Show HN: I486SX_soft_FPU – Software FPU Emulator for NetBSD 10 on 486SX

by mezantrop

1165d ago

42 comments

Description

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

Comments (42)

accrual5d ago

This is super cool and I'm very glad to see such work! Does NetBSD natively support the 486DX CPUs which still have the FPU enabled?

I know OpenBSD dropped support for i486 in 6.8, making 6.7 the last that runs natively on them (FPU or not). The support was lost when moving to LLVM 9 and enabling `-march=i586 on i386`. However, old Socket 3 boards can still run the latest version of OpenBSD if one drops a Pentium Overdrive in. :)

jabl4d ago

Just a few days ago patches were posted proposing to drop Linux kernel support for x86 cpus lacking a FPU: https://lore.kernel.org/lkml/20250425084216.3913608-1-mingo@...

userbinator4d ago

Not only the 486SX but a lot of alternative x86 SoCs aimed at embedded systems have no FPU, including the original Vortex86.

natas4d ago

I wonder if this means we will soon be able to run Netbsd-10.1 (and above) on MiSTer with ao486 core.

queenkjuul5d ago

This is awesome. I'm working on packaging a Linux distro for my 386 and 486, but I've stuck to just using very old kernels.

rzzzt5d ago

That .jpg in the readme file loaded from right to left. What is this sorcery?

hsnewman5d ago

I tried it under the Misterfpga ao486 core and it failed, not finding a partition to boot from. :(

dlachausse5d ago

These used to be very common before Pentium processors. Many (most?) compiler tool chains included a software FPU emulator.

Very cool project!

Turboblack4d ago

finally something really useful, I wish you creative success, you are doing the right thing

bezko4d ago

What are some examples of an OS needing to do floating point numbers calculations?

PrivacyAI5d ago

This is super cool!

evmar4d ago

I noticed math_emulate.c comes from Linux (it even has a " * (C) 1991 Linus Torvalds" bit on it). I was wondering what the license on that code is. It looks like Linux adopted GPL in 1992 so maybe this copy predates that, but it was under some other non-BSD license before that.