prep for 2.2 release

Co-authored-by: Peter Ferrie <peter.ferrie@gmail.com>

README.md

@@ -2,8 +2,8 @@
 
 Boot any Apple II disk on any Apple II
 
-[Download latest Anti-M disk image](https://github.com/a2-4am/anti-m/releases/download/v1.5/anti-m-v1.5-2019-06-11.dsk)
-(version **1.5**, released **2019-06-11**, runs on any 48K Apple II)
+[Download latest Anti-M disk image](https://github.com/a2-4am/anti-m/releases/latest/download/anti-m.dsk)
+(version **2.2**, released **2024-02-27**, runs on any 48K Apple II)
 
 ## What is this?
 
@@ -49,6 +49,7 @@ then press `<RETURN>`. The game should boot normally.
 - Lazer Silk (Gebelli)
 - Lunar Leepers (On-Line Systems)
 - Neptune (Gebelli)
+- Odin (Odesta)
 - Orbitron (Sirius)
 - Pest Patrol (On-Line Systems)
 - Phaser Fire (Gebelli)
@@ -56,13 +57,16 @@ then press `<RETURN>`. The game should boot normally.
 - Red Alert (Broderbund)
 - Russki Duck (Gebelli)
 - Seafox (Broderbund)
+- Sensible Speller (Sensible Software)
 - Serpentine (Broderbund) (*)
 - Sky Blazer (Broderbund)
+- Space Adventure (Sierra Software)
 - Space Eggs (Sirius)
 - Space Quarks (Broderbund)
 - Star Blazer (Broderbund)
 - Star Thief (Cavalier)
 - Trick Shot (IDSI)
+- Typing Tutor (Microsoft)
 - Zenith (Gebelli)
 - all 13-sector disks (e.g. Epyx, Edu-Ware, many others)
 - all ProDOS disks
@@ -95,6 +99,42 @@ launching Anti-M.
 
 ## History
 
+v2.2 - 2024-02-27
+
+- add support for ABM
+
+v2.1 - 2024-02-23
+
+- fix detection of 13-sector disks (thanks John A. for the report)
+
+v2.0 - 2023-09-18
+
+- fix a crash when booting "Story Maker"
+- fix a crash when booting "Micro League Baseball"
+- further drive 2 fixes for AppleWin
+
+v1.9 - 2023-05-15
+
+- support "Disk Recovery"
+- support "Space Adventure"
+- fix drive 2 detection
+
+v1.8 - 2020-11-10
+
+- support "Sensible Speller"
+- support "Typing Tutor"
+- add some compatibility fixes for Virtual ][
+
+v1.7 - 2020-08-11
+
+- support "Odin"
+- fix a crash when booting "World Karate Championship"
+
+v1.6 - 2019-11-09
+
+- support Personal Software 13-sector disks ("MicroChess 2.0," "Checker King,"
+  "Gammon Gambler")
+
 v1.5 - 2019-06-11
 
 - support "Lady Tut"

src/anti-m.a

@@ -6,7 +6,7 @@
 ;-------------------------------
 ; Anti-M
 ; a 4am hack
-; (c) 2019 by 4am
+; (c) 2019-2024 by 4am
 ;
 ; Permission is hereby granted, free of charge, to any
 ; person obtaining a copy of this software and associated
@@ -57,7 +57,7 @@ tmp      =     $FC        ; byte
          cmp   #$60
          bne   Boot
          jsr   CheckDrive2
-         bne   Boot2
+         bcs   Boot2
 @showprompt
          jsr   HOME
          lda   MACHINEID
@@ -155,25 +155,103 @@ Boot
 CheckDrive2
          lda   $C0E9
          lda   $C0EB
-         ldy   #6
---       ldx   #$11
--        dex
-         bne   -
-         sec
-         sbc   #1
+         jsr   @spinup
+         jsr   @seek
+         ldx   #21
+         ldy   #0
+---      iny
+         bne   +
+         clc
+         dex
+         bmi   @driveoff
++
+-        lda   $C0EC
+         bpl   -
+--       cmp   #$D5
+         bne   ---
+-        lda   $C0EC
+         bpl   -
+         cmp   #$AA
          bne   --
+-        lda   $C0EC
+         bpl   -
+         cmp   #$AD
+         bne   --
+
+@driveoff
+         lda   $C0E8
+         rts
+
+step=$fd
+phase=$fe
+tmptrk=$ff
+tmpsec=$3c
+@seek
+         ldy     #0
+         sty     step
+         sty     phase
+         lda     #$44
+         sta     tmptrk
+
+@copy_cur
+         lda     tmptrk
+         sta     tmpsec
+         sec
+         sbc     phase
+         beq     +++
+         bcs     +
+         eor     #$ff
+         inc     tmptrk
+         bcc     ++
++        sbc     #1
+         dec     tmptrk
+++       cmp     step
+         bcc     +
+         lda     step
++        cmp     #8
+         bcs     +
+         tay
+         sec
++        jsr     ++++
+         lda     step1, y
+         jsr     @delay
+         lda     tmpsec
+         clc
+         jsr     +++++
+         lda     step2, y
+         jsr     @delay
+         inc     step
+         bne     @copy_cur
++++      jsr     @delay
+         clc
+++++     lda     tmptrk
++++++    and     #3
+         rol
+         tax
+         lda     $C0E0, x
+         rts
+
+@spinup  ldy     #6
+-        jsr     @delay
          dey
-         bpl   --
-         lda   #$00
-         ldy   #$00
--        eor   $C0EC
-         dey
-         bne   -
-         sta   $C0E8
-         cmp   #$00
+         bpl     -
+
+@delay
+--       ldx     #$11
+-        dex
+         bne     -
+         inc     $46
+         bne     +
+         inc     $47
++        sec
+         sbc     #1
+         bne     --
 @knownret
          rts
 
