[Gumstix-users] [Gumstix-Users] GPIO pin usage

[<cod...@gm...>]

Hello,

I'm working on a C++ project to read button presses via GPIO pins from the
Gumstix board and am running into some issues.  As I understand it, there
are two different ways to read GPIO lines: 1.) reading through an API, or
2.) standard filesystem commands like cat and echo.  We are currently using
filesystem commands.

So far, I've just been trying to read the pins on the commandline via, for
example, 'cat /sys/class/gpio/gpioN' where N is the GPIO number.  As I
understand it, this gpio directory lists all the GPIO pins that have been
'exported' by the kernel to userspace.  However, if I export other GPIOs, I
can't seem to successfully read them.  Is there a way to change the
configuration of the kernel to make more GPIO pins available?  Could the
kernel be reserving certain pins for other uses so I can't actually read
button presses with them?  Am I just making this more complicated than it
needs to be?

The Gumstix board is mounted on a summit board, which has a 40-pin connector
as referenced at
http://www.gumstix.net/Hardware/view/I/O-connectors-cabling/Gumstix-Summit-board-40-pin-header-SV1/112.html.<http://www.gumstix.net/Hardware/view/I/O-connectors-cabling/Gumstix-Summit-board-40-pin-header-SV1/112.html>

However, the GPIO pins listed on that chart don't match the GPIO pins that
exist in /sys/class/gpio when I boot the system.  For example, GPIO114
exists in the filesystem, but GPIO171 does not.  If I attach a button to the
pins for GPIO114, the button appears to work (gpio114/value changes between
0 and 1).  I can 'echo 171 > export' to gain access to GPIO 171, but when I
read the value of that pin via 'cat gpio171/value' it always stays at 0
whether the attached button is pressed or not.

Any thoughts?