How does dual-slot mode *technically* work?

[jaden-preservation]

Hello all! This is my first post here so please correct me if this is not the correct forum for this question, or if this is a duplicate question.

I have been trying to figure out how the DS game communicates with the game in the GBA slot. My goal is to reverse engineer the protocol, but I have no idea where to even start.

Specifically:

How does the DS game know which GBA game is in the slot?

How is data transferred from the GBA game to the DS game?

If anyone has any helpful information it would be much appreciated!

[jaden-preservation]

Of course after I posted this I finally found a lead on the web: https://www.copetti.org/writings/consoles/nintendo-ds/

I would still appreciate any insight and info!