DOS 2.5 Enhanced Density Disk Detection

[flashjazzcat]

Can any DOS experts explain to me why DOS 2.5 would attempt to access sector 1024 (VTOC2) on a 720 sector disk? We're getting SIO errors following a directory read when 720 sector DOS disks are mounted via PBI as disk images, but not when they're running through an SIO device as normal. When listing a disk directory, DOS will read - say - two directory sectors, then make three (unsuccessful) attempts to read sector 1024, resulting in a NAK error which is reported on screen. This only happens when the disk is mounted under PBI control.

[+bob1200xl]

Does the PBI 'disk' return $80 to a Status command? I think this is how DOS senses an ED disk.

 

Bob

[Rybags]

The SIO Status command will return the density from a 1050 drive - IIRC the floppy only needs to be present with the door closed, the detection is done by the drive pre-emptively.

 

If memory serves correctly, there is no indication at all on the first 720 sectors of an ED disk that the disk is in fact formatted that way aside from the sector links residing at the end of records and the directory file entries (ie they might point to a sector >=721)

 

Chances are the Status command as processed by the PBI device is returning the bitsetting that indicates an ED floppy.

I don't have the Status record breakdown readily available to me, but it should be reasonably easy to find.

[flashjazzcat]

Nice one guys! I appreciate the quick replies!

[thorfdbg]

The SIO Status command will return the density from a 1050 drive - IIRC the floppy only needs to be present with the door closed, the detection is done by the drive pre-emptively..

I don't have the Status record breakdown readily available to me, but it should be reasonably easy to find.

 

It's bit 7 of the first status byte that needs to be set to indicate ED.

[flashjazzcat]

It's bit 7 of the first status byte that needs to be set to indicate ED.

 

Yep - as I discovered from the docs - but thanks! The fix is being tested as we speak and it's working just fine.