Konami 007121 tracing progress (Patreon)

Here's what the 007121 tracing layer looks like as of today. Just by looking at that blue cloud, one may guess that about 25% is done, but I'd give 15~20% as a closer estimate.

To give you an idea of how many traces are missing in that blue zone: only the cells marked in green are fully connected. All the others still have missing inputs or dangling outputs.

That zone is actually the same group of cells repeated 9 times and all tangled up.

Why nine ? I currently don't have the answer. They may be parallel sprite position or priority comparators, as such steps must be done very quickly.

From a reverse-engineering standpoint, replicated circuits such as those are some of the less rewarding to work on. After tracing two or three and identifying the pattern, it's tempting to skip tracing the others and just assume they're all identical.

But... what if a single one of them is different ? What if a single one out of the hundreds of outputs is inverted ? What if missing that difference causes one particular game to have one particular sprite in one particular mode to be messed up ?

It's one of those times where fear MUST take over lazyness ;)

PS: On an almost-related note, I fixed the long lasting fix layer offset bug in the MiSTer NeoGeo core. It was a stupid copy/paste accident. The repo will be updated shortly.