Core Cortex-R crates

[japaric]

This issue is for tracking progress on developing cortex-r-* crates that will
be maintained by the WG.

The current plan is

• Make the cortex-r-rt crate more generic and move it into the WG org. Issue
  Supporting more use cases paoloteti/cortex-r-rt#1 is being used to discuss how to make that crate more
  generic.

• Move the dcc and panic-dcc crates pretty much as they are into the WG
  org. PR add cortex-r, dcc and panic-dcc to crates maintained by the cortex-r team #287 needs to be approved by @rust-embedded/cortex-r before we make
  the transfer.

• Create an empty cortex-r repository in the org and progressively expand
  its API surface. When we are happy with the API we'll publish it on crates.io.

The motivation for starting from scratch is two-fold: we can enforce that the
crate always compiles on stable (with its default feature set) and we can have
@rust-embedded/cortex-r review each piece of API that gets added to it.

cc @rust-embedded/cortex-r @kenkeiter

[eddyp]

Is this supposed to support both v7r and v8r profiles? I.e. are r52 and later v8 cores the only one targeted?

[paoloteti]

@eddyp r52 is available under NDA or for approved partners only. So I prefer to wait a bit.
@japaric I’ll back tomorrow at office and I’ll review your proposal. Thanks

[japaric]

@eddyp v8r is not suppoted in rustc atm. The crates can't support something that rustc doesn't support. I don't think it would be too much work to update the crates to support v8r, when available, though.

[eddyp]

@japaric I understand. I don't have experience with older r-s, but I have access at work to an r52 implementation, and was thinking about experimenting with rust, that's why I was interested in r52.

[japaric]

Triage:

Move the dcc and panic-dcc crates pretty much as they are into the WG
org.

The arm-dcc repository has been moved into the org: https://github.com/rust-embedded/arm-dcc

---

@eddyp if you are up to it you can make a PR to add a v8-r target to rustc. You can use PR rust-lang/rust#56000 as a reference.

[paoloteti]

I just released silicon-cr4 that is a collection of workarounds for few silicon errata on Cortex-R4/R4F MCUs. I use it on my TMS570 BSP I started to port to beta/stable. So if you all can review and if everything is ok may be We can decide to move the repo under the rust-embedde/cortex-r umbrella.