Gpio access on the Raspberry pi Pico

[Darin755]

Is there any plans to add gpio access in userland? I think it would be really useful to enable to access some of the low level hardware from a program running in userland.

I think the easiest way to do this is to create simple character devices that can can be toggled with a 1 or a 0.

[EtchedPixels]

There is a GPIO interface in Linux which is used at the moment mostly for SC129 and Z80 PIO devices on 8bit systems. So you could add it.

See CONFIG_DEV_GPIO Kernel/include/gpio.h Kernel/platform-rc2014/devgpio.c

for an example. It might need extending for the Pico as I guess the Pico has rather more functionality than simple on/off and directionality. That should be fine though as tiny Z80 machines can just not implement them.

[Darin755]

I'm fairly new at this and doing something this complex is quite the learning curve. I don't mind giving it a shot but please keep in mind the quality of my code may not be as high as someone with more experience.

[Darin755]

What are the values at Line 17? I see that they are defined in gpio.h but I am unsure of what they control.

[EtchedPixels]

The first one is a byte sized mask of pins that are controllable (so if there were 8 gpio pins it would be 0xFF) - the SC129 entries are wrong. I've just fixed that!

The second is a group which is used to group together pins whose properties have to change together. On the Z80 PIO there are none but on the 82C55 for example 4 pins are either all read or all write. If it's all independent then you don't need group numbers so they can all be zero

The third is the flags - right now just bit config (can set direction R or W per bit) or GRP_CONFIG - everything with the same group number changes direction at once

wmask is the mask of writable bits (so if you set it to 0 then it's all read).

wdata is the current write value

imask isn't yet used but the idea was for interrupt bits so you could block on the GPIO eventually.

name[] is a name with meaning to the platform - so you can work out in software what is what.

So in the example the Z80 PIO ports are configurable directionally, but the SC129 and console switches are fixed direction.

[Darin755]

This seems like is a bit over my head for the time being. Anyone reading this is more than welcome to work on this but I think I'll wait until I have a little more practice in C

[czarnikjak]

You can control them using fforth. I created these forth words for that:

: PIN_OE DUP 8 * 40014004 + 5 SWAP ! 1 SWAP LSHIFT D0000024 ! ; : PIN_TOGGLE 1 SWAP LSHIFT D000001C ! ; : PIN_HIGH 1 SWAP LSHIFT D0000014 ! ; : PIN_LOW 1 SWAP LSHIFT D0000018 ! ;

All need to be run in hex mode, so issue HEX word before their stack operation is as follows: ( n -- ) Where n is a GPIO pin number you want to operate on. PIN_OE - switch pin under software control and enable it for output PIN_TOGGLE - toggle output of the pin from high to low or from low to high PIN_HIGH, PIN_LOW - self explanatory

[napicella]

Based on the info from EtchedPixels in the answer above, I have made a small change to use the gpio interface with the pico: https://github.com/napicella/FUZIX/commit/44411276edbd01f841ab894f54ba6c7243bb8e68 It's an old issue, but maybe it's useful for someone.

The picoctl binary can be used to turn on/off the pins on the pico, e.g.:

picoctl 7 1

which turns pin 7 on.

[EtchedPixels]

Nice. You appear to return 0 on an invalid or unsupported case though rather than -1 though ? Otherwise looks good and would be nice to add.

[napicella]

Cool. I hadn't originally planned to send a PR because my experience with the project is limited to the few hours I spent making the change. However, your comment encouraged me to go ahead and submit it :)

https://github.com/EtchedPixels/FUZIX/pull/1079