gumstix

Typically, the GPIOs are available but not necessarily exposed in
sysfs by the kernel e.g.
$ cd /sys/class/gpio
$ echo 10 > export
$ cd gpio10
This doesn't get around any problems where a pin is not correctly
mux'd. In this case, you'd need to set the correct mux mode in u-boot
first or use various devmem2 incantations to achieve the correct
mux'ing.

--ASh

On Wed, Feb 20, 2013 at 7:03 AM, hobbesc7 <hobbesc7@...> wrote:
> I need to use the following header pins on my Overo: 10, 114, 148, 151, 163,
> 170, 171, 172, 184, and 185.
>
> But under /sys/class/gpio I only see gpio15, 16, 144-5, 164, 168, and 250-5.
>
> I'm building the gumstix-console-image with the latest yocto stuff.
>
> How do I access these pins?
>
>
>
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Ash Charles wrote
> $ cd /sys/class/gpio
> $ echo 10 > export
> $ cd gpio10

This works well.  I also echo "out" to /sys/class/gpio/gpio10/direction.  I
have a multimeter in pin 18, and when I echo 1 to
/sys/class/gpio/gpio10/value, I see 1.8V.

I have two questions, however:

1.  What is the preferred way of doing the above at bootup?  When I reboot,
gpio10 is gone.  Put something in /lib/systemd/system/?  Tmpfiles.d?

2.  Also, with my multimeter, I notice that pin18 goes to 1.8V for the first
few seconds of boot time, then it drops to 0V.  I need this to stay at 0V
unless I explicitly write a 1 to this pin.  Do I have to make a kernel or
u-boot change to achieve this?



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On Thu, Feb 21, 2013 at 7:57 AM, hobbesc7 <hobbesc7@...> wrote:
> 1.  What is the preferred way of doing the above at bootup?  When I reboot,
> gpio10 is gone.  Put something in /lib/systemd/system/?  Tmpfiles.d?
Typically, I'd just make the change by modifying the kernel directly
(see the gpio_export() calls in the board_overo.c file).  Certainly,
it be possible to make the change by issuing these commands in
userspace.
>
> 2.  Also, with my multimeter, I notice that pin18 goes to 1.8V for the first
> few seconds of boot time, then it drops to 0V.  I need this to stay at 0V
> unless I explicitly write a 1 to this pin.  Do I have to make a kernel or
> u-boot change to achieve this?
U-boot.  Look at the MUX_OVERO() define in overo.h

--Ash

Ash Charles wrote
>> 2.  Also, with my multimeter, I notice that pin18 goes to 1.8V for the
>> first
>> few seconds of boot time, then it drops to 0V.  I need this to stay at 0V
>> unless I explicitly write a 1 to this pin.  Do I have to make a kernel or
>> u-boot change to achieve this?
> U-boot.  Look at the MUX_OVERO() define in overo.h

So I made the change in overo.h to pull down pin18, (gpio10), instead of
pulling it up.  This has improved things, but I notice that the pin still
jumps to 1.8v briefly before u-boot starts?  Is there any way to prevent
this?




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