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MTRR mystery (Announce)

posted by RayeR Homepage, CZ, 02.02.2012, 10:51

> Thanks for your efforts... By the way, on my c2d system with 4 GB RAM,
> MTRRLFBE works fine to enable WC in LFB.
Interesting. I'd like to see how BIOS set MTRRs. Please use this test version
http://rayer.ic.cz/350d/vesatest.zip
and run it twice and grab 2 logfiles. In 1st will be MTRRs before set, in second after set. Now for the test I hardcoded MTRR0 mask to 80000000h, 1 (writeback for lower 2GB). Try on both systems.

> It's only on my i7 system (with 16
> GB) and SandyBridge Intel graphics that it doesn't work. At first, it
> appears to set the WC, but then the entire system locks solid within 1
> second after the apparent success.
Hm it seems to be different kind of error. When some MTRR is overwritten wrong way it may freeze system. On my i5 at work I use nvidia GT230 and it doesn't freeze but didn't tested with inte. vga.

> Tried all BIOS options, PCI latency, etc to no avail. I suspect BIOS memory
> allocation problem is affecting the MTRRs.
This is doesn't releated to caching and MTRRs.

> Isn't there a way to limit the upper limit of RAM detected by HIMEM.SYS or
> some other extended memory manager (QHimem, etc) by use of a switch? Can't
> remember right now, but I thought there was some obscure, undocumented way.
I got this idea too but doesn't work. It must be done on lower level than memory manager.

---
DOS gives me freedom to unlimited HW access.

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