GPIO and Python?

Brian Piersel

Hi everyone. I just got my Onion Omega a couple of days ago. I'm a hardware person, but I've been away from software for a while. I'm learning Python, but I'd like to be able to control the GPIO pins directly from my Python code. Is that possible now? If not, is it coming soon?

Chris McCaslin

Im not the offical word, But In my logic The onion omega runs linux, What else runs linux a rasberry pi, a rasberry pi also has gpio's and a Python library.

So based off of that logic I would have to guess that that python library would work. I could be 100% wrong and that library could be pi specific.

The only way to know is to try. Give it a shot and let us know. https://pypi.python.org/pypi/RPi.GPIO

Brian Piersel

@chris-mccaslin Thanks for the suggestion. I wasn't able to install that library, but that may be because I'm not familiar enough with Linux to understand what it needs. I did figure out how to access the ports through the filesystem (/sys/class/gpio). If nothing else gets posted before I get my code packaged nicely, I'll post it for others.

Brian Piersel

I've posted some simple code at https://github.com/BravoPapa/OmegaGPIO on GitHub.

Uwe Stahl209

Is it possible to use Interrups (Falling;Rising;Change) like I know it from Arduino?
I would like to read a rotery-encoder with my onion.io

Thanks in advance.

Kit Bishop

@Uwe-Stahl209 While I know little about Python, I have written some C++ code that provides a library and access program for GPIO control in general - this includes code for catching and acting on interrupts. In case it is of any use for you, while I have posted information on it in this community, the information can best be found at https://github.com/KitBishop/new-gpio - see the documentation in the PDF file there - new-gpio.pdf

Uwe Stahl209

Yes, this I know, but a Python library would be nice as well

A general question: On AVR devices you have "real" interrupts in the sense that special pins provide this functionality.
Is is possible on Omega as well? Or is you code just looking for pin-change with the ordinary read functionality of the pin status?

Yours

Uwe

Brian Piersel

@Uwe-Stahl209 I'm too new to Python and the Omega to add interrupts to my code. I'm not sure that Python can handle interrupts directly, but I could be wrong.

Kit Bishop

@Uwe-Stahl209 The code I referenced above does use "real" interrupts via the use of the Omega library gpio-irq and usage of the /sys/kernel/debug/gpio-irq system file system.

As I said I don't know much about Python and what facilities it provides in connection with interrupts. My guess is that some sort of wrapper code would be needed to provide such functionality (as I am doing and have largely working for Java).

Also, while I don't know what you want to do with the interrupts in Python - i.e. to be able to respond to interrupts within Python code or to just run some Python code when a pin change occurs I would draw you attention to the capability of the new-gpio program to run ANY command in response to an interrupt on a pin. Just use a command like:

new-gpio irq <pin-number> <irq-type> "<command" <optional-debounce>
Where:
- <pin-number> is the relevant pin
- <irq-type> is one of rising or falling or both - depending upon what pin level change you want to trigger the interrupt
- <command> is the command to be executed when the interrupt occurs. So long as you have not stopped interrupt handling on the pin by using the irqstop command to new-gpio for the pin this command will be executed each and every time the interrupt occurs (i.e. the pin undergoes the relevant change)
- <optional-debounce> is a delay time in milliseconds to allow for debounce handling on noisy switches

More information can be found in the documentation in new-gpio.pdf file I supplied.

Uwe Stahl209

Hi!

I want to read a Rotary-Encoder and do some other stuff like sending data via serial output.On Arduino this is normally made with an interrupt pin.
So I don't get it: Can I use your library in Python? Or could I use your program to run a small Python script that somehow sends the rotary-value to my main Pythons script where all the rest is done?

Thanks,

Uwe

Kit Bishop

@Uwe-Stahl209 A few more comments that may assist you:

On the Omega, all GPIO pins are capable of generating interrupts, unlike on the Arduino where there is a limited number of pins that can generate interrupts
Interrupt handling is done on the hardware level and needs C/C++ to handle it. On the Arduino, all code is written in C/C++ and functions are provided that enable you to catch and react to the interrupts. My libnew-gpio code provides similar C/C++ functionality for interrupt handling.
To handle interrupts in any other language (e.g. Python) requires the ability for that language to call the relevant C/C++ (e.g. via wrapper functions) to gain that functionality. I know how to do this for Java (and have done so) but I do not know how to do this for Python - perhaps someone else does.
While as I have said, I don't know much about Python, if, as your message suggests, one Python script can send a message to another Python script, then your suggestion may work. Lets say you have two Python scripts:
- python-a that reads you rotary encoder values and sends a message to python-b indicating that the encoder value has changed
- python-b that can handle messages from python-a

Then something like the following might work:

new-gpio irq <pin-number> <irq-type> "command to run python-a" <debounce-if-required>
run python-b

Jeff Verive

@Brian-Piersel Thanks for the simple-to-use code! I've written a simple Python script that imports your omega_gpio script and controls three of four relays on a relay module to light various combinations of RGB LEDs on a light strip (the script is fairly well documented, so further description is probably not necessary here):

colors.py