Throwing Down The FPGA Gauntlet

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Gauntlet is a well-known arcade game from 1985 with many sequels and ports to more modern architectures such as Xbox and GameCube. Thanks to its popularity and relative age, the original arcade cabinet is well documented with the schematics available online. It was regarded as the most complex and ambitious hardware Atari had ever developed at the time it was released. In what can only be described as an absolute labor of love, [Alex] has recreated the arcade hardware on the Pipistrello FPGA board.

The project can actually play Gauntlet, Gauntlet II, and Vindicators II as they all ran on the same hardware. Four joysticks are supported so up to four players can play, though the EEPROM is emulated in RAM so high scores are reset when the device is powered down. The FPGA is almost out of space and can’t quite squeeze in the SRAM needed. So an SRAM expansion daughterboard is required; nothing a quick board run from our favorite purple PCB manufacturer can’t solve.

In the repo is an incredible write-up detailing the system, how it works, and the process of debugging it. This project also includes a complete simulation of the TMS5220 Voice Synthesis Processor, as Gauntlet was the first coin-operated arcade machine with a voice synthesizer. Getting the video correct was particularly tricky and it took several tries to get the color palette and motion looking right. Since [Alex] didn’t have access to an original Gauntlet arcade cabinet, they had to make do with MAME. After writing a test to make sure the FPGA was working correctly, there were differences between the MAME emulation and the FPGA output. To help out, [Colin Davies] came to the rescue. After [Colin] hooked up an original Gauntlet Arcade PCB with the motion test loaded up, the test showed that the FPGA had the correct behavior.

During development [Alex] actually simulated several frames of the game in ISIM (at a whopping 90 seconds per frame or 90 minutes per in-game second). Using ISIM allowed them to compare system state to MAME and validate the design much faster as they could better inspect the interworkings of the different modules. Using a clever trick of grabbing state from MAME after a few seconds, they primed the FPGA state and saved themselves a few hours of simulation.

If you’re looking to get into old hardware style arcade game development, give the browser-based 8bitworkshop IDE a spin. Or start with something a little smaller in scope and size with this adorable mini CRT arcade cabinet.

Thanks [Alex] for sending this one in!

 

 

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