Attempt at enabling TinyUSB with microzig

[Kytezign]

Introduction

Figured I'd share my progress so far in enabling tinyusb with microzig.
This compiles tinyusb + pico-sdk headers into a static library and links to the firmware.
The short of it is that this seems to work for RP2040 from my limited testing.

Anyway, I don't think this is ready to be pulled in but I am curious to get some feedback from people who might know what they are doing, I embarked on this as a learning exercise and stumbled through it.

Usage example here: https://github.com/Kytezign/rp2xxx_tusb_lib_build

Please let me know your thoughts.

Structural

Tinyusb submodule

I've added a tinyusb module into the microzig project and added it as a new dependency. That tinyusb sub-project is a build script with a few dependencies beyond just tinyusb including the pico-sdk and newlib (for libc headers pico-sdk & tinyUSB expect).

The submodule pulls in a specific pico-sdk and related changeset if tinyusb (based on what the pico-sdk points to as a git-submodule). I've added a function into microzig build that links a library to the firmware being built and adds the relevant tinyusb headers to the root module for usage.

microzig to tinyusb interface

In addition to that microzig submodule, there is also a new file in the RP2040 hal area which exports a few functions needed by tinyusb. A lot of it is related to debugging tinyusb (perhaps not needed when debug logging is disabled).

In the end I've done pretty limited testing - only CDC & MCS so far. But they've been pretty solid.

Other thoughts

There are a lot of issues currently I'm sure, but the ones I'm most keenly aware of are:

• Generally probably needs to be cleaned up.
• Probably not the most zig focused way to do this - builds a lot of c code and relies on the translate-C feature to bring in the API.

next steps

• pico sdk should be lazy dependency
• create basic, easy to use, cdc interface with magic baud rate setting that will reboot