Reading the button from the shell

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1

Hi:
  I’m following the instructions at :
http://groups.google.com/group/beagleboard/msg/c623a16637625685?hl=en

to read a switch. However

cd /sys/class/gpio
echo 7 > export

doesn’t cause gpio7 to appear. What’s up?

--Mark

p.s. The LEDs blink fine.

2

Fri, 12 Mar 2010, Mark A. Yoder wrote:

cd /sys/class/gpio
echo 7 > export

doesn�t cause gpio7 to appear. What�s up?

GPIO 7 has been defined in beagle's board file in the kernel. See board-omap3beagle.c for more details.
GPIOs which are defined there cannot be exported to /sys/class/gpio. In this case you can use the user button with event interface,

3

Thanks for the quick response.

Can you point me to an example of reading the user button with the
event interface?

--Mark

4

Sat, 13 Mar 2010, Mark A. Yoder wrote:

Can you point me to an example of reading the user button with the
event interface?

One example:
  http://beagleboard.googlecode.com/files/evtest.c

A very simplified (and propably flawed) example:
  http://hervanta.com/~antti/temp/readkey.c.txt

5

Thanks again for the quick reply.

The code looks interesting, however I'm wanting to read the USER
button from the shell prompt via the /sys file system. I can blink
the LEDs that way, but I don't know how to read the button.

--Mark

6

Sat, 13 Mar 2010, Mark A. Yoder wrote:

The code looks interesting, however I'm wanting to read the USER
button from the shell prompt via the /sys file system. I can blink
the LEDs that way, but I don't know how to read the button.

At least one option is to remove the reference to GPIO 7 from the board file and then recompile kernel. That will let you use the /sys method.