FSVR

The FS1R is a 1998 rack synth built around the YMP706, a tone generator Yamaha never documented and put in exactly two products. It was made for two years, nothing else sounds like it, and a working one now costs more than most people want to spend on a box with a two-line display. I wanted one and could not justify one.

In 2025 Zhiyuan Wan (rgwan) started taking a real FS1R apart. He read the SH7044's 256 KB internal flash out through a hooked UART, dumped the 2 MB EPROM and the PLG150-DX ROM, captured the board's own UART traffic, and published all of it as rgwan/fs1r_firmware_RE, with a Ghidra project that already had the boot, loader, flash and LCD code named. He posted the progress as he went on the yamahamusicians.com forum. None of this exists without that work.

I found it just over a year later, in September 2026, and started reading the decompiled firmware to see whether the CPU side could be rewritten rather than emulated. It could, so I built FSVR on top of rgwan's material. We are working on it together now: he runs a patched firmware on his own unit to poke memory and read registers back, and records the measurements the engine is calibrated against. Hardware analysis is still running, and die shots of the VOP3 are being looked into.

It is a rewrite, not an emulation of the board. The note-on path, the 192.3 Hz tick pipeline, the parameter conversion tables and the 88-algorithm routing table are read straight out of the decompiled firmware and ported to C++. Nobody has register documentation for the two custom chips, so those stay models, and every constant behind them sits in one namespace in the source where calibrating against a recording of a real unit is a single table edit.

The tooling is a large part of why this is possible at all. The first working recreation was written with Claude Fable 5.1, and the analysis has carried on with each frontier model since, reading a decompiled 1998 firmware at something close to source level. Anyone working on the project can use the same tools through the Discord.