Saturn Core Updates Added to MiSTer’s Main Branch

The lead developer of the MiSTer’s Saturn core added the last five months’ worth of test updates to the main branch yesterday, making them more accessible to users of the FPGA.

Updating the main branch makes it easier for MiSTer users to get updates — now they’ll download by running “update_all” instead of having to grab each new version of the core separately from the “unstable nightlies” channel on the MiSTer Discord server.

The update also added ST-V Titan as an official arcade core to the main branch.

Sergiy “SRG320” Dvodnenko gave a rundown yesterday of what’s new since the last time he updated the main branch in January on his Patreon page.

“The core works fine now, after years of work,” said Zet-sensei, who works closely with Dvodnenko to test updates to the core.

He said emulation of some quirks of the hardware, like SCU interrupt timings and some extreme cases of 64-bit division on the division unit, is still missing.

“Some quirks on the SH2 could be interesting, especially on the 32X (and fixing the remaining issues),” Zet-sensei added. “And creating a solid baseline for a SH2 module for future arcade boards.”

The main branch build uploaded yesterday had a compilation issue in which scaler timings were off, causing display problems for users who set “vsync_adjust” to 0. It even affected those not using scalers but simple HDMI cables.

A new compilation was pushed to the main branch today that should fix the issue.

According to the project’s GitHub, these are the updates that have been made since the last time SHIRO! reported on the Saturn core in April:

• SH7604:
  • add support for undocumented mirror addresses for WDT (croNSF)
• SCSP:
  • fix RAM access (Touryuu Densetsu Elan Doree freeze)
• VDP1:
  • fix clipping for normal/scaled sprites (Doom patched)
  • fix the timing of the sprite row rendering (Atlantis – The Lost Tales)
  • fix rendering of scaled sprites (Gokujou Parodius Da: KONAMI sign)
• VDP2:
  • fix window vertical position for V240/256 (Castlevania SOTN regression)
  • fix window vertical position in interlace mode (Touryuu Densetsu Elan Doree: last line)
  • fix mosaic function (Powerslave: credits screen)
  • implement the byte write to registers (Shenmue – Back in Yokosuka)
• SMPC:
  • fix Continue condition for INTBACK command (Nights into Dreams: blink)
• Miscellaneous:
  • some cleanup
  • add support for 48Mbit dev RAM cartridge
  • fix for Dezaemon 2 (Biometal logo)
  • update sys
• STV:
  • implement SRAM/EEPROM save
  • fix the STV build compilation
  • rename ST-V_20250612.rbf to Arcade-ST-V_20250612.rbf
  • fixed binary Arcade-ST-V_20250612.rbf

Some of the updates in the last couple months have addressed inaccuracies that came to Dvodnenko’s attention thanks to homebrew software. For example, Fafling’s patch to fix Doom caused floors not to display on the MiSTer. An update in April fixed clipping for normal and scaled sprites that caused that problem.

Another fix was for an action that Frogbull and VBT’s game Shenmue: Back in Yokosuka that official Saturn developer documents say is supposed to be impossible: accessing graphics chip VDP2’s registers by bytes rather than larger chunks of data called “words” and “long words.”

“It is very interesting,” Dvodnenko said on GitHub. “The game uses byte access to the VDP2 registers. But the documentation says that this is impossible. I have never seen this in any official game.”

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.