diff --git a/src/hal/_rules.txt b/src/hal/_rules.txt
index 65c89c5..9dae508 100644
--- a/src/hal/_rules.txt
+++ b/src/hal/_rules.txt
@@ -2,3 +2,6 @@ Use a class whenever you need to store some context data along with the function
 A typical scenario is the UART which uses some RX and TX buffers.
 
 Use a simple C-style otherwise, but it is advised to wrap the interface into a namespace as proposed in existing header files.
+
+`__attribute__((always_inline)) inline` was necessary for most functions because the generated code wasn't efficient enough otherwise.
+It will be interesting when the STM32 hal will have to be included as well. Hopefully it won't be a nightmare :P