Usage I2C or SPI in a native module?

[saraverbeecke]

Is it possible to use the communication methods I2C or SPI from inside a native module? In an external C module it is possible to include i2c or spi and use it, but will this also work for native modules? (I am just looking for a way to avoid rebuilding the full micropython build when experimenting with c modules)

[jonnor]

The MicroPython build exposes a set of symbols that native modules can use. I think it is defined in py/nativeglue.h/.c.
However, I do not think I2C or SPI is in there. Of course, you could add it, but then your native modules will only work with your very particular MicroPython build.

There might be some generic ways to call into Python code exposed in that table, which could potentially be used in sneaky ways. Like mp_load_global, mp_import_name etc.

You could also include from the native platform modules everything that is needed for I2C/SPI communication. This will be a complete separate usage from what MicroPython does, so one can easily create conflicts that way, but also possible.

A fourth way would be to pass an MicroPython object representing the I2C/SPI (or a custom class which wraps such I/O communication) one into C. Then you should be able to call methods on that object from the native C module. I feel this is conceptually the cleanest approach.

I am not sure if anyone else has done this before however, so be aware that this is likely quite uncharted territory.