/* 
    PCF8591_address_channel-in_Vout_Biff.c
    ------------------------------
    read the voltage on one A/D lines (0-3) and set the output voltage on the D/A pin
    ----------------------------------------------------------------------------
 
      1) send the i2c address
      2) choose channel 0-3
      3) send byte for D/A out
      4) read channel volts as 0 to 255
  usage :-  type with spaces but without the < >
<PCF8591_address_channel-in_Vout_Biff>  <address as decimal> <channel 0-3> <D/A value as decimal 0-255>
      (even if the D/A pin is unused type in any value 0-255)
*/

#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 channel;      /* line number 0-3 */
  int V_out;        /* value for the D/A out line */
  unsigned char buf[1];       /* use to feed the i2c driver */
  unsigned long address;      /* i2c bus address */
  int AD_input;      /* volts byte on chosen channel */

  int rc;

int main(int argc, char** argv)
{
 if (argc != 4)   /* report error if we are not getting just 3 inputs after the program name */
 {
  printf("Error. usage: %s i2c_chip_address  channel_to_read D/A_Vout(0-255)\n", argv[0]);           
 }

  address = atoi(argv[1]); /* decimal address is the first number after the program name */
  channel = atoi(argv[2]); /* choose A to D line to read 0-3 */
  V_out = atoi(argv[3]); /* volts out as decimal 0-255 */

 i2c = open("/dev/i2c-0",O_RDWR); /* open the device dev/i2c-0 */
 rc=ioctl(i2c,I2C_SLAVE,address); /* set the i2c chip address */

  channel = channel + 64;   /* enable the D/A output */
  buf[0] = channel;   /* A/D input line number is the first data byte sent */
  buf[1] = V_out;     /* D/A out value is the second data byte sent */
  write(i2c,buf,2);   /* we send 2 bytes <control register> <D/A value> */
  read(i2c,buf,1);    /* buf(0) contains the byte of data in the chip cache */
usleep (1000);		/* do it again */
  read(i2c,buf,1);    /* buf(0) now contains the byte of data from the most recent analogue input*/
  AD_input = buf[0];
  
 /* just output the number, ready for ash script to use */
printf("%d", AD_input);

 /*AD_input goes 0 to 255 as voltage input goes from 0 to supply voltage*/

  i2c = close(i2c);
  return(0);
}
/* Sunspot 090408 */