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math blaster copy protection

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Original source (ia802301.us.archive.org)
Tags: copy-protection math-blaster
Clipped on: 2016-02-28

--------------Math Blaster-------------
A 4am crack                  2014-08-29
---------------------------------------

"Math Blaster" is a 1983 educational
game programmed by Richard Eckert and
Janice Davidson, Ph.D. and distributed
by Davidson & Associates. It comes on
one double-sided disk and uses both
sides.

COPYA fails miserably and immediately
on side A. EDD 4 bit copy gives no
errors, but the copy just hangs early
in the boot process.

Side B appears unprotected. COPYA gives
no read errors, and the copy boots an
entire DOS and runs a startup program
which says "THIS IS THE MATH BLASTER
DATA DISK. PLEASE BOOT YOUR PROGRAM
DISK." Issuing a CATALOG command at
this point shows a standard DOS 3.3
disk catalog with several text files.

Back to side A. Turning to my trusty
Copy ][+ sector editor, I press "P" to
get to the Sector Editor Patcher, and
select "DOS 3.3 PATCHED". 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 track 0. But
everything beyond that is still a
mystery.

Time for boot tracing with AUTOTRACE.

[S6,D1=original disk, side A]
[S5,D1=my work disk]

]PR#5
CAPTURING BOOT0
...reboots slot 6...
...reboots slot 5...
SAVING BOOT0

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 (like
this one, apparently), it 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"), 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". There's a good
chance I'll be able to load that "RWTS"
file into a tool called Advanced
Demuffin (written in 1983 by The Stack)
to convert the disk into a standard
disk readable by unprotected DOS 3.3
disks or any other third-party tools.

If anything looks fishy or non-
standard, AUTOTRACE just stops, and I
have to check the files it saved so far
to determine why. In this case, it
stopped after capturing T00,S00. So I
need to look at that sector and figure
out why.

]CALL -151

*800<2800.28FFM

*801L
.
. all normal, until...
.
084A-   4C C0 B6    JMP   $B6F0

A little something extra before the
boot1 code. I don't like extra. Extra
is bad.

In a normal DOS 3.3 disk, the code on
T00,S00 is actually loaded twice: once
at $0800 and then again at $B600, where
it remains in memory until you reboot
or do something to intentionally wipe
it out. So I can see what's going to be
at $B6F0 by looking at $08F0.

*8F0L

; odd
08F0-   A9 AA       LDA   #$AA
08F2-   85 31       STA   $31

; odd x2
08F4-   A9 AD       LDA   #$AD
08F6-   85 4E       STA   $4E

; suspicious (since this code is loaded
at $B600, this will overwrite the $AA
byte in the LDA instruction above)
08F8-   8D F1 B6    STA   $B6F1

; continue with boot1
08FB-   4C 00 B7    JMP   $B700

This code is important, but it's not
obvious why unless you've seen the
technique before. Which I think I
have. Let me see if I'm right. First,
I'll need to let my AUTOTRACE program
capture the rest of boot1.

]BRUN AUTOTRACE1
...reboots slot 6...
...reboots slot 5...
SAVING BOOT1

]BLOAD BOOT1,A$2600
]CALL -151

*FE89G FE93G     ; disconnect DOS

*B600<2600.2FFFM ; move RWTS into place

*B92FL

B92F-   6C 6C 6C    JMP   ($6C6C)
B932-   6C 6C 6C    JMP   ($6C6C)
B935-   6C 6C 6C    JMP   ($6C6C)
B938-   6C 6C 6C    JMP   ($6C6C)
B93B-   6C 6C 6C    JMP   ($6C6C)
B93E-   6C 6C 6C    JMP   ($6C6C)

Umm, that was not what I was expecting.
At all. That's supposed to be the part
of the RWTS code that checks for the
address epilogue bytes ("DE AA"). But
that's not even real code.

(For the record, I was trying to show
that the RWTS uses those magic zero
page values that are initialized at
$B6F0. It probably does still do that,
but I can't show it yet because this
RWTS is... special.)

Let's back up. Boot1 starts at $B700.
What's at $B700?

*B700L

B700-   A0 1A       LDY   #$1A
B702-   B9 00 B7    LDA   $B700,Y
B705-   49 6C       EOR   #$6C
B707-   99 00 B7    STA   $B700,Y
B70A-   C8          INY
B70B-   D0 F5       BNE   $B702
B70D-   EE 04 B7    INC   $B704
B710-   EE 09 B7    INC   $B709
B713-   AD 09 B7    LDA   $B709
B716-   C9 C0       CMP   #$C0
B718-   D0 E8       BNE   $B702

Well, that explains it. The first thing
boot1 does is decrypt itself (well,
everything after the first $1A bytes,
which is how long the decryption loop
is). Unfortunately, there's no room to
insert a break after the decryption
loop. Fortunately, I don't have to,
because the decryption is simple enough
that I can replicate it outside of the
original boot process.

*C500G    ; because I overwrote DOS
...

]RENAME BOOT1,BOOT1 ENCRYPTED
]BLOAD BOOT1 ENCRYPTED,A$2600
]CALL -151

0300-   A0 1A       LDY   #$1A
0302-   B9 00 27    LDA   $2700,Y
0305-   49 6C       EOR   #$6C
0307-   99 00 27    STA   $2700,Y
030A-   C8          INY
030B-   D0 F5       BNE   $0302
030D-   EE 04 03    INC   $0304
0310-   EE 09 03    INC   $0309
0313-   AD 09 03    LDA   $0309
0316-   C9 30       CMP   #$30
0318-   D0 E8       BNE   $0302
031A-   60          RTS

*BSAVE DECRYPT BOOT1,A$300,L$1B

*300G

*BSAVE BOOT1 DECRYPTED,A$2600,L$A00

*FE89G FE93G     ; disconnect DOS

*B600<2600.2FFFM ; move RWTS into place

*B92FL

B92F-   00          BRK
B930-   00          BRK
B931-   00          BRK
B932-   00          BRK
B933-   00          BRK
B934-   00          BRK
B935-   00          BRK

This is not going well.

Let's back up again. The decrypted code
starts at $B71A. What's at $B71A?

*B71AL

; RWTS parameter table setup (normal)
B71A-   8E E9 B7    STX   $B7E9
B71D-   8E F7 B7    STX   $B7F7

; unfriendly reset vector
B720-   A9 6B       LDA   #$6B
B722-   8D F2 03    STA   $03F2
B725-   A9 B7       LDA   #$B7
B727-   8D F3 03    STA   $03F3
B72A-   49 A5       EOR   #$A5
B72C-   8D F4 03    STA   $03F4
B72F-   EA          NOP

; more RWTS parameters (normal)
B730-   A9 01       LDA   #$01
B732-   8D F8 B7    STA   $B7F8
B735-   8D EA B7    STA   $B7EA
B738-   AD E0 B7    LDA   $B7E0
B73B-   8D E1 B7    STA   $B7E1
B73E-   A9 02       LDA   #$02
B740-   8D EC B7    STA   $B7EC
B743-   A9 04       LDA   #$04
B745-   8D ED B7    STA   $B7ED
B748-   AC E7 B7    LDY   $B7E7
B74B-   88          DEY
B74C-   8C F1 B7    STY   $B7F1
B74F-   A9 01       LDA   #$01
B751-   8D F4 B7    STA   $B7F4
B754-   8A          TXA
B755-   4A          LSR
B756-   4A          LSR
B757-   4A          LSR
B758-   4A          LSR
B759-   AA          TAX
B75A-   A9 00       LDA   #$00
B75C-   9D F8 04    STA   $04F8,X
B75F-   9D 78 04    STA   $0478,X

; multi-sector read routine (normal)
B762-   20 93 B7    JSR   $B793

; reset stack (normal)
B765-   A2 FF       LDX   #$FF
B767-   9A          TXS

; slightly odd (usually $9D84 is the
; boot2 entry point, but OK)
B768-   4C 82 9D    JMP   $9D82

That all looks OK, and it proves that
my manual decryption loop worked. But I
still don't know why I'm not seeing the
RWTS code I expected in the location I
expected.

Let's follow the white rabbit, starting
at $B793, the entry point for the
multi-sector read routine.

*B793L

; this is not normal
B793-   4C 00 B8    JMP   $B800

; but the rest of the loop looks
; entirely normal
B796-   AD E4 B7    LDA   $B7E4
B799-   20 B5 B7    JSR   $B7B5
B79C-   AC ED B7    LDY   $B7ED
B79F-   88          DEY
B7A0-   10 07       BPL   $B7A9
B7A2-   A0 0F       LDY   #$0F
B7A4-   EA          NOP
B7A5-   EA          NOP
B7A6-   CE EC B7    DEC   $B7EC
B7A9-   8C ED B7    STY   $B7ED
B7AC-   CE F1 B7    DEC   $B7F1
B7AF-   CE E1 B7    DEC   $B7E1
B7B2-   D0 DF       BNE   $B793
B7B4-   60          RTS

Down the rabbit hole we go...

