WIP: Update to use cortex-m-rt

[maxekman]

Hey!

I wanted to test this repo using the cortex-m-rt crate, here is what I came up with to make the blinky example work.

If I clean up all examples and update the readme/instructions, is this something you would like to have contributed?

/Max

(BTW, I'm super new to the Rust world, this is basically the first real changes I have made after reading a lot...)

[jamesmunns]

Hey @maxekman, thanks for the contribution! I think this should be okay, the only concern that I have is that the Nordic Softdevice makes certain assumptions, like which interrupts/interrupt levels are reserved for use by the softdevice, and I am not sure if there is a way to prevent the cortex-m-rt and the nordic softdevice from interfering with eachother.

Here is what I found after a quick search: http://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.s132.sds%2Fdita%2Fsoftdevices%2Fs130%2Fprocessor_avail_interrupt_latency%2Fexception_mgmt_sd.html.

I am actually not too familiar with exactly what/how cortex-m-rt works. It would be nice to see these invariants covered either by code, or by documentation.

[maxekman]

Thanks for the info, I’ll look into how the interrupts works. It may be possible to do something along these lines: https://github.com/japaric/cortex-m-rt/blob/master/examples/device.rs

Another option could be a custom device.x file: https://github.com/japaric/cortex-m-rt/blob/master/device.x

I’m also new to cortex-m-rt, but the library seems minimal enough to have as a dependency.

[maxekman]

When reading more about the interrupts, it seems like only certain priorities are reserved, not the actual interrupt vectors. Does that seem correct?

Cortex-m-rt only seems to deal with the interrupt vectors not the priorities, which would put that level of protection in a HAL for the nrf52. I would guess it would affect implementing the embedded-hal timer traits for example.

[jamesmunns]

Sounds good! I agree that a comment/note in the -sys crate is good enough, and adding the checked restriction (or being careful when implementing) to the hal crate should work.

:+1: from me, let me know when you are ready to merge.

[kamathba]

I'm continuing development on this here: https://github.com/kamathba/nrf52dk-sys/tree/crate-updates

Have some experience with the nordic parts and using this as an exercise to learn some embedded rust. Might try having configs for softdevice / no-softdevice, and extend the example a bit. I actually still need to test on hardware.

[maxekman]

Sounds good! I’ll close this as soon you open a (WIP) PR here.