Raspberry Pi 4 model B :: GPIO Pull modes

[jsimmonds2]

Have a simple app which uses GPIO 12 as input connected to an open-drain output on a DS3231 RTC. Have tried setting :pull_mode in the GPIO.open options according to the documentation but cannot get a :falling edge interrupt.

    {:ok, gpio_pin_12} = GPIO.open 12, :input, [{:pull_mode, :pullup}]    # A 1 Hz SQW or Alarm 1 interrupt from the DS3231

    GPIO.set_interrupts gpio_pin_12, :falling

As I don't have a scope, I'm going to try a 47k external pullup and see if that helps . . now off to order that resistor :)

[mdsebald]

Are you getting the initial message on the GPIO.set_interrupts call?

Then, if you disconnect the RTC and just manually short GPIO 12 to ground, are you still not getting the interrupt message?

[jsimmonds2]

Are you getting the initial message on the GPIO.set_interrupts call?

Only when GPIO 12 is tied to GND and not when tied to +3V3.

Then, if you disconnect the RTC and just manually short GPIO 12 to ground, are you still not getting the interrupt message?

That is so.

Sure looks like there's a :pulldown on that GPIO. I can take that lead from GND and dab it onto the +3V3 rail and I get :falling edge interrupts, with pin value 0.

[mdsebald]

I don't own an RPi 4. I hope nothing has changed in the GPIOs. I'll take a closer look when I have more time this evening (US Central TZ).

[mdsebald]

Sorry, unable to verify if issue exists on my setup or not. Will try again tomorrow evening. I have ordered an RPi 4. I will test with that, also.

[jsimmonds2]

Wow ! Thanks for digging deeper . . I was actually thinking about offering to send you an RPi4 to test with.

[mdsebald]

First I verified that the internal pull-up and pull-down resistors are still working as expected with Circuits.GPIO on the RPi3. I tried the same on an RPi4, and indeed, it appears the internal pull-up resistors (I only tried on GPIOs 12 and 23 so far) are not being switched in via the pullmode pullup option. I don't know what is wrong and not sure what it will take to fix it yet. Hopefully, you can get by with an external pull-up resistor for now. Just in case the pullmode option is doing something undefined on the RPi4, I would also take out that option, when opening an input pin. Thanks for bringing this to our attention.

[fhunleth]

Oh wow, the GPIO interface changed on the BCM2711 (RPi4)!

Here's the best of what I was able to find quickly on the new way: https://github.com/RPi-Distro/raspi-gpio/blob/master/raspi-gpio.c#L476-L492. The peripheral spec that's currently on the Raspberry Pi site doesn't seem to talk about this or I haven't found it.

Would either of you like to take a crack at updating https://github.com/elixir-circuits/circuits_gpio/blob/master/src/hal_rpi.c#L85?

[mdsebald]

Thanks for finding that new code. I was not able to find anything about that myself. I'll take a look at updating the code.

[mdsebald]

FYI: I found this code too https://github.com/raspberrypi/linux/blob/e2a6ce9ff7c94cce5c1d40d2c79a2cd0498d5f88/drivers/pinctrl/bcm/pinctrl-bcm2835.c#L933-L954

[jsimmonds2]

FYI: I found this code too https://github.com/raspberrypi/linux/blob/e2a6ce9ff7c94cce5c1d40d2c79a2cd0498d5f88/drivers/pinctrl/bcm/pinctrl-bcm2835.c#L933-L954

Hi Mark. Could you edit your link to put the URL inside the parentheses rather than the brackets. :)

That reference you provided explains what I'm seeing, I think.

[mdsebald]

Done. Thanks!

[mdsebald]

I updated src/hal_rpi.c to include RPi4 pull modes code (branch: implement_rpi4_pullmodes). Tested pull-up and pull-down modes on one GPIO pin (12) on the RPi4 and it worked OK. Still need to do more testing including regression tests on other Pi models, before submitting PR.

[fhunleth]

Fixed in #63. Thanks @mdsebald.

[jsimmonds2]

Appreciate your fixes, @mdsebald 👍 I'm now "one happy end-user", getting the ( Active Low ) Alarm interrupts from the DS3231 RTC exactly as described 🙂 . . without any external pullup resistor.

[mdsebald]

Thanks to @fhunleth for pushing it over the finish line too, Glad we were able to resolve this issue.