Re: [Gumstix-users] Overo: How do I adjust the pin mux to enable more GPIO pins?

[Dirk B. <dir...@go...>]

kindredvendetta wrote:
> Hello,
> 
> I have an Overo Earth and Summit expansion board and am trying to enable
> more of the GPIO pins for use. I have 6 of them working, but others I cannot
> access when testing through the sysfs interface - they will not respond to a
> change in applied value. Not tried through C, but I assume it would be the
> same. Namely, I would like to get the GPIO171-175 (The SPI port), as well as
> 144 and 145 if possible. 
> 
> I've already built a kernel with SPI support disabled, and can see from
> posts on the forum that I have to alter the pin multiplexing in order to use
> pins as GPIO, but I'm not sure how. I would like to do it without rebuilding
> the kernel, if this is possible... I've seen some references to "edit the
> muxing in u-boot" but not sure what this is or what changes to make.

U-Boot is the boot loader used to load the kernel. So yes, you can 
modify pin mux in boot loader without changing the the kernel. But you 
have to rebuild the boot loader U-Boot.

Overo U-Boot support is in U-Boot mainline:

git clone git://git.denx.de/u-boot.git u-boot-main
cd u-boot-main
git checkout --track -b omap3 origin/master

Build (assuming Code Sourcery GCC):

make CROSS_COMPILE=arm-none-linux-gnueabi- mrproper
make CROSS_COMPILE=arm-none-linux-gnueabi- omap3_overo_config
make CROSS_COMPILE=arm-none-linux-gnueabi-

There, pin mux is done in file

board/overo/ overo.h

http://git.denx.de/?p=u-boot.git;a=blob;f=board/overo/overo.h;h=4c7ac27fa6818d4f474bc42330134fd0a5520a37;hb=HEAD

To get an idea how to change pin mux there have a look to

http://elinux.org/BeagleBoardPinMux#U-Boot

(it's done the same way for Beagle and Overo).

Best regards

Dirk