Path: utzoo!attcan!uunet!kddlab!trl!rdmei!ptimtc!olivea!apple!usc!elroy.jpl.nasa.gov!ames!lll-winken!sol.ctr.columbia.edu!emory!ogicse!littlei!intelisc!hays
From: hays@isc.intel.com (Kirk Hays)
Newsgroups: comp.arch
Subject: Re: True 46 Bit Addressing with 586?
Summary: Silly stunts with the 386
Keywords: Intel 586
Message-ID: <1040@intelisc.isc.intel.com>
Date: 30 Nov 90 22:13:51 GMT
References: <21691@well.sf.ca.us> <8833@scolex.sco.COM> <17126@netcom.UUCP>
Distribution: comp
Organization: Intel Supercomputer Systems Division
Lines: 35

>I doubt even one fullsized 386 segment can be used on a 386 since at
>least 2 segments are required to execute in protected mode; however,
>I would be happy to be shown to be wrong. Please demonstrate without
>aliasing any segments.

That's too easy - just have a single code segment, and never load any
of the other segment registers with anything but 0.  Write a program
that does only reads from memory, never writes to memory, never calls,
never pushes or pops, never switches tasks, and never interrupts.

The spoiler, of course, is the need for areas for page tables, gdt,
tss...

With enough effort, though, you can work around this, too.  Once
you're bootstrapped into 32 bit mode, and you're done loading segment
registers, and interrupts are disabled, all the tables can be
discarded.

I wrote one of these once, as a special purpose black-box, which
received input through the io ports, manipulated it in the registers,
did a lookup in a big memory table, and wrote the result back through
the io ports.  It didn't require 4GB of memory, but similar
applications could.  RAM was used only during initialization, ROM was
mapped into low memory by writing a port after initialization.

A giant state-machine router.

>--
>David Feustel, 1930 Curdes Ave, Fort Wayne, IN 46805, (219) 482-9631

I'm an i860 man, now...
-- 
Kirk Hays - NRA Life.
People should be enabled, not dependent - guns are an enabling
technology.


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