How are MICROPY_HW_PIN_EXT_COUNT being defined / used?

[bstin]

Firstly let me describe my problem. I've run out of pins so I'm using a I2C IO Expander to be able to access more pins. However this has the problem that these "new pins" are not accessible via machine.Pin module.

This got me to researching how is this being handled on boards like PICO_W where there are special pins like LED / EXT_GPIO0 which is in reality being controlled via the wireless controller (SPI?). I'm not a good enough C programmer to fully understand how its working....I mean I get the basics but not sure how to add my own....

In essence, I'd like to define EXT_GPIO3 (the next available), and have that controlled via a call to I2C IO expander.

Would be a really great feature if I could do this all from micropython without needing to write any custom C code. I realize there would be a performance hit not doing it in C, but in my usecase it wouldn't matter too much.

[andrewleech]

You certainly can write i2c gpio expander interfaces in pure python, here's one for example: https://github.com/mcauser/micropython-mcp23017

It's got a few different interfaces described, the virtual pin one I believe is intended to work similar to a machine.Pin object.

You simply create your pin object using the library functions rather than machine.Pin then pass that created object to whatever would normally be given a "real" pin object.

[bstin]

Thank you @andrewleech - In fact I'm using an MCP23017 as IO expander...however I was unaware that I could pass the mcp.pin as if it was a machine.pin (in hindsight its obvious).

Having said that, it seems like it would be really useful if we could do something like this:

@micropython.Pin(name=EXT_GPIO3)
def get():
    //i2c get methods go here

def set():
    //i2c set methods go here

And then later you could just do pin=Pin('EXT_GPIO3') and have a "virtual pin" to use anywhere you need.

Maybe that is already possible by subclassing Pin class??