maemo.org - Talk - How to control N900's GPIO?

I think this is a very basic but important question.
I did a trial just now but failed. The code is below.
GPIO 0x48002110 is the CAM_B_EN signal of N900, which could change the camera to A or B. If success, when you open N900's camera application(that's camera A, the big one), it will be influenced due to 1/0 in turn each 1000ms.

Then I compile it in the scratchbox and upload it to N900. When running it, below feedback comes.

Code:

Nokia-N900:~# ./gpio 

Segmentation fault

Can anyone help to find the reason? Thanks!

Code:

#include <sys/types.h>

#include <stdio.h>

#include <sys/ioctl.h>

#include <sys/mman.h>

#include <fcntl.h>

#include <memory.h>



#define GPIO 0x48002110

#define INT *(volatile unsigned int*)



void *map_base;

int n,fd;



int main(int argc,char *argv[])

{

    if((fd=open("/dev/mem",O_RDWR | O_SYNC))==-1){

    perror("open error!\n");

    return(-1);

    }



    map_base = mmap(0,0xff,PROT_READ | PROT_WRITE,MAP_SHARED,fd,GPIO);

    while(1){

        INT(map_base) = 1; //set it high

        sleep(1000);

        INT(map_base) = 0; //set it low

        sleep(1000);

    }



    close(fd);   



    munmap(map_base,0xff);

}