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44 lines
1.5 KiB
Markdown
44 lines
1.5 KiB
Markdown
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# Tips & tricks
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## Running tasks from RAM
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The main goal of moving the specification of RTFM applications to attributes in
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RTFM v0.4.x was to allow inter-operation with other attributes. For example, the
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`link_section` attribute can be applied to tasks to place them in RAM; this can
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improve performance in some cases.
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> **IMPORTANT**: In general, the `link_section`, `export_name` and `no_mangle`
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> attributes are very powerful but also easy to misuse. Incorrectly using any of
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> these attributes can cause undefined behavior; you should always prefer to use
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> safe, higher level attributes around them like `cortex-m-rt`'s `interrupt` and
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> `exception` attributes.
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>
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> In the particular case of RAM functions there's no
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> safe abstraction for it in `cortex-m-rt` v0.6.5 but there's an [RFC] for
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> adding a `ramfunc` attribute in a future release.
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[RFC]: https://github.com/rust-embedded/cortex-m-rt/pull/100
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The example below shows how to place the higher priority task, `bar`, in RAM.
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``` rust
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{{#include ../../../examples/ramfunc.rs}}
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```
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Running this program produces the expected output.
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``` console
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$ cargo run --example ramfunc
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{{#include ../../../ci/expected/ramfunc.run}}```
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One can look at the output of `cargo-nm` to confirm that `bar` ended in RAM
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(`0x2000_0000`), whereas `foo` ended in Flash (`0x0000_0000`).
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``` console
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$ cargo nm --example ramfunc --release | grep ' foo::'
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{{#include ../../../ci/expected/ramfunc.grep.foo}}```
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``` console
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$ cargo nm --example ramfunc --release | grep ' bar::'
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{{#include ../../../ci/expected/ramfunc.grep.bar}}```
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