Saturn 3D Fighters Run Better on MiSTer Single RAM After Update

An update today for the MiSTer FPGA’s Saturn core improves the performance of many 3D fighting games when using just one memory module. Doing so has stretched the MiSTer’s hardware platform, the DE-10 Nano, to its limits — and beyond, initially.

When the new builds hit the unstable nightlies channel on the MiSTer Discord server this morning, users got an error with the single RAM version that stated, “Fitter requires 4202 LABs to implement the design, but the device contains only 4191 LABs.” In other words, the core was trying to use more resources than the DE-10 Nano has.

Zet-sensei, who works closely with Saturn core developer Sergiy “SRG320” Dvodnenko to test updates, then got to work to make the new core fit in the FPGA’s silicon. Within a few hours, he generated a working build, which can be downloaded from his post in the Saturn thread on the official Discord server.

“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.

While the Saturn core emulates real Saturn hardware nearly perfectly, many 3D fighters are still too resource-intensive for MiSTer setups with just one RAM module instead of two. Users have the option of enabling “fast timings” in the core’s settings to improve performance, but even then, there was noticeable slowdown.

With today’s update, that slowdown has been mitigated or eliminated in games like Fighting Vipers, Virtua Fighter 2 and Dead or Alive for single RAM with fast timing on.

“Just done two runs through Arcade mode on Dead or Alive with Kasumi,” said a member of the MiSTer community, Phobes. “Slow down is now gone from what I have played. Good job indeed.”

An off-screen video illustrating the slowdown improvements between the February and March MiSTer cores on the third arcade level in Dead or Alive.

But another 3D fighter, Last Bronx, still exhibits slowdown with single RAM even after the update, unfortunately.

“Dual RAM remains king,” Zet-sensei said. “We are closing the gap, but won’t fill it completely.”

The update makes no improvements on those with two RAM modules.

A collaborative effort

While he was the one to make emergency fixes today, Zet-sensei credited Dvodnenko for all his work on the core.

“srg320 did all the hard work and research,” Zet-sensei said on Bluesky today.

He pointed out that Jotego helped, too, although one of their ideas didn’t pan out.

“Jotego also submitted some excellent ideas, which are partially included,” Zet-sensei said on Bluesky. “One was rejected, even though it’s in the SH7604 development manual. In our tests from a real chip, if I add that change, the test returns some errors.”

Dvodnenko has been somewhat quiet since the last time SHIRO! reported on the Saturn core in November. He made small updates in December and February — the former to fix SMPC timings for a bug in Shinobi Legion, and the latter to add keyboard support contributed by kconger.

According to the project’s GitHub, these are the updates that have been made since mid-November:

• SH1:
  • merge ROM and RAM into a single module to save on memory blocks
• DDRAM:
  • additional cache for RAM-H channel (single SDRAM build)
• SMPC:
  • fix timings of INTBACK status filling (Shinobi-X)
• Miscellaneous:
  • Keyboard emulation
• STV:
  • Fix STV build

None of these updates are available on the main branch of the MiSTer, accessible when users run “update_all,” which was last updated in October. Instead, they’re in “unstable nightlies” cores that can be downloaded from the unstable nightlies channel on the MiSTer Discord server.

Dvodnenko first released a playable build of the core to the public in May 2022 and has updated it many times since then. It was first added to the main MiSTer branch in October 2023, indicating that it was mature enough to be available to all MiSTer users rather than as an optional core that had to be added manually.

Anyone interested in supporting Dvodnenko can do so at his Patreon.

The MiSTer is a field-programmable gate array, a chip that can be changed by programming it to physically emulate retro video game consoles. It includes an SD card reader from which “cores” and games can be loaded.

The cores are the programming that tells the FPGA chip how to configure itself to reproduce the performance of a console. There are cores for a wide array of consoles, from the Atari 2600 to the PlayStation — and, of course, the Saturn.