> > >> Disassembling a standard MSX-DOS V1 boot sector I've come across the
> > >following:
> > >>
> > >> It uses a BDOS function 6 loop to output the boot error string instead
> of
> > >> function 9 (!). Any reason?
> > >
> > >Yes. It probably is a null-terminated string, which sometimes is
> nessacary
> > >if you for instance want to display a '$'-sign, or when you are printing
> an
> > >ASCIIZ-string Dos2 uses for its diskroutines.
> >
> > But this string:
> >
> > C085 426F6F74206572 DEFM "Boot error"
> > 726F720D0A DEFB #0D,#0A
> > C091 50726573732061 DEFM "Press any key for retry"
> > 6E79206B657920 DEFB #0D,#0A
> > 666F7230726574
> > 72790D0A
>
> Ah, no. You have to include the byte after #0A too!!! I bet it is a 0.
>
Well don't bet anymore, because it ends with a '$'.
The next byte is a 0-byte but that is the first byte of a File Control Block (FCB).
>
> > Has not a single $. Neither DOS2 did exist. It's the bootsector as found
> in
> > the Philips NMS 8250 MSX-DOS release *1*.
> >
> > I really don't understand the programming style of the bootsector. Really
> > BAD habits.
>
> Well at the start of COMMAND.COM there is a reason they don't want to use
> "$". Because you can, exept for using the command for it, also view the
> DOS-version by executing COPY COMMAND.COM CON. If they used "$" then at the
> end you would have seen an ugly "$"... When they use a 0, it is not visible.
>
> Only nasty thing is that they didn't let the string start with a code 13
> (Carriage Return)... Then the code of the first Jump wouldn't have been
> visible either.
>
> > >By the way, if you disassemble function 9 you'll see it's nothing more
> but a
> > >loop which calls function 6 until it encounters an '$'.
> >
> > I guess so, but that's precisely the reason to use 9 instead of
> reinventing
> > it and the wheel!
>
> No, it saves some time... :) It saves a CALL and a RET-instruction. And
> besides, they use 0 as terminate-character, and not "$"... (I don't
> understand why, for god's sake why does the stringroutine use "$" as
> terminating character??? CP/M-compatibility, okay. But then why did the
> developers of CP/M choose "$" instead of a 0????
>
> > >Haven't checked that but I'm quite sure, I know quite a bit how Dos is
> > >programmed and I really expect those kind of tricks of them.
> >
> > Tricks? To repeat a ROM function? To use JPs in loopless near jumps??? 8:?
>
> Well okay that's not a trick, I meant it as an expression. But if you want
> to see a Microsoft-trick, try to disassemble (and understand!) the first
> part of the MSXDOS2.SYS-file.
>
> > >> There're spurious JPs where it should have been JRs (!). Plenty of
> > >space??? *:D
> > >
> > >Well JPs are a bit faster than JRs. Speed is more important on MSX than
> > >space I think. Although in the case of Dos they don't seem to use that
> > >policy. But the mapperroutines are as fast as they can get. They get
> credits
> > >from me for that.
> >
> > Faster for an error branch (no S/M code)?
>
> Yes I know it is bullshiddd...
>
> But if you really want to know why they used JP: let's just say that JP is
> generally faster than JR, and you will never get 'out of range'-problems, so
> most programmers use JP all the time. I do too. I hardly use
> JR-instructions. Only sometimes, when it's faster than JPs (for example in
> conditional jumps which are 'false' more than 60% of the times they are
> executed).
>
> So they have probably put an JP there because they always use it, and saw no
> real reason to do it different. Or rather: they even didn't notice that it
> could have been done different.
>
> > >> Is the whole MS firmware this quality?
> > >
> > >:) Well looking to Windows...
> >
> > So now imagine a Windows MegaROM! 8:D
> >
> > GigaROM(tm) with a whole fancooled mapper daughterboard 8:D 8:D
>
> hehehe...
>
> ~Grauw
>
> --
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> email me: [EMAIL PROTECTED] or ICQ: 10196372
> visit the Datax homepage at http://datax.cjb.net/
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>
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