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Index > DOS > No SSE/SSE2 under DOS!!!!!?????

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MCD



Joined: 21 Aug 2004
Posts: 604
Location: Germany
MCD
Crying or Very sad
How does it come that SSE/SSE2 instructions don't work under DOS with my AMD Athlon XP+? Do they generally don't work under DOS, or are there some MSR to change to enable these instructions?

If yes, are they disabled for energy saving reasons, or just to keep compatibility?
well , they don't destroy any compatibility if proper programming, just like MMX works fine under DOS!

Are there perhaps any AMD/Intel engineers out there who know about this?

I discovered another thing:
Right after starting, SSE/SSe2 instr. are disabled, but after returning from Windows into DOS, these instr. are still enabled, so probably Windows switch something from what I have no idea.

I have already compared lots of MSR/CPUID entries from before and after the windows start, but there are no differences!

HELP!!! Crying or Very sad

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Post 15 Sep 2004, 16:17
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f0dder



Joined: 19 Feb 2004
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f0dder
You must enable them in a control register - iirc it has to do with context switches and generated faults, but I'm probably wrong and the intel manuals holds your answers.
Post 15 Sep 2004, 22:14
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MCD



Joined: 21 Aug 2004
Posts: 604
Location: Germany
MCD
Well ,I actually already tried many control registers, but none of CR0,CR2,CR3 and CR4 was different before and after a Windows start.
Perhaps some undocumented control registers?
Post 17 Sep 2004, 12:51
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MCD



Joined: 21 Aug 2004
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MCD
Crying or Very sad Crying or Very sad Crying or Very sad HEEEEEEEEEEELP, han't anyone a specific idea?

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Post 17 Sep 2004, 13:46
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Matrix



Joined: 04 Sep 2004
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Matrix
MCD wrote:
Crying or Very sad Crying or Very sad Crying or Very sad HEEEEEEEEEEELP, han't anyone a specific idea?


look at the intel.com

i have taken a look yesterday and the only example i have found on the fist visit was: how to optimize 3d on SSE

Smile

MATRIX
Post 17 Sep 2004, 13:48
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MCD



Joined: 21 Aug 2004
Posts: 604
Location: Germany
MCD
Very Happy Cool Exclamation Razz Shocked I FINALLY FOUND OUT!

It's as simple as effective: simply

SET BIT 9 of CR4, an everything is alright!!! Twisted Evil
disabling SSE by resetting this bit works also!

(I simply compared these registers before and after Windows started. I think I must have missed this one before)

Till now, it is only tested on my Athlon XP+.

Has anyone an idea if this works on other CPUs? Anyone an idea?

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Post 22 Sep 2004, 18:04
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f0dder



Joined: 19 Feb 2004
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f0dder
Intel Systems Programming Guide, section 11.4.1: Enabling SIMD Extensions Support... Does *all* SSE instructions fails when bit9 isn't set, or only FXSAVE/FXRSTOR?
Post 23 Sep 2004, 15:06
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MCD



Joined: 21 Aug 2004
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Location: Germany
MCD
On my Athlon XP, ALL SSE-instructions fail, not just FXSAVE/FXRSTOR.
Post 14 Oct 2004, 18:24
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