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Merge #599

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599: Docs: SW and HW tasks r=korken89 a=AfoHT

Reword and (hopefully) clarify SW and HW tasks

Closes #576


Co-authored-by: Henrik Tjäder <henrik@grepit.se>
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11
book/en/src/by-example/hardware_tasks.md
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@ -14,11 +14,18 @@ start execution in reaction to a hardware event.
Specifying a non-existing interrupt name will cause a compilation error. The interrupt names
are commonly defined by [PAC or HAL][pacorhal] crates.
Any available interrupt vector should work, but different hardware might have
added special properties to select interrupt priority levels, such as the
[nRF “softdevice”](https://github.com/rtic-rs/cortex-m-rtic/issues/434).
Beware of re-purposing interrupt vectors used internally by hardware features,
RTIC is unaware of such hardware specific details.
[pacorhal]: https://docs.rust-embedded.org/book/start/registers.html
[NVIC]: https://developer.arm.com/documentation/100166/0001/Nested-Vectored-Interrupt-Controller/NVIC-functional-description/NVIC-interrupts
The example below demonstrates the use of the `#[task]` attribute to declare an
interrupt handler.
The example below demonstrates the use of the `#[task(binds = InterruptName)]` attribute to declare a
hardware task bound to an interrupt handler.
``` rust
{{#include ../../../../examples/hardware.rs}}

22
book/en/src/by-example/software_tasks.md
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@ -1,19 +1,25 @@
# Software tasks & spawn
Software tasks are tasks which are not directly assigned to a specific interrupt vector.
The RTIC concept of a software task shares a lot with that of [hardware tasks][hardware_tasks.md]
with the core difference that a software task is not explicitly bound to a specific
interrupt vector, but rather a “dispatcher” interrupt vector running
at the same priority as the software task.
They run as interrupt handlers where all software tasks at the
same priority level shares a "free" interrupt handler acting as a dispatcher.
Thus, what differentiates software and hardware tasks are the dispatcher versus
bound interrupt vector.
These free interrupts used as dispatchers are interrupt vectors not used by hardware tasks.
Thus, software tasks are tasks which are not directly assigned to a specific interrupt vector.
The `#[task]` attribute used on a function declare it as a software tasks.
Observe the absence of a `binds = InterruptName` argument to the attribute.
The static method `task_name::spawn()` spawns (starts) a software task and
given that there are no higher priority tasks running the task will start executing directly.
A list of “free” and usable interrupts allows the framework to dispatch software tasks.
All software tasks at the same priority level shares an interrupt handler acting as a dispatcher.
What differentiates software and hardware tasks are the dispatcher versus bound interrupt vector.
The interrupt vectors used as dispatchers can not be used by hardware tasks.
A list of “free” (not in use by hardware tasks) and usable interrupts allows the framework
to dispatch software tasks.
This list of dispatchers, `dispatchers = [FreeInterrupt1, FreeInterrupt2, ...]` is an
argument to the `#[app]` attribute.