[ARM] Enabling GPIO through registers in FriendlyARM mini2440 board

[hale2bopp]

I want to write to a physical address to change the voltage of a pin using an ARM board- but in order to write to a physical address, I need to take a virtual address, and map it to the physical address using mmap. So I did that, in this way:

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Code C - [expand]
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/mman.h>
 
#define MAP_SIZE 4096UL
#define MAP_MASK (MAP_SIZE - 1)
 
int main(void) {
int fd;
int *map_base_c,*map_base_d, *map_base_p, *virt_addr;
off_t target,control,data,pullup;
 
control=0x56000050;
 
if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
 
map_base_d = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd,data & ~MAP_MASK);
 
printf("Memory mapped at address %p.\n", map_base_d);
 
virt_addr = map_base_d; //+ (data & MAP_MASK)
*virt_addr = 0x00;  //This is where it goes off. find out why!!!
printf("Value at address 0x%X (%p): 0x%X\n", data, virt_addr,(*virt_addr));
 
close(fd);
return 0;
}

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But, The pin didn't get a high voltage as I'd expected. Is there something wrong with the way I'm changing the address? Also, is there a way to see the physical address which was mapped to the virtual address? Thanks!