+step1           !byte   1, $30, $28, $24, $20, $1e, $1d, $1c
+step2           !byte   $70, $2c, $26, $22, $1f, $1e, $1d, $1c
+
 Tracer
          jsr   IDBroderbund
          bcc   BeginTheBoot
@@ -187,18 +265,46 @@ Tracer
          bcc   BeginTheBoot
          jsr   IDProgame
          bcc   BeginTheBoot
+         jsr   IDAlphaBeta
+         bcc   BeginTheBoot
 ; [execution falls through here]
 ; [and runs anyway]
 
 BeginTheBoot
+         lda   #$CD ;Virtual II fixes
+         sta   $9D
+         sta   $A2
+         lda   #4
+         sta   $AC
          lda   #$11 ;Virtual II fix
          pha
          plp ;match boot-time flags and registers
-         lda   #1
+         lda   $800 ;might not be 1
          ldy   #0
          ldx   #$60
          jmp   $0801
 
+Tracer13
+         jsr   PatchBoot13
+         jsr   IDPersonal
+         bcc   BeginTheBoot13
+         jsr   IDBoot13
+         bcc   BeginTheBoot13
+         jsr   IDSensible
+         bcc   BeginTheBoot13
+; [execution falls through here]
+; [and runs anyway]
+
+BeginTheBoot13
+         lda   #$CD ;Virtual II fixes
+         sta   $9D
+         sta   $A2
+         lda   #4
+         sta   $AC
+         ldx   #$33 ;Sensible Software fix
+         ldy   $0300
+         jmp   $0301
+
 PrintByID
          cmp   #STRINGCOUNT
          bcs   @exit
@@ -240,7 +346,7 @@ StringTable
          !word @mainmenu
 
 @header
-         !text "Anti-M v1.5 by 4am            2019-06-11"
+         !text "Anti-M v2.2 by 4am            2024-02-27"
          !text "________________________________________",$8D
          !text $8D,$8D,$8D,$8D,$8D,$8D,$8D,$8D,$00
 @mainmenu
@@ -256,3 +362,6 @@ StringTable
          !src  "src/idboot.a"
          !src  "src/idprodos.a"
          !src  "src/idprogame.a"
+         !src  "src/idpersonal.a"
+         !src  "src/idalphabeta.a"
+         !src  "src/idsensible.a"

src/idalphabeta.a

@@ -0,0 +1,37 @@
+; Alpha-Beta tracer
+; written by qkumba
+;
+; tested on
+; - Odin
+;
+IDAlphaBeta
+         lda   #8
+         ldx   #1
+         ldy   #15
+         jsr   CompareMemory
+         !byte $48         ;PHA
+         !byte $28         ;PLP
+         !byte $8C,$F4,$03 ;STY $03F4
+         !byte $2C,$81,$C0 ;BIT $C081
+         !byte $2C,$81,$C0 ;BIT $C081
+         !byte $98         ;TYA
+         !byte $99,$08,$FF ;STA $FF08,Y
+         bcs   @exit
+
+; patch code to offer magic values
+         lda   #$A9        ;LDA
+         sta   $833
+         sta   $83B
+         sta   $841
+         ldx   #$FA
+         stx   $834
+         lda   #$EA
+         sta   $835
+         sta   $83D
+         sta   $843
+         inx
+         stx   $83C
+         lda   #3
+         sta   $842
+@exit
+         rts

src/idboot.a

@@ -10,6 +10,11 @@ IDBoot
          ldy   #$5C
          sty   @patch+1
          bcc   +
+
+; we found D5 AA 96 T00S00 D5 AA ..
+; check for weird Sensible Software 13-sector disk with D5 AA 96 sectors
+         cmp   #$B5
+         beq   ++
          lda   #$90
          sta   $867B
 
