Merge #405 #406

405: Updated migration guide with symmetric locks and new spawn r=AfoHT a=korken89



406: book.toml/by-example/app r=korken89 a=perlindgren

Book update

Co-authored-by: Emil Fresk <emil.fresk@gmail.com>
Co-authored-by: Per Lindgren <per.lindgren@ltu.se>

book/en/book.toml

@@ -1,5 +1,5 @@
 [book]
-authors = ["Jorge Aparicio"]
+authors = ["Jorge Aparicio, Per Lindgren and The Real-Time Interrupt-driven Concurrency developers"]
 multilingual = false
 src = "src"
 title = "Real-Time Interrupt-driven Concurrency"

book/en/src/by-example/app.md

@@ -34,14 +34,13 @@ And optionally, device specific peripherals through the `core` and `device` fiel
 of `init::Context`.
 
 `static mut` variables declared at the beginning of `init` will be transformed
-into `&'static mut` references that are safe to access.
+into `&'static mut` references that are safe to access. Notice, this feature may be deprecated in next release, see `task_local` resources.
 
 [`rtic::Peripherals`]: ../../api/rtic/struct.Peripherals.html
 
 The example below shows the types of the `core`, `device` and `cs` fields, and
 showcases safe access to a `static mut` variable. The `device` field is only
-available when the `peripherals` argument is set to `true` (it defaults to
-`false`).
+available when the `peripherals` argument is set to `true` (default). In the rare case you want to implement an ultra-slim application you can explicitly set `peripherals` to `false`.
 
 ``` rust
 {{#include ../../../../examples/init.rs}}
@@ -71,12 +70,12 @@ then sends the microcontroller to sleep after running `init`.
 [SLEEPONEXIT]: https://developer.arm.com/docs/100737/0100/power-management/sleep-mode/sleep-on-exit-bit
 
 Like in `init`, `static mut` variables will be transformed into `&'static mut`
-references that are safe to access.
+references that are safe to access. Notice, this feature may be deprecated in the next release, see `task_local` resources.
 
 The example below shows that `idle` runs after `init`.
 
-**Note:** The `loop {}` in idle cannot be empty as this will crash the microcontroller due to a bug
-in LLVM which miss-optimizes empty loops to a `UDF` instruction in release mode.
+**Note:** The `loop {}` in idle cannot be empty as this will crash the microcontroller due to
+LLVM compiling empty loops to an `UDF` instruction in release mode. To avoid UB, the loop needs to imply a "side-effect" by inserting an assembly instruction (e.g., `WFI`) or a `continue`.
 
 ``` rust
 {{#include ../../../../examples/idle.rs}}
@@ -146,9 +145,9 @@ $ cargo run --example preempt
 ```
 
 Note that the task `gpiob` does *not* preempt task `gpioc` because its priority
-is the *same* as `gpioc`'s. However, once `gpioc` terminates the execution of
-task, `gpiob` is prioritized over `gpioa` due to its higher priority. `gpioa`
-is resumed only after `gpiob` terminates.
+is the *same* as `gpioc`'s. However, once `gpioc` returns, the execution of
+task `gpiob` is prioritized over `gpioa` due to its higher priority. `gpioa`
+is resumed only after `gpiob` returns.
 
 One more note about priorities: choosing a priority higher than what the device
 supports (that is `1 << NVIC_PRIO_BITS`) will result in a compile error. Due to

book/en/src/migration/migration_v5.md

@@ -6,6 +6,32 @@ This section describes how to upgrade from v0.5.x to v0.6.0 of the RTIC framewor
 
 Change the version of `cortex-m-rtic` to `"0.6.0"`.
 
+## `mod` instead of `const`
+
+With the support of attributes on modules the `const APP` workaround is not needed.
+
+Change
+
+``` rust
+#[rtic::app(/* .. */)]
+const APP: () = {
+  [code here]
+};
+```
+
+into
+
+``` rust
+#[rtic::app(/* .. */)]
+mod app {
+  [code here]
+}
+```
+
+Now that a regular Rust module is used it means it is possible to have custom
+user code within that module.
+Additionally, it means that `use`-statements for resources etc may be required.
+
 ## Move Dispatchers from `extern "C"` to app arguments.
 
 Change
@@ -36,31 +62,6 @@ mod app {
 
 This works also for ram functions, see examples/ramfunc.rs
 
-## Module instead of Const
-
-With the support of attributes on modules the `const APP` workaround is not needed.
-
-Change
-
-``` rust
-#[rtic::app(/* .. */)]
-const APP: () = {
-  [code here]
-};
-```
-
-into
-
-``` rust
-#[rtic::app(/* .. */)]
-mod app {
-  [code here]
-}
-```
-
-Now that a regular Rust module is used it means it is possible to have custom
-user code within that module.
-Additionally, it means that `use`-statements for resources etc may be required.
 
 ## Init always returns late resources
 
@@ -75,7 +76,8 @@ mod app {
     fn init(_: init::Context) {
         rtic::pend(Interrupt::UART0);
     }
-    [more code]
+
+    // [more code]
 }
 ```
 
