[Coco] Trouble with OmniFlop

[Gene Heskett]

Alex Evans wrote:
> On May 28, 2006, at 10:21 AM, Mike Pepe wrote:
> 
>> 3.5" disks are 96tpi regardless of their capacity. 5.25" disks are 
>> 48tpi if the 40 track variety, 96tpi if the 80 track variety.
> 
> Actually most 3.5" floppies are 192tpi, though I do have a 40 track 3.5" 
> floppy drive which is 96tpi.
> 

wrong...

In fact, all 3.5" floppy drives are 135tpi, even the oddball variable 
speed drives some macs used in times past.  The difference is that 
drivers wrongly assume they have to double step some drives.  This is 
generally a symptom of the descriptor for that drive being 
miss-configured.  If that particular drive software actually uses a 
descriptor, rsdos and most of its ilk do not.

For use on a coco, os9 in particular, specifying 96 tpi is one way of 
preventing the driver from double-stepping the drive.  All os9 device 
descriptors addressing a 3.5" drive should have the DNS byte set for 96 
tpi.  The point being the tpi is a non-item as long as it matches.  A 
descriptor set for 48 tpi will not double step a drive if the drive's 
LSN0 contains data saying it is a 48 tpi drive.  This is true even if 
the drive might be a 233 tpi in actual fact, the important item is that 
one step=one step if they match.

This is totally independent of the number of tracks specified.

-- 
Cheers, Gene