Microcode, which is a no-go for modern designs

[dwight]

I believe that is the one. Intel tried to say it wasn't an issue until it was shown that the error was significant when using floating point numbers near integer values. I suspect that the fellow that forgot to include the mask file for that ROM got a bad review.
Dwight

________________________________
From: Eric Smith <spacewar at gmail.com>
Sent: Wednesday, January 2, 2019 3:42 PM
To: dwight; General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Microcode, which is a no-go for modern designs

On Wed, Jan 2, 2019 at 4:12 PM dwight via cctalk <cctalk at classiccmp.org<mailto:cctalk at classiccmp.org>> wrote:
I  thought I'd note that the divide problem couldn't have been patched with a micro code patch.

If you're talking about the Pentium FDIV bug, present on the early 80501 chips (60 and 66 MHz) and 80502 chips (75, 90, and 100 MHz), they weren't able to fix that with a microcode patch. They actually issued a recall for those chips.

However, Intel has successfully fixed other bugs using microcode patches, including some but not all of the recent speculative execution side channel problems (Meltdown and Spectre). They have also used microcode patches to disable instructions that were broken and couldn't be fixed by microcode, including the TSX-NI instructions of some Haswell, broadwell, and Skylake CPUs.