NetBSD 10.x kernel MATH_EMULATION | #define me human

This is my battle-worn, falling-apart laptop rocking an #i486SX CPU from the early ’90s. It’s so ancient that it doesn’t even have an FPU (Actually, that’s not true, they just cut-out FPU from i486DX to make CPU cheaper)! Anyway, I’ve always dreamed of running a modern UNIX-like OS on it.

So, I spent some time resurrecting math emulation in the #NetBSD-10.x kernel, and guess what? I did it! But here’s the kicker—the very moment I finished compiling the kernel, ready to test my work, my laptop decided to stop recognizing the Enter key. Just like that. Now, I have no idea if my FPU emulation actually works or not!

So, #retrocomputing folks—if anyone out there has an i486SX machine and is willing to give this a spin, I’d really appreciate it!

UPD: 11.03.2025: Significant progress

1. FPU-emulation code is triggered by the kernel – done
2. First successful addition operation using FPU instruction: fadd 3.5 + 2.5 for single precision short real – done
3. All other instructions and formats to be checked and probably fixed.

UPD: 31.03.2025: Results delivered to the user

Today the simple, yet correct, calculation results were successfully delivered to the user!

UPD 2025.04.27:🚀 First Release is Here! 🚀

I’m excited to announce the first release of i486SX_soft_FPU — a software FPU emulator for the classic Intel 486SX CPU, running on NetBSD 10!

This project brings floating-point support back to life for 486SX machines, even though modern NetBSD versions no longer natively support processors without a hardware FPU.
If you’re into retrocomputing, operating system hacking, or just love old-school hardware, check it out!

👉 Project page: https://github.com/mezantrop/i486SX_soft_FPU
Contributions, feedback, and testing are all very welcome!

Let’s keep these vintage machines alive! 🔥🖥️

#retrocomputing #NetBSD #486SX #opensource

UPD 2025.05.03: 86Box

Just successfully tested #NetBSD-10.1 with #i486SX #FPU_emulation on #86Box