pokeldn

pokeldn is a Linux implementation of Nintendo Switch local wireless (LDN) that speaks to Pokemon games running on retail Switch hardware. These pages document the protocols involved, with the decompilation citations, disassembly addresses and hardware measurements behind each finding.

Installation, the command-line reference and the code layout are in the repository README.

Targets

Two kinds of title share one wireless layer.

FireRed and LeafGreen run as a GBA ROM inside an emulator on the Switch, so two protocol layers are stacked: the console’s LDN/Pia wireless underneath, and the ROM’s own GBA link above it. Proven on retail hardware: Mystery Gift in both directions, trade host and joiner, every Union Room activity including link battles, Wonder News, the cable-club colosseum, a visiting Battle Tower trainer, and arbitrary ARM code on the console: its memory read and written, its ROM mapped, its own functions called, and a Pokemon built by its own CreateMon.

Brilliant Diamond and Shining Pearl and Sword and Shield are native Switch titles. Pia is the game’s own transport, with Unity/IL2CPP (BDSP) or native C++ with protobuf messages (Sword/Shield) above it. Both have completed a trade with a retail console.

Sections

section	contents
The wireless layer	LDN and Pia: advertisements, association, packet formats by version, session-key derivation. Game-independent.
Reverse-engineering a Switch title	Reading a retail game’s own code: NCA/RomFS extraction in place, IL2CPP metadata, C++ RTTI. General method.
FireRed and LeafGreen	The GBA link, Mystery Gift, code execution on the console, the RNG, the two cartridges.
Brilliant Diamond and Shining Pearl	Pia 5.27-5.45, the Union Room, and the trade flow.
Sword and Shield	Pia 4, the sync framework, trading, and the Mystery Gift local branch.
Hardware and setup	Adapters, Raspberry Pi deployment, Switch keys.

Credits

Built on kinnay’s LDN library and the NintendoClients wiki, and read against pret/pokefirered, the FireRed/LeafGreen decompilation.