From e487b235eb26b3f9254e21df15907039156670b3 Mon Sep 17 00:00:00 2001
From: Emil Fresk <emil.fresk@gmail.com>
Date: Tue, 15 Sep 2020 15:41:14 +0200
Subject: [PATCH] Improved loop example docs to highlight that one cannot have
 empty loops in idle

---
 book/en/src/by-example/app.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/book/en/src/by-example/app.md b/book/en/src/by-example/app.md
index e0f4f941ec..9a073ac4cf 100644
--- a/book/en/src/by-example/app.md
+++ b/book/en/src/by-example/app.md
@@ -77,6 +77,9 @@ references that are safe to access.
 
 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.
+
 ``` rust
 {{#include ../../../../examples/idle.rs}}
 ```