Beaglebone: GPIO configuration at startup

[Rico]

Hello

I have some questions concerning the GPIOs of the beaglebone:

1)
Is there somewhere a definition of the configuration of the GPIOs immediately at startup? (input / output / pullup / pulldown)

2)
When using Angstrom, does the kernel changes this configuration during boot?

3)
Is it possible to change the startup configuration of the GPIOs (before the kernel is loaded)?

4)
If its not possible to change the startup configuration, does the current configuration remain the same for further revisions of the beaglebone?

Thanks a lot for any help!

[özen özkaya]

Hello Rico,

I think it is my turn :)

1.) you can find the definition of the configuration of the GPIO's under:

/sys/kernel/debug/omap_mux/

for example if you want to learn the current configuration of the gpmc_ad6 pin

you should look for:

cat /sys/kernel/debug/omap_mux/gpmc_ad6

to make it availible for output you should write

echo 7 >  /sys/kernel/debug/omap_mux/gpmc_ad6

and then if you want to use it you should export that pin.

echo 38 > /sys/class/gpio/export

after you exported it you can make it output

echo "out" > /sys/class/gpio/gpio38/direction

or input

echo "out" > /sys/class/gpio/gpio38/direction

you can change the output value as low:

echo "0" > /sys/class/gpio/gpio38/value

or as high

echo "0" > /sys/class/gpio/gpio38/value

you can find the manings of the numbers like 7 or 37 from the user guide of AM335X.

2. As I know, normally first configuration is made by bootloader. (like mux.h) After bootloader, kernel changes the configuration as in the

/sys/kernel/debug/omap_mux/ directory. Whatever you write here will be executed with kernel.

3. I think you should edit u-boot's pin mux configurations and recompile it.

4. As I know there is no major pin config changes on revisions of Beaglebone.

Regards

2012/12/3 Rico <rico....@gmail.com>

--
 
 

Web:        http://www.teknotel.com.tr
 

[özen özkaya]

You can find detailed explanation in the links below, also:

http://www.nathandumont.com/node/250

http://akademii.blogspot.com/2012/02/beaglebone-gpio-testing.html

http://www.gigamegablog.com/2012/03/16/beaglebone-coding-101-buttons-and-pwm/

Regards

2012/12/4 özen özkaya <ozeno...@gmail.com>

--
Özen Özkaya

[Jack Mitchell]

> --
>
>

I was looking into this issue some time ago. You can find default "from
cold" pin configurations in the AM335x TRM, however you also have to
take into account the changes u-boot makes and also the changes that the
Linux kernel also makes. It's a tough chain to follow so you need some
motivation to do it and also be prepared for changes to it in future
revisions of software!

Regards,
Jack.

--

Jack Mitchell (ja...@embed.me.uk)
Embedded Systems Engineer
http://www.embed.me.uk

--

[Claudio La Rosa]

I have a problem with IO pins.
If I understand correctly, some of these pins can not be used at boot time, I can connect them to my circuit only after the BeagleBone has booted. It's really like this?

[evilwulfie]

yes

On 4/12/2018 4:44 AM, Claudio La Rosa wrote:

I have a problem with IO pins.
If I understand correctly, some of these pins can not be used at boot time, I can connect them to my circuit only after the BeagleBone has booted. It's really like this?

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[Claudio La Rosa]

Can I know what these pins are? I'm using a Beaglebone green