*B800L

; Hmm, the first thing this routine
; does is restore the code that should
; have been at $B793 (but wasn't,
; because it jumped here instead).
; Which tells me that this is designed
; to be run exactly once, during boot,
; the first time anything uses the
; multi-sector read routine at $B793.
B800-   A9 AC       LDA   #$AC
B802-   8D 93 B7    STA   $B793
B805-   A9 E5       LDA   #$E5
B807-   8D 94 B7    STA   $B794
B80A-   A9 B7       LDA   #$B7
B80C-   8D 95 B7    STA   $B795
B80F-   A9 07       LDA   #$07
B811-   85 4F       STA   $4F

; oh look, we're turning on the drive
; motor manually
B813-   AE E9 B7    LDX   $B7E9
B816-   BD 8D C0    LDA   $C08D,X
B819-   BD 8E C0    LDA   $C08E,X
B81C-   10 12       BPL   $B830

; do something (below)
B81E-   20 3E B8    JSR   $B83E
B821-   8D 00 02    STA   $0200

; do it again
B824-   20 3E B8    JSR   $B83E

; got the same result?
B827-   CD 00 02    CMP   $0200

; apparently "no" is the correct answer
B82A-   D0 0F       BNE   $B83B

; try again
B82C-   C6 4F       DEC   $4F
B82E-   D0 F4       BNE   $B824

; give up
B830-   A9 08       LDA   #$08
B832-   8D 7A B7    STA   $B77A
B835-   8D F4 03    STA   $03F4

; jump to The Badlands
B838-   4C 6B B7    JMP   $B76B

; success path ($B82A branches here) --
; continue to real multi-sector read
; routine
B83B-   4C 93 B7    JMP   $B793

; main subroutine starts here -- looks
; for the standard address prologue
B83E-   AE E9 B7    LDX   $B7E9
B841-   BD 8C C0    LDA   $C08C,X
B844-   10 FB       BPL   $B841
B846-   C9 D5       CMP   #$D5
B848-   D0 F7       BNE   $B841
B84A-   EA          NOP
B84B-   EA          NOP
B84C-   BD 8C C0    LDA   $C08C,X
B84F-   10 FB       BPL   $B84C
B851-   C9 AA       CMP   #$AA
B853-   D0 F1       BNE   $B846
B855-   EA          NOP
B856-   EA          NOP
B857-   BD 8C C0    LDA   $C08C,X
B85A-   10 FB       BPL   $B857
B85C-   C9 96       CMP   #$96
B85E-   D0 E1       BNE   $B841
B860-   48          PHA
B861-   68          PLA

; skips over the first half of the
; address field
B862-   A0 04       LDY   #$04
B864-   BD 8C C0    LDA   $C08C,X
B867-   10 FB       BPL   $B864
B869-   48          PHA
B86A-   68          PLA
B86B-   88          DEY
B86C-   D0 F6       BNE   $B864

; look for track number 0
B86E-   BD 8C C0    LDA   $C08C,X
B871-   10 FB       BPL   $B86E
B873-   C9 AA       CMP   #$AA
B875-   D0 CA       BNE   $B841
B877-   48          PHA
B878-   68          PLA

; look for sector number 0
B879-   BD 8C C0    LDA   $C08C,X
B87C-   10 FB       BPL   $B879
B87E-   C9 AA       CMP   #$AA
B880-   D0 BF       BNE   $B841

; skip the rest of the address field,
; then get the value of the raw nibble
; that follows
B882-   A0 05       LDY   #$05
B884-   BD 8C C0    LDA   $C08C,X
B887-   10 FB       BPL   $B884
B889-   48          PHA
B88A-   68          PLA
B88B-   88          DEY
B88C-   D0 F6       BNE   $B884
B88E-   60          RTS

The original disk has two address
fields for T00,S00. One of them is the
start of the actual sector data. The
other one is a decoy that has an
address field but no data field. The
raw nibbles immediately following the
two address prologues are different,
and this routine checks to ensure that
they are different.

The routine in the disk controller ROM
(usually at $C65C) that looks for track
0 sector 0 will ignore the decoy if it
happens to find it before the real one.
(Technically, it will look for the data
field, not find it in a reasonable time
frame, and start over, and eventually
it will find the real address field as
the disk continues to spin.) This decoy
is apparently enough to fool bit copy
programs.

Never a dull moment in the land of
Apple II copy protection.

This is all very interesting -- and it
explains why my bit copy would just
hang during boot -- but it doesn't get
me any closer to understanding this
disk's custom RWTS.

Let's back up.

*B793L

B793-   4C 00 B8    JMP   $B800
B796-   AD E4 B7    LDA   $B7E4
B799-   20 B5 B7    JSR   $B7B5

Ignoring the JMP for the moment, the
multi-sector read routine calls the
standard $B7B5 entry point to actually
read a single sector.

*B7B5L

; this is normal
B7B5-   08          PHP
B7B6-   78          SEI

; definitely not normal (usually $BD00)
B7B7-   20 00 BA    JSR   $BA00

; the rest is all normal
B7BA-   B0 03       BCS   $B7BF
B7BC-   28          PLP
B7BD-   18          CLC
B7BE-   60          RTS
B7BF-   28          PLP
B7C0-   38          SEC
B7C1-   60          RTS

That explains why I couldn't find the
RWTS code I expected in the location I
expected. This RWTS is laid out
completely differently in memory than
the standard DOS 3.3 RWTS. Even the
entry point is different ($BA00 instead
of $BD00).

*BA00L

BA00-   85 48       STA   $48
BA02-   84 49       STY   $49
BA04-   A0 02       LDY   #$02
BA06-   8C F8 06    STY   $06F8
BA09-   A0 04       LDY   #$04
BA0B-   8C F8 04    STY   $04F8
BA0E-   A0 01       LDY   #$01
BA10-   B1 48       LDA   ($48),Y
BA12-   AA          TAX
BA13-   A0 0F       LDY   #$0F
BA15-   D1 48       CMP   ($48),Y
BA17-   F0 1B       BEQ   $BA34

Yup, that looks like an RWTS entry
point.

After seconds of furious investigation,
I found the RWTS code that looks for
the data prologue:

*BDE1L

BDE1-   BD 8C C0    LDA   $C08C,X
BDE4-   10 FB       BPL   $BDE1
BDE6-   49 D5       EOR   #$D5
BDE8-   D0 F4       BNE   $BDDE
BDEA-   BD 8C C0    LDA   $C08C,X
BDED-   10 FB       BPL   $BDEA
BDEF-   C5 31       CMP   $31     <-- !
BDF1-   D0 F3       BNE   $BDE6
BDF3-   A0 56       LDY   #$56
BDF5-   BD 8C C0    LDA   $C08C,X
BDF8-   10 FB       BPL   $BDF5
BDFA-   C5 4E       CMP   $4E     <-- !
BDFC-   D0 E8       BNE   $BDE6

And there it is, in living color: this
RWTS uses two magic zero page values to
find the data prologue while it's
reading a sector from disk. 

Why? Because f--- you, that's why.
Because it makes the extracted RWTS
useless without initializing the magic
zero page location with the right magic
number. Automated RWTS extraction
programs wouldn't find this. If I load
this RWTS into Advanced Demuffin, it
will not be able to read the original
disk, because the RWTS itself is not
what initializes the magic zero page
location.

This calls for an IOB module. 

What's an IOB module? Well, the author
of Advanced Demuffin anticipated that
he couldn't anticipate everything, so
he made the program extensible. Quoting
from the Advanced Demuffin softdocs:

                 --v--

An IOB module is an interface for the
source RWTS. Advanced Demuffin uses the
IOB module to set up the IOB table and
jump to RWTS.  The IOB module is stored
from $1400-$14FB. When Advanced
Demuffin loads in a IOB module, it
reads the first sector of the file off
the track-sector list and stores it at
$13FC-$14FB. When Advanced Demuffin
wants to read a sector it JSRs to the
IOB module with the phase number,
sector number, and the page number
stored in the A, Y and X registers
respectively. Since the source drive
always has to be drive one, Advanced
Demuffin can make the IOB module very
compact. After it gets the page,track
and sector Advanced Demuffin sets up
the IOB for RWTS using this infor-
mation, and JMPs to RWTS. (It jumps
instead of JSRing, because it lets the
RWTS do the RTS.) Here is a list of the
IOB module that is built in to Advanced
Demuffin:

; Convert phase # to track #
1400-   4A          LSR

; Store track number
1401-   8D 22 0F    STA   $0F22

; Store sector number
1404-   8C 23 0F    STY   $0F23

; Store page number
; [note: original docs have incorrect
;        hex opcode on this line]
1407-   8E 27 0F    STX   $0F27

140A-   A9 01       LDA   #$01

; Store the drive number
140C-   8D 20 0F    STA   $0F20

; Store the read code
140F-   8D 2A 0F    STA   $0F2A

; With high byte of IOB
1412-   A9 0F       LDA   #$0F

; With low byte of IOB
1414-   A0 1E       LDY   #$1E

; Goto RWTS
1416-   4C 00 BD    JMP   $BD00

                 --^--

Basically, Advanced Demuffin only knows
how to call a custom RWTS if it

1. is loaded at $B800..$BFFF

2. uses a standard RWTS parameter table

3. has an entry point at $BD00 that
   takes the address of the parameter
   tables in A and Y

4. doesn't require initialization

As it turns out, that covers a *lot* of
copy protected disks, but it doesn't
cover this one. This disk fails
assumption #3 (the entry point is at
$BA00, not $BD00) and #4 (the RWTS
relies on the values of zero page $31
and $4E, which are initialized outside
the RWTS).

