Re: [Freedos-kernel] Boot drive incompatibility with other boot sectors

2004-09-14 Thread Luchezar Georgiev 
The trouble is that most SYSes don't bother to set this value - they 
just copy the whole data area from the old boot sector and replace only 
the code and OEM ID. So the FF remains there. Verified.
_And_ their boot code reuse this field?
Yes. No DOS boot sector trusts BIOS DL value like us...
(Because as I wrote it just can't be trusted very much)
Well, right now I look at boot code of MS-SYS6, and found, that it not 
uses 24h offset itself
Wrong. The read sector subroutine does use it.
See http://www.kzin.com/bootsec/dos5pbra.txt
but pass value from there to kernel.
So the kernel uses it too, thus it's even more important.
I not check what SYS does with original 24h field, but image inside SYS 
contains 80h value, so I doubt that MS-SYS preserves this field.
That the image in SYS contains 80 doesn't prove nothing.
Again, it hurts to be smart when eveyone else is dumb :)
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Re: [Freedos-kernel] Boot drive incompatibility with other boot sectors

2004-09-13 Thread Luchezar Georgiev 
No, they state several times that ONLY 0 AND 80 may be boot drives.
Ok. What about boot managers?
The option mentioned below is for boot managers too.
For this, an option of SYS will revert back to DL = boot drive
Hm. Your arguments sounds reasonable. But I continue to _feel_, that 
using BIOS info instead fixed value is better (except buggy BIOSes, 
which pass wrong drive#).
Did you read my other message about these BIOSes? I repeat it below.
You _suggest_, that _some_ SYS (may) remain untouched 24h field when it 
overwrite boot sector _and_ its boot code reuse this value? Or you know 
such _known and usable_ SYS with such (strange!) behavior? If first, 
then we shouldn't worry about this; if second, then, probably, we should 
force bugfixing of those SYS.
It's like waiting a letter from a dead person, as we say here ;-)
Let me repeat my other message, because it seems that it vanished.
Award BIOS dated 1999 for Intel i810, and the original IBM PC/AT BIOS 
don't seem to pass anything in DL on Int 19h. How did I verify it? For 
those who can't guess, let this be my little secret ;-G

(Table 00653)
Values Bootstrap loader is called with (IBM BIOS):
CS:IP = h:7C00h
DH = access
bits 7-6,4-0: don't care
bit 5: =0 device supported by INT 13
DL = boot drive
00h first floppy
80h first hard disk
The above excerpt from the RBIL also proves that not all BIOSes pass boot 
drive in DL on Int 19h, and even if they do (e.g. IBM BIOS), they pass 
*only* 0 or 80h. Period. (And end of FF kludge ;-)

Regards,
Lucho
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