Swap to USB pad trait for thumv7em targets

[ryankurte]

Supersedes #362, related to #363

An alternative approach that:

• Introduces UsbPadD{m,p} marker traits for implementation over USB pads
• Implements UsbPadD{m, p} marker trait over GPIO v1 and v2 types
• Adds <Dm, Dp> generic arguments to UsbBus and other types that default to existing (v1) pad types

This allows USB pad types to be overridden with something like:

// Override default USB GPIO types to v2
pub type UsbBus = atsamd_hal::usb::UsbBus<Pin<gpio::PA24, Alternate<H>>, Pin<gpio::PA25, Alternate<H>>>;

While (hopefully) maintaining compatibility with previous users of UsbBus and v1 GPIOs.

[twitchyliquid64]

Awesomesauce!

[twitchyliquid64]

I thought you looked familiar! I was at Kawaiicon last year + distantly work with Grace's team! 😀

Small world ^^

[ryankurte]

hah, wild how small it is sometimes ^_^

[twitchyliquid64]

(WRT the PR, LGTM but as mentioned in #363 (comment) I'll wait till @bradleyharden has had a chance to look at it)

[bradleyharden]

@ryankurte,

From #362:

I couldn't find an .into() bound that would work between v1 and v2, i might have just missed it though?

I added an implementation of From in both directions between v1 and v2, but it missed the cut for the v0.11 release. @twitchyliquid64 just released v0.12, which now includes it. Instead of your current approach, you could make the new function generic with bounds like Dm: Into<Pin<PA24, AlternateH>>. That should be backwards compatible and accept both versions.

If you want to stick with a new trait for other reasons, you might want to make crate::typelevel::Sealed a super trait. That way, users won't be able to implement your new trait themselves, even if they try.

[twitchyliquid64]

The GPIO trait changes are merged in - is this ready to go @ryankurte / @bradleyharden or should we track one of the newer types?

[ryankurte]

I'd be happy either way, just haven't yet had a moment to revisit / rebase to use the .into() approach, whatever y'all prefer?

[ryankurte]

Went with the sealed approach which is a bit more complex but... also kindof nice in that you can click the trait and see the types it's implemented over more directly in the docs than looking via .into().

[twitchyliquid64]

Thanks! Looks good to merge once we get CI green:

error[E0432]: unresolved import `cortex_m_0_6::peripheral::itm`
  --> /home/runner/.cargo/registry/src/github.1485827954.workers.dev-1ecc6299db9ec823/cortex-m-0.5.10/src/peripheral/mod.rs:91:46
   |
91 | pub use cortex_m_0_6::peripheral::{cbp, fpb, itm, tpiu};
   |                                              ^^^ no `itm` in `peripheral`

[twitchyliquid64]

Hmmm i may have to fix this on master

lmao wut
Rerunning CI, lets see if it was transient

[twitchyliquid64]

According to the embedded rust chat something mad derped in cortex-m, that might have been the issue

Fixed in rust-embedded/cortex-m#317