So, let's make an IOB module.

*C500G    ; because I overwrote DOS
...

]CALL -151

; Most of this is identical to the
; standard IOB module that comes with
; Advanced Demuffin (explained above).
1400-   4A          LSR
1401-   8D 22 0F    STA   $0F22
1404-   8C 23 0F    STY   $0F23
1407-   8E 27 0F    STX   $0F27
140A-   A9 01       LDA   #$01
140C-   8D 20 0F    STA   $0F20
140F-   8D 2A 0F    STA   $0F2A

; initialize the magic zero page values
1412-   A9 AA       LDA   #$AA
1414-   85 31       STA   $31
1416-   A9 AD       LDA   #$AD
1418-   85 4E       STA   $4E

; get the address of the RWTS parameter
; table at $0F1E and call the RWTS at
; its non-standard entry point, $BA00
141A-   A9 0F       LDA   #$0F
141C-   A0 1E       LDY   #$1E
141E-   4C 00 BA    JMP   $BA00

Now let's tell Advanced Demuffin to use
this custom IOB as well as the RWTS we
captured from the original disk.

For the longest time, I thought that
Advanced Demuffin would only load RWTS
files from slot 6, drive 1. That's
where the original disk was during boot
tracing, and that's where it needs to
be during demuffining (which is a real
word that I totally just made up), and
that means I ended up swapping floppy
disks like some kind of 24th century
time traveling retronaut.

Then I re-read the Advanced Demuffin
tech notes (which I have included on
almost every work disk I've ever
produced, but apparently never read in
their entirety). And I discovered that
it's trivial to tell Advanced Demuffin
to load RWTS files from slot 5. Note to
self: read the fine manual.

[S6,D1=original disk, side A]
[S6,D2=blank disk]
[S5,D1=my work disk]

]PR#6
]BRUN ADVANCED DEMUFFIN 1.1

--> EXIT TO MONITOR

*F1F:50      ; use slot 5
*800G        ; resume

--> LOAD NEW RWTS MODULE
    At $B8, load "RWTS"
    from drive 1

--> LOAD NEW IOB MODULE
    "IOB" from drive 1

--> EXIT TO MONITOR

*F1F:60      ; use slot 6
*800G        ; resume

--> FORMAT TARGET DISK

...grind grind grind...

--> 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.

I press RETURN to start the conversion
process, and... Advanced Demuffin
crashes.

Wait, what?

Specifically, it crashes the very first
time it tries to read a sector from the
original disk. That probably means that

(a) the RWTS code I extracted from the
    original disk (and decrypted) is
    somehow corrupted or incomplete, or

(b) my IOB module is calling that RWTS
    incorrectly

Since decryption of executable code is
generally an all-or-nothing affair, and
I've already listed through much of it
and confirmed that it contains real
6502 assembly language code (for
example, to find the data prologue),
I'm going to go with (b) my IOB module
is incorrect.

But how? What did I miss? I don't know.

I sat on this for several days, stuck
right here. Then I took another look at
the boot1 code from the original disk.

]PR#5
...

]BLOAD BOOT1 DECRYPTED,A$2600
]CALL -151

*FE89G FE93G     ; disconnect DOS

*B600<2600.2FFFM ; move RWTS into place

*B793L

B793-   4C 00 B8    JMP   $B800
B796-   AD E4 B7    LDA   $B7E4
B799-   20 B5 B7    JSR   $B7B5

That "JMP $B800" instruction gets
replaced immediately at $B800.

B800-   A9 AC       LDA   #$AC
B802-   8D 93 B7    STA   $B793
B805-   A9 E5       LDA   #$E5
B807-   8D 94 B7    STA   $B794
B80A-   A9 B7       LDA   #$B7
B80C-   8D 95 B7    STA   $B795

So, the routine at $B793 ends up
looking like this:

B793-   AC E5 B7    LDY   $B7E5
B796-   AD E4 B7    LDA   $B7E4
B799-   20 B5 B7    JSR   $B7B5

Perfectly ordinary, no? Actually, no.
Here's what it looks like on an
ordinary (unprotected) DOS 3.3 disk.

B793-   AD E5 B7    LDA   $B7E5
B796-   AC E4 B7    LDY   $B7E4
B799-   20 B5 B7    JSR   $B7B5

Spot the difference. Go ahead, I'll
wait.

A and Y get passed through to the RWTS
entry point, which is usually at $BD00
but on this disk is at $BA00.

DOS 3.3 disk:

*BD00L

BD00-   84 48       STY   $48
BD02-   85 49       STA   $49

This disk:

*BA00L

BA00-   85 48       STA   $48
BA02-   84 49       STY   $49

Now do you see it? On a normal disk,
the Y register holds the low byte of
the RWTS parameter table address, and
the accumulator holds the high byte.
But on this disk, those are reversed;
the accumulator holds the low byte, and
the Y register holds the high byte.

Why? Because f--- you, that's why.

Of course, the IOB module I created to
interface with this RWTS was still
putting the low byte in Y and the high
byte in A, so the RWTS was reading a
completely bogus parameter table and
God only knows what happened next.
(Thank goodness the original disk was
write-protected.)

I need a new IOB module.

*C500G
...

]BLOAD IOB,A$1400
]CALL -151

*141A:A0
*141C:A9
*1400L

1400-   4A          LSR
1401-   8D 22 0F    STA   $0F22
1404-   8C 23 0F    STY   $0F23
1407-   8E 27 0F    STX   $0F27
140A-   A9 01       LDA   #$01
140C-   8D 20 0F    STA   $0F20
140F-   8D 2A 0F    STA   $0F2A
1412-   A9 AA       LDA   #$AA
1414-   85 31       STA   $31
1416-   A9 AD       LDA   #$AD
1418-   85 4E       STA   $4E
141A-   A0 0F       LDY   #$0F ; Y=high
141C-   A9 1E       LDA   #$1E ; A=low
141E-   4C 00 BA    JMP   $BA00

*BSAVE IOB SWAPPED,A$1400,L$FB

And here we go again.

[S6,D1=original disk, side A]
[S6,D2=blank disk]
[S5,D1=my work disk]

*C500G
...

]BRUN ADVANCED DEMUFFIN 1.1

--> EXIT TO MONITOR

*F1F:50      ; use slot 5
*800G        ; resume

--> LOAD NEW RWTS MODULE
    At $B8, load "RWTS"
    from drive 1

--> LOAD NEW IOB MODULE
    "IOB SWAPPED" from drive 1

--> EXIT TO MONITOR

*F1F:60      ; use slot 6
*800G        ; resume

--> CONVERT DISK

                 --v--

ADVANCED DEMUFFIN 1.1  - COPYRIGHT 1983
WRITTEN BY THE STACK -CORRUPT COMPUTING
=======PRESS ANY KEY TO CONTINUE=======
TRK:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
+.5:
    0123456789ABCDEF0123456789ABCDEF012
SC0:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC1:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC2:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC3:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC4:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC5:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC6:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC7:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC8:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC9:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCA:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCB:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCC:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCD:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCE:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCF:RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
=======================================
16 SC $00,$00 TO $22,$0F BY $01 TO DRV2

                 --^--

Well, technically it didn't crash. But
it didn't actually work either. Those
"R" flags? Read errors. Every track,
every sector. Remember when I said the
default options don't need to be
changed unless something goes horribly
wrong? (Seriously, I just said that,
like, a minute ago.) This is what
"horribly wrong" looks like. The RWTS
on this disk can't read... the disk.
Seriously, RWTS, you had one job...

Let's back up.

But to where? Either my IOB is still
incorrect (in a new and exciting way
that I haven't figured out yet), or my
extracted RWTS is incorrect. But they
both look fine.

I... I am at a loss.

                   ~

[...time passes...]

[...time passes...]

[...it is pitch black...you are likely
to be eaten by a grue...]

           T
            H
             R
              E
               E

                 M
                  O
                   N
                    T
                     H
                      S

                        P
                         A
                          S
                           S

...and I am no closer to a solution...

                   ~

OK, I picked this up again. This is now
the equivalent of a "cold case" for a
detective -- an old, half-finished
crack that has gone nowhere. On a lark,
and perhaps out of sheer frustration, I
searched the internet for "Advanced
Demuffin bug". Wherein I came upon this
discussion thread on comp.sys.apple2
from none other than Hot Rod (yes,
*the* Hot Rod, from the 1980s):

https://groups.google.com/forum/#!msg/c
omp.sys.apple2/ZhoZd7edtOY/1cZMYIGjjFMJ

Quoting the opening message in full:

                 --v--

Greetings, 

I don't know if anyone still has cause
to use Advanced Demuffin much anymore,
but back in the day, it was a main tool
used to normalize disks (aka 'crack').
Back in 1986, I happened across a bug
in it, wrote it down, and never opted
to fix it.

I had reason to dust it off and use it
again this week, and wouldn't you know
it - I hit that same darn bug again
(which of course I'd forgotten all
about).

The gist of it is that Advanced
Demuffin loads IOBs and RWTS files by
reading the first sector of the file
into memory at a page offset of #$FC
(e.g. $13FC for an IOB, or $B5FC for an
RWTS or wherever the page is set to).
So if you set the page to load an RWTS
as B6, it would read the first sector
starting at $B5FC, not actually $B600.

