Update delay.md file to be a bit easier to read, and add spoiler tags for the walls of code

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

@@ -1,18 +1,20 @@
 # Tasks with delay
 
-A convenient way to express *miniminal* timing requirements is by means of delaying progression. 
+A convenient way to express miniminal timing requirements is by delaying progression. 
 
-This can be achieved by instantiating a monotonic timer:
+This can be achieved by instantiating a monotonic timer (for implementations, see [`rtic-monotonics`]):
+
+[`rtic-monotonics`]: https://github.com/rtic-rs/rtic/tree/master/rtic-monotonics
+[`rtic-time`]: https://github.com/rtic-rs/rtic/tree/master/rtic-time
 
 ``` rust
 ...
-rtic_monotonics::make_systick_handler!();
-
 #[init]
 fn init(cx: init::Context) -> (Shared, Local) {
     hprintln!("init");
 
-    Systick::start(cx.core.SYST, 12_000_000);
+    let token = rtic_monotonics::create_systick_token!();
+    Systick::start(cx.core.SYST, 12_000_000, token);
     ...
 ```
 
@@ -28,11 +30,14 @@ async fn foo(_cx: foo::Context) {
 
 ```
 
-Technically, the timer queue is implemented as a list based priority queue, where list-nodes are statically allocated as part of the underlying task `Future`. Thus, the timer queue is infallible at run-time (its size and allocation is determined at compile time).
+<!-- TODO: move technical explanation to internals -->
+
+Technically, the timer queue is implemented as a list based priority queue, where list-nodes are statically allocated as part of the underlying task `Future`. Thus, the timer queue is infallible at run-time (its size and allocation are determined at compile time).
 
 Similarly the channels implementation, the timer-queue implementation relies on a global *Critical Section* (CS) for race protection. For the examples a CS implementation is provided by adding `--features test-critical-section` to the build options.
 
-For a complete example:
+<details>
+<summary>A complete example</summary>
 
 ``` rust
 {{#include ../../../../rtic/examples/async-delay.rs}}
@@ -46,11 +51,15 @@ $ cargo run --target thumbv7m-none-eabi --example async-delay --features test-cr
 {{#include ../../../../rtic/ci/expected/async-delay.run}}
 ```
 
+</details>
+
 ## Timeout
 
-Rust `Futures` (underlying Rust `async`/`await`) are composable. This makes it possible to `select` in between `Futures` that have completed.
+Rust [`Future`]s (underlying Rust `async`/`await`) are composable. This makes it possible to `select` in between `Futures` that have completed.
 
-A common use case is transactions with associated timeout. In the examples shown below, we introduce a fake HAL device which performs some transaction. We have modelled the time it takes based on the input parameter (`n`) as `350ms + n * 100ms)`. 
+[`Future`]: https://doc.rust-lang.org/std/future/trait.Future.html
+
+A common use case is transactions with an associated timeout. In the examples shown below, we introduce a fake HAL device that performs some transaction. We have modelled the time it takes based on the input parameter (`n`) as `350ms + n * 100ms`. 
 
 Using the `select_biased` macro from the `futures` crate it may look like this:
 
@@ -62,19 +71,13 @@ select_biased! {
 }
 ```
 
-Assuming the `hal_get` will take 450ms to finish, a short timeout of 200ms will expire.
+Assuming the `hal_get` will take 450ms to finish, a short timeout of 200ms will expire before `hal_get` can complete.
 
-``` rust
-// Call hal with long relative timeout using `select_biased`
-select_biased! {
-    v = hal_get(1).fuse() => hprintln!("hal returned {}", v), // hal finish first
-    _ = Systick::delay(1000.millis()).fuse() =>  hprintln!("timeout", ),
-}
-```
+Extending the timeout to 1000ms would cause `hal_get` will to complete first.
 
-By extending the timeout to 1000ms, the `hal_get` will finish first.
+Using `select_biased` any number of futures can be combined, so its very powerful. However, as the timeout pattern is frequently used, more ergonomic support is baked into RTIC, provided by the [`rtic-monotonics`] and [`rtic-time`] crates. 
 
-Using `select_biased` any number of futures can be combined, so its very powerful. However, as the timeout pattern is frequently used, it is directly supported by the RTIC [rtc-monotonics] and [rtic-time] crates. The second example from above using `timeout_after`:
+Rewriting the second example from above using `timeout_after` gives:
 
 ``` rust
 // Call hal with long relative timeout using monotonic `timeout_after`
@@ -84,7 +87,7 @@ match Systick::timeout_after(1000.millis(), hal_get(1)).await {
 }
 ```
 
-In cases you want exact control over time without drift. For this purpose we can use exact points in time using `Instance`, and spans of time using `Duration`. Operations on the `Instance` and `Duration` types are given by the [fugit] crate.
+In cases where you want exact control over time without drift we can use exact points in time using `Instant`, and spans of time using `Duration`. Operations on the `Instant` and `Duration` types come from the [`fugit`] crate.
 
 [fugit]: https://crates.io/crates/fugit
 
@@ -109,10 +112,20 @@ for n in 0..3 {
 }
 ```
 
-`instant = Systick::now()` gives the baseline (i.e., the absolute current point in time). We want to call `hal_get` after 1000ms relative to this absolute point in time. This can be accomplished by `Systick::delay_until(instant).await;`. We define the absolute point in time for the `timeout`, and call `Systick::timeout_at(timeout, hal_get(n)).await`. For the first loop iteration `n == 0`, and the `hal_get` will take 350ms (and finishes before the timeout). For the second iteration `n == 1`, and `hal_get` will take 450ms (and again succeeds to finish before the timeout).  For the third iteration `n == 2` (`hal_get` will take 5500ms to finish). In this case we will run into a timeout.
+`let mut instant = Systick::now()` sets the starting time of execution. 
 
+We want to call `hal_get` after 1000ms relative to this starting time. This can be accomplished by using `Systick::delay_until(instant).await`. 
 
-The complete example:
+Then, we define a point in time called `timeout`, and call `Systick::timeout_at(timeout, hal_get(n)).await`. 
+
+For the first iteration of the loop, with `n == 0`, the `hal_get` will take 350ms (and finishes before the timeout). 
+
+For the second iteration, with `n == 1`, the `hal_get` will take 450ms (and again succeeds to finish before the timeout).  
+
+For the third iteration, with `n == 2`, `hal_get` will take 550ms to finish, in which case we will run into a timeout.
+
+<details>
+<summary>A complete example</summary>
 
 ``` rust
 {{#include ../../../../rtic/examples/async-timeout.rs}}
@@ -125,3 +138,4 @@ $ cargo run --target thumbv7m-none-eabi --example async-timeout --features test-
 ``` console
 {{#include ../../../../rtic/ci/expected/async-timeout.run}}
 ```
+</details>