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Dif. MTRR WC setting behavior under v86-question for Japheth (Developers)

posted by RayeR(R) Homepage, CZ, 29.12.2018, 01:11

Hi,
FalcoSoft from VOGONS discovered (and I confirmed that) a strange behavior of DOS programs using LFB when MTRR WC setting is appllied under v86 mode. All you know well my MTRRLFBE tool. It can run under realmode as well as in v86 mode (JEMM/EMM386 doesn't matter what mmgr). It does its job to set MTRRs. Under real mode all games and apps benefits from significant speed up that WC mode brings. But under v86 only SOME programs make speed up. I discovered that modern programs and game engines like QDos, Q2Dos and Hexen II compiled by DJGPP that use a DPMI server makes speed up even under v86 while older games like Blood, Duke 3D or profile benchmark from SciTech tools that use DOS4GW extender doesn't make any speed up. This is a question for true memory management expert :) I suspect that it may have something to do how the extender maps physical LFB address to linear address of the application. I never wrote a program with Watcom C for DOS4GW but I suppose it has something similar to __djgpp_map_physical_memory (that is alias to a DPMI function) and it might do things different way.

So how to fix this problem? Do we need some update of DOS4GW (or DOS32A?) or can it be fixed in JEMM?

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

 

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