OSL GPIO user space application

The following user space application was used to test the GPIO using the sysfs interface.

This code can be downloaded by clicking on the files button at the bottom of the page.

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
// The specific GPIO being used must be setup and replaced thru
// this code.  The GPIO of 240 is in the path of most the sys dirs
// and in the export write.
// Figuring out the exact GPIO was not totally obvious when there
// were multiple GPIOs in the system. One way to do is to go into
// the gpiochips in /sys/class/gpio and view the label as it should
// reflect the address of the GPIO in the system. The name of the
// the chip appears to be the 1st GPIO of the controller.
// The export causes the gpio240 dir to appear in /sys/class/gpio.
// Then the direction and value can be changed by writing to them.
// The performance of this is pretty good, using a nfs mount,
// running on open source linux, on the ML507 reference system,
// the GPIO can be toggled about every 4 usec.
// The following commands from the console setup the GPIO to be
// exported, set the direction of it to an output and write a 1
// to the GPIO.
// bash> echo 240 > /sys/class/gpio/export
// bash> echo out > /sys/class/gpio/gpio240/direction
// bash> echo 1 > /sys/class/gpio/gpio240/value
// if sysfs is not mounted on your system, the you need to mount it
// bash> mount -t sysfs sysfs /sys
// the following bash script to toggle the gpio is also handy for
// testing
// while [ 1 ]; do
//  echo 1 > /sys/class/gpio/gpio240/value
//  echo 0 > /sys/class/gpio/gpio240/value
// done
// to compile this, use the following command
// gcc gpio.c -o gpio
// The kernel needs the following configuration to make this work.
int main()
    int valuefd, exportfd, directionfd;
    printf("GPIO test running...\n");
    // The GPIO has to be exported to be able to see it
    // in sysfs
    exportfd = open("/sys/class/gpio/export", O_WRONLY);
    if (exportfd < 0)
        printf("Cannot open GPIO to export it\n");
    write(exportfd, "240", 4);
    printf("GPIO exported successfully\n");
    // Update the direction of the GPIO to be an output
    directionfd = open("/sys/class/gpio/gpio240/direction", O_RDWR);
    if (directionfd < 0)
        printf("Cannot open GPIO direction it\n");
    write(directionfd, "out", 4);
    printf("GPIO direction set as output successfully\n");
    // Get the GPIO value ready to be toggled
    valuefd = open("/sys/class/gpio/gpio240/value", O_RDWR);
    if (valuefd < 0)
        printf("Cannot open GPIO value\n");
    printf("GPIO value opened, now toggling...\n");
    // toggle the GPIO as fast a possible forever, a control c is needed
    // to stop it
    while (1)
        write(valuefd,"1", 2);
        write(valuefd,"0", 2);
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