configure header pin as an output on initial boot of device.

General Discussion
1

hello,

I need a little help setting a pin as an output on boot. For instance I use > config-pin P9.12 out , but a reboot returns it to default which is “in” . Do I have to export it? , or is there a file I can alter ?

Thank you

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2

https://docs.beagleboard.org/latest/boards/capes/cape-interface-spec.html

https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html

3

thanks for the response. I am just learning about the Device tree and how it supports hardware on the board. not real confidant in changing or creating Device tree files at the moment. I did see somewhere that this is more for UART and SPI interfaces. To get more control of the actual digital pin values set at boot it is done by accessing PRU. Do you think that this is true?

4

How are you using the gpio, thru what peripheral? Depending on that some ways are better then others…

5

I am not setting to use the UART or SPI peripheral, I am just looking to use the Pin as a digital-out that is set LOW on boot. Of course the pins are set as default and are pulled HIGH. A bash file could be used after boot but I want to make sure this is set LOW as soon as possible.
As I am new to Device Tree overlay, it does not seem to complicated, just the syntax I have to get used to and start on the basics on this topic,

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6

You don’t say what board you are using.
However have you checked the boot pins ? I don’t have a schematic to hand currently, but from memory some of these might be pulled low by a resistor. If that is the case this is the easiest option as the pin woukd be low as soon as power is applied.
You can then reconfigure the pin once you are up and running.

7

I am using Beaglebone Balck. Yes, that is true I can just use a physical Pull-Down, I am just trying to learn how to configure the Device Tree. Thanks

8

A pull down is not the best option on any good pin that defaults to pull up on boot. The reason i mentioned the boot pins is because I believe the pull up/down is disabled on boot and some of the pins are pulled high, others low.
You said you need a low on boot and that is the quickest way to get a low at boot.
After that the next quickest option would be to set is low from uboot. After that yes the device tree, although by then you may just a well do it once the is boots.

I believe someone posted here before about setting a gpio to a certain state by modifying the devicetree. Have you searched the forum ? It was in the past few months think.