Increase max_size in pwm.proto

[brentru]

Expander pins take the form EXP_{I2c_Address}_Pin#. The max_size field for a PWM pin is 6 characters, too small for the component API to support expanders.

This pull request aims to match the size for the pin field used by pwm.proto with digitalio.options and analogio.options.

[lorennorman]

makes sense to make them all the same across protos, but i gotta ask why 64? isn't that much larger than we'll ever need, or should i have a more open mind about that?

[brentru]

@lorennorman 64 is far larger than we'd ever need, yes.

Looking at the expander format, the worst-case is: EXP_0xFF_15 = 11 chars. The worst case for simple pins is 3 ('D21`).

I think a max_size of 16 could be fine, fits a2^n, and could be universally applied across these APIs.

Interested in @tyeth's thoughts, too, though!

[tyeth]

16 sounds sensible. I wondered in future (or now) if we need the i2c bus number included in the pin name (which would fit in 16), as we don't know from this format which bus it will be on.
Presumably we keep a list of initted expanders on device and can therefor easily distinguish by i2c address only, and as our first v2 plan is a single mux for i2c I wonder if the expanders are similarly limited to single use (by intent not by design).

SPI expanders are also a thing, so we might need an ID instead of including all expander info in pin name (SPI has chip select + d/c + optional reset iirc), or some way of looking them up.

[tyeth]

See comment in PR about i2c bus number, and SPI expanders

[brentru]

@tyeth You mean moving from
Expander on bus N: EXP_{ADDR}_{BUS#}_{PIN#}
to:
Expander on bus N: EXP_{ADDR}_{BUS#}_{PIN#}

I'm open to it. In both scenarios' worst-case, we don't hit the 16char limit proposed by this PR.

[tyeth]

@tyeth You mean moving from
Expander on bus N: EXP_{ADDR}_{BUS#}_{PIN#}
to:
Expander on bus N: EXP_{ADDR}_{BUS#}_{PIN#}

I'm open to it. In both scenarios' worst-case, we don't hit the 16char limit proposed by this PR.

Assuming that first example [the FROM] was meant to not include bus number, only the new/proposed variant includes bus, then yeah!

[brentru]

Assuming that first example [the FROM] was meant to not include bus number, only the new/proposed variant includes bus, then yeah!

yep my mistake!

[tyeth]

16 not 64, but looks good and was group reviewed.

[brentru]

@tyeth thanks for the catch, set to 16 across the PR