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Diffstat (limited to 'book/en/src/by-example/tips.md')
| -rw-r--r-- | book/en/src/by-example/tips.md | 32 |
1 files changed, 27 insertions, 5 deletions
diff --git a/book/en/src/by-example/tips.md b/book/en/src/by-example/tips.md index c0bfc56..79b9d71 100644 --- a/book/en/src/by-example/tips.md +++ b/book/en/src/by-example/tips.md @@ -24,8 +24,8 @@ of tasks. You can use conditional compilation (`#[cfg]`) on resources (`static [mut]` items) and tasks (`fn` items). The effect of using `#[cfg]` attributes is that -the resource / task will *not* be injected into the prelude of tasks that use -them (see `resources`, `spawn` and `schedule`) if the condition doesn't hold. +the resource / task will *not* be available through the corresponding `Context` +`struct` if the condition doesn't hold. The example below logs a message whenever the `foo` task is spawned, but only if the program has been compiled using the `dev` profile. @@ -37,7 +37,7 @@ the program has been compiled using the `dev` profile. ## 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 +RTFM v0.4.0 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. @@ -78,8 +78,6 @@ $ cargo nm --example ramfunc --release | grep ' bar::' ## `binds` -**NOTE**: Requires RTFM ~0.4.2 - You can give hardware tasks more task-like names using the `binds` argument: you name the function as you wish and specify the name of the interrupt / exception in the `binds` argument. Types like `Spawn` will be placed in a module named @@ -91,3 +89,27 @@ after the function, not the interrupt / exception. Example below: ``` console $ cargo run --example binds {{#include ../../../../ci/expected/binds.run}}``` + +## Indirection for faster message passing + +Message passing always involves copying the payload from the sender into a +static variable and then from the static variable into the receiver. Thus +sending a large buffer, like a `[u8; 128]`, as a message involves two expensive +`memcpy`s. To minimize the message passing overhead one can use indirection: +instead of sending the buffer by value, one can send an owning pointer into the +buffer. + +One can use a global allocator to achieve indirection (`alloc::Box`, +`alloc::Rc`, etc.), which requires using the nightly channel as of Rust v1.34.0, +or one can use a statically allocated memory pool like [`heapless::Pool`]. + +[`heapless::Pool`]: https://docs.rs/heapless/0.4.3/heapless/pool/index.html + +Here's an example where `heapless::Pool` is used to "box" buffers of 128 bytes. + +``` rust +{{#include ../../../../examples/pool.rs}} +``` +``` console +$ cargo run --example binds +{{#include ../../../../ci/expected/pool.run}}``` |