Merge #97

97: v0.4.0 r=japaric a=japaric

closes #32
closes #33

Co-authored-by: Jorge Aparicio <jorge@japaric.io>

1 files changed, 43 insertions, 0 deletions

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