Hi,
I think at this point a comparison should be done with Microsoft's version
on this machine to see if any differences can be detected. Also, I would
run Microsoft's OS in the emulator to see
On Wed, Jul 20, 2016, 3:34 PM Maarten Vermeulen <netraa...@gmail.com> wrote:
> I looked at int 15h lately, int 15h is not supported on older BIOS
> versions but every BIOS has it in the time called now. :)
>
> Error code 86h means "function not supported" and if you get 80h it means
> "invalid command"
>
>
>
>
> Op woensdag 20 juli 2016 heeft Eric Auer <e.a...@jpberlin.de> het
> volgende geschreven:
> >
> > Hi experts,
> >
> > some interesting observations about an old 486 PC in the thread
> > with Dimitris about "Which freedos on 486" on freedos-user...
> >
> > His BIOS answers with AH=86h, carry=UNCHANGED to int 15.e801,
> > also leaving AL unchanged. So it seems to be a good idea to
> > STC before INT 15 when doing the 15.e801 call :-) Note that
> > AH=86 is a common failure code for int 15 functions. I would
> > also suggest to, in addition, treat AH=UNCHANGED as failure.
> >
> > Another issue is that RBIL says for this call that if AX=BX=0,
> > one should use CX and DX as memory size info instead. However,
> > DOSEMU only sets AX and BX and returns CX=DX=0 while FreeDOS
> > HIMEMX and JEMMEX both look ONLY at CX and DX, without even
> > checking for AX and BX! Luckily DOSEMU also supports the two
> > other int 15 calls for memory info afair, but it seems tricky
> > that DOSEMU and FreeDOS disagree about 15.e801, no?
> >
> > Also, it is interesting that the FreeDOS drivers say that if
> > CX is not 3c00 (the max value) then DX must be treated as 0.
> >
> > This sounds like "memory hole below 16 MB means end of RAM"?
> >
> > Finally, JEMMEX and HIMEMX both say "if CX plus scaled DX < 64
> > then fall back to 15.88", which is a somewhat weird way to say
> > "if CX and DX are both 0".
> >
> > RBIL writes about int 15.88 versus the carry flag:
> >
> >> the standard BIOS only returns memory between 1MB and 16MB; use AH=C7h
> >> for memory beyond 16MB
> >
> >> not all BIOSes correctly return the carry flag, making this call
> >> unreliable unless one first checks whether it is supported through
> >> a mechanism other than calling the function and testing CF
> >
> > Interestingly, JEMMEX and HIMEMX decide to trust int 15.88
> > even if it leaves carry unchanged: They CLC before int 15.
> >
> > I think it would be a good idea to check if AH=80, 86 or 88
> > after the int 15 call even if carry is not set, as all those
> > values would be possible return values if int 15.88 failed.
> >
> > What is confusing: JEMMEX works on the mentioned 486, while
> > HIMEMX does not work, not even with /NOABOVE16 and /X, why?
> >
> > Regards, Eric
> >
> > PS: In theory, int 15.c7 would also be a possible call to get
> > info about memory beyond the first 16 MB without 15.e??? BIOS
> > support, but that would only help for a very specific group
> > of PS/2 machines identified by int 15.c0 - not very useful.
> >
> > PPS: The same PC also fails to boot from FAT32 with any SYS
> > newer than 2.6, so SYS apparently sees LBA support while it
> > does not really boot later? See freedos-user, still ongoing.
> > Unclear regarding SYS 3.6e /FORCE:LBA and /FORCE:CHS options.
> >
> >
> >
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> Project founder and developer of BirdOS by FeatherCode
>
>
>
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