Allow manual muxing?

[caternuson]

Should we provide some mechanism to manually set the TCA mux? For use cases where this library is being used in conjunction with I2C devices that do not have a CircuitPython driver.

Example:
https://forums.adafruit.com/viewtopic.php?f=60&t=177241

Maybe something like a new channel property?

tca.channel = 3

Could probably add a new class variable to track this also, to provide a read of current channel.

[ladyada]

yah im not against it!

[tannewt]

I don't think you want a second way to change the channel because it'll lead to confusion when using both ways at the same time. Instead, they should just use the appropriate channel object like a busio.I2C for driverless use.

[caternuson]

The current code only switches the mux via try_lock(), which works fine with BusDevice since it calls try_lock() as part of the context manager.
https://github.com/adafruit/Adafruit_CircuitPython_BusDevice/blob/c322a567512277cc94f152b7f359d7c011d51d96/adafruit_bus_device/i2c_device.py#L137

None of the other busio.I2C-like methods do this. So something like this would not do any mux changes:

tca[1].writeto(stuff)
tca[2].writeto(stuff)

One would have to do this:

tca[1].try_lock()
tca[1].writeto(stuff)
tca[1].unlock()
tca[2].try_lock()
tca[2].writeto(stuff)
tca[2].unlock()

For some 3rd party driver that does not use BusDevice, one would have to do this:

sensor = SomeSensor(tca[1])
tca[1].try_lock()
sensor.read_value()
tca[1].unlock()

Could maybe add mux changing code to all the busio.I2C methods, like writeto? Track current channel and only actually mux change if needed, to reduce unnecessary I2C traffic.