It does this because the first four
bytes of the first sector of a file
contain the address and length of the
file, and so then the first bytes of
the actual file will then start on the
next page boundary (e.g. $1400, $B600).

This wouldn't be so bad (although you
could clobber four bytes you weren't
expecting on the page preceeding what
you thought was the start), except that
in doing this, it fails to read the
LAST four bytes of the file.

The routine that transfers the sector
data into the target page is at $15C2.
It stores data using the Y-reg as
offset, starting at Y=0 and
incrementing to 0 again. The problem is
that the base address is always the
$xxFC address (obtained indirectly via
$3E.$3F as lo-byte/hi-byte). So when Y
= 0 again, the last address stored to
is only $xxFB, and $xxFC.$xxFF (the
last four bytes) never get stored.

So if the RWTS you're loading has
critical data in those last four bytes
(like say, the read translate table),
it will create all sorts of problems
trying to convert a disk. This is
exactly the issue I hit in 1986, and
then again this week.

Fixing it would be possible, but
cumbersome, as there's no really good
patch space inline. One approach would
be to relocate the routine that's at
$15C2 (e.g. move it out to $1D00) and
patch it with an extra loop that just
gets those last four bytes. Might make
a good 1.2 version.

Anyway, I wanted to mention it so at
least a reference to the info existed.

Anyone end up with a copy of The
Stack's source code?

]HR

                 --^--

Hot Rod claims that Advanced Demuffin
has a bug: it always fails to load the
last 4 bytes of an RWTS file. (Later in
the thread, some replies question
whether this is always true, or indeed
whether this is ever true.) This is
normally not a problem, because those
bytes are unused. (They sometimes
contain patches to DOS 3.3 itself, but
they're not used during the normal
course of reading sectors from the
disk.)

But what if the last 4 bytes *were*
used by the RWTS? What if an RWTS was
arranged... differently?

[S5,D1=my work disk]

]PR#5
...
]BLOAD RWTS,A$2800
]CALL -151

*FE89G FE93G     ; disconnect DOS

*B800<2800.2FFFM ; move RWTS into place

*BF80.BFFF

BF80- 00 00 00 00 00 00 00 00
BF88- 00 00 00 00 00 00 00 00
BF90- 00 00 00 00 00 00 00 01
BF98- 98 99 02 03 9C 04 05 06
BFA0- A0 A1 A2 A3 A4 A5 07 08
BFA8- A8 A9 AA 09 0A 0B 0C 0D
BFB0- B0 B1 0E 0F 10 11 12 13
BFB8- B8 14 15 16 17 18 19 1A
BFC0- C0 C1 C2 C3 C4 C5 C6 C7
BFC8- C8 C9 CA 1B CC 1C 1D 1E
BFD0- D0 D1 D2 1F D4 03 20 21
BFD8- D8 22 23 24 25 26 27 28
BFE0- E0 E1 E2 E3 E4 29 2A 2B
BFE8- E8 2C 2D 2E 2F 30 31 32
BFF0- F0 F1 33 34 35 36 37 38
BFF8- F8 39 3A 3B 3C 3D 3E 3F

That is a nibble table; it is an
integral part of one of the primary
functions of any RWTS: converting the
nibbles that are actually stored on the
disk into the bytes that get stored in
memory (and vice versa).

It is, in a word, extremely important.

That's two words.

*C500G
...

]BRUN ADVANCED DEMUFFIN 1.1

--> EXIT TO MONITOR

*BFFC:00 00 00 00 ; clear last 4 bytes
*F1F:50           ; use slot 5
*800G             ; resume

--> LOAD NEW RWTS MODULE
    At $B8, load "RWTS"
    from drive 1

--> EXIT TO MONITOR

*BFFC.BFFF

BFFC- 00 00 00 00

Hot Rod was right. There is a bug in
Advanced Demuffin.

                   ~

The next chapter of this story centers
on Advanced Demuffin itself. I could
probably work around this bug, perhaps
by making an IOB module that filled in
the 4 bytes at $BFFC..$BFFF with the
values that this particular RWTS needs.
But that's a poor-man's workaround. I
want a real solution.

I'm going to fix Advanced Demuffin.

[S5,D1=my work disk]

]PR#5
...

]BLOAD ADVANCED DEMUFFIN 1.1
]CALL -151

For all the times I've used Advanced
Demuffin, I've never looked very hard
at how it works. I don't even know
where to start looking for the RWTS
load routine. I don't have the source
code. I suppose I'll start at the
beginning.

*800L

0800-   EA          NOP
0801-   78          SEI
0802-   D8          CLD

; disconnect DOS from output vector
0803-   A9 FD       LDA   #$FD
0805-   A0 F0       LDY   #$F0
0807-   84 36       STY   $36
0809-   85 37       STA   $37

; subroutine sets reset vector to $801
080B-   20 B0 12    JSR   $12B0

; text mode
080E-   20 2F FB    JSR   $FB2F

; clear screen
0811-   20 58 FC    JSR   $FC58

; print header and footer
0814-   A2 27       LDX   #$27
0816-   BD D8 12    LDA   $12D8,X
0819-   9D 00 04    STA   $0400,X
081C-   BD 00 13    LDA   $1300,X
081F-   9D 80 04    STA   $0480,X
0822-   BD 28 13    LDA   $1328,X
0825-   9D D0 07    STA   $07D0,X
0828-   A9 BD       LDA   #$BD
082A-   9D 00 05    STA   $0500,X
082D-   9D 50 07    STA   $0750,X
0830-   CA          DEX
0831-   10 E3       BPL   $0816

; set header and footer margins for
; output vector
0833-   A9 03       LDA   #$03
0835-   85 22       STA   $22
0837-   A9 16       LDA   #$16
0839-   85 23       STA   $23

; clear rest of screen (excluding and
; footer)
083B-   20 58 FC    JSR   $FC58

; print text that follows this
; instruction
083E-   20 63 0D    JSR   $0D63

0841..08B6 main menu text
  (high bit 0 except last byte)

; main menu input loop
; X register holds current selection
; (0-4)
08B7-   A2 00       LDX   #$00

; subroutine displays inverse bar on
; current selection
08B9-   20 84 0D    JSR   $0D84

; subroutine waits for keypress (ESC is
; handled within subroutine, all other
; keys are returned in accumulator)
08BC-   20 51 0D    JSR   $0D51

; RETURN key branches to $08DF
08BF-   C9 8D       CMP   #$8D
08C1-   F0 1C       BEQ   $08DF

; <- key branches to $08D5
08C3-   C9 88       CMP   #$88
08C5-   F0 0E       BEQ   $08D5

; -> key falls through, all other keys
; branch back to $08B9
08C7-   C9 95       CMP   #$95
08C9-   D0 EE       BNE   $08B9

; handle -> keypress
; "deselect" current selection by
; printing normal text over inverse bar
08CB-   20 97 0D    JSR   $0D97

; X is index of current selection (0-4)
; so X=X+1 with wrap-around to 0
08CE-   E8          INX
08CF-   E0 05       CPX   #$05
08D1-   90 E6       BCC   $08B9
08D3-   B0 E2       BCS   $08B7

; handle <- keypress
; "deselect" current selection by
; printing normal text over inverse bar
08D5-   20 97 0D    JSR   $0D97

; X is index of current selection (0-4)
; so X=X-1 (with wrap-around to 4)
08D8-   CA          DEX
08D9-   10 DE       BPL   $08B9
08DB-   A2 04       LDX   #$04
08DD-   D0 DA       BNE   $08B9

; handle RETURN keypress first, clear
; screen (excluding header and footer)
08DF-   20 58 FC    JSR   $FC58

; if current selection is not "EXIT TO
; MONITOR", branch to $08F3
08E2-   E0 04       CPX   #$04
08E4-   D0 0D       BNE   $08F3

; handle "EXIT TO MONITOR" text mode
08E6-   20 2F FB    JSR   $FB2F

; clear screen (including header and
; footer, which get reset in $FB2F)
08E9-   20 58 FC    JSR   $FC58
08EC-   58          CLI

; subroutine sets reset vector to $801
08ED-   20 B0 12    JSR   $12B0

; jump to monitor
08F0-   4C 59 FF    JMP   $FF59

; if current selection is not "FORMAT
; TARGET DISK", branch to $08FA
08F3-   E0 03       CPX   #$03
08F5-   D0 03       BNE   $08FA

; jump to routine that handles format
08F7-   4C 9B 0F    JMP   $0F9B

; if current selection is not "LOAD NEW
; IOB MODULE", branch to $0901
08FA-   E0 02       CPX   #$02
08FC-   D0 03       BNE   $0901

; jump to routine that handles loading
; an IOB module
08FE-   4C 00 11    JMP   $1100

; if current selection is not "LOAD NEW
; RWTS MODULE", branch to $0908
0901-   E0 01       CPX   #$01
0903-   D0 03       BNE   $0908

; jump to routine that handles loading
; an RWTS module
0905-   4C 55 10    JMP   $1055

(On a side note, it's a nice change of
pace to disassemble code that's not
intentionally obfuscated.)

