		      DOUBLE SIDE DISKS ON V9T9
		      =========================
This zip file contains the V9T9DS.EXE file, which is the V9T9.EXE modified 
by Andy Becker on July 2001 so as to handle Double Side Disks on 
V9T9 (TI emulator on a a PC). 

A well known bug in V9T9 was the impossibility of reading Double Sided 
Disks, something that the original TI Floppy Disk Controller was able to do.
The Andy Becker's patch fixes this bug.

Please read the below e-mail message from the author to TI OLUG 
(On Line User Group). For your convenience, the V9T9.EXE file is already 
patched. You simply have to copy V9T9DS.EXE file to your V9T9 directory and 
modify your links and references to point to the new V9T9DS.EXE file. 
So, you will be able to execute the new V9T9DS.EXE and not the old V9T9.EXE. 

Alternatively, and to avoid changing links and references, you can: 
1) Go to your V9T9 directory
2) Rename the old V9T9.EXE as V9T9OLD.EXE
3) Copy to V9T9 directory the V9T9DS.EXE file
4) Rename V9T9DS.EXE as V9T9.EXE

===========================================================================
Da: <ab31@juno.com>
A: <ti99-4a@yahoogroups.com>
Oggetto: [ti-99/4a] Re: V9T9 bug fix
Data: mercoled 4 luglio 2001 16.47

I figured out how to assemble a new V9T9.EXE file with the modification
to handle double sided disks. The 180 KB disk image files are in logical
sector number order and can be created by Paolo's TI99-PC or by running a
disk manager program in V9t9 and using the function to initialize a disk.
I was told that there are already many 180 KB disk images on the whtech
FTP site. I suppose they are usable by PC99. Does anybody use V9t9 and
want 180 KB disks for it? Do you want to see the new version on whtech?

If you would like to fix your V9T9.EXE file yourself, it should be
possible by using PKLITE and a file editing program such as Norton
Utilities. You would use the PKLITE "-x" option to make a decompressed
version of V9T9.EXE. You could use the command "PKLITE -x V9T9.EXE
V9T9BIG.EXE". Then use the file editor in hexadecimal mode to find the
ten byte hexadecimal string "33 C9 8A 0E 1D 9D 2B C1 F7 D0" in the
decompressed file. I'm assuming that the file editor has a search
function because searching for it with your eyes would take a long time
and I wouldn't recommend it. Change those bytes to "F6 D0 8A 0E 1D 9D 00
C9 00 C8" and save the changes to disk. Then you can use PKLITE again to
make another compressed version of V9t9 (something like "PKLITE
V9T9BIG.EXE V9T9DS.EXE" if your decompressed file is V9T9TBIG.EXE and
your new compressed V9t9 for double sided disks is V9T9DS.EXE). If
anybody tries this, I hope you will report to me or the OLUG whether it
worked well. I recommend testing it on a RAM disk or floppy disk at first
to make sure it is working right to minimize the risk to your hard disk.
If you can run a formatting program like Disk Manager II or Disk Manager
1000 and you can create a 180 KB disk image file by initializing a double
sided disk then it is probably working right. The new V9t9 that I tested
was done by assembling all the source code. I only realized that PKLITE
could decompress a compressed executable file after that. Here are the
opcode strings again where you can find them easily.

33 C9 8A 0E 1D 9D 2B C1 F7 D0  original code
F6 D0 8A 0E 1D 9D 00 C9 00 C8  my code

This is the source code for the new opcodes (copied from my message sent
on 06/15/01):

-----
; old buggy part that doesn't work for second side

;	xor	cx,cx
;	mov	cl,DSKtracksside
;	sub	ax,cx
;	not	ax

; corrected routine (by Andy Becker, 06/14/01)

	not	al		; al = -1 - DSKtrack
	mov	cl,DSKtracksside	; tracks per side, normally 40
	add	cl,cl		; cl=cl*2, normally 80
	add	al,cl		; al=al+cl=79-DSKtrack
-----

My newest version of the modification is a little different so it can
handle more than 127 tracks per side but it couldn't be used as a patch
because it assembles to more than ten bytes. The DSR code still can't
handle more than 40 tracks per side. I didn't change that.

If there are any other V9t9 bugs you would like fixed, it might be useful
to let me know what they are. Maybe I can fix more of them.

Andy B. 

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