#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>

int main(int argc, char **argv)
{
	int fd_i2c;
	unsigned char buf[2];

	if((fd_i2c = open("/dev/i2c-1", O_RDWR)) < 0){
		printf("failed to open i2c port\n");
		return 1;
	}

	if(ioctl(fd_i2c, I2C_SLAVE, 0x20) < 0){
		printf("unable to get bus access to talk to slave\n");
		return 1;
	}

	//set GPIOA as output
	buf[0] = 0;
	buf[1] = 0;
	if(write(fd_i2c, buf, 2) != 2){
		printf("error writing to i2c slave\n");
		return 1;
	}

	//set GPIOB as output
	buf[0] = 1;
	buf[1] = 0;
	if(write(fd_i2c, buf, 2) != 2){
		printf("error writing to i2c slave\n");
		return 1;
	}

	//output 0xaa from GPIOA
	buf[0] = 0x12;
	buf[1] = 0xaa;
	if(write(fd_i2c, buf, 2) != 2){
		printf("error writing to i2c slave\n");
		return 1;
	}

	//output 0xf0 from GPIOB
	buf[0] = 0x13;
	buf[1] = 0xf0;
	if(write(fd_i2c, buf, 2) != 2){
		printf("error writing to i2c slave\n");
		return 1;
	}

	close(fd_i2c);
}