Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!ucsd!ogccse!sparky!harlow
From: harlow@sparky.UUCP (Jay B. Harlow)
Newsgroups: comp.unix.i386
Subject: Re: VP/ix and Merge instruction sets (Was: Re: Can protected mode...)
Message-ID: <2939@sparky.UUCP>
Date: 28 Nov 89 20:51:45 GMT
References: <256D58FD.14619@maccs.dcss.mcmaster.ca> <128383@sun.Eng.Sun.COM> <16784@nuchat.UUCP> <128424@sun.Eng.Sun.COM> <1791@crdos1.crd.ge.COM>
Reply-To: harlow@sparky.UUCP (Jay B. Harlow)
Organization: North Dakota State University, Fargo ND
Lines: 53

In article <1791@crdos1.crd.ge.COM> davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr) writes:
>In article <128424@sun.Eng.Sun.COM> plocher@sun.UUCP (John Plocher) writes:
>
>| If the instructions exist on the 8086 you can use them in the
>| virtual 8086 mode.  
>
>  Correct.
>
>|                     This is a "hardware" mode of the 80386, not
>| a software emulation under Unix.  
>
>  Also correct.
>
>|                                   If the program won't run on
>| an IBM XT, it won't run under 80386 VP/ix or 80386 Merge.
>
>  Grain of truth. If a program runs using protected mode it won't run
>under V86 mode. But there are programs which won't run on an XT which
>do run on a 386, under DOS or V86 mode. Any program which uses only the
>32 bit arithmetic instructions will run fine (and much faster). It may
>NOT use the protected mode, nor addressing modes not available on the
>8088.
>
>  I know what you meant, but what you said was wrong. The arithmetic IS
>available, the addressing modes are NOT available.
                                     ^^^ wrong.

All 386 addressing modes are available in 8086 real mode, & Virtual 86 mode,
(dig out your manuals, assemblers, debuggers & try it, i did it works ;-)

when reading the manual I have there are a few warnings about going over
64K displacements, cause you will cause an exception. (naturaly ;-)

	sample code:

	.data
index	dw ?			; index for table
table	dd 1,2,3,4,5,6		; ok this is a silly table ;-)

	.code
	movzx eax,index		; the index needs to be in 32 bit reg
	mov eax,table[eax*4]	; pull value out of table
;		^^^^^^^^^^^^	; 386 extended addressing mode

			Hope this corrected information helps.
			Jay B. Harlow


-- 
		Jay B. Harlow	<nuharlow@plains.nodak.edu>
	uunet!plains!nuharlow (UUCP)	nuharlow@plains (Bitnet)

Of course the above is personal opinion, And has no bearing on reality...