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63 lines
2.2 KiB
Markdown
63 lines
2.2 KiB
Markdown
# Software tasks
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RTFM treats interrupt and exception handlers as *hardware* tasks. Hardware tasks
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are invoked by the hardware in response to events, like pressing a button. RTFM
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also supports *software* tasks which can be spawned by the software from any
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execution context.
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Software tasks can also be assigned priorities and are dispatched from interrupt
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handlers. RTFM requires that free interrupts are declared in an `extern` block
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when using software tasks; these free interrupts will be used to dispatch the
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software tasks. An advantage of software tasks over hardware tasks is that many
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tasks can be mapped to a single interrupt handler.
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Software tasks are declared by applying the `task` attribute to functions. To be
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able to spawn a software task the name of the task must appear in the `spawn`
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argument of the context attribute (`init`, `idle`, `interrupt`, etc.).
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The example below showcases three software tasks that run at 2 different
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priorities. The three tasks map to 2 interrupts handlers.
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``` rust
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{{#include ../../../examples/task.rs}}
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```
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``` console
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$ cargo run --example task
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{{#include ../../../ci/expected/task.run}}```
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## Message passing
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The other advantage of software tasks is that messages can be passed to these
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tasks when spawning them. The type of the message payload must be specified in
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the signature of the task handler.
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The example below showcases three tasks, two of them expect a message.
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``` rust
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{{#include ../../../examples/message.rs}}
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```
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``` console
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$ cargo run --example message
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{{#include ../../../ci/expected/message.run}}```
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## Capacity
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Task dispatchers do *not* use any dynamic memory allocation. The memory required
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to store messages is statically reserved. The framework will reserve enough
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space for every context to be able to spawn each task at most once. This is a
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sensible default but the "inbox" capacity of each task can be controlled using
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the `capacicy` argument of the `task` attribute.
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The example below sets the capacity of the software task `foo` to 4. If the
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capacity is not specified then the second `spawn.foo` call in `UART0` would
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fail.
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``` rust
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{{#include ../../../examples/capacity.rs}}
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```
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``` console
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$ cargo run --example capacity
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{{#include ../../../ci/expected/capacity.run}}```
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