#include <stdio.h>
#include "/usr/include/linux/i2c-dev.h"
#include <stdlib.h>
#include <fcntl.h>

int main(void)
{
	int file;
	file = open("/dev/i2c-1", O_RDWR);
	if(file > -1){
		checkKeys(file);
	}
	else{
		printf("File can't be opened.");
	}

	return 0;
}

void checkKeys(file){
	int res;
	res = ioctl(file, I2C_SLAVE, 0x20);
	if(res>-1){
		unsigned char data = i2c_smbus_read_byte(file);
		unsigned char mask = 1;
		unsigned char dataResult[8];
		int prevCol = 0, prevRow = 0;

		while(1){
			int column = 0, row = 0;
			int i = 0, j = 4;

			i2c_smbus_write_byte(file, 0x0f); //columns
			data = i2c_smbus_read_byte(file);
			for(i;i<4;i++){
				dataResult[i] = (data & (mask << i)) != 0;
				if(dataResult[i] == 0){
					column = i+1;
				}
			}

			i2c_smbus_write_byte(file, 0xf0); //rows
			data = i2c_smbus_read_byte(file);
			for(j;j<8;j++){
				dataResult[j] = (data & (mask << j)) != 0;
				if(dataResult[j] == 0){
					row = j-3;
				}
			}
			if(column != prevCol && row != prevRow){
				if(column != 0 && row != 0){
					getCode(column, row);
				}
				prevCol = column;
				prevRow = row;
			}
		}

	}
	else{
		printf("Error with res.");
	}
}

void getCode(col, row){
	char *key;
	switch (row) {
		case 1 :
			switch(col) {
				case 1:
					key = "1";
					break;
				case 2:
					key = "2";
					break;
				case 3:
					key = "3";
					break;
				case 4:
					key = "F";
					break;
			}
			break;
		case 2 :
			switch(col) {
				case 1:
					key = "4";
					break;
				case 2:
					key = "5";
					break;
				case 3:
					key = "6";
					break;
				case 4:
					key = "E";
					break;
			}
			break;
		case 3 :
			switch(col) {
				case 1:
					key = "7";
					break;
				case 2:
					key = "8";
					break;
				case 3:
					key = "9";
					break;
				case 4:
					key = "D";
					break;
			}
			break;
		case 4 :
			switch(col) {
				case 1:
					key = "A";
					break;
				case 2:
					key = "0";
					break;
				case 3:
					key = "B";
					break;
				case 4:
					key = "C";
					break;
			}
			break;
	}
	printf("%s \n",key);
}