Progress January I - Something meaningful (paid post) (Patreon)

Finally something meaningful for those who simply want to enjoy playing games without thinking about the technical stuff:

We have a basic NeoGeo core for MiSTer running !

Take a look at the video. There's no commentary at all so you can skip through it as I try a few of the smaller games (and one not that small).

The first obvious point is that there's no audio for now. I'm planning to hook up Jotego's YM core soon to at least get the SSG and FM channels going. The ADPCM part will come later as I still need to figure out how it exactly works from the die shot. Talking about Jotego: I'm also planning on forwarding him part of this post's pledges for his outstanding work on the Yamaha soundchips. He also has a Patreon account ( https://www.patreon.com/topapate ) and other projects going on.

Related to the missing audio is the current usage of memory. In its current state the core only needs the normal 32MB SDRAM extension board running at 96MHz. However this imposes a 1-wait cycle on program data access, which makes code execution slower. This causes slowdowns and color glitches on the top of the screen, which are both noticeable in the video.

Clocking the SDRAM at 120MHz (24*5 instead of 24*4) could be a solution but it would require division by an odd number to get the 50% duty cycle 24MHz NeoGeo main clock. It may be surprising but using both edges of a signal can become messy very fast ! Also, 120MHz is dangerously close to the max. achievable speed with the extension connector type, distance and routing of the boards.

I feel it would be better if both the SDRAM speed and capacity problems were solved all at once. Either by storing the large ROMs in DDR3 (which I didn't try yet), or by using a whole new SDRAM extension board. This still hasn't been decided.

If you want to try it out, use my hacked-up MiSTer loader binary from here: https://github.com/furrtek/Main_MiSTer
Grab the core .rbf from here: https://github.com/furrtek/Neogeo_MiSTer/tree/master/output_files
And he XML romset file here: https://github.com/furrtek/Neogeo_MiSTer/blob/master/romsets.xml

Create a "neogeo" folder at the root of your MiSTer SD card, put romsets.xml in it along with the easily found "neo-epo.sp1" bios, and correctly named folders with ROMs. See the xml file for currently supported games (you can try adding some if you can figure out the format).