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---------------Bridge 4.0--------------
A 4am crack 2014-10-28
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"Bridge 4.0" is a 1983 card game
written by Arthur Walsh and distributed
by Artworx.
COPYA fails miserably and immediately.
EDD 4 bit copy works, and the copy
boots and runs without complaint. This
tells me that there is some structural
protection (i.e. data is stored on the
disk in a non-standard way) but
probably no secondary protection
(e.g. an assembly language routine that
executes during the boot process to
determine whether it's booting from the
original disk).
The original disk appears to boot a
modified DOS 3.3. Listening to the disk
drive, it quickly moves out to track 2,
then back to track 1, then track 0,
then swings out to track $11 to read
the disk catalog and load the startup
program (HELLO or similar). You can
hear a lot just by listening.
Turning to my trusty Disk Fixer sector
editor, I go to "Input/Output Control"
(press "O") and set CHECKSUM ENABLED =
NO. This option ignores checksum bytes
and epilogue sequences -- as long as
the address and data prologue are
standard ("D5 AA 96" and "D5 AA AD",
respectively), this will allow me to
read each sector. And lo and behold, it
works! I can read the data from every
sector on every track.
Given the (relatively) weak structural
protection, I used to turn to the DOS
3.3 master disk, patch the RWTS to
ignore checksums and epilogue bytes
(changing $B942 from "SEC" to "CLC"),
and run COPYA. Then, one fine day, and
completely by accident, I came across
an original disk with a bad sector. I
suppose this shouldn't surprise me.
These floppies are decades old by now;
it's amazing any of them work at all.
The point is, I shouldn't be using
tools that ignore potentially serious
read errors. So no more COPYA+B942:18
patch. From now on, it's Super Demuffin
or Advanced Demuffin to convert disks
to a standard format. Let's see if
AUTOTRACE can capture the RWTS from the
original disk. If not, I'll have to
resort to manual investigation.
[S6,D1=original disk]
[S5,D1=my work disk]
]PR#5
...
CAPTURING BOOT0
...reboots slot 6...
...reboots slot 5...
SAVING BOOT0
CAPTURING BOOT1
...reboots slot 6...
...reboots slot 5...
SAVING BOOT1
SAVING RWTS
For those of you just tuning in, my
work disk uses a custom program that I
affectionately call "AUTOTRACE" to
automate the process of boot tracing as
far as possible. For some disks, this
just captures track 0, sector 0 (saved
in a file called "BOOT0") and stops.
For other disks that load in the same
way that an unprotected DOS 3.3 disk
loads, it captures the next stage of
the boot process as well (in a file
called "BOOT1"). BOOT1 contains sectors
0-9 on track 0, which are loaded into
memory at $B600..$BFFF. This generally
contains the RWTS routines which the
program uses to read the rest of the
disk.
If the RWTS is fairly normal as well
(and my AUTOTRACE program just spot-
checks a few memory locations to guess
at its "normalcy"), there's a good
chance I'll be able to use a tool
called Advanced Demuffin (written in
1983 by The Stack) to convert the disk
from whatever weird format it uses to
store its sector data into a standard
disk readable by unprotected DOS 3.3
disks or any other third-party tools.
In this case, AUTOTRACE extracts the
RWTS routines (generally loaded from
track 0, sectors 2-9 into $B800..$BFFF)
and saves *that* into a third file
called "RWTS".
If anything looks fishy or non-
standard, AUTOTRACE just stops, and I
have to check the files it saved so far
to determine why. But in this case, it
ran all the way through, automatically
capturing BOOT0, BOOT1, and RWTS files.
Now I use plug that RWTS file into
Advanced Demuffin and try to convert
the data on this disk to a standard
format.
[S6,D1=original disk]
[S6,D2=blank disk]
[S5,D1=my work disk]
]PR#5
...
]BRUN ADVANCED DEMUFFIN 1.5
[press "5" to switch to slot 5]
[press "R" to load a new RWTS module]
--> At $B8, load "RWTS" from drive 1
[press "6" to switch to slot 6]
[press "C" to convert disk]
This disk is 16 sectors, and the
default options (copy the entire disk,
all tracks, all sectors) don't need to
be changed unless something goes
horribly wrong.
--v--
ADVANCED DEMUFFIN 1.5 (C) 1983, 2014
ORIGINAL BY THE STACK UPDATES BY 4AM
=======PRESS ANY KEY TO CONTINUE=======
TRK:...................................
+.5:
0123456789ABCDEF0123456789ABCDEF012
SC0:...................................
SC1:...................................
SC2:...................................
SC3:...................................
SC4:...................................
SC5:...................................
SC6:...................................
SC7:...................................
SC8:...................................
SC9:...................................
SCA:...................................
SCB:...................................
SCC:...................................
SCD:...................................
SCE:...................................
SCF:...................................
=======================================
16SC $00,$00-$22,$0F BY1.0 S6,D1->S6,D2
--^--
The disk's own RWTS gave no read errors
on any track. This is the power and the
genius of Advanced Demuffin. Every disk
must be able to read itself. So, let it
read itself, then capture the data and
write it out in a standard format.
]PR#5
...
]CATALOG,S6,D2
C1983 DSR^C#254
426 FREE
A 002 ARTWORX
A 068 BRIDGE4
]RUN ARTWORX
Success! The program loads and runs
without complaint. All further disk
access is done through standard DOS
functions. (It even runs from drive 2!)
While that's excellent progress, I'm
not quite done yet. Booting the
demuffin'd disk directly just grinds
endlessly, because it still has the
original RWTS on it. That is, it still
assumes that the data on the disk is
stored in a non-standard format. But
that's not true anymore, because
Advanced Demuffin just normalized the
disk format. So I need to patch the
RWTS on my copy so it can read itself.
A lot of disks need this sort of post-
demuffin patching, and I got tired of
doing it manually, so I wrote a program
to do it for me. It is called,
unsurprisingly, Post-Demuffin Patcher.
It prompts you to select a slot and
drive, then reads the demuffin'd disk,
checks for a modified DOS 3.3-shaped
RWTS, and applies the necessary patches
so the disk can read itself. (It can
also detect and bypass some nibble
checks.) I've included a copy of Post-
Demuffin Patcher on my work disk; the
full source code is currently available
at <https://archive.org/details/
PostDemuffinPatcher4am>.
[S6,D1=demuffin'd copy]
]PR#5
...
]BRUN PDP
T00,S03,$91 change DF to DE
T00,S06,$AE change DF to DE
(This is the actual output of the
program. Post-Demuffin Patcher prints
out the changes it is going to make
before it writes them to the disk.)
]PR#6
Success! The disk boots and runs with
no complaint. There doesn't appear to
be any further protection. Hooray for
automation.
Quod erat liberandum.
---------------------------------------
A 4am crack No. 153
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