MiSTer Saturn Core Update Fixes 3D Fighting Slowdown on Single-RAM Boards

Eleven blocks of silicon separated MiSTer Saturn users from smoother 3D fighting — and a small arithmetic tweak plus a changed compilation seed closed the gap.

Community tester Zet-sensei generated and posted a working single-RAM build to the Saturn thread on the official MiSTer Discord within hours of a broken nightly exposing the problem on March 20. The fix addressed persistent slowdown in many Saturn 3D fighting games for users running MiSTer setups with only one RAM module, a limitation that even the core's existing "fast timings" setting couldn't fully overcome.

"The sole change I've done was an arithmetic on the DMAC (suggested by Jotego on the pending [pull request]) and compile it with seed 6 instead of 1," Zet-sensei said.

That description undersells how close to the edge the fix landed. When the update first hit the MiSTer Discord's unstable nightlies channel, single-RAM builds immediately threw a hard stop: "Fitter requires 4202 LABs to implement the design, but the device contains only 4191 LABs." The DE-10 Nano, the FPGA hardware at the heart of every MiSTer setup, simply didn't have the logic resources to accommodate the new build as initially compiled. The core was trying to claim 4,202 Logic Array Blocks; the device offers only 4,191.

Zet-sensei, who works closely with Saturn core developer Sergiy "SRG320" Dvodnenko on testing, took the DMAC arithmetic change that contributor Jotego had suggested on a pending pull request and recompiled using seed 6 rather than the previous seed 1. Changing the compilation seed alters how Quartus, the FPGA synthesis tool, routes logic through the chip, and in this case shaved enough resources to push the design under the device's ceiling. The working build appeared in the Saturn thread on the official Discord server within a few hours of the fitter error being discovered.

For single-RAM users, the "fast timings" toggle in the core's settings was the previous workaround, but it only went so far. Many Saturn 3D fighters remained noticeably sluggish even with that option enabled, because the games themselves are among the most resource-intensive titles the Saturn library offers. Dual-RAM setups have more headroom and were not the target of this fix.

The Saturn core Dvodnenko has been refining since he released a playable public build in May 2022. It was brought into the main MiSTer branch in October 2023, a milestone that signaled the core was stable enough to reach the full MiSTer userbase rather than requiring a manual install. The MiSTer itself is a field-programmable gate array, a chip that can be reconfigured through software to physically replicate retro hardware, loading cores and game ROMs from an SD card. That physical emulation approach is what makes resource ceilings like the 4,191-LAB limit a hard constraint rather than a tunable parameter.

Dvodnenko accepts support through his Patreon, and the working single-RAM build remains available through Zet-sensei's post in the Saturn thread on the official MiSTer Discord server.