MiSTer's Sega Saturn core now uses physical LEDs for CD reading

The MiSTer FPGA Sega Saturn core just received an update that maps the physical LEDs on the IO board to show CD reading and save state activity. I think it is so cool that the MiSTer LEDs now indicate CD reading and saved states. It is genuinely handy.

The Sega Saturn is a notoriously complex machine. Sega packed it with two Hitachi SH-2 processors, a custom sound chip from Yamaha, and two separate video display processors. Getting all of these components to talk to each other accurately on a field-programmable gate array takes an enormous amount of work. Software emulators like Mednafen require powerful computer processors to keep all these emulated chips synchronized. The MiSTer recreates the actual hardware logic on a single board. This approach cuts down on input latency and provides a highly accurate way to play the library today.

Developer srg320 (Sergey Dvodnenko) has been maintaining and building this core for years. Our readers should consider supporting him on his Patreon page. He is doing the heavy lifting on one of the most difficult consoles of the 32-bit generation.

Watching the disc spin

The core now assigns the disk LED to the CD buffer read state and the user LED to the backup state. The lights on your MiSTer setup will flicker just like the access light on a real console. Saturn games like Panzer Dragoon Saga and Burning Rangers have notoriously long loading screens. Having a physical light blink to confirm the system is actually reading data and not just frozen is a nice touch. It brings back a bit of the tactile feedback from the 1990s.

A busy week for the dual CPUs

The LED mapping is just one part of a larger batch of updates pushed over the last week. The core received several optimizations for the VDP1 and VDP2 graphics chips. The VDP1 handles the distorted sprites that the Saturn uses to simulate 3D polygons. The VDP2 handles the infinite planes and background layers. Getting these two chips to render frames in perfect harmony is usually the biggest hurdle in Saturn development. Any optimization here helps games run closer to original hardware specifications.

There are also fixes for emulated controllers and lightguns. The core now resets the lightgun registers to prevent the system from using battery-backed RAM as a shift register. Contributor drizzt also pushed a fix for the System Manager and Peripheral Control unit. This corrects the detection precedence for the Stunner lightgun. The core will now properly recognize when the peripheral is plugged in.

Another contributor named Kuba-J fixed the compilation for the ST-V hardware. The ST-V is Sega's arcade board built on the exact same architecture as the home console. It powered arcade cabinets for games like Die Hard Arcade, Radiant Silvergun, and Cotton 2. Keeping the ST-V side of the core running smoothly is a nice bonus for arcade fans who want to play the coin-op versions of these titles.

The Saturn core has come a long way since its early alpha days. You can now boot up Nights into Dreams or Virtua Fighter 2 and expect a highly accurate experience. The addition of physical hardware lights just makes the whole setup feel a little more complete.