pi-gpio-tests

Raspberry pi gpio.

You can use bash:

root@bladderpi:~# echo 0 > /sys/class/gpio/export 
root@bladderpi:~# echo out > /sys/class/gpio/gpio0/direction
root@bladderpi:~# echo 1 > /sys/class/gpio/gpio0/value
root@bladderpi:~# echo 0 > /sys/class/gpio/gpio0/value
root@bladderpi:~# while true; do (echo 0 > /sys/class/gpio/gpio0/value); (echo 1 > /sys/class/gpio/gpio0/value); done

You get ~0.5 KHz waves (i.e. 1 KHz toggles) from this (no nice), considerable jitter

You can use python:

from RPi.GPIO import setmode, setup, output, OUT, BOARD

setmode(BOARD)
setup(3, OUT)
val = 0
while True:
 output(3, val)
 val = 1 - val

You get ~50 KHz, considerable jitter

You can use c:
#include <fcntl.h>

int main(void)
{
	int val;
	int fd = open("/sys/class/gpio/export", O_WRONLY);

	write(fd, "0", 1);
	close(fd);
	fd = open("/sys/class/gpio/gpio0/direction", O_WRONLY);
	write(fd, "out", 3);
	close(fd);
	val = 0;
	fd = open("/sys/class/gpio/gpio0/value", O_WRONLY);
	while (1) {
		write(fd, val ? "1" : "0", 1);
		val = 1 - val;
	}
	close(fd);
	return 0;
}

250 KHz, much less jitter but still considerable (perhaps real time execution will improve this)