Update crate versions in 03-setup

Cargo.toml:
  * edition             2018 -> 2021
  * cortex-m            0.7.3 -> 0.7.7, added feature `critical-section-single-core`
  * cortex-m-rt         0.7.0 -> 0.7.3
  * rtt-target          0.3.1 -> 0.5.0, removed feature `cortex-m`
  * panic-rtt-target    0.1.2 -> 0.1.3, removed feature `cortex-m`

src/main.rs:
  * To prevent a link error regarding undefined symbols
    (`_critical_section_1_0_acquire` and `_critical_section_1_0_release`)
    I have added `use cortex_m as _;`

The code compiles, and I see the RTT output from cargo embed.

Author: nikgul

microbit/src/03-setup/Cargo.toml

@@ -2,10 +2,10 @@
 name = "rtt-check"
 version = "0.1.0"
 authors = ["Henrik Böving <hargonix@gmail.com>"]
-edition = "2018"
+edition = "2021"
 
 [dependencies]
-cortex-m = "0.7.3"
-cortex-m-rt = "0.7.0"
-rtt-target = { version =  "0.3.1", features = ["cortex-m"] }
-panic-rtt-target = { version =  "0.1.2", features = ["cortex-m"] }
+cortex-m = { version = "0.7.7", features = ["critical-section-single-core"] }
+cortex-m-rt = "0.7.3"
+rtt-target = "0.5.0"
+panic-rtt-target = "0.1.3"

microbit/src/03-setup/IDE.md

@@ -28,4 +28,4 @@ When editing the IntelliJ build configuration, here are a few non-default values
 You'll need to replace the default value `run` by the command `embed FLAGS`,
 * You should enable "Emulate terminal in output console". Otherwise, your program will fail to print text to a terminal
 * You should ensure that the working directory is `microbit/src/N-name`, with `N-name` being the directory of the chapter you
-are reading. You can not run from the `src` directory since it contains no cargo file.
+are reading. You can not run from the `src` directory since it contains no cargo file.

microbit/src/03-setup/src/main.rs

@@ -4,6 +4,7 @@
 use panic_rtt_target as _;
 use rtt_target::{rtt_init_print, rprintln};
 
+use cortex_m as _;
 use cortex_m_rt::entry;
 
 #[entry]