[Coco] high density floppy controller mods

[Mike Pepe]

Warren Hoslet wrote:

> -
> The extra gaps required for the additional 18 sectors may make things 
> pretty tight. Isn't that why PC disks went to 512 bytes per sector (to 
> double the data bytes per-track without increasing the sector count)?
> 
> In any event, to modify Disk Basic 1.1 (2.1) to format more 
> sectors-per-track, you need to poke the new sector count into the 
> following addresses:
> 
> $D5B6   $D5B8   $D5C5   $D5C9   $D5D2   $D67B   $D6BC
> 
> Also note that the DSKINI routine will only check to make sure that 
> there is enough unreserved memory available in the 32K Basic RAM to 
> format the standard 18 sector track.
> 
> If you want to allow the DSKI$ and DSKO$ commands to be able to read and 
> write to the higher sector numbers, then you should poke the new sector 
> count minus one into location $D540.
> 
> DISCLAIMER: I have never actually tested this, so I can't gaurantee that 
> these are the ONLY changes required. You should check out the Disk Basic 
> Unravelled book to learn more about the ROM routines.
> 

Hi Warren,

I poked 36 into all those addresses and successfully formatted a disk. 
DIR returns a blank directory.

The smaller sector size does mean more overhead when compared with a PC 
1.44MB disk, but the spec allows for sectors as small as 128 bytes. So, 
there shouldn't be an issue. Also we know the mod on the old 26-3022 
controller works.

I remember hearing that the unraveled books were available for download 
as a PDF, but I haven't come across them yet. Got a url for me?

Thanks!

-Mike