-------------Ace Detective------------- A 4am crack 2015-07-24 --------------------------------------- Name: Ace Detective Version: revision 2 Genre: educational Year: 1987 Authors: Methods & Solutions Publisher: Mindplay, Inc. Media: double-sided 5.25-inch floppy OS: custom Previous cracks: none Similar cracks: Design Your Own Home: Landscape Design (crack no. 341) Only side A is bootable, so I'll start there. ~ Chapter 0 In Which Various Automated Tools Fail In Interesting Ways COPYA immediate disk read error Locksmith Fast Disk Backup unable to read any track EDD 4 bit copy (no sync, no count) no errors, but copy grinds on boot Copy ][+ nibble editor modified address epilogue "AF FF FF" odd-numbered tracks (1, 3, 5...) also have a modified address prologue ("D4 AA 96") Disk Fixer ["O" -> "Input/Output Control"] set Address Epilogue to "AF FF FF" -> even-numbered tracks readable T00 looks like a DOS 3.3 RWTS set Address Prologue to "D4 AA 96" -> odd-numbered tracks also readable T01 readable. Also T03, T05, T07... no sign of a disk catalog anywhere Why didn't COPYA work? modified prologue and epilogue Why didn't Locksmith FDB work? modified prologue and epilogue Why didn't my EDD copy work? I don't know. Maybe a nibble check during boot? Next steps: 1. capture RWTS with AUTOTRACE 2. convert disk to standard format with Advanced Demuffin 3. patch RWTS to read demuffin'd disk 4. find the nibble check & bypass it ~ Chapter 1 In Which We Attempt To Use The Original Disk As A Weapon Against Itself [S6,D1=original disk] [S6,D2=blank disk] [S5,D1=my work disk] ]PR#5 ... CAPTURING BOOT0 ...reboots slot 6... ...reboots slot 5... SAVING BOOT0 /!\ BOOT0 JUMPS TO $08F1 CAPTURING BOOT1 ...reboots slot 6... ...reboots slot 5... SAVING BOOT1 SAVING RWTS ]BLOAD BOOT0,A$800 ]CALL -151 *801L . . all normal until... . 084A- 4C F1 08 JMP $08F1 *8F1L 08F1- A9 00 LDA #$00 08F3- 8D F4 03 STA $03F4 08F6- A9 AA LDA #$AA 08F8- 85 31 STA $31 08FA- 6C FD 08 JMP ($08FD) I've seen this before. The RWTS uses zero page $31 to check the second byte of the address (or data (or both)) prologue (or epilogue (or both)). *BLOAD RWTS,A$2800 *FE89G FE93G ; disconnect DOS *B800<2800.2FFFM ; move RWTS into place *B944L ; routine to read address prologue B944- A0 FC LDY #$FC B946- 84 26 STY $26 B948- C8 INY B949- D0 04 BNE $B94F B94B- E6 26 INC $26 B94D- F0 F3 BEQ $B942 B94F- BD 8C C0 LDA $C08C,X B952- 10 FB BPL $B94F ; find prologue nibble #1 B954- 4A LSR B955- C9 6A CMP #$6A B957- D0 EF BNE $B948 B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 ; find #2 B95E- C5 31 CMP $31 B960- D0 F2 BNE $B954 B962- A0 03 LDY #$03 B964- BD 8C C0 LDA $C08C,X B967- 10 FB BPL $B964 ; find #3 B969- C9 96 CMP #$96 B96B- D0 E7 BNE $B954 The code to find prologue nibble #1 explains how this disk can read its odd-numbered tracks (with non-standard address prologue "D4 AA 96"). Normal address prologue byte 1 is $D5. In binary: $D5 = 1101 0101 After LSR: 0110 1010 = $6A Odd-numbered tracks use $D4 instead. In binary: $D4 = 1101 0100 After LSR: 0110 1010 = $6A So this code will match either prologue and work on both odd and even tracks. Furthermore, RWTS code is time-critical between reading the last bit of one nibble and reading the first bit of the next. If it's too fast or too slow, it will get out of phase (because the disk spins independently of the CPU). Compare DOS 3.3 (cycle count in margin) B94F- BD 8C C0 LDA $C08C,X B952- 10 FB BPL $B94F B954- C9 D5 CMP #$D5 | 2 B956- D0 F0 BNE $B948 | 2 * B958- EA NOP | 2 B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 (*) on the time-critical path, this branch is not taken, so always 2 ...and this disk's RWTS: B94F- BD 8C C0 LDA $C08C,X B952- 10 FB BPL $B94F B954- 4A LSR | 2 B955- C9 6A CMP #$6A | 2 B957- D0 EF BNE $B948 | 2 * B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 Despite being more "flexible" (matching $D5 or $D4), this disk's RWTS uses the same number of bytes of code and runs in the same number of cycles. Nice. Now look at this code to match the second nibble of the address prologue: *B959L B959- BD 8C C0 LDA $C08C,X B95C- 10 FB BPL $B959 B95E- C5 31 CMP $31 B960- D0 F2 BNE $B954 There's zero page $31, initialized at $08F0 during boot. Solution: an IOB module that Advanced Demuffin calls before calling the original disk's RWTS. (Read the docs on my work disk.) *C500G ... ]CALL -151 ]BLOAD ADVANCED DEMUFFIN 1.5 ; standard Advanced Demuffin setup ; (unchanged) 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 $0F2A ; initialize zero page 1412- A9 AA LDA #$AA 1414- 85 31 STA $31 ; call RWTS 1416- A9 0F LDA #$0F 1418- A0 1E LDY #$1E 141A- 4C 00 BD JMP $BD00 *BSAVE IOB $31,A$1400,L$FB *BRUN ADVANCED DEMUFFIN 1.5 ["5" to switch to slot 5] ["R" to load a new RWTS module] --> At $B8, load "RWTS" from drive 1 [press "I" to load a new IOB module] --> load "IOB $31" from drive 1 ["6" to switch to slot 6] ["C" to convert disk] --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 --^-- [S6,D1=demuffin'd copy] ]PR#6 ...works... Wait, what? ~ Chapter 2 In Which We Angrily Investigate Why We Suddenly Have A Working Copy [S6,D1=mysteriously working copy] [S5,D1=my work disk] ]PR#5 ]BLOAD RWTS,A$2800 ]CALL -151 *FE89G FE93G *B800<2800.2FFFM *B944L . . all weirdness accounted for, until... . ; find epilogue byte #1 B98B- BD 8C C0 LDA $C08C,X B98E- 10 FB BPL $B98B B990- C9 DE CMP #$DE ; if found $DE, immediately exit with ; a "success" status (clear carry bit) B992- F0 0A BEQ $B99E ; if not $DE, do... this thing B994- 48 PHA B995- 68 PLA B996- BD 8C C0 LDA $C08C,X ; Note: no BPL loop here! It only reads ; the data latch once. B999- C9 08 CMP #$08 B99B- B0 A5 BCS $B942 B99D- EA NOP B99E- 18 CLC B99F- 60 RTS It's looking for a timing bit after the first epilogue byte. It doesn't even care what the first epilogue byte was, as long as it wasn't $DE. This RWTS will accept two different address prologues, "D5 AA 96" or "D4 AA 96". It will also accept two different address epilogues, "DE" or anything- other-than-DE-followed-by-a-timing-bit. Why didn't the EDD copy work? EDD preserved the original prologue epilogue but not the timing bits. The prologue checker (at $B944) finds "D5 AA 96" (even-numbered tracks) or "D4 AA 96" (odd-numbered tracks). But the epilogue checker's first compare (at $B98B) didn't match because the first epilogue byte was still the original value ($AF), and its second compare (at $B999) didn't match because there was no timing bit after the first byte. There was never any separate nibble check; the structure of the disk itself is designed to foil nibble copiers. Why did the demuffin'd copy work? Advanced Demuffin wrote out the data from each sector onto a standard disk that uses "D5 AA 96" prologue and "DE AA EB" epilogue. The RWTS always matches "D5 AA 96" and doesn't care that it never sees a "D4 AA 96" for a prologue. The epilogue checker always matches "DE" and never checks the timing bit. Thus, no RWTS patches are necessary. Side B is unprotected. Quod erat liberandum. ~ Epilogue: On Versioning I've previously cracked a version of "Ace Detective," but this one is different. There is no visible version number (why would you do that?) but I diff'd the two disks and found many small fixes and improvements in the game text itself. For example, the previous version will say "We have two witness who saw..." but in this version the text has been corrected to "We have two witnesses who saw..." (Track $18, sector $06) Thus, I'm calling that revision 1 and this revision 2. --------------------------------------- A 4am crack No. 367 ------------------EOF------------------