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From: burgess%creek.decnet@hqhsd.brooks.af.mil (CREEK::BURGESS)
Newsgroups: comp.os.minix
Subject: Re:  IBMPC Demo Disk
Message-ID: <45302@nigel.ee.udel.edu>
Date: 20 Feb 91 23:40:31 GMT
Sender: mmdf@ee.udel.edu
Lines: 61

Quoting:  Stephen Quigg <steveq%SYD.DMS.CSIRO.AU>
> What I tried was the following; (we're talking MSDOS here)
>
>debug demo_dsk.ibm
>-w 100,0,0,2d0
>-q
>
>( the "-" is the debug prompt.) What happens is that debug reads in the
>file, and then dumps the image in ram to drive a: ( command means "write
>from memory starting at CS:100 to drive a: (0), starting at sector 0; 720
>blocks (sectors) to be written").
> HOWEVER, when I tried to boot the disk (on several different machines), it
>started to load (got the welcome message), but it fell over before the prompt
>came up. I'm fairly sure that debug dumped the image properly, and the image
>has the correct CRC, so I don't know what the problem is. I'd like to hear
>from anyone else who tries the same.
Steve, & *,
  I am replying here since I can't get to a foreign host.
  This is a good start.  Points to look for the next time:
  1.  Make sure the image size is represented properly.  The file size will
be the BX (high order word)*64K+CX (low order word).  To compute the number
of sectors to dump, take this value and shift right an appropriate amount 
(usually nine bits) to compute the correct number of sectors.  Remember to 
add one to the final count if any bit in the first nine were not zero.
  2.  After the write, restart debug, fill the low end of the workspace with
nulls, and use the load ('l') command to load the disk image back.  With that
accomplished, use the 'n' command to give this image a name, and 'w' it out
to a new file.  Compare these; they should be identical.  For example:

C:\> debug
-ndemo_dsk.ibm			 (identify the file)
-lcs:100			 (no defaults for this boy)	
-r				 (dump registers)
AX:0000  BX:0004  CX:F200 ...    (for example.  BX:CX >> 9 = 0x279)
-wcs:100,0,0,279		 (assuming 512 byte sectors, the default)
 -or-				 (  >--- These are examples. NOT VERBATIM)
-wcs:100,0,0,4F2		 (assuming 256 byte sectors, BX:CX >> 8 = 4F2)
-q
C:\> debug
-fcs:100 L 1000 0		 (fills memory with zeroes)
-lcs:100,0,0,279		 (number of sectors from before)
-nsteve.ibm			 (name the default output file 'steve.ibm')
-w				 (write the file)
4F200 bytes written
-q
C:\> dir *.ibm
   compare the sizes.
   use debug to compare the resulting files.
   Once loaded into debug, they should be identical.

3.  Finally, make sure that the systems you are working on are really minimal 
configurations.  It should work on an IBM-PC XT compatible, assuming you don't
have an 'unoriginal' hard drive, video, keyboard, etc.  The fact that it fails 
on many systems implies a problem with the image (IMHO).  

4.  BTW, good idea.  I was writing a PROGRAM to do this.  Silly me, I had a
wheel here all along...

TSgt Dave Burgess
Armstrong Lab, Det 4
Brooks AFB, TX