Konami 007121 schematics release (Patreon)

Finally !

Of the few chips I've traced until now, this one has been by far the most tiring. Much worse than the Neo Geo's video controler.

The first reason for that, is that the memory used to store the row and line scroll values wasn't made of a common and easily identifiable RAM block as found in later chips.
But with 288 latches, 320 NOR gates, and whatever was needed for the CPU and the rendering logic to access it alternately.
This tangled cluster of gates take up almost a third of the die, and tracing it was some of the less rewarding work I've ever done.
It doesn't do anything special, it could just have been a RAM block. Maybe those weren't available from Oki (the makers of the chip) at the time, or Konami decided to implement it all in logic cells... Whatever the case, I'm glad it's done !

The second reason is related to the first: counters were also implemented as small gates scattered all over the place.
In later chips, in particular Fujitsu gate arrays, such counters are implemented in tightly packed blocks of gates. These are much easier to identify and much quicker to trace.

There are some good news however: there aren't any mystery zones in the schematics, some will require careful analysis if they need to be reproduced exactly in HDL, but nothing raising any new questions. A few guessed, misunderstood or unemplemented configuration bits (see MAME's k007121.cpp) are also figured out now.

Needless to say, I won't be undertaking a new tracing project of that size anytime soon.
Only bite-sized chips for the months to come.

The schematics could still benefit from a bit more work, but I think that they're currently in a clean enough state to be released: https://github.com/furrtek/VGChips/blob/master/Konami/007121/k007121_schematics.PDF

This is the final paid post for this project.
Thank you very much to everyone who has supported my work, it eases the pain a WHOLE lot :)

Schematics updates and source code contributions will happen but won't be mentioned in future posts.

Now to work with Jotego to come up with the necessary fixes !