I want to avoid the word "message" since PRET has already chosen "battle message" as the term for predefined strings usable in the battle scripts and UI.
I was considering the term "battle link packet" instead, but the library for wireless communications already uses the word "packet" even though GBATEK does not. I'm going with "battle link communication type" instead. For this particular context, I don't think we need a compound noun ("X type"); the singular noun "type" is fine enough.
Created "exposition" macros to describe operations performed on gBattleControllerExecFlags. Updated the battle engine internals to use them, to more clearly document how battle link communications actually work.
Replaced the BUFFER_A and BUFFER_B constants with the BATTLELINKMSGTYPE enum, which also identifies the "controller becoming idle" message type.
Named the task data for the link send task and the link receive task. Added macros to functions related to those tasks, for legibility.