//
//  How to access GPIO registers from C-code on the Raspberry-Pi
//  Example program
//  15-January-2012
//  Dom and Gert
//


// Access from ARM Running Linux

#define BCM2708_PERI_BASE        0x20000000
#define GPIO_BASE                (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */


#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <dirent.h>
#include <fcntl.h>
#include <assert.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <unistd.h>

#define PAGE_SIZE (4*1024)
#define BLOCK_SIZE (4*1024)

int  mem_fd;
char *gpio_mem, *gpio_map;
char *spi0_mem, *spi0_map;


// I/O access
volatile unsigned *gpio;


// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))

#define GPIO_SET *(gpio+7)  // sets   bits which are 1 ignores bits which are 0
#define GPIO_CLR *(gpio+10) // clears bits which are 1 ignores bits which are 0

void setup_io();

int main(int argc, char **argv)
{ 
    int g,rep;
    
    // Set up gpi pointer for direct register access
    setup_io();
    
    printf("Initializing\n") ;
    
    // Switch GPIO 7..11 to output mode
    
    /************************************************************************\
     * You are about to change the GPIO settings of your computer.          *
     * Mess this up and it will stop working!                               *
     * It might be a good idea to 'sync' before running this program        *
     * so at least you still have your code changes written to the SD-card! *
     \************************************************************************/
    
    // Set GPIO pins 7-11 to output
    for (g=7; g<=11; g++)
    {
        INP_GPIO(g); // must use INP_GPIO before we can use OUT_GPIO
        OUT_GPIO(g);
    }
    
    printf("Pin test\n") ;
    
    for (rep=0; rep<10; rep++)
    {
        printf("rep = %d\n",rep) ;
        
        for (g=7; g<=11; g++)
        {
            printf("   setting = %d\n",g) ;
            GPIO_SET = 1<<g;
            sleep(1);
        }
        for (g=7; g<=11; g++)
        {
            printf("   clearing = %d\n",g) ;
            GPIO_CLR = 1<<g;
            sleep(1);
        }
    }
    
    printf("Complete\n") ;
    
    return 0;
    
} // main


//
// Set up a memory regions to access GPIO
//
void setup_io()
{
    /* open /dev/mem */
    if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0) {
        printf("can't open /dev/mem \n");
        exit (-1);
    }
    
    /* mmap GPIO */
    
    // Allocate MAP block
    if ((gpio_mem = malloc(BLOCK_SIZE + (PAGE_SIZE-1))) == NULL) {
        printf("allocation error \n");
        exit (-1);
    }
    
    // Make sure pointer is on 4K boundary
    if ((unsigned long)gpio_mem % PAGE_SIZE)
        gpio_mem += PAGE_SIZE - ((unsigned long)gpio_mem % PAGE_SIZE);
    
    // Now map it
    gpio_map = (unsigned char *)mmap(
                                     (caddr_t)gpio_mem,
                                     BLOCK_SIZE,
                                     PROT_READ|PROT_WRITE,
                                     MAP_SHARED|MAP_FIXED,
                                     mem_fd,
                                     GPIO_BASE
                                     );
    
    if ((long)gpio_map < 0) {
        printf("mmap error %d\n", (int)gpio_map);
        exit (-1);
    }
    
    // Always use volatile pointer!
    gpio = (volatile unsigned *)gpio_map;
    
    
} // setup_io