*1055L

; clear screen
1055-   20 58 FC    JSR   $FC58

; print text that follows this
; instruction
1058-   20 63 0D    JSR   $0D63

105B..109D "PAGE TO LOAD AT..." text
  (high bit 0 except last byte)

; input subroutine for first digit
109E-   20 C0 0E    JSR   $0EC0
10A1-   B0 FB       BCS   $109E

; range check
10A3-   C9 02       CMP   #$02
10A5-   90 F7       BCC   $109E
10A7-   C9 0C       CMP   #$0C
10A9-   B0 F3       BCS   $109E
10AB-   20 F9 0E    JSR   $0EF9
10AE-   0A          ASL
10AF-   0A          ASL
10B0-   0A          ASL
10B1-   0A          ASL

; store partial value in zero page $4C
10B2-   85 4C       STA   $4C

; input subroutine for second digit
10B4-   20 C0 0E    JSR   $0EC0
10B7-   90 0A       BCC   $10C3

; handle <- keypress
10B9-   C9 88       CMP   #$88
10BB-   D0 F7       BNE   $10B4
10BD-   20 ED FD    JSR   $FDED
10C0-   4C 9E 10    JMP   $109E

; store full value in zero page $4C
10C3-   20 F9 0E    JSR   $0EF9
10C6-   05 4C       ORA   $4C
10C8-   85 4C       STA   $4C

; print text that follows this
; instruction
10CA-   20 63 0D    JSR   $0D63

10CD..10CF three carriage returns
  (high bit 0 except last byte)

10D0-   20 30 11    JSR   $1130

*1130L

; print
1130-   20 63 0D    JSR   $0D63

1133..1168 "FILE TO LOAD" prompt

; handle character input for filename
1169-   20 51 0D    JSR   $0D51
116C-   C9 88       CMP   #$88
116E-   F0 1B       BEQ   $118B
1170-   C9 8D       CMP   #$8D
1172-   F0 27       BEQ   $119B
1174-   C9 A0       CMP   #$A0
1176-   90 F1       BCC   $1169
1178-   E0 00       CPX   #$00
117A-   D0 04       BNE   $1180
117C-   C9 C0       CMP   #$C0
117E-   90 E9       BCC   $1169
1180-   20 ED FD    JSR   $FDED

; store filename in $0200
1183-   9D 00 02    STA   $0200,X
1186-   E8          INX
1187-   E0 1E       CPX   #$1E
1189-   90 D9       BCC   $1164

...

; print
11AC-   20 63 0D    JSR   $0D63

11AF..11B1 ",D_" prompt

; handle input for drive number
11B3-   20 51 0D    JSR   $0D51
11B6-   C9 B1       CMP   #$B1
11B8-   F0 04       BEQ   $11BE
11BA-   C9 B2       CMP   #$B2
11BC-   D0 F5       BNE   $11B3
11BE-   20 ED FD    JSR   $FDED

; munge and store directly in RWTS
; parameter table
11C1-   29 03       AND   #$03
11C3-   8D 20 0F    STA   $0F20

Advanced Demuffin doesn't use the
standard DOS 3.3 BLOAD function, on the
theory that by the time you need to
load an RWTS file, you may not have a
working DOS in memory anymore. Also, to
avoid disturbing any other memory,
Advanced Demuffin loads the RWTS file
into its final location immediately.
(It has its own copy of a standard
RWTS, relocated to $1500.) So it does
everything manually: reading the disk
catalog to find the file's first
sector, then reading that sector to get
the list of tracks and sectors, then
reading each sector into memory one at
a time.

; read T11,S00 into $1F00..$1FFF
11C6-   A9 1F       LDA   #$1F
11C8-   85 4B       STA   $4B
11CA-   A9 11       LDA   #$11
11CC-   A0 00       LDY   #$00
11CE-   20 34 12    JSR   $1234

; find next directory sector (first one
; is usually T11,S0F, then that points
; to T11,S0E, and so on) and read it
; into $1F00..$1FFF
11D1-   20 2B 12    JSR   $122B
11D4-   B0 2E       BCS   $1204

; parse the raw catalog listing to find
; the filename you requested
11D6-   A9 0B       LDA   #$0B
11D8-   85 4A       STA   $4A
11DA-   A0 02       LDY   #$02
11DC-   B1 4A       LDA   ($4A),Y
11DE-   29 04       AND   #$04
11E0-   F0 19       BEQ   $11FB
11E2-   C8          INY
11E3-   B1 4A       LDA   ($4A),Y
11E5-   D9 FD 01    CMP   $01FD,Y
11E8-   D0 11       BNE   $11FB
11EA-   C8          INY
11EB-   C0 21       CPY   #$21
11ED-   90 F4       BCC   $11E3
11EF-   A0 00       LDY   #$00
11F1-   B1 4A       LDA   ($4A),Y
11F3-   48          PHA
11F4-   C8          INY
11F5-   B1 4A       LDA   ($4A),Y
11F7-   A8          TAY
11F8-   68          PLA
11F8-   68          PLA

; found it
11F9-   10 39       BPL   $1234

; didn't find it
11FB-   A5 4A       LDA   $4A
11FD-   18          CLC
11FE-   69 23       ADC   #$23

; try next sector
1200-   F0 CF       BEQ   $11D1

; try next file in this sector
1202-   D0 D4       BNE   $11D8

; print
1204-   20 63 0D    JSR   $0D63

1207..1227 "NO SUCH BINARY FILE EXISTS"

; start over
1228-   4C 30 11    JMP   $1130

...

; read track/sector list of the RWTS
; file into $1F00..$1FFF
1234-   A2 1F       LDX   #$1F
1236-   8E 27 0F    STX   $0F27
1239-   A2 00       LDX   #$00
123B-   8E 26 0F    STX   $0F26
123E-   8D 22 0F    STA   $0F22
1241-   8C 23 0F    STY   $0F23
1244-   A9 01       LDA   #$01
1246-   8D 2A 0F    STA   $0F2A
1249-   20 A9 0D    JSR   $0DA9
124C-   B0 06       BCS   $1254
124E-   A2 00       LDX   #$00
1250-   8E 26 0F    STX   $0F26
1253-   60          RTS

If all goes well, by the time we return
from $1130, the page $1F00..$1FFF looks
something like this:

1F00- 00 00 00 00 00 00 00 00
1F08- 00 00 00 00 1E 01 1E 00
1F10- 1F 0F 1F 0E 1F 0D 1F 0C
1F18- 1F 0B 1F 0A 1F 09 00 00

(The rest of the page is all zeroes.)

That's a track/sector list, stored in
the first sector of every DOS 3.3 file.
Starting at $1F0C, it contains pairs of
[track,sector] in order, followed by
a pair of zeroes. So if this RWTS file
expects to be loaded at $B800, T1E,S01
contains the code from $B800..$B8FF;
T1E,S00 contains $B900..$B9FF;
T1F,S0F contains $BA00..$BAFF; and so
forth.

The subroutine at $1130 was called from
$10D0, so let's continue at $10D3.

Now we have a loop that reads each of
those sectors from disk into the
appropriate page in memory. (Remember,
the high byte of the starting address
is in zero page $4C.)

*10D3L

; get high byte of target address
10D3-   A5 4C       LDA   $4C

; store it in RWTS parameter table
10D5-   8D 27 0F    STA   $0F27

; minus 1, for reasons that will become
; clear shortly
10D8-   CE 27 0F    DEC   $0F27

; get a track and sector from the list
10DB-   A2 10       LDX   #$10
10DD-   86 4A       STX   $4A
10DF-   BD FD 1E    LDA   $1EFD,X

; Y register has track number
10E2-   A8          TAY

; accumulator has sector number
10E3-   BD FC 1E    LDA   $1EFC,X

; branch if out of sectors
10E6-   F0 15       BEQ   $10FD

; actually read the sector into memory
; 4 bytes earlier, to compensate for
; the fact that every DOS 3.3 binary
; file includes a 4-byte header (the
; starting address and program length)
; 
; so, for example, the first sector of
; an RWTS file starting at $B800 would
; actually be read into $B7FC, so that
; the real data ends up being loaded at
; $B800 as expected
;
; this saves a bunch of memory moves
10E8-   A2 FC       LDX   #$FC
10EA-   20 3B 12    JSR   $123B

; increment target page
10ED-   EE 27 0F    INC   $0F27

; check if we've run up against the top
; of writeable memory ($C000 and above
; are not writeable)
10F0-   AD 27 0F    LDA   $0F27
10F3-   C9 BF       CMP   #$BF

; out of space, don't load the rest of
; the file even if there's more to load
10F5-   B0 06       BCS   $10FD

; increment our index into the
; track/sector list
10F7-   A6 4A       LDX   $4A
10F9-   E8          INX
10FA-   E8          INX

; this should always branch unless you
; loaded a ridiculously large RWTS file
; for some reason
10FB-   D0 E0       BNE   $10DD

; all done, jump back to main menu
10FD-   4C 03 08    JMP   $0803

Hot Rod was slightly wrong but mostly
right. There is a bug in this loop, but
it only manifests itself with RWTS
files that are loaded into the highest
writeable part of main memory (just
below $C000).

Suppose you have an RWTS file that is
loaded at $3800 and is $0800 bytes in
length. (I've seen real copy protected
disks like this.) This file will take
up 10 sectors on disk.

S01: track/sector list

S02: 4-byte header (starting address
     and length), followed by $FC bytes
     of data that should be stored in
     $3800..$38FB

S03: $100 bytes of data that should be
     stored in $38FC..$39FB

S04: $100 bytes of data that should be
     stored in $39FC..$3AFB

...