@@ -90,11 +92,12 @@ mod app {
 
         init::LateResources {}
     }
-    [more code]
+
+    // [more code]
 }
 ```
 
-## Resources struct - #[resources]
+## Resources struct - `#[resources]`
 
 Previously the RTIC resources had to be in in a struct named exactly "Resources":
 
@@ -118,19 +121,86 @@ In fact, the name of the struct is now up to the developer:
 
 ``` rust
 #[resources]
-struct whateveryouwant {
+struct Whateveryouwant {
     // Resources defined in here
 }
 ```
 
 would work equally well.
 
+## Spawn/schedule from anywhere
+
+With the new "spawn/schedule from anywhere", old code such as:
+
+
+
+``` rust
+#[task(spawn = [bar])]
+fn foo(cx: foo::Context) {
+    cx.spawn.bar().unwrap();
+}
+
+#[task(schedule = [bar])]
+fn bar(cx: bar::Context) {
+    cx.schedule.foo(/* ... */).unwrap();
+}
+```
+
+Will now be written as:
+
+``` rust
+#[task]
+fn foo(_c: foo::Context) {
+    bar::spawn().unwrap();
+}
+
+#[task]
+fn bar(_c: bar::Context) {
+    foo::schedule(/* ... */).unwrap();
+}
+```
+
+Note that the attributes `spawn` and `schedule` are no longer needed.
+
+## Symmetric locks
+
+Now RTIC utilizes symmetric locks, this means that the `lock` method need to be used for all resource access. In old code one could do the following as the high priority task has exclusive access to the resource:
+
+``` rust
+#[task(priority = 2, resources = [r])]
+fn foo(cx: foo::Context) {
+    cx.resources.r = /* ... */;
+}
+
+#[task(resources = [r])]
+fn bar(cx: bar::Context) {
+    cx.resources.r.lock(|r| r = /* ... */);
+}
+```
+
+And with symmetric locks one needs to use locks in both tasks:
+
+``` rust
+#[task(priority = 2, resources = [r])]
+fn foo(cx: foo::Context) {
+    cx.resources.r.lock(|r| r = /* ... */);
+}
+
+#[task(resources = [r])]
+fn bar(cx: bar::Context) {
+    cx.resources.r.lock(|r| r = /* ... */);
+}
+```
+
+Note that the performance does not change thanks to LLVM's optimizations which optimizes away unnecessary locks.
+
 ---
 
 ## Additions
 
 ### Extern tasks
 
-Both software and hardware tasks can now be defined external to the `mod app`. Previously this was possible only by implementing a trampoline calling out the task implementation.  
+Both software and hardware tasks can now be defined external to the `mod app`. Previously this was possible only by implementing a trampoline calling out the task implementation.
+
+See examples `examples/extern_binds.rs` and `examples/extern_spawn.rs`.
 
-See examples `examples/extern_binds.rs` and `examples/extern_spawn.rs`.