Interfacing to the PandaBoard GPIO, SPI, etc...

Here is my experience/adventure with PandaBoard trying to use its SPI, GPIO interfaces.

This is a work in progress so, I am documenting as I progress.

GPIO are found @

/sys/class/gpio

and then need to export as root...

#echo "50" > export
# echo "39" > export
# echo "38" > export
# echo "37" > export
# echo "out" >  gpio51/direction
# echo "out" >  gpio50/direction
# echo "out" >  gpio39/direction
# echo "out" >  gpio38/direction
# echo "out" >  gpio37/direction

# echo "1" > gpio38/value
# echo "0" > gpio38/value
# echo "1" > gpio38/value
# echo "0" > gpio38/value
# echo "1" > gpio38/value
# echo "1" > gpio37/value
# echo "0" > gpio37/value

To read from GPIO that is set as Input:
# cat /sys/class/gpio/gpio34/value

I will need to use 

chmod 666 /sys/class/gpio/gpio38/value

OR

Change the rc.local  

Now, How do I do this from C program:

This file will show in details how to do all the above from C program.
Note: You will have to run this program using sudo ./Test_IO_1 until I find how to create the GPIO on boot and make it accessible to all users
Makefile
Test_IO_1.c

I included the Makefile so you can compile the C program.  I compiled the code natively, which is on the Pandaboard itself.

1. Make a folder, Test_IO_1
2. Copy these two files to the new folder
3. run make
4. you should have Test_IO_1.0 and Test_IO_1
5. type sudo ./Test_IO_1
6. monitor GPIO38 with a scope, multimeter or a LED

Use this image or PandaBoard datasheet to find the correct pin for GPIO38

Open a file-socket to read or write from /sys/class/gpio/gpio38/value

To Read:

rewind(fp);

fread(&read_value, sizeof(char), 1, fp);

To Write:

rewind(fp);

fwrite(&set_value, sizeof(char), 1, fp);

OK, How to modify device read/write permission on boot:
I found this tile /etc/mtab
is this the one?

Also, I found SPI stuff @

/sys/class/spi_master

There is spi1, spi2, spi3, spi4

References:

http://lxr.free-electrons.com/source/Documentation/gpio.txt

http://www.haifux.org/lectures/258/gpio_spi_i2c_userspace.pdf

https://www.kernel.org/doc/Documentation/spi/spi-summary

http://www.youtube.com/watch?v=fuEB0VCkslQ

http://comments.gmane.org/gmane.comp.embedded.pandaboard/9743

http://lxr.free-electrons.com/source/drivers/input/keyboard/gpio_keys.c

http://lxr.free-electrons.com/source/arch/arm/mach-u300/spi.c?v=2.6.34

http://elinux.org/BeagleBoard/SPI

http://www.egr.msu.edu/classes/ece480/capstone/fall12/group02/documents/Mark-Birdsall_App-Note.pdf