// Rapsberry Pi: I2C in C - Versione 0.6 - Luglio 2013
// Copyright (c) 2013, Vincenzo Villa (https://www.vincenzov.net)
// Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.
// Creative Commons | Attribution-Share Alike 3.0 Unported
// https://www.vincenzov.net/tutorial/RaspberryPi/i2c_c.htm

// Compile:  gcc MCP23017.c -std=c99 -o MCP23017
// Run as user with R&W right on /dev/i2c-* (NOT ROOT!)
// vv@vvrpi ~ $ ./MCP23017 X
// 0 <= X <= 255 
// Using MCP23017 - I2C 

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

#define I2C_ADDR 0x20				// Device adress

#define MCP23017_IODIRA 0                       // IODIRA (see data sheet)
#define MCP23017_IODIRB 1			// IODIRB (see data sheet)
#define MCP23017_GPPUA 0x0C                     // GPPUA (see data sheet)
#define MCP23017_GPIOA 0x012                    // GPIOA (see data sheet)
#define MCP23017_GPIOB 0x013                    // GPIOB (see data sheet)

static const char *device = "/dev/i2c-1";	// I2C bus

static void exit_on_error (const char *s)	// Exit and print error code
{ 	perror(s);
  	abort();
} 

int main(int argc, char *argv[])
{
	int fd;
	
	uint8_t buffer[2];

        printf("Rapsberry Pi: I2C in C - Versione 0.6 - Luglio 2013\n");
        printf("Copyright (c) 2013, Vincenzo Villa (https://www.vincenzov.net)\n");
        printf("Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.\n");
        printf("Creative Commons | Attribution-Share Alike 3.0 Unported\n");
        printf("https://www.vincenzov.net/tutorial/elettronica-di-base/RaspberryPi/i2c-c.htm\n\n");                                       

        if (argc != 2) 
        { 
          printf ( "Usage: \n rpi ~ $ ./MCP23017 X\n X is an integer number from 0 to 255\n\n");
          exit(-1);        
         }

       	// Open I2C device
       	if ((fd = open(device, O_RDWR)) < 0) exit_on_error ("Can't open I2C device");

	// Set I2C slave address
	if (ioctl(fd, I2C_SLAVE,I2C_ADDR) < 0) exit_on_error ("Can't talk to slave");
        
        // Configure PortB as output      
        buffer[0] = MCP23017_IODIRB;
        buffer[1] = 0x00;       
        if (write(fd,buffer,2) != 2 ) exit_on_error ("Failed to write to the i2c bus [1]");
         
        // Put data to PortB      
        
        buffer[0] = MCP23017_GPIOB;
        buffer[1] = atoi(argv[1]);
        printf("Write 0x%X to PortB\n\n", buffer[1] );
        if (write(fd,buffer,2) != 2) exit_on_error ("Failed to write to the i2c bus [2]");

        // Configure PortA as input          
        buffer[0] = MCP23017_IODIRA;
        buffer[1] = 0xFF;
        if (write(fd,buffer,2) != 2 ) exit_on_error ("Failed to write to the i2c bus [3]");
                                
        // Enable pull-up on PortA                                  
        buffer[0] = MCP23017_GPPUA;
        buffer[1] = 0xFF;                                              
        if (write(fd,buffer,2) != 2) exit_on_error ("Failed to write to the i2c bus [4]");
        
        // Read from PortA                                                
        buffer[0] = MCP23017_GPIOA;
        if (write(fd,buffer,1) != 1) exit_on_error ("Failed to write to the i2c bus [5]");                                                            
        if (read(fd,buffer,1) != 1 ) exit_on_error ("Failed to read from the i2c bus");  
        printf("Data read from PortA: 0x%X\n\n", buffer[0]);      
        
        close(fd);

	return (0);
}