Form a Cortex-R team?

[japaric]

We have a Cortex-M team focused on bare metal (no_std) development for
Cortex-M devices.

Should we make a similar Cortex-R team focused on bare metal development for
Cortex-R devices? This team would be involved in improving the developer
experience in this area, collecting or writing resources on the topic, and
maintaining and developing widely used crates.

I don't know of open source projects that use Cortex-R devices but I know people
that are working with them.

Opportunities I see:

• Identify what targets, other than armebv7r-none-eabihf, need to be added to
  the compiler to support all the existing Cortex-R devices.

• Enable builds of a rust-std component for the armebv7r-none-eabihf target.

• Create core crates like cortex-m and cortex-m-rt but for the Cortex-R
  architecture.

• Push for a stable core::arch::arm module (see Stable assembly operations #63) to make the future
  cortex-r crate (see cortex_m::asm module) work on stable w/o depending on GCC.

Who would be interested in forming part of such team?

cc @Lakier15 @paoloteti

[paoloteti]

Yes I'd like to join the team.

May be We can add a 'little-endian' variant (armv7r) for all TI RMxx devices and a soft-float variant.
But, even if hard-float is optional on R-profile, all devices I know are hard-float.

In the future We can add a v8r target. Yes, in the future, not now becase v8r is really new and not in the market yet.

Crates like cortex-m/cortex-m-rt can be derived from my work on TMS570

[japaric]

Done in #199.