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From: blk@mitre.org (Brian L. Kahn)
Newsgroups: comp.sys.ibm.pc.hardware,comp.os.msdos.programmer
Subject: Re: XMS -> EMS without using protected mode?
Message-ID: <BLK.91Jan11124410@vanity.mitre.org>
Date: 11 Jan 91 17:44:10 GMT
References: <4602@ruuinf.cs.ruu.nl> <22515@well.sf.ca.us>
	<BLK.91Jan10105610@vanity.mitre.org> <3864@ns-mx.uiowa.edu>
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In-reply-to: williams@umaxc.weeg.uiowa.edu's message of 10 Jan 91 20:20:34 GMT

In article <3864@ns-mx.uiowa.edu> williams@umaxc.weeg.uiowa.edu (Kent Williams) writes:
]In article <BLK.91Jan10105610@vanity.mitre.org> blk@mitre.org (Brian L. Kahn) writes:
]
]>I would like to convert some XMS memory to EMS, without using
]>protected mode.
] ...
]The VLSI and C&T chipsets have hardware that can enable RAM on a page by
]page basis throughout the Processor's address space.  TLB works by mapping
]in RAM to the holes between the ROMS, on top of graphics RAM when you're
]not using Graphics, etc.

Thanks for responding.  This might be general interest, so I'll come
back in a posting.  You seem to understand this, a few more questions:

1) Can these chipsets relocate RAM, or is the RAM "behind" ROMs and 
   adapter buffers lost when in real mode?
2) Do any readily available DOS programming books cover some of the
   chipset capabilities?  I know that each chipset will be different,
   but many functions are apparently similar or equivalent.

]>I have seen a manager called LASTBYTE that claims to
]>do this by twiddling the chipset DMA's or something, but LASTBYTE
]>won't run on my machine.  I do have the kind of chipset they support,
]>so I bet my hardware could do this with the right software.
]
]The two sentences contradict each other.  Try the latest version off of
]SIMTEL20, V1.17.  It understands nearly all C&T chipsets for 286 and 386,
]and has recently added support for a VLSI chipset.  It comes with a test
]program that can tell you whether it will work with your computer.  This
]program is available in a separate smaller ZIP file, so you don't waste
]time downloading the whole thing if it won't work.

If your lucky.  The reason these sentences contradict is that the test
program says "Lastbyte 1.17 will work on your computer" but I can't
get it to work.  No matter how I configure my setup, I get an error
message complaining "Shadow ram disabled/relocated - change setup",
and I just can't get Lastbyte (v1.17) to run.  Too bad, looks like
just what I want.

I've got an Enhanced Phoenix BIOS that includes setup in ROM.  The
setup screen gives me three options for the Intel 82335 (?) Memory
Controller, enabling or disabling DOS BIOS shadow, Video BIOS shadow,
and memory relocation.  I think that relocation moves otherwise unused
RAM up above 1 meg.  Another series of screens supports some 'extended
features', but these seem to all be associated with protected mode.
Disabling 'extended features' boots the machine in real mode.

] ...
]There are commercial products that simulate EMS using expanded memory, but
]they're an order of magnitude slower than the real thing.

Is it true that EMS -> XMS runs slower because those drivers use the
CPU to copy data from XMS to the EMS window?  What does "real" EMS do,
use DMA from the chipsets or remap the hardware?

--
B<   Brian Kahn   blk@security.mitre.org   "may the farce be with you"