[Coco] OS9 RBF IT.TYP ????

[gene heskett]

On Friday, June 17, 2011 10:29:54 PM Willard Goosey did opine:

> Bit 5 of the TYP byte in an RBF device descriptor is a flag for "CoCo
> format" or "non-coco format".
> 
> What exactly does this imply?
> 
> I'm looking at reading/writing foreign disk formats but this is
> confusing me.
> 
> Thanks,
> Willard

I believe that if set, placing a hexidecimal $20 in that byte, that is the 
flag that says its a std coco floppy disk.

But this a std that encompasses the 35T SS, 40T SS, 40T DS, and 80T DS or 
SS formats.

If this bit is not set (AND($20, IT.TYP)=$00, then it is up to your driver 
to use other means to identify the disk.  This might even involve doing a 
seek to LSN0 by directly driving the stepper outward until the drive says 
its on track zero, letting the disk turn at least a turn, and then reading 
both the sector register and track register of the fdc chip.  Or ask it to 
read sector zero of track zero, if error, try sector 1 of track zero.  If 
that works, try sector zero of track one.  At some combination of 0,0; 0,1; 
1,0; 1,1, you should be able to get a valid read but be sure and ask for 
512 bytes if expecting a messydos disk, or even less than 256 for some of 
the other older formats.

I fooled with that sort of thing using disk basic's discon routines, but 
its 20+ years back up the log, so I don't recall a lot of details.

Cheers, gene
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