S09: $100 bytes of data that should be
     stored in $3EFC..$3FFB

S10: 4 bytes of data that should be
     stored in $3FFC..$3FFF, followed
     by $FC bytes of unused space

Advanced Demuffin will load S01 into
$1F00..$1FFF, then load the rest of the
sectors (S02-S10) into $37FC..$40FB.
Since it reads each sector directly
into its final memory location (minus
4 bytes), it will end up overwriting
the 4 bytes from $37FC..$37FF, and the
$FC bytes from $4000..$40FB. This is
generally not a problem, since there's
nothing there of any consequence.

Now consider the case of an RWTS file
that starts at $B800 and is $0800 bytes
long. Again, it will take up 10 sectors
on disk.

S01: track/sector list

S02: 4-byte header (starting address
     and length), followed by $FC bytes
     of data that should be stored in
     $B800..$B8FB

S03: $100 bytes of data that should be
     stored in $B8FC..$B9FB

S04: $100 bytes of data that should be
     stored in $B9FC..$BAFB

...

S09: $100 bytes of data that should be
     stored in $BEFC..$BFFB

S10: 4 bytes of data that should be
     stored in $BFFC..$BFFF, followed
     by $FC bytes of unused space

Again, Advanced Demuffin will load S01
(the track/sector list) into $1F00..
$1FFF. Then it will loop through the
next 8 sectors (S02-S09) and load them
into $B7FC..$BFFB. And then it will
stop, because at $10F0 there is a check
to ensure that it doesn't ever write to
nonwriteable memory.

10F0-   AD 27 0F    LDA   $0F27
10F3-   C9 BF       CMP   #$BF
10F5-   B0 06       BCS   $10FD

That branch is taken to avoid writing a
sector's worth of data to $BFFC..$C0FB
(which would indeed cause all sorts of
problems, since there are lots of soft
switches in the $C0xx range). But that
means that it never loads sector 10, so
the last 4 bytes of the RWTS file never
make it into $BFFC..$BFFF.

Now, how do I fix it? Well, according
to the TECH NOTES softdocs, Advanced
Demuffin has some unused space in the
$1D00..$1EFB range. That's plenty of
space to put a patch or two.

Here's what I came up with:

*10D3L

; unchanged
10D3-   A5 4C       LDA   $4C
10D5-   8D 27 0F    STA   $0F27
10D8-   CE 27 0F    DEC   $0F27
10DB-   A2 10       LDX   #$10
10DD-   86 4A       STX   $4A
10DF-   BD FD 1E    LDA   $1EFD,X
10E2-   A8          TAY
10E3-   BD FC 1E    LDA   $1EFC,X
10E6-   F0 15       BEQ   $10FD
10E8-   A2 FC       LDX   #$FC
10EA-   20 3B 12    JSR   $123B
10ED-   EE 27 0F    INC   $0F27

; jump to patch
10F0-   4C 00 1D    JMP   $1D00

; now unused
10F3-   EA          NOP
10F4-   EA          NOP
10F5-   EA          NOP
10F6-   EA          NOP

; unchanged
10F7-   A6 4A       LDX   $4A
10F9-   E8          INX
10FA-   E8          INX
10FB-   D0 E0       BNE   $10DD
10FD-   4C 03 08    JMP   $0803

And here is the actual patch:

*1D00L

; check the target memory address (like
; the original did)
1D00-   AD 27 0F    LDA   $0F27
1D03-   C9 BF       CMP   #$BF

; if we're up against nonwriteable
; memory space, branch
1D05-   B0 03       BCS   $1D0A

; no problem, go back to read loop
1D07-   4C F7 10    JMP   $10F7

; read into $1F00..$1FFF
1D0A-   A9 1F       LDA   #$1F
1D0C-   8D 27 0F    STA   $0F27

; get track and sector of the last
; sector of the RWTS file
1D0F-   A6 4A       LDX   $4A
1D11-   BD FF 1E    LDA   $1EFF,X
1D14-   A8          TAY
1D15-   BD FE 1E    LDA   $1EFE,X
1D18-   F0 0E       BEQ   $1D28

; read the last sector (into $1F00..
; $1FFF)
1D1A-   A2 00       LDX   #$00
1D1C-   20 3B 12    JSR   $123B

; copy the first 4 bytes into place
1D1F-   A2 03       LDX   #$03
1D21-   BD 00 1F    LDA   $1F00,X
1D24-   9D FC BF    STA   $BFFC,X
1D27-   CA          DEX
1D28-   10 F7       BPL   $1D21

; jump back to end of the read loop to
; return to the main menu
1D2A-   4C FD 10    JMP   $10FD

I just fixed a 31-year-old bug without
the original source code.

(While I was in there, I took the
opportunity to make a few other minor
interface modifications. In particular,
I added some keyboard support in the
main menu to change the slot number
without having to exit to the monitor.
Now I can just press "5" to load RWTS
and IOB files from slot 5, then press
"6" to convert the disk in slot 6. I
also added direct keyboard shortcuts
for each item in the main menu. For
example, you can just press "R" to load
an RWTS file or "I" to load an IOB
file. Version 1.1 made you move one
line at a time with the left and right
arrow keys and press RETURN. Oh, and I
also added support for the up and down
arrow keys, because it's the 21st
century and why not.)

And so, Advanced Demuffin 1.5 was born.

                   ~

When I left off, I was trying to
convert side A of "Math Blaster" to a
standard format. I had decrypted the
boot1 code and extracted the RWTS. I
had written an IOB module (actually two
IOB modules, the most recent one called
"IOB SWAPPED") to act as a liaison
between the non-standard RWTS and
Advanced Demuffin. The only thing I
didn't have was a version of Advanced
Demuffin that could load the entire
RWTS file into memory.

But now I do.

[S6,D1=original disk, side A]
[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 "I" to load a new IOB module]
  --> load "IOB SWAPPED" from drive 1

[press "6" to switch to slot 6]

[press "C" to convert disk]

                 --v--

ADVANCED DEMUFFIN 1.5    (C) 1983, 2014
ORIGINAL BY THE STACK    UPDATES BY 4AM
=======================================
TRK:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
+.5:
    0123456789ABCDEF0123456789ABCDEF012
SC0:...RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC1:...RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC2:...RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC3:...RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC4:...RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC5:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC6:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC7:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC8:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SC9:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCA:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCB:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCC:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCD:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCE:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
SCF:..RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
=======================================
16SC $00,$00-$22,$0F BY1.0 S6,D1->S6,D2

                 --^--

Make no mistake: this is definitely
progress. Advanced Demuffin 1.1 failed
to read this disk at all (because of
the 4-byte RWTS bug). Now that I've
fixed that, it can use the RWTS that I
extracted (and decrypted) to read the
disk... but only up to T02,S04.

That track/sector sounds suspiciously
familiar. It's the last sector of DOS,
and it's the first sector read by the
boot1 code.

; relevant boot1 code
B73E-   A9 02       LDA   #$02
B740-   8D EC B7    STA   $B7EC
B743-   A9 04       LDA   #$04
B745-   8D ED B7    STA   $B7ED

After DOS is loaded, I guess the RWTS
is modified to look for a different
data epilogue sequence. But remember,
the third byte of the data epilogue is
stored in zero page $4E (initially set
up at $B6F0). So the DOS doesn't even
need to modify the RWTS code directly;
it just changes zero page $4E.

Turning to the Copy ][+ nibble editor,
it appears that every sector from
T02,S05 to T22,S0F uses "D5 AA B5" as
the data epilogue.

                 --v--

   COPY ][ PLUS BIT COPY PROGRAM 8.4
(C) 1982-9 CENTRAL POINT SOFTWARE, INC.
---------------------------------------

TRACK: 03  START: 2CCB  LENGTH: 015F

2CA8: 9E 9D BE CB 96 9A B7 AC   VIEW
2CB0: A7 DE AA EB DB DB DB DB
         ^^^^^^^^
      data epilogue

2CB8: DB DB DB DB DB D7 AA 97
                     ^^^^^^^^
                 address prologue

2CC0: AA AA AB AB AE AA AF AB
2CC8: AF FF FF FF FF FF FF FF  <-2CCB
      ^^^^^^^^
  address epilogue

2CD0: FF D5 AA B5 A6 E6 FB D3
         ^^^^^^^^
      data prologue

2CD8: AD EC AB F3 B5 DE E5 AE
2CE0: 97 B9 D9 E5 FE D6 E5 F3
2CE8: BD AC B2 DF EA A6 DB DF

---------------------------------------

  A  TO ANALYZE DATA  ESC TO QUIT

  ?  FOR HELP SCREEN  /  CHANGE PARMS

  Q  FOR NEXT TRACK   SPACE TO RE-READ

                 --^--

It appears I need to make a *third* IOB
module.

]PR#5
...

