[BeagleBone] help using GPIO pins with C

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1

Hello all,

I am currently working with the BeagleBone as part of a school project. We are transmitting various signals between two BeagleBones which are connected over the internet. To implement this, we need to read the signals through a GPIO bank and output a similar signal through a different GPIO bank on the other side of the network.

We are looking for resources to help interface with the GPIOs in a daemon, or possibly a kernel module. We are using the default version of Angstrom that ships with the board. We plan to program in C. Any help is much appreciated.

Thanks!

John

2

Here is my sample code for it. Hope it does the trick for you. Any
questions, feel free to ask. Developed for Angstrom C. It's messy but
it works.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define UNEXPORT fopen( "/sys/class/gpio/unexport",
"w" )
#define EXPORT fopen( "/sys/class/gpio/export", "w" )
#define GSTRING( s, i, g ) sprintf( s, "/sys/class/gpio/gpio%d
%s", i, g );
#define GDIRECTION "/direction"
#define GVALUE "/value"
#define GOPEN( s ) fopen( (s), "w" )

int gpio_init ( int pin )
{
        FILE *p = NULL;
        char gpio[50];

        if( ( p = EXPORT ) == NULL )
        {
                printf( "Problem opening gpio%d\n", pin );
                return -1;
        }
        fprintf( p, "%d", pin );
        fclose( p );

        GSTRING( gpio, pin, GDIRECTION );
        if( ( p = GOPEN( gpio ) ) == NULL )
        {
                printf( "Problem opening gpio%d\n %s\n", pin, gpio );
                return -1;
        }
        fprintf( p, "out");
        fclose( p );

        return 0;
}
int gpio_clean ( int pin )
{
        FILE *p = NULL;
        if( ( p = UNEXPORT) == NULL )
        {
                printf( "Problem closing gpio%d\n", pin );
                return -1;
        }
        fprintf( p, "%d", pin );
        fclose( p );
        return 0;
}
int gpio_control ( int pin, int value )
{
        FILE *p = NULL;
        char gpio[50];

        GSTRING( gpio, pin, GVALUE );
        if( ( p = GOPEN( gpio ) ) == NULL )
        {
                printf( "Problem controlling gpio%d\n", pin );
                return -1;
        }
        fprintf( p , "%d", value );
        pclose( p );
}

3

Hello,

I am also working on a little project of mine and I also would want to
use C/C++ programming for beaglebone. Until now I've been able to
setup a cross compiling environment and to generate a simple "hello
world" program executable for ARMv7.

I used the tutorial http://www.lvr.com/eclipse1.htm
As a next step I will also try to toggle a user LED using cross
compiling.

4

John,

Here are a couple of good links in using userspace sysfs to access the GPIO and “C” example.

Mark

5

There is also discussion of accessing GPIO pins from user space in the
BeagleBoard community FAQ: http://elinux.org/BeagleBoardFAQ#Programming_GPIO_pins