GB Interceptor Testing (Game Boy Capture Cart)

Hey, I am the guy who made the Interceptor and it seems like I have some explaining to do 🙂
(So far I have watched until 0:45:00, but I hope to get to watch the rest later.)

So, in general you might want to watch my video about the GB Interceptor on my channel as it explains a few of the things, but in principle you need to understand that the Interceptor can only see the data that the Game Boy requests from the cartridge. So, it does not help if a game "could" run in both DMG and GBC mode, because if it is plugged into a GBC or GBA it will just run in GBC mode – and the Interceptor can indeed not handle GBC games because they run at twice the clock speed and the microprocessor in the Interceptor is not fast enough for this. That's why that session with black cartridges in the GBC and GBA was so little fun. They would probably have worked in a DMG or GBP.

Then about individual games not working: The Interceptor needs to interpret the game code it intercepts from the game which is directly connected to the Game Boy. So, if a game is running on the Game Boy, but the Interceptor fails to render it properly it is very certainly never an electrical problem but a "logical" one. The game is doing something that the Interceptor cannot handle or, well, maybe just a bug in the Interceptor code. For example, the strange background tiles of the first homebrew look like something that will be fixed in the upcoming firmware 1.1.0, although I cannot be 100% sure without testing that particular game.

There is a list of games that I already know to be working or failing at https://github.com/Staacks/gbinterceptor/wiki/Game-compatibility and I am currently working through the not working titles to massively increase compatibility for version 1.1.0. Unfortunately, the second game you picked in the stream, Dr. Mario, is my current nemesis, because the issue of the missing viruses is the first and only issue on that list so far on which I have given up on (at least for version 1.1.0).

The reason is actually easily explained: The game uses the internal counter of the Game Boy (div register) as a random number generator to create the levels and these random numbers do not go through the cartridge slot. They are therefore unknown to the Interceptor. And in contrast to other games that do this (like for example Tetris generating the stack in B mode) it does not do anything that gives away the location of the viruses, but instead uses the random numbers directly to place them on the screen (write locations in VRAM). The funny thing is that once you clear a line the game has to actually apply some logic to the viruses, which reveals them to the Interceptor and makes them visible. This is the one game so far where I am not sure if I will ever be able to fix this (aside from color games).

Oh, and the Analogue Pocket is also explained in my video. It behaves slightly differently which causes the problem, but it should be fixable – it's just a low priority for me as it has the dock and therefore little need for the Interceptor.

I hope to get around to watch the rest later. It is really helpful for me to see which games fail and what else causes problems. BTW: Can you name the homebrews you tried? I am not that familiar with homebrews but would like to test and fix some of them. They tend to do fancy things with very narrow timing, which should reveal interesting details that need to be fixed.