Jotego adds Rainbow Islands and Thunder Force II to his FPGA arcade cores

FPGA developer Jose Tejada has updated his JTCORES project to include hardware-accurate support for Rainbow Islands and Thunder Force II. The cores are available for MiSTer FPGA, Analogue Pocket, and MiST setups. The JTCORES repository currently supports over 1,050 arcade titles. The project relies on reverse-engineering original arcade printed circuit boards down to the schematic level. This allows modern field-programmable gate arrays to configure digital circuits that match the original chips.

Vertical scrolling on the Amstrad CPC

The new Rainbow Islands support runs on the JTRASTAN core. Tejada noted on his Patreon page that the core relies on a solid base of reverse-engineered chips. The tilemap chip is the only piece derived from MAME documentation. It is a simple component shared with Rastan and Operation Wolf, giving the team high confidence in the core's accuracy. Contributors Andrea, Fulvio, Furrtek, Skutis, and IkaMusume helped build the release.

Tejada recalled playing the Amstrad CPC conversion in his personal notes, highlighting how the use of vertical scrolling helped 8-bit home computer versions of the game. The arcade original is a pure delight with incredibly well thought out design.

An extension of the Ninja Turtles

The addition of Technosoft's Thunder Force II was a surprise contribution by developer NikNakNikNak. It runs as an extension to the JTTMNT core. While the code derives from MAME, it leverages the existing reverse-engineered chips from the Teenage Mutant Ninja Turtles hardware.

Coin overflows and sprite bugs

The update includes several arcade bug fixes across the broader JTCORES library. The Final Round sprite bug at the end scene is fixed. Caliber 50 and Ghosts'n Goblins no longer have random crashes. The Arkanoid 2 coin overflow bug is also resolved. The alternatives folder now has support for an OutRun hack and new Street Fighter 2 versions.

The JTCORES project is a massive undertaking, with Tejada and his contributors mapping out custom chips from Konami, Namco, and Capcom to prevent these games from disappearing when the original capacitors leak or custom chips fail. Tejada asked Patreon backers to link their accounts to GitHub to help manage the workload. Backers who link their accounts receive an automatic invite to the jtbeta repository on GitHub. Posting issues in the jtbeta repository gives them higher priority than the standard public tracker. The system requires the automated Patreon link to manage access, just like the project's Discord server.