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
