At  4:05 PM 2/28/94 -0600, Alan Bair wrote:
>Mike Schwartz writes:
>>
>> I have a bit of advise here.  When I wrote MS-DOS or AmigaOS formatted
>> floppies with my own drivers, I wrote two sectors on track 40 of the floppy
>> to fool amigaos into thinking that the disk was indeed an AmigaOS disk but
>> that it was 100% full.  My reasoning was that when someone sticks a disk in
>> the drive and sees a bad volume reported by amigaos, they'd consider
>> formatting it to use it :-)  With the 100% full (fill BAM sector with
>> 0xffff), they saw the disk was valid and could not use DOS or some other
>> program to write on the disk.
>>
>> What was involved was to use ADos to format a blank floppy then use a
>> sector editor to dump track 40 sectors 0 and 1 and see for yourself what
>> the format is.  To add an ADOS disk label, there was an offset into sector
>> 0 for a count+string
>> (not null terminated) and a checksum.  Sector 1 is the bam and should be all
>> 0xffff.  My floppy disk drivers would automatically skip writing or reading
>> data from these two "magic" sectors.
>>
>> You also have to deal with track 0, where the boot sector goes.  Otherwise
>> ADOS will not see it is a valid dos disk.
>>
>
>If bad blocks are supported for floppies under NetBSD, the special ADOS
>blocks could be marked as bad to avoid requiring special code to skip them.
>This could be setup when the disk is formated under NetBSD, though then the
>foramting program would need the special processing code, which could be an
>option. Also, it may be nice to put an ADOS name like "NetBSD_floppy" to
>make it easy to know what kind of disk this is on the ADOS side.
>

Sounds like the hard way to do things...  However, to label the disk, there's
an offset as I mentioned in sector 0 of track 40 where you can put any label
you want.  You need to checksum the track and store it in the right offset as
well.

>
>--
>Alan Bair                       MCTG AMCU DSCS
>Motorola, Inc.                      (Design Software &
>Mail Stop OE-320                     Computer Services)
>6501 William Cannon Dr. West    (512) 891-2336
>Austin, TX  78735-8598          abair@amcu-tx.sps.mot.com



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