z486: A 486-Class Pipelined FPGA CPU with Integrated Floating-Point

nand2mario.github.io

20 points·matt_d··8 comments

This is the closer we have for having a full 32-bit x86 system with FPU. Even with the lower precision in the x87 FPU by using the FPGA DSP blocks, eventually having a "486DX" (i486 instruction set + FPU) would enable running a massive amount of PC software (1980..2000's). Taking his z386 core (based in the i386 microcode) and adding 486-class optimizations, including a simplified dual I/D L1 cache, vs the unified but more complex L1 cache in i486's, really is a beautiful and imaginative approach.

How many DOS games used an FPU though? I can only think of one.

Games, very few, if any. But software in general, quite a lot.

Mobygames got a list [1]. No idea on accuracy.

1. [https://www.mobygames.com/game/attribute:115/include_dlc:tru...]

A lot more than I thought! I wonder if that’s _requires_ FPU or can use an FPU.

The $64k question! The very first title on the list f. e., Falcon 3.0, only requires it for the "hi-fi" flight model. Quake certainly needs an FPU. Don't know about the others.

So or so, the info needs to be verified for accuracy, e. g. if a 486DX-specced title really needed (or profited from the the presence of) an FPU, or if was just a speed requirement/recommendation. And some of the game covers's spec boxes don't mention anything about an FPU at all. Etc.

> Related work and future work

> ao486 is the closest related open-source design and the CPU behind the established ao486 MiSTer core.

ao486 from 2014 recently mentioned on HN: https://news.ycombinator.com/item?id=49141236

Absolutely excellent!

Open Hardware takes another step forward!

Well done!

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