From 50fdc339083a34d91ada1c462c67978e58f87f11 Mon Sep 17 00:00:00 2001
From: Lotte Steenbrink <lotte.steenbrink@ferrous-systems.com>
Date: Mon, 19 Apr 2021 11:21:21 +0200
Subject: [PATCH] point out parts of a embedded program in helo.rs, Cargo.toml

---
 beginner/apps/.cargo/config.toml |  1 +
 beginner/apps/src/bin/hello.rs   | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/beginner/apps/.cargo/config.toml b/beginner/apps/.cargo/config.toml
index be9aeec..7a1c918 100644
--- a/beginner/apps/.cargo/config.toml
+++ b/beginner/apps/.cargo/config.toml
@@ -12,4 +12,5 @@ rustflags = [
 ]
 
 [build]
+# cross-compile to this target
 target = "thumbv7em-none-eabihf" # = ARM Cortex-M4
\ No newline at end of file
diff --git a/beginner/apps/src/bin/hello.rs b/beginner/apps/src/bin/hello.rs
index 62a8ad0..9d20aa2 100644
--- a/beginner/apps/src/bin/hello.rs
+++ b/beginner/apps/src/bin/hello.rs
@@ -1,12 +1,20 @@
-#![no_main]
+// this program does not use the standard library to avoid heap allocations.
+// only the `core` library functions are available.
 #![no_std]
+// this program uses a custom entry point instead of `fn main()`
+#![no_main]
 
 use cortex_m::asm;
 use cortex_m_rt::entry;
 use panic_log as _; // the panicking behavior
 
+
 #[entry]
+// ˆˆˆˆ the custom entry point
 fn main() -> ! {
+    //      ˆˆˆ
+    //      ! is the 'never' type: this function never returns
+
     // initializes the peripherals
     dk::init().unwrap();