Hacker News Reader

Comment by raverbashing | Hacker News Reader

Some things seem downright scary in the first erratas

> Misaligned Selectors: If a 16-bit memory operand is loaded into a segment register, the 80386 hangs if the selector is not word-aligned

> Incorrect Interrupt Vector: If a maskable interrupt occurs immediately after the 80386 has executed an instruction with an 8-bit operand, the interrupt is always assigned a vector number of 0.

I can understand, since they probably did a lot of it by hand. It was also more advanced than the 80286 being 32-bit, memory protection (though I think some of it was on the 80286), etc

View on HN

Actually 386 was almost 100% autogenerated. Only bits done by hand was a glue logic between code generated blocks.

Intel embedded its engineers at Berkeley (afaik) for a full year to work with students on the brand new VLSI software that made 386 possible.

Intel started doing formal proofing of its logic blocks after Pentium FPU fiasco.

I'm not entirely sure if it was quite so heavily software synthesized at that point. I think a lot of the logic and datapath was still done by hand.

The grad student I think you're talking about is (now) Dr. Carl Sechen who developed an Auto Place and Route tool he named Timberwolf. Those tools don't synthesize logic so much as they choose optimal locations and orientations for the standard cells on the wafer and then attempt to route the metal interconnects (all with respect to timing). I think it wound up being rather buggy (to the point they had to keep calling him back from school work to patch some things up) and a fair number of things had to be corrected by hand.

I did hear that some of the units on the 386 were written in some Stanford devised programming language from the pre Verilog/VHDL toolstack days and that a few engineers in design automate hacked up a tool flow to turn that programming language into something synthesizable.

That said I wasn't there and so I can't claim to know for sure. I would wager there are some good interviews and documents either with the Intel Museum folks or the Computer History Museum in Mountain View (which seems to always have both contacts from the day and documents for all the old fun computing hardware).

I read it here http://webee.technion.ac.il/people/kolodny/ftp/IntelCADPaper... plus some stuff written by Randal Bryant (of mossim/cosmos fame)

That's a great article!

The 386 was certainly an ambitious design in comparison to the 286, but the iAPX 432 which was several years before that was even more complex. I wonder what errata there were for the '432...

I guess it wasn't an Errata so much as a "documentation update"

If it's a new design, with no backwards compatibility issues I guess lots of "bugs" became documentation items or "features"

I believe the 286 supported virtual memory and memory protection but lacked a way to go from protected mode back to real mode, so it couldn't multitask real-mode DOS programs.

Sure you could you just wrote into NVRAM the magic cookie "Hey I'm really coming out of protected mode" and pulled reset low. (sarcasm of course)

I worked at Intel at the time and this "hack" really bothered me as a young engineer.

BTW, I read that you were involved in testing early 80386 chips. I have an email sent to you asking for more information on 80386 steppings.

Reply on news.ycombinator.com