embedded support via Zephyr

[sadguitarius]

Hi @jcelerier, I'm really excited about the recent progress with this library! I was thinking about the possibility of getting it to work on embedded platforms, and it occurred to me that Zephyr RTOS might be a good fit, since it already has some Linux-like features built in and some MIDI support as well. Do you have any thoughts on how best to integrate new backends into libremidi?

[jcelerier]

Hello! oh that would be amazing! I have some ESP32s and raspberry pi picos on which I could try it.
Adding a new backend is fairly straightforward: there's a lot of existing back-ends to start from.

https://github.com/celtera/libremidi/tree/master/include/libremidi/backends

The steps are:

0/ Add the necessary steps to the build system, I try to have one file per back-end here: https://github.com/celtera/libremidi/tree/master/cmake referenced here: https://github.com/celtera/libremidi/blob/master/CMakeLists.txt#L59

1/ Add an enum here: https://github.com/celtera/libremidi/blob/master/include/libremidi/api-c.h and here: https://github.com/celtera/libremidi/blob/master/bindings/python/pylibremidi.cpp#L195

2/ Add a new backend here: https://github.com/celtera/libremidi/tree/master/include/libremidi/backends

I recommend starting from a copy-paste of the JACK one which is very straightforward.

3/ Add a new header like this one: https://github.com/celtera/libremidi/blob/master/include/libremidi/backends/jack.hpp which centralizes the information of the backend

4/ Add the back-end here so that the library knows about it when enumerating backends: https://github.com/celtera/libremidi/blob/master/include/libremidi/backends.hpp

5/ Add the new configuration types here: https://github.com/celtera/libremidi/blob/master/include/libremidi/configurations.hpp

And you should be good to go :)

[sadguitarius]

Great, thank you! That seems pretty straightforward. I'm working on ESP32 and Picos as well. I haven't tried mixing C++ with Zephyr but I think with the C header it shouldn't be too difficult. I'll let you know once I get it going.

[jcelerier]

c++20 should work on Zephyr AFAIK!

[sadguitarius]

Awesome! Honestly I hadn’t even looked into it yet

[groutoutlook]

hi, how are we doing with embedded support in general?

EDIT: asking that since this MIDI 2.0 C++ Library also have some works toward embedded, and currently looking at commits I think that will be a better place for embedded baremetal developer to start on...

[groutoutlook]

oh I see, that's why I see 6.0 in milestones.

EDIT: yeah for baremetal guys we badly need a header to parse the bytestream/embedded files sent from PC to device, or devices to devices there. I actually want to care less about MIDI and go straight to convert those button to sound/actuator..

[jcelerier]

gave a shot at it in #206 ; that said, I think most of the time you will be happy just using the state machine classes: https://github.com/celtera/libremidi/blob/master/include/libremidi/detail/midi_stream_decoder.hpp and feeding them bytes.

[groutoutlook]

Thanks for the pointer. For MIDI to work I have cranked up -std=gnu++2c, hope there wont be weird error.

[jcelerier]

should work, i build some code that involves libremidi (https://ossia.io) with c++26 here :)

[jcelerier]

also added: https://github.com/celtera/libremidi/blob/master/tests/unit/midi_stream_decoder.cpp which shows how to use the midi stream parsers (midi 1 and midi 2) directly, for embedded use-cases this will really reduce binary size since you don't really need all the observation and API abstraction infrastructure (unless you want to share the same code between MCUs and desktop).