According to R.P. McMurphy above, "you need to set the mux to enable the
output and disable both pull up and pull down."  If I understand correctly, this means that in the pin mux settings of git/board/overo/overo.h you need to set the parameters of the appropriate pin mux setting for each LED GPIO pin to the following:

MUX(CP(......))        (IDIS | PTU | DIS | M4) /* GPIO_XXX */\

IDIS = input disable (in otherwords, output).  PTU = pull type up, but I'm guessing this can also be PTD (pull type down) because the 3rd parameter is DIS = disable pull type up/down, and M4 = mode 4.  I have no idea what the modes are.

Is this a correct interpretation?  Disable input and disable pull type selection -> gives you a GPIO pin that is output and not pulled up or down.  Then you can change it to high/low in the filesystem with 'echo (1 or 0) > gpioXXX/value' to change the LED.

On Sat, Feb 6, 2010 at 12:23 PM, <gumstix@status.e4ward.com> wrote:
Victhor, thank you for the great guide. Unfortunately, I have no
/sys/class/gpio/gpioX/direction. All I have in there is power, uevent,
subsystem, and value. What's different between our two systems?

    Kyle Fazzari

On 2/6/10, Kyle Fazzari <kyrofa@gmail.com> wrote:
> Victhor, thank you for the great guide. Unfortunately, I have no
> /sys/class/gpio/gpioX/direction. All I have in there is power, uevent,
> subsystem, and value. What's different between our two systems?
>
>      Kyle Fazzari
>
> On 2/6/10, Victhor <victhor.foster@gmail.com> wrote:
>> The LEDs on the Palo43 are buffered by a 74xx chip, I don't remember the
>> exact model.
>>> On the hardware pin setting you need to set the mux to enable the
>>> output and disable both pull up and pull down.
>>>
>>> Also it would be a good idea to buffer the output from the pin. The
>>> CPU pin drivers are not really designed to drive an LED directly.
>>>
>>> On 2/6/10, coderdrone@gmail.com <coderdrone@gmail.com> wrote:
>>> > I've been struggling with turning LEDs on and off myself the past few
>>> > days.
>>> > I have LEDs connected to GPIOs 170, 127, and 128.  I have all 3 LEDs
>>> > enabled
>>> > in the pin mux configuration of u-boot in the overo.h header.  If I
>>> > remember
>>> > correctly, 2 of the GPIOs are pull type up (PTU) and the other one is
>>> > pull
>>> > type down (PTD).  I have all 3 pins exported in /sys/class/gpio, and
>>> > can
>>> > echo a 1 or a 0 to each of the pins, and 'cat gpioX/value' returns the
>>> > appropriate number.  However, the LEDs do not change at all.  One of
>>> > the
>>> > LEDs, I believe GPIO128, is constantly on no matter what I set the
>>> > gpio
>>> > to
>>> > in the filesystem.
>>> >
>>> > What is the appropriate setting for LED pins in the pin mux
>>> > configuration?
>>> > Should they be a certain mode, pull type up/down?
>>> >
>>> > On Sat, Feb 6, 2010 at 6:24 AM, Victhor <victhor.foster@gmail.com>
>>> > wrote:
>>> >
>>> >> It's rather easy, I didn't even know that it would be like that :)
>>> >> X is the GPIO port number. Just type in those commands and your led
>>> >> should light up :)
>>> >> echo X > /sys/class/gpio/export
>>> >> echo out > /sys/class/gpio/gpioX/direction # This should make the LED
>>> >> light up. At least it does on my Palo43
>>> >> echo 1 > /sys/class/gpio/gpioX/value # On my Palo43, it turns the LED
>>> >> connected to that port turn off
>>> >> echo 0 > /sys/class/gpio/gpioX/value # Turns it on again
>>> >> If you don't want to use that GPIO port again, use the first command,
>>> >> replacing export with unexport.
>>> >> > Hello all.
>>> >> >
>>> >> > I feel rather stupid. Let me explain: I have an Overo Air, and a
>>> >> > Tobi.
>>> >> > I figured that I'd be able to get some document that says "LED 3 is
>>> >> > tied to port X" or something similar, which would then allow me to
>>> >> > light those LEDs (I have experience writing RTOS's, so I'm used to
>>> >> > a
>>> >> > little lower level than Linux). Of course, I could find no such
>>> >> > document, nor could I find anything on Google to help me with this.
>>> >> > The LEDs are pretty teeny, but it does look like I have a few that
>>> >> > are
>>> >> > not being used. Can someone please explain how I light them? I'm
>>> >> > very
>>> >> > sorry, I feel like this should be easy, but I can't figure it out.
>>> >> > Thank you very much!
>>> >> >
>>> >> >      Kyle Fazzari
>>> >> >
>>> >> >
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