Hammer LED Userspace App

This is an example program that uses the /dev/mem device node to access the physical memory registers directly(source)

Usage

to compile the source use your toolchain command line

#arm-linux-uclibc-gcc -o ledblink ledblink.c

then transfer the ledblink binary to the hammer file system. make sure that the permissions on the file are set to executable.

#chmod 755 ledblink
#./ledblink

the default setting in the source is to blink the LED for 30 seconds

Source

/*
 * ledblink.c: Simple program to blink a led on GPIO F0
 *
 *	Copyright (c) 2008 TinCanTools
 *	David Anders <danders@amltd.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#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 FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \
  __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0)
 
#define MAP_SIZE 4096UL
#define MAP_MASK (MAP_SIZE - 1)

#define GPIOF_CON	0x56000050
#define GPIOF_DAT	0x56000054
#define SECONDS		30

int main(int argc, char **argv) {
    int fd;
    void *map_base, *virt_addr; 
	unsigned long read_result, writeval;
    int count;

    /* open the memory device file descriptor */
    if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) FATAL;
    
    /* Map one page */
    map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, GPIOF_CON & ~MAP_MASK);
    if(map_base == (void *) -1) FATAL;
    
    /* set the virtual memory address to the GPIO F control register */
    virt_addr = map_base + (GPIOF_CON & MAP_MASK);

    /* read the current value for GPIO F control register */
    read_result = *((unsigned long *) virt_addr);

    writeval = read_result;
    writeval &= ~0x03;		/* mask off the first two bits */
    writeval |= 0x01;		/* set gpio f0 to output with value of 0x01 */ 

    /* write the modified value to GPIO F0 control register to set GPIO F0 to output */
    *((unsigned long *) virt_addr) = writeval;


    /* change virtual memory address to GPIO F data register */
    virt_addr = map_base + (GPIOF_DAT & MAP_MASK);

    for ( count=0; count < SECONDS ; count++) { 

	/* read the current value for GPIO F data register */
	read_result = *((unsigned long *) virt_addr);
	writeval = read_result;
    
	if ( (read_result&(1<<0)) )
	    writeval &= ~(1<<0);	/* set GPIO F0 to a value of 0(low-on) */
	else
	    writeval |= (1<<0);		/* set GPIO F0 to a value of 1(high-off) */ 

	/* write the modified value to the GPIO F0 data register */
	*((unsigned long *) virt_addr) = writeval;
	sleep(1);

    }
	
	if(munmap(map_base, MAP_SIZE) == -1) FATAL;
    close(fd);
    return 0;

}