GPIO problems

[Hellgringo]

Hi,

I connected a green LED and a 600ohm resistor between pin 18 and 2 of the 40pin GPIO connector.
The LED lights up at startup but if I change the gpio state (/sys/class/gpio51) to 0 the LED is still
on. I checked the pins several times... no idea.

I use arch linux 2.6.35-8-ARCH+ without modifications.

[Fadil Berisha]

The LED lights up at startup but if I change the gpio state (/sys/class/gpio51) to 0 the LED is still
on.

To help you beter, we need to know your sequence to change state. If pin is defined in kernel as GPIO ,try this sequence:

Export and set direction:

echo 51 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio51/direction

Change value on pin 51:

echo 0 > /sys/class/gpio/gpio51/value
echo 1 > /sys/class/gpio/gpio51/value
echo 0 > /sys/class/gpio/gpio51/value

Regards
Fadil Berisha

[Hellgringo]

I tried it this way which worked for the onboard led

echo out > /sys/class/gpio/gpio65/direction
echo 0 > /sys/class/gpio/gpio65/value
echo 1 > /sys/class/gpio/gpio65/value
echo 0 > /sys/class/gpio/gpio65/value

the same thing for gpio51 didn't work.

The following command results in an error
echo 51 > /sys/class/gpio/export
-bash: echo: write error: Device or resource busy

Regards
Holger

[Hellgringo]

Sorry, my fault.

There was a short circuit...

I have another question, what would be the fastest way to read the gpios values with in a C program?
I thought of opening the gpios as files, read the content and close. But I think this won't be very
fast cause of the usage of open() close() sys calls.

Thx

[olimex]

http://olimex.wordpress.com/2012/09/11/imx233-olinuxino-gpios-faster-and-faster/ using /dev/mem is the fastest