gpio.cpp

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h> // mmap
#include <fcntl.h> // open

static unsigned int *gpio_mmap = 0; 

int init_gpio() 
{ 
    int gpio_file = -1;
  
    gpio_file = open("/dev/gpiomem", O_RDWR | O_SYNC);
    if (gpio_file < 0) 
    {
        printf("gpio open failed\n");
        return 1;
    }
  
    gpio_mmap = mmap(
        NULL,					// Address offset, docs say to use null =)
        4*1024,				    // Map Length
        PROT_READ|PROT_WRITE,	// Enable Read and Write
        MAP_SHARED,				// The map can be used by other processes
        gpio_file, 			    // The file opened for the map
        0						// Offset - none required
    );

    // mmap done, don't need file anymore
    close(gpio_file);
  
    if (gpio_mmap == MAP_FAILED) 
    {
        printf("gpio mmap failed\n");
        gpio_mmap = 0;
        return 1;
    };
  
  return 0;
}

void gpio_deinit()
{
    if (gpio_mmap)
    {
        munmap(gpio_mmap, 4*1024);
    }
    gpio_mmap = 0;
}

void set_gpio_io(int pin, int output)
{
    if (!gpio_mmap) return;
    // input or output state is set as 3 bits per pin, stored as 10 pins per dword
    // 000 = input, 001 = output, (010 = special peripheral whatever)
    int block = pin / 10;
    int pinofs = (pin % 10) * 3;
    // mask out the 3 bits and set the one bit as requested
    *(gpio_mmap + block) = (*(gpio_mmap + block) & ~(7 << pinofs)) | (output << pinofs);
}

void set_gpio_val(int pin, int val)
{
    if (!gpio_mmap) return;
    int block = (val ? 7 : 10); // SET and CLEAR register offsets
    *(gpio_mmap + block) = 1 << pin;
}

int get_gpio_val(int pin)
{
    if (!gpio_mmap) return 0;
    int block = 13; // LEVEL register offset
    return !!(*(gpio_mmap + block) & (1 << pin));
}