Link cables

Two machines in the same room can be cabled together, and the data really crosses. This is not a netplay session dressed up as a wire: both machines are emulated here, in your room, and the lead between them carries the same serial traffic the hardware did.

New in v0.4.0. In v0.5.0 the link became event-driven rather than polled: the cores wake each other when there is something to send instead of checking a shared lock on every step, which cuts the contention three to fourfold and is felt as a smoother run with up to four cores cabled together.

A GameCube with two Game Boy Advances on link cables — the console on the TV, each handheld running its own screen. Recorded on PCVR.

What can be linked

Cable	Machines	What it needs
Game Boy link cable	Two Game Boys or Game Boy Colors	Nothing extra
GBA link cable	Up to four Game Boy Advances	A GBA BIOS for single-pak play
GBA – GameCube cable	A GameCube and up to four GBAs	A GBA BIOS
PlayStation serial cable	Two PlayStations	Nothing extra

Each lead is offered on the system’s own card in SPAWN → Systems — open the card for the machine you are cabling and the right cable is listed with its controllers. Push each end into the matching socket: the link port on a handheld’s edge, the SERIAL I/O socket on the back of a PlayStation, or, for the GBA-to-GameCube cable, a controller port on the console.

The three handheld and console leads are three different cables, not one — a Game Boy lead is not a GBA lead and neither is a PlayStation serial cable, exactly as on the shelf. The GBA lead carries a junction in the middle, which is how a third and fourth handheld chain on; the Game Boy’s is a plain two-machine cord. The GC-GBA cable is listed on both the GameCube’s card and the Game Boy Advance’s, so you can find it from either end.

Multiplayer on one cartridge

The GBA cable does single-pak as well as multi-pak, which is the mode where one cartridge feeds up to four handhelds:

1. Spawn as many Game Boy Advances as you want players, and enough link cables to chain them.

2. Put the game in one of them. The others stay empty.

3. Plug the purple end into the machine holding the cartridge — that is the host, and single-pak will not start if the cable is the other way round.

4. Power up. The host uploads the game to the others over the wire, as the hardware did.

Single-pak boots the empty handhelds from their BIOS, so a GBA BIOS is required for it. See BIOS files.

The GameCube cable

The GameCube end of that lead goes into a controller port, not a link socket — a GameCube had no link port. Four cables means four handhelds on one console.

Two things worth knowing before you judge it:

• Games that use the GBA as a second screen work best with an empty handheld. Those titles upload their own program over the cable, so a GBA holding its own cartridge is a legitimate way to plug it in but not the pairing the game was written for.
• The lead costs a few percent of the frame rate, not a slice of it. Expect one hitch around a second long while the program uploads, then nothing.

Mixing cores

A link is between machines, not between copies of one core. A Game Boy running gambatte and a Game Boy running mGBA join the same cable and trade bytes quite happily.

This wants a PC

Recommended on PCVR

A link is two or more cores running at once in the same room, and that is more than a standalone headset comfortably carries. It runs on a Quest — try it — but PCVR is the place to expect it to be smooth. Four Game Boy Advances with three of them empty is known to stutter at first while the program upload happens.

Where the support comes from

Serial link is not something libretro offered. RetroXR added a core-agnostic serial link API upstream to RetroArch, and the cores it runs are forks carrying the other half: mGBA, Dolphin, pcsx_rearmed and gambatte. The core manager downloads them for you; there is nothing to build.

Needs an in-headset pass

The cable rules above are read from the source and from probe runs against real cores. The exact spawn-menu wording and the feel of seating each plug have not been checked against a running build.