GPIO Digital Inputs with Internal Pull-up on Raspberry PI 4

[dpotts-sc]

I have code that has been working great on the Raspberry PI3; I just assigned a GPIO as a digital input (Raspberry PI GPIO21, pin 40, WiringPi 29) with a pull-up on it, and then my switch pulls it down to ground when it is pressed.

I've upgraded to a PI4 and now this code doesn't work. If I move to GPIO2 (WiringPi 8, Pin 3), it works fine, but this is not ideal due to the additional wiring and various devices connected to the PI.

I'm guessing it has to do with WiringPi not fully upgraded to support PI4 and / or Java. Or maybe Pi4J not updated yet for the 4. Is this something I have to wait until 2.0, or is there some work around (not sure yet, might put on an external pull-up and see how that works, because it seems to be the pullup is the problem).

[dpotts-sc]

Some additional information, SOME of the pins are usable with pullups on them. The all seem to work if they are Push-Pull.

Pin	Name	Good?		Pin	Name	Good?
1	3.3v	--		2	5v	--
3	GPIO2	Yes		4	5v	--
5	GPIO3	Yes		6	gnd	--
7	GPIO4	Yes		8	GPIO14	No
9	gnd	--		10	GPIO15	Yes
11	GPIO17	No		12	GPIO18	No
13	GPIO27	No		14	gnd	--
15	GPIO22	No		16	GPIO23	No
17	3.3v	--		18	GPIO24	No
19	GPIO10	No		20	gnd	--
21	GPIO9	No		22	GPIO25	No
23	GPIO11	No		24	GPIO8	Yes
25	gnd	--		26	GPIO7	Yes
27	ID_SC	--		28	ID_SC	--
29	GPIO5	Yes		30	gnd	--
31	GPIO6	Yes		32	GPIO12	No
33	GPIO13	No		34	gnd	--
35	GPIO19	No		36	GPIO16	No
37	GPIO26	No		38	GPIO20	No
39	gnd	--		40	GPIO21	No

EDIT : I just re-ran the same test on another RaspberryPI4, and got different pins working. So it seems like there is a setup issue somewhere and the pullups (at least, I have not tried pull downs) are being applied randomly. Most likely they were moved registers and something isn't initialized.

[dpotts-sc]

I seem to have found a temporary work-around. Hopefully this will help someone.

In the /boot/config.txt file you can define what the default states are for the GPIO. I went in and changed the default for the GPIO pins I needed and added the PullUp to the pin there. This appears to be working now.

Doesn't fix the fundamental problem, but it can keep me moving forward. I'm guessing it could be the reason I don't see the changes to the interrupts coming in as well.

BTW, I wrote a walking test that goes pin by pin and displays the status of every GPIO and then turns on/off the pull up / down on each one and on the PI4, it is clear that NONE of the PU/PDs work at all. The same test works perfectly on the PI3.

[matthiesenj]

Configuring pull-up/-down on Pi4 works differently than on the Pi3 (other registers, etc), so you'll need wiringPi updated to support that, but as far as I know, it's no longer maintained!?

[pablo67340]

Any solutions on this yet? I am having similar problems with reading a DHT11 sensor. Unable to do so

[dpotts-sc]

Not directly, this is a problem with Wiring PI and it doesn't appear that there will be any updates with it anymore. So we are, well screwed.

If you don't require changing the PINs from input to output you can use the method I ended up using, changing the /boot/config.txt file so that some pins are inputs, some are outputs. Then I was able to successfully use the pins but I cannot programmatically change their functionality.

[pablo67340]

Unfortunately I do need to set the pin between input/output so your workaround will not work for me. For some reason it works fine in Python, just not Pi4J

[Maddinthebrain]

I just ran into the same problem with the pullup resistors, I guess there is now solution yet, right??

[valdar]

@Maddinthebrain compile a new version of wiringpi from here https://github.com/WiringPi/WiringPi and use that one should be a good start.

[Maddinthebrain]

well I have the original version 2.52. It doesn't work with it.

[eitch]

@dpotts-sc @Maddinthebrain @pablo67340 can you guys try my fork of wiringPI: https://github.com/eitch/wiringPi or at least try the latest https://github.com/WiringPi/WiringPi version 2.60 and see if the issue persists? I have been using an I2C bus with interrupts on GPIO BCM pins 9, 10, 22, 23, 24 and have not had any issues. I am on aarch64 with my wiringPi branch.

[savageautomate]

Issue confirmed. WiringPi v2.52 added support for the RPi 4B but does not include changes to properly handle the pin PULL UP/DOWNs.

Using the unofficial WiringPi v2.60 (https://github.com/WiringPi/WiringPi ) as @eitch suggested does resolve this problem. I have added comments in the site documentation for the Pi4J v1.3 release as well as an installer script to make this as easy as possible.

See:

• https://pi4j.com/1.3/install.html#WiringPi_Native_Library
• https://webtechie.be/post/2020-10-10-pi4j-on-raspberry-pi-4/