,1,2 number comes as just 0-1023
./PIC_i2c_one_ADnumber_only_a 80 2 0 0 0 0 0    read line 1 (use 0,2,4)
*/

#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#define I2C_SLAVE	0x0703	/* Change slave address	*/


  int i2c; 
  int BufferAddress;       /* which buffer[] to hold start of data */
  int DataForBuffer[8];       /* values for the PIC buffer[BufferAddress] */
  int PicData[8];             /* byte sent by PIC*/
  unsigned char tx_buf[8];    /* bytes to send */
  unsigned char rx_buf[8];    /* received bytes */
  unsigned long address;   /* i2c bus address */

  int rc;

int main(int argc, char** argv)
{
 if (argc != 8)   /* report error if we are not getting just 7 inputs after the program name */
 {
  printf("Error. usage: %s i2c_chip_address  BufferAddress  (6 data numbers)\n", argv[0]);           
 }

  address = atoi(argv[1]); /* i2c decimal address is the first number after the program name */
  tx_buf[0] = atoi(argv[2]);
  tx_buf[1] = atoi(argv[3]);
  tx_buf[2] = atoi(argv[4]);
  tx_buf[3] = atoi(argv[5]); 
  tx_buf[4] = atoi(argv[6]); 
  tx_buf[5] = atoi(argv[7]); 
  
  //-----------------------------------------------------------------get lo byte 
 i2c = open("/dev/i2c-0",O_RDWR); /* open the device dev/i2c-0 */
 rc=ioctl(i2c,I2C_SLAVE,address); /* set the i2c chip address */
 
  write(i2c,tx_buf,6);   /* we send 7 bytes <Address> <buf[0-5]> */

  read(i2c,rx_buf,1);    /* rx_buf(0) now contains 2 data byte from PIC */
  PicData[1] = rx_buf[0];
//  printf("lo byte %d \n", PicData[1]);

  //-----------------------------------------------------------------get hi byte 
  tx_buf[0] = tx_buf[0] + 1;     /* increment x to get hi byte*/
  write(i2c,tx_buf,6);   /* we send data again with x incremented */
  
  read(i2c,rx_buf,1);    /* rx_buf(0) now contains 1 data byte from PIC */
  PicData[2] = rx_buf[0];
// printf("hi byte %d \n", PicData[2]);
  i2c = close(i2c);
  
 printf("%d \n", PicData[1] + 256*PicData[2]);
    
}
// NB x on the display show value sent + 1