v6.0.0

With the release of tock-registers 0.7.0, the main dependency of this crate, register-rs, became obsolete. So we exchanged this crate's dependency to tock-registers only.

register-rs always was a wrapper around tock-registers, adding the same semantics and interfaces that tock-registers provided for MMIO to CPU registers as well. With 0.7.0, this can be achieved with tock-registers alone. Depending on tock-registers alone now is also a win for the cortex-a crate itself, because tock-registers is better and more regularly maintained.

Please take notice of the new usage guidelines in the README when adding this crate as a dependency to your project.

The switch to tock-registers obviously was a breaking change. So while we were at it, two other things were changed:

1. cortex_a::regs::* is now cortex_a::registers::*.
2. barrier instructions were moved inside the asm path: cortex_a::barrier became cortex_a::asm::barrier.