Support for #[cfg] on #[monotonic] about rtic

[ia0]

here I hope for your help to see how your usecases might be supported

As original author of this issue, my usecase doesn't exist anymore (I moved out of RTIC for different reasons). But for reference, my original usecase was: Use monotonic for defmt::timestamp! and thus only use it when logging is enabled. The cfg would have been something like #[cfg(feature = "defmt")]. And in the init task I would call defmt::timestamp! on monotonics::now(), gated by feature = "defmt".

[David-OConnor]

Scope goes beyond Monotonic. Also applies to Shared and Local. I also would like this.

[korken89]

Hi,

The cfg support in RTIC 1 is broken and on the path of wont-fix.
This usr case is already supported in (under development) RTIC 2, so I think it's best to go for that

[AfoHT]

As an experiment to see what can be done for RTIC 1 I've created #691

The obvious limitation, as shown in examples/cfg-monotonic, is that rtic-syntax does not know what is cfg-ed out, and thus "correctly" refuses code that uses the same type, or same interrupt. Might work for other cases, here I hope for your help to see how your usecases might be supported :)

From the example, showing the rtic-syntax errors

    // A monotonic timer to enable scheduling in RTIC
    #[cfg(feature = "killmono")]
    #[monotonic(binds = SysTick, default = true)]
    type MyMono = Systick<100>; // 100 Hz / 10 ms granularity

    // Not allowed by current rtic-syntax:
    // error: `#[monotonic(...)]` on a specific type must appear at most once
    //   --> examples/cfg-monotonic.rs:23:10
    //    |
    // 23 |     type MyMono = Systick<100>; // 100 Hz / 10 ms granularity
    //    |          ^^^^^^
    // #[monotonic(binds = SysTick, default = true)]
    // type MyMono = Systick<100>; // 100 Hz / 10 ms granularity

    // Not allowed by current rtic-syntax:
    // error: this interrupt is already bound
    //   --> examples/cfg-monotonic.rs:31:25
    //    |
    // 31 |     #[monotonic(binds = SysTick, default = true)]
    //    |                         ^^^^^^^
    // #[monotonic(binds = SysTick, default = true)]
    // type MyMono2 = DwtSystick<100>; // 100 Hz / 10 ms granularity