Genesis ym2612: Add Ladder Effect

[birdybro]

The ladder effect currently does not seem to exist within jt12 (unless I'm missing something and it's called something else). I was able to restore the functionality with what I thought was minimal impact to your design:

https://github.com/MiSTer-devel/Genesis_MiSTer/pull/210/files

This method restores the ladder effect to Genesis, but sorgelig does not want to deviate from your module but instead would prefer if the ladder effect were implemented in your core directly. I am working on it to learn about it, but I would have no problem if it were done by someone other than me because I may miss something or make a big mistake.

Additionally the audio balance controls between FM, PSG, PCM, etc... might need to be extended to the jt12 module, if they aren't already, I'm not sure if they are or aren't totally. sorry if I'm a bit of an amateur.

[thehughhefner]

Is the ladder effect also missing in SiDi or MiST? Could you also confirm this gyurco?

[birdybro]

I think that has always been exclusive to MiSTer and to the Analogue Mega SG (in terms of FPGA-based emulation, plenty of software emulators have the ladder effect nowadays).

https://github.com/mist-devel/fpgagen/blob/master/Board/mist/MIST_Toplevel.vhd#L186-L208

There isn't any toggle between ym2612 and ym3438 mode, nor any mention of the ladder effect that I can see. There might be a good reason for that though. If you go with the methodology or principles of never deviating from the modules you are sourcing from, then you could go without ladder for many years.