]BLOAD IOB SWAPPED,A$1400
]CALL -151

*1417:B5

*1400L

1400-   4A          LSR
1401-   8D 22 0F    STA   $0F22
1404-   8C 23 0F    STY   $0F23
1407-   8E 27 0F    STX   $0F27
140A-   A9 01       LDA   #$01
140C-   8D 20 0F    STA   $0F20
140F-   8D 2A 0F    STA   $0F2A
1412-   A9 AA       LDA   #$AA
1414-   85 31       STA   $31
1416-   A9 B5       LDA   #$B5  ; new
1418-   85 4E       STA   $4E
141A-   A0 0F       LDY   #$0F
141C-   A9 1E       LDA   #$1E
141E-   4C 00 BA    JMP   $BA00

*BSAVE IOB 3+,A$1400,L$FB

[S6,D1=original disk, side A]
[S6,D2=partially demuffin'd disk]
[S5,D1=my work disk]

*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 "I" to load a new IOB module]
  --> load "IOB 3+" from drive 1

[press "6" to switch to slot 6]

[press "C" to convert disk]

[press "Y" to change default values]

                 --v--

ADVANCED DEMUFFIN 1.5    (C) 1983, 2014
ORIGINAL BY THE STACK    UPDATES BY 4AM
=======================================


INPUT ALL VALUES IN HEX


SECTORS PER TRACK? (13/16) 16

START TRACK: $02
              ^^
           important

START SECTOR: $05
               ^^
         also important

END TRACK: $22
END SECTOR: $0F

INCREMENT: 1

MAX # OF RETRIES: 0

COPY FROM DRIVE 1
TO DRIVE: 2
=======================================
16SC $02,$05-$22,$0F BY$01 S6,D1->S6,D2

                 --^--

And here we go...

                 --v--

ADVANCED DEMUFFIN 1.5    (C) 1983, 2014
ORIGINAL BY THE STACK    UPDATES BY 4AM
=======================================
TRK:  .................................
+.5:
    0123456789ABCDEF0123456789ABCDEF012
SC0:   ................................
SC1:   ................................
SC2:   ................................
SC3:   ................................
SC4:   ................................
SC5:  .................................
SC6:  .................................
SC7:  .................................
SC8:  .................................
SC9:  .................................
SCA:  .................................
SCB:  .................................
SCC:  .................................
SCD:  .................................
SCE:  .................................
SCF:  .................................
=======================================
16SC $02,$05-$22,$0F BY$01 S6,D1->S6,D2

                 --^--

Halle-freaking-lujah.

Now look at this:

]PR#5
...

]CATALOG,S6,D2

C1983 DSR^C#254
281 FREE

 A 058 HELLO
 A 032 MATH BLASTER DEMONSTRATION
 T 002 MATH 1.OBJ
 T 002 MATH 3.OBJ
 A 040 MATH BLASTER EDITOR
 A 081 MATH BLASTER

And look at this:

]RUN HELLO

ERROR #6 FILE NOT FOUND

Wait, what?

Firing up my trusty Copy ][+ sector
editor and pointing it to my newly
demuffin'd copy, I see the problem: all
of the files on this disk have control
characters in their names.

                 --v--

SECTOR EDITOR                   DRIVE 2

00- 00 11 0E 00 00 00 00 00  ........
08- 00 00 00 12 0F 02 C8 9A  ......H.
                         ^^
                      <Ctrl-Z>

10- C5 CC CC CF A0 A0 A0 A0  ELLO
18- A0 A0 A0 A0 A0 A0 A0 A0
20- A0 A0 A0 A0 A0 A0 A0 A0
28- A0 A0 A0 A0 3A 00 16 0F      :...
30- 02 CD 9A C1 D4 C8 A0 C2  .M.ATH B
          ^^
       <Ctrl-Z>

38- CC C1 D3 D4 C5 D2 A0 C4  LASTER D
40- C5 CD CF CE D3 D4 D2 C1  EMONSTRA
48- D4 C9 CF CE A0 A0 A0 20  TION
50- 00 08 0F 00 CD 9A C1 D4  ....M.AT
                   ^^
                <Ctrl-Z>

58- C8 A0 B1 AE CF C2 CA A0  H 1.OBJ
60- A0 A0 A0 A0 A0 A0 A0 A0
68- A0 A0 A0 A0 A0 A0 A0 A0
70- A0 A0 02 00 20 0F 00 CD    .. ..M
78- 9A C1 D4 C8 A0 B3 AE CF  .ATH 3.O
    ^^
 <Ctrl-Z>

80- C2 CA A0 A0 A0 A0 A0 A0  BJ


TRACK $11  SECTOR $0F   DOS 3.3

[?]-HELP SCREEN

                 --^--

OK, one thing at a time. I have a non-
bootable disk with a standard disk
catalog and what appear to be standard,
though awkwardly named, files. So let's
put a standard DOS on this puppy. I'm
not even going to try to patch the DOS
from the original disk. The sooner I
can forget about that DOS, the better.

Using Copy ][+, I can "copy DOS" from a
freshly initialized DOS 3.3 disk onto
the demuffin'd copy. This function of
Copy ][+ just sector-copies tracks 0-2
from one disk to another, but it's
easier than setting that up manually in
some other copy program.

Copy ][+
  --> COPY
    --> DOS
      --> from slot 6, drive 2
      -->   to slot 6, drive 1

[S6,D1=demuffin'd copy]
[S6,D2=newly formatted DOS 3.3 disk]

...read read read...
...write write write...

Now I need to change the boot program
to "H<Ctrl-Z>ELLO". This feature of
Copy ][+ just presents a list interface
to choose a file from the catalog, then
sector-edits T01,S09 to set the name of
the program that DOS runs (instead of
"HELLO").

Copy ][+
  --> CHANGE BOOT PROGRAM
    --> on slot 6, drive 1
      --> H<Ctrl-Z>ELLO

(The catalog listing doesn't actually
show the control character, so it looks
like I'm changing the boot program from
"HELLO" to "HELLO". But it does make
the necessary changes.)

Rebooting loads DOS (of course, I just
put it there), appears to load the
H<Ctrl-Z>ELLO program successfully...
then immediately reboots.

There is still more copy protection.

]PR#6
...
<Ctrl-C>

BREAK
]LIST

 10  POKE 104,32: RUN
 65535  REM COPYRIGHT 1983
 65535  REM DAVIDSON & ASSOCIATES

According to the framed Beagle Bros.
"Peeks, Pokes and Pointers" chart that
hangs above my desk and reminds me that
technical writing should be wondrous,
useful, and fun (but not always in that
order), zero page 104 ($68) is the high
byte of the starting address of the
Applesoft BASIC program in memory.
Which means that this HELLO program
contains an entirely separate, entirely
hidden BASIC program within it.

]POKE 104,32
]LIST

 10  REM
 400  IF  PEEK (40324) = 173 OR  PEEK
     (47094) <  > 0 THEN 1000
 402  POKE 216,0: ONERR  GOTO 100
     0
 520 K = 768:L = 1000
 530  FOR I = K TO L: READ J: POKE
     I,J: NEXT
 595  POKE 765,32
 650  DATA  76, 55, 3, 164, 1, 17
     3, 48, 192, 230, 2, 208, 5,
     230, 3, 208, 5, 96, 234, 76,
      21, 3, 136, 240, 5
 670  DATA  76, 27, 3, 208, 235,
     164, 0, 173, 48, 192, 230, 2
     , 208, 5, 230, 3, 208, 5, 96
     , 234, 76, 47, 3, 136
 690  DATA  240, 209, 76, 53, 3,
     208, 235, 173, 255, 2, 10, 1
     68, 185, 127, 3, 133, 0, 173
     , 253, 2, 74, 240, 4, 70
 710  DATA  0, 208, 249, 185, 127
     , 3, 56, 229, 0, 133, 1, 200
     , 185, 127, 3, 101, 0, 133,
     0, 169, 0, 56, 237, 254
 730  DATA  2, 133, 3, 169, 0, 13
     3, 2, 165, 1, 208, 152, 234,
      234, 76, 112, 3, 230, 2, 20
     8, 5, 230, 3, 208, 5
 750  DATA  96, 234, 76, 125, 3,
     208, 236, 0, 0, 246, 246, 23
     2, 232, 219, 219, 207, 207,
     195, 195, 184, 184, 174, 174
     , 164
 770  DATA  164, 155, 155, 146, 1
     46, 138, 138, 130, 130, 123,
      123, 116, 116, 109, 110, 10
     3, 104, 97, 98, 92, 92, 87,
     87, 82
 790  DATA  82, 77, 78, 73, 73, 6
     9, 69, 65, 65, 61, 62, 58, 5
     8, 54, 55, 51, 52, 48, 49, 4
     6, 46, 43, 44, 41
 810  DATA  41, 38, 39, 36, 37, 3
     4, 35, 32, 33, 30, 31, 29, 2
     9, 27, 28, 26, 26, 24, 25, 2
     3, 23, 21, 22, 20
 830  DATA  21, 19, 20, 18, 18, 1
     7, 17, 16, 16, 15, 16, 14, 1
     5, 255, 255, 255, 0
 900  POKE 2049,104: POKE 2050,16
     8: POKE 2051,104: POKE 2052,
     166: POKE 2053,223: POKE 205
     4,154
 910  POKE 2055,72: POKE 2056,152
     : POKE 2057,72: POKE 2058,96

 911  PRINT  CHR$ (4);"OPEN MATH
     1.OBJ": PRINT  CHR$ (4);"REA
     D MATH 1.OBJ": INPUT YES,NO,
     MAYBE,YY,ZZ: PRINT  CHR$ (4)
     ;"CLOSE MATH 1.OBJ"
 915  POKE YY,ZZ: GOTO 10
 1000  PRINT  CHR$ (4)"PR#6"

But wait... there's more. I mean, there
has to be more. Other than creating a
little assembly language routine at 768
($300), this program doesn't actually
*do* anything. It doesn't even call the
assembly language routine it creates.
It pokes and pokes and... GOTO 10? How
does that do, well, anything?

