Implement support for XipCS1 pin function.

[Altaflux]

Implement support for XipCS1 pin function which is necessary to implement support for external ram or flash.

Note: The rp235x-pac is missing function select definition for XipCS1:
https://github.com/rp-rs/rp235x-pac/blob/main/svd/RP2350.yaml#L321

But FUNCSEL_A::GPCK has the same value (9). We should add a variant specific for XipCS1.

[Altaflux]

Hey @thejpster let me know if there is anything else you would like to be changed or if you would like to wait until rp-rs/rp235x-pac#7 gets addressed.

thanks

[thejpster]

Looks ok. I'd like to try it though. Do you have an example?

[Altaflux]

I am not sure how to test it without a Pimoroni Pico Plus 2. I use this functionality on my project to enable its PSRAM.
Here is the relevant code, I know for a fact that not setting the pin 47 to the correct function will not let PSRAM be initialized:

https://github.com/Altaflux/gb-rp2350/blob/main/src/main.rs#L375
https://github.com/Altaflux/gb-rp2350/blob/main/src/hardware/psram.rs

If you have a Pimoroni Pico Plus 2 I am more than happy to build a sample project for the PSRAM only for you to test if you want to.

[thejpster]

If you have a Pimoroni Pico Plus 2

I do. I used it to run the Neotron OS demo at RustConf, as it happens.

[Altaflux]

@thejpster sorry for the delay, got caught up with other work.
I have built a sample project that uses FunctionXipCs1 to enable the usage of the PSRAM module of a Pimoroni Pico Plus 2.
It uses the PSRAM as the Heap for the example code (based on the alloc.rs example from rp235x-hal-examples).

https://github.com/Altaflux/rp2350-psram-test

[thejpster]

The LED is blinking away! Gosh I wish we had probe-rs and defmt working though.