Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!sun!pitstop!sundc!seismo!uunet!mcvax!hp4nl!philmds!nlgvax!johan
From: johan@nlgvax.UUCP (Johan Stevenson)
Newsgroups: comp.os.minix
Subject: Re: MINIX-ST: Can't boot MINIX from .IMG
Message-ID: <218@nlgvax.UUCP>
Date: 23 Feb 89 21:03:58 GMT
References: <9222@louie.udel.EDU>
Reply-To: johan@nlgvax.UUCP (Johan Stevenson)
Organization: Philips Research Geldrop
Lines: 29

In article <9222@louie.udel.EDU> jack@csmunix.larc.nasa.gov (Jack Dunn) writes:
>I don't think the problem is with using FIXKEYS. I have had the same 
>problem with out using FIXKEYS. In my analysis, the booting program 
>will never work with a correct .IMG file. The error is generated
>when, if I calculated the address right, the 16 bit word located
>at offset 508 ( wp[-2] ) is not zero or when the 16 bit word
>at offset 506 ( wp[-3] ) does not equal the 16 bit word at offset 
>510 ( wp[-1] ). It appears that wp[-1] is a check sum and
>wp[-3] is the start of the data segment. I can not see
>how these words would ever be equal. I have concluded that
>the MINIX.PRG is the not coded correctly. I have go any further
>into trying to correct the problem since it is just as easy to
>boot the system from floppy.

MINIX.PRG is correct. But it needs an exact byte-by-byte copy of the
first 130Kbyte or so of the 00.BOOT floppy.
The problem is caused by TOS copy programs that modify the contents
of the first sector. They force a new random number as disk
identification (not a real problem), but also adjust the checksum.
Unfortunately, bytes 510 and 511 are used for this TOS checksum.
And this coincides with three words of information MINIX stores at
the end of the first sector of MINIX.IMG.
MINIX-ST uses bytes 504 and 505 as checksum.
If I had foreseen all these problems I would have used 510 and 511,
but I haven't. Sorry.
Please use copy programs that do not modify sector 0, for instance
the programs RFLOP.PRG and WFLOP.PRG on diskette 08.TOS.
--
Johan W. Stevenson	johan@pcg.philips.nl		Philips Research