stm: enable RGBMatrix

[jepler]

Testing performed: on stm32f405 feather, drove a 16x32 display.

As far as going to other stm microcontrollers, the main sticking point is the timer. I statically allocated TIM6 for this purpose (because TIM6 is not associated with any PWM pins); we need to have a "timer allocator" in the stm port, which @tannewt and @hierophect have both commented on. Not even the whole F4 family has TIM6, so this enables only STM32F405xx for now.

[ladyada]

i can test once you need a verifier!

[jepler]

@ladyada Give this a whirl now. The artifacts are ready -- looks like your download link is https://github.com/adafruit/circuitpython/suites/642483319/artifacts/5391473

[jepler]

Leaving this in Draft state until the PR in protmatter gets merged, adafruit/Adafruit_Protomatter#6

[hierophect]

So what's the distinction between rgbmatrix and protomatter again? Are we transitioning to just one, or using both for different things?

[hierophect]

Also @ladyada should I pick one of these up so I can test it when reworking this basic vs general-purpose timer issue?

[dhalbert]

So what's the distinction between rgbmatrix and protomatter again? Are we transitioning to just one, or using both for different things?

Protomatter is the name of the original Arduino library, which forms the core implementation in Cpy. That name is not going to change. The user-visible interface was called protomatter in CPy, too, but was renamed to rgbmatrix for clarity.

[ladyada]

@hierophect yah a 32x32 is plenty large!

[jepler]

I retitled the PR for clarity.

[jepler]

@ladyada whoops, wiring details:

matrix = rgbmatrix.RGBMatrix(
    width=64, height=32, bit_depth=1,
    rgb_pins=[board.D13, board.D12, board.D11, board.A4, board.A5, board.D6],
    addr_pins=[board.A0, board.A1, board.A2, board.A3],
    clock_pin=board.D5, latch_pin=board.D9, output_enable_pin=board.D10, doublebuffer=False)

[jepler]

Testing performed: simple scroller on stm32f405 feather, and re-tested simple scroller on nrf52840 feather

[hierophect]

@jepler This looks good to me generally, but I've got questions about your addition of the common-hal functions which imply iterable pins, which I've tried to avoid for this port.

[hierophect]

Looks good to me

[tannewt]

Looks good to me too.

[ladyada]

@jepler ok finally got around to testing on the stm32f405 and works great :) please add the feather fritzing documentation in the next week or two to the guide