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book/resources: remove mentions of the field attribute #[init(<expr>)]
it no longer exists. all resources are now late resources
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2 changed files with 6 additions and 25 deletions
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@ -13,17 +13,16 @@ One `struct` must be annotated with the attribute `#[local]`.
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The other `struct` must be annotated with the attribute `#[shared]`.
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The difference between these two sets of resources will be covered later.
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Resources can optionally be given an initial value using the `#[init]`
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attribute. Resources that are not given an initial value are referred to as
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*late* resources and are covered in more detail in a follow-up section in this
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page.
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Each context (task handler, `init` or `idle`) must declare the resources it
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intends to access in its corresponding metadata attribute using either the
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`local` or `shared` argument. This argument takes a list of resource names as
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its value. The listed resources are made available to the context under the
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`local` and `shared` fields of the `Context` structure.
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All resources are initialized at runtime, after the `#[init]` function returns.
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The `#[init]` function must return the initial values for all resources; hence its return type includes the types of the `#[shared]` and `#[local]` structs.
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Because resources are uninitialized during the execution of the `#[init]` function, they cannot be accessed within the `#[init]` function.
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The example application shown below contains two interrupt handlers.
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Each handler has access to its own `#[local]` resource.
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@ -56,7 +55,7 @@ The critical section created by the `lock` API is based on dynamic priorities: i
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[icpp]: https://en.wikipedia.org/wiki/Priority_ceiling_protocol
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[srp]: https://en.wikipedia.org/wiki/Stack_Resource_Policy
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In the example below we have three interrupt handlers with priorities ranging from one to three. The two handlers with the lower priorities contend for the `shared` resource and need to lock the resource for accessing the data. The highest priority handler, which do nat access the `shared` resource, is free to preempt the critical section created by the
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In the example below we have three interrupt handlers with priorities ranging from one to three. The two handlers with the lower priorities contend for the `shared` resource and need to lock the resource for accessing the data. The highest priority handler, which do not access the `shared` resource, is free to preempt the critical section created by the
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lowest priority handler.
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``` rust
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@ -76,25 +75,6 @@ As an extension to `lock`, and to reduce rightward drift, locks can be taken as
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{{#include ../../../../examples/multilock.rs}}
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```
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## Late resources
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Late resources are resources that are not given an initial value at compile time using the `#[init]` attribute but instead are initialized at runtime using the `init::LateResources` values returned by the `init` function.
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Late resources are useful e.g., to *move* (as in transferring the ownership of) peripherals initialized in `init` into tasks.
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The example below uses late resources to establish a lockless, one-way channel between the `UART0` interrupt handler and the `idle` task. A single producer single consumer [`Queue`] is used as the channel. The queue is split into consumer and producer end points in `init` and then each end point is stored in a different resource; `UART0` owns the producer resource and `idle` owns the consumer resource.
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[`Queue`]: ../../../api/heapless/spsc/struct.Queue.html
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``` rust
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{{#include ../../../../examples/late.rs}}
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```
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``` console
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$ cargo run --example late
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{{#include ../../../../ci/expected/late.run}}
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```
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## Only shared (`&-`) access
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By default the framework assumes that all tasks require exclusive access (`&mut-`) to resources but it is possible to specify that a task only requires shared access (`&-`) to a resource using the `&resource_name` syntax in the `resources` list.
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@ -28,6 +28,7 @@ mod app {
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(
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Shared {},
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// initial values for the `#[local]` resources
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Local {
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local_to_uart0: 0,
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local_to_uart1: 0,
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