Saturn MiSTer Core Gets Mouse Support

The Saturn MiSTer core has seen a flurry of updates in the last week, partially thanks to an unexpected source — another developer.

A developer named Rattboi did a lot of work to add mouse support, and the core’s creator, Sergiy Dvodnenko, aka SRG320, merged that work into the main unstable branch Wednesday.

Earlier this month and in late August, Dvodnenko also fixed a background issue affecting Princess Crown and used a homebrew audio-testing tool to make improvements to emulating the Saturn’s sound chip.

On the left is Princess Crown with a missing background on an earlier version of the Saturn MiSTer core. On the right is Princess Crown running on the current version of the core with its background intact.

The updated core must be manually applied after downloading it from the official MiSTer Discord server’s unstable nightlies channel.

Mouse support brings new functionality to dozens of games, even some light gun games, which is particularly helpful considering MiSTers typically are played on HDTVs that aren’t compatible with light gun controllers.

In fact, Rattboi said he worked on mouse support for the core for Policenauts, a game that has light gun shooter segments.

“[I] was playing Policenauts with my friend and he was like ‘this seems like it should be a mouse game,'” Rattboi said on the MiSTer server.

Meanwhile, the sound chip testing tool developed by Celeriyacon that Dvodnenko first used last month paid dividends almost immediately.

While the tool itself has increased how precisely it measures emulation of the SCSP chip, and the MiSTer core is not yet passing one of those new metrics, it’s nonetheless improved dramatically since last month.

On the left is the SCSP test when it was run on the Saturn MiSTer core in mid-August. On the right is the test when it was run on the core on Sept. 11.

The core’s GitHub lists all of the updates since SHIRO! last reported on its progress in mid-August:

SCSP:

• fix the phase calculation (Bug! sounds)
• fix Alternative loop mode (Sakura Taisen 2 long counter sound)
• some fixes for accuracy (scsptest)
• fix Monitor register update (X-Men vs. Street Fighter, Sega Rally Championship regression)
• some fixes for accuracy (scsptest)

SCU:

• fix IO access (Digital Monster Ver. S)
• cycle accurate B-BUS port to SCSP (scsptest)

VDP1:

• fix update User clipping coordinate (Albert Odyssey)
• fix sprite rendering (Battle Garegga regression)

VDP2:

• fix the Sprite window (Idol Janshi Suchie Pai II)
• fix NBG2/3 rendering when reduction mode is enabled for NBG0/1 (Princess Crown)
• fix Shadow priority (Legend of Oasis, Princess Crown)
• fix the Vertical Counter value (Senkutsu Katsuryu Taisen: Chaos Seed)

SH7604 core:

• fix TE flag clearing (Black Dawn crashes)

Mouse support from Rattboi:

• 3 buttons work, mapped as L->A, R->B, M->C
• The start button still only comes from the controller
• Use either the usb mouse or joystick mouse, and either one works — Swap between to your heart’s delight
• Small refactors to keep ps2 mouse code together
• More cleanup/retab
• Remove some refactor mess w/ mouse buttons

Dvodnenko first released to the public a playable build of the core 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 now the Saturn.