Adds new error message for SAMD busio UART RX buffer size

[AdamCummick]

Raises an error when a busio UART "receiver_buffer_size" is not a multiple of 4. Behavior referenced in issue #3901 and tested using same setup: SAMD51 and CircuitPython 6.0.0

Example:

import board
import busio

buffer_len = 5 # will fail unless this is a multiple of 4
port1 = busio.UART(board.TX1, board.RX1, baudrate=115200, receiver_buffer_size=buffer_len)

Will raise an error with the message: ValueError: Invalid RX buffer size of 5, must be a multiple of 4

[dhalbert]

Thanks for noticing this. I think we should explore the causation behind the error: whether SAMD actually requires this or we are doing something wrong somewhere.

We suggest creating a branch in your forked repo, instead of changing your own main. That causes your main to get out of sync with the upstream main. See https://learn.adafruit.com/contribute-to-circuitpython-with-git-and-github/always-work-on-a-branch.

[dhalbert]

See non-review comment as well.

[dhalbert]

This is a long message, and we need to save space. We don't need to print out the input argument, so I'd suggest this (using the argument name in shared-bindings/busio/UART.c):

Suggested change

	mp_raise_msg_varg(&mp_type_ValueError, translate("Invalid RX buffer size of %d, must be a multiple of 4"), receiver_buffer_size);
	mp_raise_ValueErorr( translate("receiver_buffer_size must be a multiple of 4"), receiver_buffer_size);

[AdamCummick]

Thanks for noticing this. I think we should explore the causation behind the error: whether SAMD actually requires this or we are doing something wrong somewhere.

It looks like it's based on the requirements of the ATMEL hal ringbuffer: https://github.com/adafruit/asf4/blob/84f56af13292d8f32c40acbd949bde698ddd4507/samd51/hal/utils/src/utils_ringbuffer.c#L53

Looks like my assumptions were wrong anyhow, power of 2 instead of multiples of 4.

[dhalbert]

It looks like it's based on the requirements of the ATMEL hal ringbuffer: https://github.com/adafruit/asf4/blob/84f56af13292d8f32c40acbd949bde698ddd4507/samd51/hal/utils/src/utils_ringbuffer.c#L53

Looks like my assumptions were wrong anyhow, power of 2 instead of multiples of 4.

We might consider rounding up to the nearest power of 2, and changing the documentation to note that the buffer size might be bigger. And/or noting that some platforms might have specific requirements.