Dynamically Loadable Module

Published on 2019-12-26 in Stage, a Tile and Sprite Engine.

MicroPython 1.12 is released, and the new release includes an interesting feature: the .mpy modules can now contain native code compiled with C or any other language that produces standard object files. Of course such .mpy files are then architecture-specific. This is great news for the stage library, because it means that you won’t need to compile it into the firmware anymore — you should be able to just copy the .mpy file to the filesystem and import it as any other Python module.

But how to actually do this? There is very brief documentation at  http://docs.micropython.org/en/latest/develop/natmod.html  and there are some examples at https://github.com/micropython/micropython/tree/master/examples/natmod  — not much to go by, but I will try anyways.

The first, naive, try failed badly. Just removing the module initialization code and replacing it with mpy_init with equivalent functions is maybe enough for the factorial example, but not for my library — in particular, the dicts that act as namespaces for the two classes that I defined fail to compile, because they would normally go to fixed code, and that is not supported with dynamic loading. So I started to dig through the examples, and figured out from the framebuf and regexp modules how to dynamically declare those classes. So far so good. Now the mpy_ld.py script crashes. Great. After naively fixing the script, the compilation still fails, because it can’t locate the mp_obj_get_array function. Which is super-weird, because it has no problem locating other functions from the py/obj.c file.

My code is available  https://github.com/python-ugame/micropython-stage/tree/master/mpy  if anybody wants to give it their try.

At this point I’ve given up. I might try it again after the next release, maybe this feature will be more ready for actual use.