Jaroslav Sýkora Builds a Modern Equivalent to Yamaha's Classic YM2151 Synth, From an iCE40 FPGA

Engineer and vintage computing enthusiast Jaroslav Sýkora, PhD, has built a replacement for the long-discontinued Yamaha YM2151 FM synthesis chip out of a Lattice Semiconductor iCE40UP5k field-programmable gate array (FPGA): AURA.

"[The] YM2151 was created by Yamaha in 1980s, being used by Atari and Sega arcade systems starting in 1984," Sýkora writes of the chip's storied history in a blog post brought to our attention by Adafruit. "As of 2023, this chip is perhaps a quarter of century out of production. The chip interfaces with then-standard 5V TTL logic, and the D/A [Digital to Analog] converter YM3012 even requires +/- 12V rails for its analog output."

Sýkora wanted a modern and easily-obtainable equivalent to the YM2151 for use in the X65, an open source "ultimate computer for everyone interested in the venerable 65-series of 8-bit and 16-bit CPUs" he is in the process of designing, and the similar Commander X16. "I wanted to use a Lattice iCE40 FPGA, to keep in line with the rest of my x65 design (both NORA [for system control] and VERA [for video generation] are iCE40 FPGAs).

"I call the FPGA device implementing the compatible FM-synthesis 'AURA,' from AUdio Retro Adapter. The emulation main part is done by [the] IKAOPM project, which is a Verilog synthesizable replica of the YM2151. AURA outputs the sound in the stereo 16-bit I2S format, which is converted to the analog signal by the WM8524 D/A converter."

To prove the device's capability, and its ability to run without the ±12V supply required by Yahama's original implementation, Sýkora showed off a jukebox program: Calliope. "It can play files in the ZSM format," he explains, "[and] it supports output through the VERA PSG and YM2151 FM-synth."

The full project write-up is available on Sýkora's blog, while the source code and machine hardware design files has been published as part of the X65 project on GitHub under the permissive MIT license.

Main article image courtesy of Baz1521, Creative Commons Attribution-Share Alike 3.0 Unported.