Re: Mapping GPIO Pins from Wandboard to Fedora/libpiod

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Peter,

On Mon, April 15, 2024 1:47 pm, Peter Robinson wrote:

>> >> I'm using
>> >> https://download.technexion.com/development_resources/wandboard/wbquad-revb1-userguide.pdf
>> >> as a reference for the board layout.  Specifically, on page 27, it
>> shows
>> >> me that the JP4 header connects to GPIO3_12, GPIO3_27, GPIO6_31,
>> >> CPIO1_24,
>> >> GPIO7_8, GPIO3_26, GPIO_18, and GPIO_19.
>> >>
[snip]

>> Being only ancillarily associated with Arm/Embedded HW -- what does it
>> mean for a GPIO to be "used for other things"?  And more importantly,
>> why
>> would it be wired to a header if it's being used for something else?
>
> So in the case I mention below the GPIO pin is used for i2c and it's
> on that header so you could add say a i2c based temp sensor or other
> i2c device.
>
> Also board designers may use a GPIO to hook up a mSD card detect pin,
> or a WiFi interface reset pin, or something else on the board layout.

I guess I don't understand why they would expose GPIO-x on a header and
ALSO use it elsewhere on the board.   In my case, I just need to find 4
open "button" inputs.

> You can see the default pin allocation here from line 152-195:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/nxp/imx/imx6qdl-wandboard.dtsi#n152
>
> And the GPIOs mapped to i2c here on lines 103-104 and again 113-114,
> and then as a camera enable/reset at 139-140:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/nxp/imx/imx6qdl-wandboard.dtsi#n103

Thanks.  I see the duplication of scl-gpois and sda-gpios names in those
two sections, but in the first section it uses gpio3 21/28 and in the
second section is used gpio4 13/14.

I also don't see the specific bindings for the pins on the JP4 header
(e.g. I don't see gpio3 12 being specified here).

>> > A quick look at the dtsi for the wandboards some of the GPIOs re used
>> > for SCL/SDA pins on two of the i2c buses. The i2c1 seems to not have
>> > anything attached so I guess in on a pin header for end user use, and
>> > i2c12 has a audio codec and for the camera connector.
>>
>> How exactly is this done?  Is the pin wired to two places on the PCB?
>
> It depends, for example on a RPi header you can use a DT overlay to
> change the default use of a PIN, by default is might be a standard
> GPIO but you apply an overlay that remaps it so it routes a i2s audio
> interface so you can use a DAC to output sound. So it's generally more
> about being able to use the reduced amounts of external pins for
> different usecases, someone might want it in a robot, someone else
> might want it to output audio.

How would an end-user do that without building a custom kernel?  Like I
said, all I need is to read from four input GPIOs for a water-detection
system, so instead of using a 'sleep' after opening the relay, it waits
for the appropriate gpio to turn on based on a water detector connected to
it (so it will turn off the relay as soon as it detects the water tank is
full).

So really I just need to choose 4 pins that I can use, and map those to an
event manager to wait for the pin to go on.  JP4 seems to be the only
layout with GPIO labeled, so I just need to figure out which pins to use
and how to read those inputs in this brave new world.

Thanks,

-derek

-- 
       Derek Atkins                 617-623-3745
       derek@xxxxxxxxx             www.ihtfp.com
       Computer and Internet Security Consultant
--
_______________________________________________
arm mailing list -- arm@xxxxxxxxxxxxxxxxxxxxxxx
To unsubscribe send an email to arm-leave@xxxxxxxxxxxxxxxxxxxxxxx
Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/
List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines
List Archives: https://lists.fedoraproject.org/archives/list/arm@xxxxxxxxxxxxxxxxxxxxxxx
Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue




[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Linux ARM (Vger)]     [Linux ARM]     [ARM Kernel]     [Fedora User Discussion]     [Older Fedora Users Discussion]     [Fedora Advisory Board]     [Fedora Security]     [Fedora Maintainers]     [Fedora Devel Java]     [Fedora Legacy]     [Fedora Desktop]     [ATA RAID]     [Fedora Marketing]     [Fedora Mentors]     [Fedora Package Announce]     [Fedora Package Review]     [Fedora Music]     [Fedora Packaging]     [Centos]     [Fedora SELinux]     [Coolkey]     [Yum Users]     [Tux]     [Yosemite News]     [Linux Apps]     [KDE Users]     [Fedora Tools]     [Fedora Art]     [Fedora Docs]     [Asterisk PBX]

Powered by Linux