Date   : Fri, 14 Sep 2007 01:57:02 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: 720K DFS disks anybody?

I've just successfully formatted a disk to 720K double density
with 18 sectors of 256 bytes on each track and installed an HADFS
image on it.
 
Unfortunately, and realllyyyyy annoyingly, there is a bug in all
the Master DFSs that makes it useless. On the B+ the DENSITY signal
is b3 of the drive control register, and b3 of the drive number
passed to OSWORD &7F is copied to it.
 
On the Master, the DENSITY signal was move to b5. Unfortunately,
b3 of the drive number is still passed to b3 of the drive control
register! All it needed was 'ASL A:ASL A' at the appropriate
point! A test with a patched version of DFS 2.24 works perfectly.
 
I can't use the ADFS OSWORD &72 call as that is hard-wired to do
disksec=sector AND 15, disktrk=sector DIV 16, so only disk sectors
0 to 15 are accessible.  Double Grrrr.
 
And it would have just needed another 20 bytes of code in HADFS to
do 720K disks otherwise.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
Sheffield Boundary Review at http://mdfs.net/User/JGH/Docs/Politics/ParlReview