I gently want to suggest that we revisit the idea of board.I2C(), board.UART(), board.SPI() as implemented recently in PR's #842, #844, and #845. I think it introduces a new, somewhat weak, shortcut API that doesn't work out well if you need to change your program to use different pins. I suggest instead that we add defaults to the pin args for busio.I2C(), busio.UART(), and busio.SPI().

I'll take board.I2C() as an example. It returns a singleton instance that is busio.l2C(board.SCL, board.SDA). So now how might it be used? Well, instead of

i2c = board.I2C(board.SCL, board.SDA)
...
i2c.write_to(...)

you can do:

board.I2C().write_to(...)

But suppose you later decide you want to use different pins? The singleton call doesn't take pin args, so you don't do this (which is too verbose anyway):

board.I2C(board.D0, board.D1).write_to(...)    # DOESN'T WORK

Instead you need to go back to the original way and rewrite it as i2c = busio.I2C(board.D0, board.D1) You have to change all the uses of board.I2C() throughout your program to the first way.

You might argue that instead one should just assign the value:

i2c = board.I2C()
...
i2c.write_to(...)

but in that case, I think the better API is to have busio.I2C() have default args (as suggested by @deshipu in #340 (comment), and @ladyada in an offline discussion), i.e. the equivalent of:

    def I2C(scl=board.SCL, sda=board.SDA, *, frequency=400000):

so that you can just do:

i2c = busio.I2C()     # Note busio, not board.
                      # Will use the defaults of board.SCL and board.SDA.

It's true you lose the convenience of the singleton, but you don't need to specify the pin names or remember their order, and you don't need to import board (vs. not having to import busio).

The motivation for the original is issue #340, which was much more about adafruit_bus_device than about providing a convenience singleton. Note also that (usually?) busio.SOMEBUS is implemented to invisibly fall over to bitbangio.SOMEBUS if busio.SOMEBUS doesn't exist on the particular board.

Tagging @matt-land, @tannewt, @deshipu, @caternuson, and @tannewt for comments.

(This bothered me enough that it woke me up. On the other hand, my middle-of-the-night thoughts might not be so coherent.)

Add default buses to board #372

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