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

#define GPIO_BASE 0x3F200000 
#define GPFSEL1 0x04 
#define GPSET0 0x1C 
#define GPCLR0 0x28 

int main() { 
	int fd = open( "/dev/mem", O_RDWR|O_SYNC ); 
	if ( fd < 0 ){ 
		printf( "can't open /dev/mem \n" ); 
		exit(-1); 
	} 

	char *gpio_memory_map
	  = (char *)mmap(0, 4096, PROT_READ|PROT_WRITE, 
				 MAP_SHARED, fd, GPIO_BASE ); 

	if ( gpio_memory_map == MAP_FAILED ) { 
		printf( " Error : mmap \n" ); 
		exit(-1); 
	}

	volatile unsigned int* gpio 
		= (volatile unsigned int*)gpio_memory_map; 

	gpio[GPFSEL1/4] = (1<<18); 

	int i; 
	for ( i=0; i<5; i++ ) {
		gpio[GPCLR0/4] = (1<<16); 
		sleep(1); 

		gpio[GPSET0/4] = (1<<16); 
		sleep(1); 
	} 
	
	munmap( gpio_memory_map, 4096); 
	return 0; 
}