Implemented asyncio SPI for rp2040 & rp2350

[kamocat]

Implements asynchronous SPI on rp2040 and rp2350.
Created with the help of an LLM - please let me know if specific cleanup is needed.

This has been tested on a rp pico 2 W. The current tests are pretty basic:

• async_spi.py verifies that SPI can send long transfers without blocking
• spi_mode_test.py checks that the phase and polarity options work as expected

We have discussion of async busio over in #10856. What I am looking for here is discussion around

• style and documentation
• implementation performance and robustness
• tests methods and gaps

[dhalbert]

Thank you for working on this! I have some minor comments and some higher-level comments.

[dhalbert]

In MicroPython, there is an asyncio.ThreadSafeFlag and also asyncio.event. Tjey are not in CPython asyncio, so I removed it from CircuitPython's asyncio. However, it would be worth looking at them to see if their semantics are similar to what you are doing here. They could be added as CircuitPython-specific classes if they would also be useful to someone writing CircuitPython async code.

[tannewt]

This is what I came up with for a standard awaitable object from the native core of CP. There is similar discussion about how to do this in CPython here: https://discuss.python.org/t/adding-a-c-api-for-coroutines-awaitables/22786/16

The third-party library for doing it is here too: https://pyawaitable.zintensity.dev/

[tannewt]

Thank you for working on this! I'm really excited to bring more async to CP. I think it'll really make it easy and performant to do the multiple things.

I've got a restructuring suggestion to remove the data packing and unpacking. In short, make another function specific macro to handle it for you. My example only showed the one argument case, yours is the kwarg case.

[tannewt]

My intention was to introduce corresponding ASYNC macros to match the SYNC ones from MP. This will remove the need to pack and unpack all of the args because you can use a slightly different awaitable for each one. (Or one that has all of the args at the end of a variable length struct.)

Suggested change

	static MP_DEFINE_CONST_FUN_OBJ_KW(abusio_spi_write_obj, 1, abusio_spi_write);
	static CIRCUITPY_DEFINE_ASYNC_FUN_OBJ_KW(abusio_spi_write_obj, 1, abusio_spi_write);

The macro will then assume there are corresponding abusio_spi_write (which calls start), common_hal_abusio_spi_write_cancel and common_hal_abusio_spi_write_end. There is a subtle behavior thing here because CPython validates arguments once the object is awaited, not before. That's why the awaitable is returned before validating args.

[kamocat]

Thanks for the feedback!
I fixed the easy stuff and marked as resolved.
The awaitable constructors will take some more consideration.

[tannewt]

Thanks for continuing work on this. I'm back from vacation so please let me know how I can help get you figure out the constructor stuff.

[kamocat]

Welcome back!

I have been tied up at work and have not made tangible progress.

I did read up on the ThreadSafeFlag, which is written in Python but based on IoBase. I think instead it would make more sense to treat the whole SPI object as a stream. I'm not sure how that would work with the chip select, but this seems like a pretty big paradigm shift that may be best left for later.

I not yet looked at your suggestion to allow named arguments in the macros. Any help here would be appreciated.

[tannewt]

I not yet looked at your suggestion to allow named arguments in the macros. Any help here would be appreciated.

My intent would be to create ASYNC versions of these macros:

circuitpython/py/obj.h

Lines 377 to 386 in 47a9a55

	// These macros are used to declare and define constant function objects
	// You can put "static" in front of the definitions to make them local
	#define MP_DECLARE_CONST_FUN_OBJ_0(obj_name) extern const mp_obj_fun_builtin_fixed_t obj_name
	#define MP_DECLARE_CONST_FUN_OBJ_1(obj_name) extern const mp_obj_fun_builtin_fixed_t obj_name
	#define MP_DECLARE_CONST_FUN_OBJ_2(obj_name) extern const mp_obj_fun_builtin_fixed_t obj_name
	#define MP_DECLARE_CONST_FUN_OBJ_3(obj_name) extern const mp_obj_fun_builtin_fixed_t obj_name
	#define MP_DECLARE_CONST_FUN_OBJ_VAR(obj_name) extern const mp_obj_fun_builtin_var_t obj_name
	#define MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(obj_name) extern const mp_obj_fun_builtin_var_t obj_name
	#define MP_DECLARE_CONST_FUN_OBJ_KW(obj_name) extern const mp_obj_fun_builtin_var_t obj_name

That way you use almost the same pattern between the two. My example only covered the one argument case but the others should be the same formula with slightly different function signatures.