/*

PCF8591_addr_line_V-slug.c
--------------------------
read the voltage on one A/D line (0-3) and set the output voltage on the D/A pin
--------------------------------------------------------------------------------

1) send the i2c address
2) send A/D line number (program adds 64 to enable D/A in control register)
3) send byte for D/A out
3) read the chosen A/D
usage :- type with spaces but without the < >
<PCF8591_address_readvolts> <address as decimal> <A/D line 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 AD_line; /* 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 byte_in_0; /* the 8 bit byte that represents the voltage on the AD_line */
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 */
    fprintf(stderr, "Error. usage: %s i2c_chip_address A/D_line_(0-3) D/A_Vout(0-255)\n",argv[0]);
    exit(1);
}

address = atoi(argv[1]); /* address is the first number after the program name */
AD_line = atoi(argv[2]); /* A/D input line 0-3 */
AD_line = AD_line + 64; /* enable the D/A output pin */

V_out = atoi(argv[3]); /* A/D input line 0-3 */

i2c = open("/dev/i2c-0",O_RDWR); /* open the device dev/i2c-0 */

rc=ioctl(i2c,I2C_SLAVE,address); /* set the i2c chip address */

buf[0] = AD_line; /* 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 */
/* do it again */
usleep (1000);
read(i2c,buf,1); /* buf(0) now contains the byte of data from the most recent analogue input*/

printf("%d \n", buf[0]);
/* buf[0] goes 0 to 255 as voltage input goes from 0 to supply voltage*/

i2c = close(i2c);
return(0);
}
/* Sunspot 070128 */