@@ -29,7 +34,7 @@ IDBoot
          bne   @patch
 
 ; and loop anyway in case it's a hybrid disk and we missed the D5 AA 96
-         dec   @retries
+++       dec   @retries
          bne   @patch
 
 ; found nothing but D5 AA B5, proceed as 13-sector
@@ -37,138 +42,95 @@ IDBoot
          sta   $867B
 
 ; build 5-and-3 decoder table
-         ldx   #$00
-         ldy   #$AB
--        tya
+         ldx   #$20 ;now you know why the boot PROM
+         ldy   #$00 ;starts with these magic values
+--       lda   #$03
          sta   $3C
-         lsr
-         ora   $3C
-         cmp   #$FF
-         bne   +
+         clc
+         dey
+         tya
+-        bit   $3C
+         beq   --
+         rol   $3C
+         bcc   -
          cpy   #$D5
-         beq   +
+         beq   --
+         dex
          txa
-         asl
-         asl
-         asl
-         sta   $300,y
-         inx
-+        iny
-         bne   -
+         sta   $800,y
+         bne   --
 
 ; patch boot PROM to recognise 13-sector instead
-         lda   #$B5
-         sta   $8677
-         lda   #$9A
-         sta   $86A7
-         sty   $86B0
-         inc   $86B1
-         sty   $86C2
-         inc   $86C3
-         sty   $86D1
-         inc   $86D2
--        lda   @decode53,y
-         sta   $86D5,y
-         lda   @decode53+$100,y
-         sta   $86D5+$100,y
-         iny
+         ldy   #$B5
+         sty   $8677
+         dec   $86A1
+         ldy   #$9A
+         sty   $86A7
+         sta   $86B0
+         ldy   #$08
+         sty   $86B1
+         sty   $86B7
+         sta   $86C2
+         sty   $86C3
+         sta   $86D1
+         sty   $86D2
+-        lda   @decode53,x
+         sta   $86D5,x
+         lda   @decode53 + $100,x
+         sta   $86D5 + $100,x
+         inx
          bne   -
-         lda   #$02
+         lda   #$03
          sta   $27
-         sty   $42
-         lda   #$08
-         ldx   #<@callback53
-         ldy   #>@callback53
--        sta   $43
-         stx   $44
-         sty   $45
-         clc
-         jmp   @run53
-
-@callback53
-         lda   $8FF
-         lsr
-         lsr
-         lsr
-         tay
-         iny
-         sty   @patch53+1
-         ldy   $8FE
-         tya
-         pha
-         lda   #$FF
-         pha
-         iny
-         tya
-         ldx   #<@callback53_2
-         ldy   #>@callback53_2
-         bne   -
+         sta   $2A
+         ldx   #$60
+         jsr   $865D
+         jmp   $86D6
 
 @decode53 !pseudopc $86D5 {
 @decode53x
-         ldx   #$32
-         ldy   #$00
--        lda   $300,x
-         lsr
+         rts
+         tay
+--       ldx   #$00
+-        lda   $800,y
          lsr
+         rol   $3CC,x
          lsr
+         rol   $399,x
          sta   $3C
-         lsr
-         sta   $2A
-         lsr
-         ora   $200,x
-         sta   ($42),y
+         lda   ($26),y
+         asl
+         asl
+         asl
+         ora   $3C
+         sta   ($26),y
          iny
-         lda   $333,x
-         lsr
-         lsr
-         lsr
-         lsr
-         rol   $3C
-         lsr
-         rol   $2A
-         ora   $233,x
-         sta   ($42),y
-         iny
-         lda   $366,x
-         lsr
-         lsr
-         lsr
-         lsr
-         rol   $3C
-         lsr
-         rol   $2A
-         ora   $266,x
-         sta   ($42),y
-         iny
-         lda   $2A
-         and   #7
-         ora   $299,x
-         sta   ($42),y
-         iny
-         lda   $3C
-         and   #7
-         ora   $2CC,x
-         sta   ($42),y
-         iny
-         dex
-         bpl   -
-         lda   $399
-         lsr
-         lsr
-         lsr
-         ora   $2FF
-         sta   ($42),y
-         inc   $3D
-         inc   $43
-         lda   $3D
-@patch53
-         cmp   #$01
-@run53
-         ldx   #$60
-         bcs   +
-         jmp   $865D
-+        jmp   ($44)
+         inx
+         cpx   #$33
+         bne   -
+         dec   $2A
+         bne   --
+         cpy   $300
+-        bne   -
+         jmp   Tracer13
+
+IDBoot13
+         lda   $33C
+         cmp   #$AD
+         sec
+         bne   +
+         lda   #$4C
+         sta   $33C
+         lda   $33D
+         sta   @dispatch+1
+         lda   #<@callback53
+         sta   $33D
+         lda   $33E
+         sta   @dispatch+2
+         lda   #>@callback53
+         sta   $33E
+         clc
++        rts
 
