Introduction to reverse-engineering vintage synth firmware

Summary

In this article we're going to take a look at how to reverse-engineer vintage synthesiser firmware. The synthesiser I've chosen for us to look at is the Yamaha DX7 (See Appendix: Why Choose This Synth?). You don't need a DX7 to follow along at home, but you will need a copy of the DX7 V1.8 firmware (available here) and the Ghidra disassembler. Who is this article for? This article's intended audience is people from a technical background who are new to reverse-engineering, 8-bit architectures, or embedded development. If you come from an electrical-engineering or embedded-software background, you'll probably find the content here a little basic. You'll only need to know a little bit about low-level programming: A basic understanding of how binary and pointers work should be enough. You don't need to know assembly language, or understand any specific processor architecture. A few years ago I decided to give myself a crash course on what goes on inside synthesisers. I ended up writing the article Yamaha DX7 Technical Analysis about what I'd learned. In order to tease out some more details about the DX7's inner-workings, I decided to disassemble the synth's firmware ROM. I didn't have any experience with reverse-engineering binaries, so I had to figure it out as I went. I'm still by no means an expert (if you see any mistakes in this article, please let me know!), but I'd like to share what I've learned. All I had when I started was a copy of the firmware, a copy of the service manual, and a can-do attitude. I knew nothing about 8-bit systems, and absolutely nothing about electronics, but I was willing to give anything a shot. If this sounds like you, read on, and I hope you find this article helpful! Reverse-engineering vintage synthesisers is a great introduction to embedded systems, and can be a lot of fun. In a lot of ways reverse-engineering is a bit like putting together a big jigsaw puzzle. Sometimes putting a new piece in place unlocks a lot of new progress, an...