Enable optional RTIC support for Xiao_m0

[kadencartwright]

Summary

It would be nice if the seeduino xiao_m0 supported RTIC. I'm a bit of a rust newbie, so maybe this is a naive fix¿? but it seems as simple as adding a feature flag to enable the rtic feature in the hal dependency.

Checklist

• CHANGELOG.md for the BSP or HAL updated
• All new or modified code is well documented, especially public items
• No new warnings or clippy suggestions have been introduced (see CI or check locally)

[TDHolmes]

I think this is the right thing to do, but could you add an RTIC example as well? You should be able to copy/paste an existing M0 one. I think feather_m0 has one?

[kadencartwright]

@TDHolmes yea, I'll do that!

[kadencartwright]

I had to update the Hal to dependency in Cargo.toml to reference the repo version using path = ... because a Monotonic related trait bound was not being satisfied otherwise. Feather M0 does the same in it's repo, which I would assume for this same reason.

[bradleyharden]

@kadencartwright, we actually have a tier system for the BSPs. Tier 1 boards are kept up-to-date with master and must be updated with every change to the HAL. Tier 2 boards, on the other hand, are tied to a specific release of the HAL. We did this because it was becoming too much of a burden to update all of the BSPs for every change to the HAL.

Moving to a path = ... dependency would make this a Tier 1 board. But unfortunately, I don't think we want anymore Tier 1 boards at the moment. It sounds like you need an unreleased feature of the HAL to make this work, so I don't think we can merge this until we release v0.15. Fortunately, I don't think that is too far away (see #570).

[kadencartwright]

@bradleyharden Ah, I see. Makes sense to me. What's the best thing to do with this PR for the time being -- should I just leave it here as is or is there something else more helpful I can do with it?

[TDHolmes]

I think we just need to wait on this one until v0.15 is released

[TDHolmes]

Make changes now that there has been a HAL release

[bradleyharden]

Pinging @kadencartwright. Do you want to finish this up now that #570 has been merged?