Add .frequency property to BusIO's I2C

[brentru]

Despite being a kwarg within the constructor (https://circuitpython.readthedocs.io/en/4.x/shared-bindings/busio/I2C.html#busio.I2C), Frequency is not a set-able property.

Would it be possible to set the frequency via a call to i2c.Frequency?

>>> i2c.
deinit          readfrom_into   scan            try_lock
unlock          writeto

Currently, I need to de-init the i2c object, change the frequency, then re-init it with a new frequency.

[tannewt]

Why do you need to change it as you go?

[brentru]

@tannewt The ATECC608A requires the frequency to be decreased to wake the chip up, then increased again when a command needs to be sent.

[tannewt]

Ugh, weird.

[sommersoft]

Ugh, weird.

Agreed. I looked at the sheet, and from what I can tell it's similar to a clock stretch, by holding SCL high for a minimum amount of time to wake from sleep.

Dropping the frequency does seem the best approach. I peeked at the M4 sheet and saw an SCL hold register/property, but that would likely be just as bleh to implement; if it would even address this. Not to mention far less useable across the ecosystem.

[siddacious]

I ran into this indirectly while trying to use an MCP9600 because the MCP9600 library will fail with a cryptic "Input/Output Error" when you use board.I2C or otherwise use the default frequency.

It would be helpful for the library to be able to read the frequency in __init__ and raise an exception if it isn't within an acceptable range (datasheet says 100K, examples use 200K apparently).

@cogliano your input would be appreciated

[dhalbert]

Another example of why this would be useful is here: https://forums.adafruit.com/viewtopic.php?f=60&t=165077.

User wants to use the standard I2C bus for an external sensor that needs 100kHz instead of the standard 400kHz, but board.I2C() provides no way to set the frequency, and the CLUE library has already instantiated board.I2C().

[kevinjwalters]

Would this help those who are running the i2c bus over long cable lengths too?