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Idle: Switch to NOP instead of WFI

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Add example how to get old WFI behaviour
This commit is contained in:
Henrik Tjäder 2021-12-14 21:52:57 +01:00
parent 3741d431be
commit 8c8f7f12c3
6 changed files with 77 additions and 13 deletions
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31
book/en/src/by-example/app_idle.md
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@ -8,11 +8,6 @@ When present, the runtime will execute the `idle` task after `init`. Unlike
`init`, `idle` will run *with interrupts enabled* and it's not allowed to return
so it must run forever.
When no `idle` function is declared, the runtime sets the [SLEEPONEXIT] bit and
then sends the microcontroller to sleep after running `init`.
[SLEEPONEXIT]: https://developer.arm.com/docs/100737/0100/power-management/sleep-mode/sleep-on-exit-bit
Like in `init`, locally declared resources will have `'static` lifetimes that are safe to access.
The example below shows that `idle` runs after `init`.
@ -25,3 +20,29 @@ The example below shows that `idle` runs after `init`.
$ cargo run --target thumbv7m-none-eabi --example idle
{{#include ../../../../ci/expected/idle.run}}
```
By default the RTIC `idle` task does not try to optimise for any specific targets.
A common useful optimisation is to enable the [SLEEPONEXIT] and allow the MCU
to enter sleep when reaching `idle`.
>**Caution** some hardware unless configured disables the debug unit during sleep mode.
>
>Consult your hardware specific documentation as this is outside the scope of RTIC.
The following example shows how to enable sleep by setting the
[`SLEEPONEXIT`][SLEEPONEXIT] and providing a custom `idle` task replacing the
default [`nop()`][NOP] with [`wfi()`][WFI].
[SLEEPONEXIT]: https://developer.arm.com/docs/100737/0100/power-management/sleep-mode/sleep-on-exit-bit
[WFI]: https://developer.arm.com/documentation/dui0662/b/The-Cortex-M0--Instruction-Set/Miscellaneous-instructions/WFI
[NOP]: https://developer.arm.com/documentation/dui0662/b/The-Cortex-M0--Instruction-Set/Miscellaneous-instructions/NOP
``` rust
{{#include ../../../../examples/idle-wfi.rs}}
```
``` console
$ cargo run --target thumbv7m-none-eabi --example idle-wfi
{{#include ../../../../ci/expected/idle-wfi.run}}
```