Line 911 reads a series of values from
a text file ("MATH 1.OBJ", although I'm
pretty sure there are some control
characters in there somewhere). Looks
innocuous, until line 915 where you
realize that it's using those values to
POKE something. Using Copy ][+'s "view
file as text" function, here are the
entire contents of "MATH 1.OBJ":

                 --v--

8131
-936
6084
104
64

                 --^--

The first three values go into the
variables YES, NO, and MAYBE. (Really.)
The last two go into YY and ZZ, and
that's what gets POKE'd in line 915.

Hey, poking address 104. That sounds
familiar...

]POKE 104,64
]LIST

 10  CALL YES: CALL NO: HGR : CALL
     MAYBE
 20  VTAB 22: HTAB 11
 30  PRINT "2( LOADING PROGRAM )"

 40 P =  PEEK ( - 16384)
 50  IF P = 196 THEN  PRINT  CHR$
     (4);"RUN MATH BLASTER DEMONS
     TRATION"
 60  IF P = 197 THEN  PRINT  CHR$
     (4);"RUN MATH BLASTER EDITOR
     "
 70  PRINT  CHR$ (4);"RUN MATH BL
     ASTER"

Un-freaking-believable. This BASIC
program changes the starting memory
address of the currently running BASIC
program and re-runs itself. Twice.

Apple-ception!

Anyway, back to the... I don't even
know what to call it. Back to the
second program-within-a-program, I
guess.

]POKE 104,32
]LIST 400

 400  IF  PEEK (40324) = 173 OR  PEEK
     (47094) <  > 0 THEN 1000

This is the problem.

40324 is $9D84, which (reaching waaay
back to the beginning of this journey
when I decrypted the boot1 code) is
*not* the entry point to the boot2
code. On a standard DOS 3.3 disk, it
is, but on this disk, the entry point
is at $9D82 instead. So this line of
BASIC is spot-checking the DOS in
memory to ensure that we booted from
the original non-standard DOS. (Hint:
we didn't, because I just replaced that
DOS with a standard DOS 3.3.)

It also checks 47094 ($B7F6), which is
part of the RWTS parameter table. On a
standard DOS 3.3 disk, this location
would be the actual volume number found
the last time the RWTS successfully
read a sector. Apparently the original
disk's RWTS (which, again, I just
replaced with a standard DOS 3.3 RWTS)
always sets it to 0 instead.

Let's see if I can skip past it...

]RUN 402

Success! The program loads and runs all
the way up to the main menu.

But how can I patch this program? It's
not even the real program; it's the
second-level program-within-a-program.
There's a program above it and another
program below it, all self-contained in
the same "A" type file. If I delete the
line, all of that will be ruined.

I'm going to have to hack the Applesoft
opcodes from the monitor.

]PR#6
...
<Ctrl-C>

]POKE 104,32
]CALL-151

*2000.203F

2000- 00 07 20 0A 00 B2 00 2A
2008- 20 90 01 AD E2 28 34 30
               ^^ ^^^^^ ^^^^^
               IF PEEK(  4  0

2010- 33 32 34 29 D0 31 37 33
      ^^^^^^^^^^^ ^^ ^^^^^^^^
       3  2  4  )  =  1  7  3

2018- CE E2 28 34 37 30 39 34
      ^^ ^^^^^ ^^^^^^^^^^^^^^
      OR PEEK(  4  7  0  9  4

2020- 29 D1 CF 30 C4 31 30 30
      ^^ ^^^^^ ^^ ^^ ^^^^^^^^
       )  <  > 0 THEN 1  0  0

2028- 30 00 3C 20 92 01 B9 32
      ^^
       0

2030- 31 36 2C 30 3A A5 AB 31
2038- 30 30 30 00 4D 20 08 02

Looking at address $2005, it appears
that the opcode for a "REM" statement
is $B2. Let's try changing the "IF"
statement to a "REM" statement.

*200B:B2

*3D0G       ; return to BASIC prompt

]LIST 400

 400  REM  PEEK (40324) = 173 OR
      PEEK (47094) <  > 0 THEN 10
     00

Success! Line 400 is now a comment and
shouldn't do any harm. (Listing the
rest of the code confirms that this
hasn't disturbed the delicate balance
of the three programs in memory.)

]RUN

Success! It runs without complaint.

Now to make this patch permanent.
Turning to my trusty Copy ][+ sector
editor (version 5.5, the last version
that can "follow" files), I press "F"
to follow, select "HELLO" from the disk
catalog listing, "S" to scan and "H"
for hex. Searching for "34 30 33 32 34"
(the string "40324" as it's represented
in hex within an Applesoft program), I
find it on T13,S06.

T13,S06,$0C change "AD" to "B2"

Success! The disk boots and loads with
no complaint. That is, until -- and I
am not making this up -- I select a
game and try to play it. Then it
reboots.

There is still more copy protection.

]PR#6
<Ctrl-C>

The HELLO program eventually (in the
third-level program-within-a-program)
runs the BASIC program "M<Ctrl-Z>ATH
BLASTER", which appears to be the
entire game. So let's start there.

]LOAD M<Ctrl-Z>ATH BLASTER
]LIST
.
.
.
 404  FOR I = 17000 TO 33000 STEP
     20: POKE I, RND (1) * 253: NEXT
     : PRINT  CHR$ (13); CHR$ (4)
     ;"PR#6"

Well that last line certainly looks
suspicious. A bit of searching through
this 81-sector Applesoft program (AND
BOY THAT WAS FUN, LET ME TELL YOU) led
me to these two lines, which look both
suspicious and familiar:

]LIST 360

 360  IF  PEEK (40324) = 173 THEN 404

]LIST 400

 400  IF  PEEK (47094) <  > 0 OR
      PEEK (40324) = 173 THEN 402

It's the same protection as the HELLO
program! It looks at memory location
$9D84 as a spot check to make sure we
booted from the original disk. (Hint:
we didn't.)

(Here's a fun fact: I'm almost certain
that line 400 has a bug. It should
branch to line 404, not 402. Line 404
is the failure path; it destroys random
bits of memory and reboots. Line 402
is, incidentally, the success path, and
skipping line 401 has no ill effects.
So this check doesn't do anything.)

At any rate, I should be able to
neutralize these checks the same way I
did in the HELLO program, by changing
the "IF" to a "REM". Firing up my
trusty Copy ][+ (5.5) sector editor, I
press "F" to follow a file, select
"MATH BLASTER" from the catalog, then
"S" to scan and "H" for hex. Searching
for "34 30 33 32 34" ("40324"), I find
it on T03,S06.

                 --v--

SECTOR EDITOR                    DISK A

00- AD 50 52 24 D1 CF 22 46  -PR$QO"F
08- 52 41 43 54 49 4F 4E 53  RACTIONS
10- 22 CD 43 48 D1 CF 34 C4  "MCHQO4D
18- BA C3 31 32 29 00 33 50  :C12)@3P
20- 68 01 AD E2 28 34 30 33  (A-b(403
          ^^ ^^^^^ ^^^^^^^^
          IF PEEK(  4  0  3

28- 32 34 29 D0 31 37 33 C4  24)P173D
    ^^^^^ ^^ ^^ ^^^^^^^^ ^^
     2  4  )  =  1  7  3 THEN

30- 34 30 34 00 39 50 69 01  404@9P)A
    ^^^^^^^^
     4  0  4

38- B1 00 90 50 6A 01 4A D0  1@.P*AJP
40- 32 32 3A 4B D0 32 36 36  22:KP266
48- 3A 92 34 3A 81 4C D0 31  :.4:.LP1
50- 36 34 C1 31 37 38 3A B0  64A178:0
58- 33 31 38 3A 82 3A A2 32  318:.:"2
60- 32 3A 96 35 3A BA 43 48  2:.5::CH
68- 3B 22 2E 20 13 48 4F 52  ;". SHOR
70- 49 5A 4F 4E 54 41 4C 2C  IZONTAL,
78- 20 13 56 45 52 54 49 43   SVERTIC
80- 41 4C 20 4F 52 20 13 4D  AL OR SM

FILE: MATH BLASTER
TRACK $03, SECTOR $6    DOS 3.3

[?]-HELP SCREEN

                 --^--

To neuter the check on line 360:

T03,S06,$22 change "AD" to "B2"

To neuter the check on line 400 (even
though it doesn't appear to function
properly):

T03,S00,$73 change "AD" to "B2"

I searched the entire disk for other
instances of "34 30 33 32 34" and found
two, one on T0B,S00 and one on T1F,S04.
According to the Copy ][+ track/sector
map, neither sector is actually in use
by any file. This disk doesn't use any
raw sector reads, so I suspect these
are just remnants of deleted files or
previous versions that were still
present on the final master disk.

After extensive testing, I can find no
evidence of further copy protection.

Quod erat liberandum.

---------------------------------------
A 4am crack                     No. 121
------------------EOF------------------