Optimisation

[FORTRANS]

Hi,

"Actual microcode would probably require employment at a chip maker."

Yes, you'd think, but no: I actually found some posted online. (Decided to get un-lazy and do my research.) Here's what I found:

   Thanks, quite interesting.

From these images, he was able to trace the operation of the microcode ROM which was part of that chip (yes, even back then in the 1980s, μprocessors used microcode, contrary to some of what you read).

   Here I am quoting from random pages of "Understanding x86
Microprocessors", Ziff-Davis Press, '99 articles originally
published in Microprocessor Report between September 1987 and
April 1993'.

   One article is titled "Microcode Engine Offers Enhanced
Emulation".  Subtitled "IMS's 3250 Emulates 486, 68040, 6502".
A general microcode discussion covers emulation of existing
CPU architectures and the support of user-defined microcode.

"Very few processor implementations have ever allowed user-
defined microcode, and the few that did--such as DEC's Vax
11/780--the capability usually went unused".

The IMS 3250 instruction set was then discussed.

   In the section titled "Legal Issues", three articles
discuss the Intel and NEC 8086/88 microcode copyright
cases.  Also mentioned is the Intel and AMD 80386 cases.
And Intel and Cyrix cases were mentioned.  And others as
well.  And AMD lost a 287 microcode case.

   So microcode has a fairly long history.

   A different recollection was Transmeta's Crusoe chip
emulating the Pentium.  Described as a virtual machine
using code morphing software to translate different
instruction sets to its internal instruction set.  (IIRC
and Google searches.  I thought it was called a microcode
emulation.)

Cheers,

Steve N.

[daydreamer]

Interesting 
Does this mean we start a microcode subforum?