Message-Id: <m0zfOab-000S5AC@inti.gov.ar>
Comments: Authenticated sender is <salvador AT natacha DOT inti DOT gov DOT ar>
From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT gov DOT ar>
Organization: INTI
To: djgpp AT delorie DOT com, shawn AT talula DOT demon DOT co DOT uk
Date: Mon, 16 Nov 1998 10:27:01 +0000
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Subject: Re: Disable DPMI memory caching?
References: <+M9M3kANnJT2EwOV AT talula DOT demon DOT co DOT uk>
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Eli Zaretskii <eliz AT is DOT elta DOT co DOT il> replied to  Shawn Hargreaves 
<shawn AT talula DOT demon DOT co DOT uk>:
> 
> On Fri, 13 Nov 1998, Shawn Hargreaves wrote:
> 
> > with the use of memory-mapped IO registers that are located in the low
> > megabyte of physical memory (0xB8000). At the moment the CPU is caching
> > any writes to these registers, which obviously causes the hardware to
> > miss a lot of commands!
> 
> Does this happen on several types of motherboards?  It surely seems as
> a chipset bug to me!  The motherboard should have no business caching
> memory regions mapped into peripheral devices, ever.

I agree with Eli. In my TGUI9440 driver I map the accelerator in the 0xB7F00 
range and I never experimented such a thing.
 
> > Is there any way to disable caching for a range of conventional memory
> > addresses? I can't find any mention of this in the DPMI spec
> 
> This is not a DPMI issue, so the DPMI spec is IMHO the wrong place to
> look for a solution.
> 
> Many motherboards have a BIOS setup program that allows to
> enable/disable caching of specific memory address regions.  Maybe
> somebody has set that machine to cache those areas?  If such an option
> is available, you could use it to explicitly disable caching.
> 
> Another possibility might be that some memory manager shadows the B800
> region, and the caching actually happens in the remapped addresses.
> To see whether this is the cause, boot into plain-vanilla DOS
> configuration (empty CONFIG.SYS and AUTOEXEC.BAT) and see if the
> problem goes away.  If it does, fiddling with the memory manager
> command line should do the trick.
> 
> Shadowing is also sometimes controlled from the BIOS setup, so looking
> there might also provide some hints.

I vote for this theory ;-)

SET 
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