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Update tips on Monotonic implemenations

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book/en/src/by-example/tips_monotonic_impl.md
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# Implementing a `Monotonic` timer for scheduling # Implementing a `Monotonic` timer for scheduling
The framework is flexible because it can use any timer which has compare-match and optionally supporting overflow interrupts for scheduling. The single requirement to make a timer usable with RTIC is implementing the [`rtic-time::Monotonic`] trait. The framework is flexible because it can use any timer which has compare-match and optionally supporting overflow interrupts for scheduling. The single requirement to make a timer usable with RTIC is implementing the `rtic-time::Monotonic` trait.
For RTIC 1.0 and 2.0 we instead assume the user has a time library, e.g. [`fugit`] or [`embedded_time`], as the basis for all time-based operations when implementing `Monotonic`. These libraries make it much easier to correctly implement the `Monotonic` trait, allowing the use of For RTIC 1.0 and 2.0 we instead assume the user has a time library, e.g. [`fugit`] or [`embedded_time`], as the basis for all time-based operations when implementing `Monotonic`. These libraries make it much easier to correctly implement the `Monotonic` trait, allowing the use of almost any timer in the system for scheduling.
almost any timer in the system for scheduling.
The trait documents the requirements for each method, and for inspiration The trait documents the requirements for each method. There are reference implementations available in [`rtic-monotonics`](https://github.com/rtic-rs/rtic/tree/master/rtic-monotonics/src) that can be used for inspriation.
there is a reference implementation based on the `SysTick` timer available on all ARM Cortex M MCUs.
- [`Systick based`], runs at a fixed interrupt (tick) rate - with some overhead but simple and provides support for large time spans - [`Systick based`], runs at a fixed interrupt (tick) rate - with some overhead but simple and provides support for large time spans
- [`RP2040 Timer`], a "proper" implementation with support for waiting for long periods without interrupts. Clearly demonstrates how to use the `TimerQueue` to handle scheduling.
- [`nRF52 timers`] implements monotonic & Timer Queue for the RTC and normal timers in nRF52's
## Contributing
Contributing new implementations of `Monotonic` can be done in multiple ways:
* Implement the trait behind a feature flag in [`rtic-monotonics`], and create a PR for them to be included in the main RTIC repository. This way, the implementations of are in-tree, and RTIC can guarantee their correctness, and can update them in the case of a new release.
* Implement the changes in an external repository.
<!-- TODO: remove 1.0.x examples? -->
# V1.0.x
Here is a list of `Monotonic` implementations for RTIC 1.0: Here is a list of `Monotonic` implementations for RTIC 1.0:
@ -27,3 +36,6 @@ If you know of more implementations feel free to add them to this list.
[`Nordic nRF52 series RTC`]: https://gist.github.com/korken89/fe94a475726414dd1bce031c76adc3dd [`Nordic nRF52 series RTC`]: https://gist.github.com/korken89/fe94a475726414dd1bce031c76adc3dd
[`Systick based`]: https://github.com/rtic-monotonics [`Systick based`]: https://github.com/rtic-monotonics
[`DWT and Systick based`]: https://github.com/rtic-rs/dwt-systick-monotonic [`DWT and Systick based`]: https://github.com/rtic-rs/dwt-systick-monotonic
[`rtic-monotonics`]: https://github.com/rtic-rs/rtic/blob/master/rtic-monotonics
[`RP2040 Timer`]: https://github.com/rtic-rs/rtic/blob/master/rtic-monotonics/src/rp2040.rs
[`nRF52 timers`]: https://github.com/rtic-rs/rtic/blob/master/rtic-monotonics/src/nrf.rs