 @CompareMemoryRel
          sta   cmp1+1
@@ -203,9 +165,9 @@ IDBoot
          ldx   cmp1
          rts
 
-@callback53_2
+@callback53
          lda   $85FF
-         beq   @skip2
+         beq   @jmp_dispatch
          lda   #$29
          ldx   #$6E
          ldy   #8
@@ -215,8 +177,8 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notinfocom
          inc   $296F
-@skip2
-         rts
+@jmp_dispatch
+         jmp   @dispatch
 
 @notinfocom
          lda   #$3D
@@ -228,8 +190,7 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notdos32a
          inc   $3D60
-         ldx   #$60
-         rts
+         jmp   @dispatch
 
 @notdos32a
          lda   #$BD
@@ -241,8 +202,7 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notdos32b
          inc   $BD6F
-         ldx   #$60
-         rts
+         jmp   @dispatch
 
 @notdos32b
          lda   #$3D
@@ -254,8 +214,7 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notdos32c
          inc   $3D6F
-         ldx   #$60
-         rts
+         jmp   @dispatch
 
 @notdos32c
          lda   #$BD
@@ -267,8 +226,7 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notdos32d
          inc   $BD60
-         ldx   #$60
-         rts
+         jmp   @dispatch
 
 @notdos32d
          lda   #$24
@@ -280,8 +238,7 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notdos32e
          inc   $246F
-         ldx   #$60
-         rts
+         jmp   @dispatch
 
 @notdos32e
          lda   #$7D
@@ -293,9 +250,61 @@ IDBoot
          !byte $BD,$8B,$C0 ;LDA $C08B,X
          bcs   @notdos32f
          inc   $7D60
-         ldx   #$60
-         rts
+         jmp   @dispatch
 
 @notdos32f
+         lda   #$7D
+         ldx   #$6E
+         ldy   #8
+         jsr   @CompareMemoryRel
+         !byte $BD,$8A,$C0 ;LDA $C08A,X
+         !byte $B0,$03     ;BCS *+5
+         !byte $BD,$8B,$C0 ;LDA $C08B,X
+         bcs   @notdos32g
+         inc   $7D6F
+         jmp   @dispatch
+
+@notdos32g
+
+@dispatch
+         lda   $d1d1 ;SMC
+         pha
+         lda   #$ff
+         pha
+         ldx   #$60
          rts
 }
+
+PatchBoot13
+         lda   #3
+         ldx   #$1B
+         ldy   #8
+         jsr   CompareMemory
+         !byte $4A         ;LSR
+         !byte $4A         ;LSR
+         !byte $4A         ;LSR
+         !byte $4A         ;LSR
+         !byte $09,$C0     ;ORA #$C0
+         !byte $85,$3F     ;STA $3F
+         bcs   @retry
+         lda   #$80
+         sta   $320
+         bcc   @exit
+
+@retry
+         lda   #3
+         ldx   #$25
+         ldy   #8
+         jsr   CompareMemory
+         !byte $4A         ;LSR
+         !byte $4A         ;LSR
+         !byte $4A         ;LSR
+         !byte $4A         ;LSR
+         !byte $09,$C0     ;ORA #$C0
+         !byte $85,$3F     ;STA $3F
+         bcs   @exit
+         lda   #$80
+         sta   $32A
+
+@exit
+         rts

src/idbroderbund.a

@@ -24,6 +24,8 @@
 ; - Phaser Fire (Gebelli)
 ; - Russki Duck (Gebelli)
 ; - Zenith (Gebelli)
+; - Disk Recovery (Sensible Software)
+; - ABM (MUSE)
 ;
 IDBroderbund
 ; first stage is just a standard hybrid DOS 3.2/3.3 bootloader
@@ -266,9 +268,15 @@ IDBroderbund
          ldx   #<@DOS33Callback
          ldy   #>@DOS33Callback
          cmp   #$B6
+         beq   @hookhybrid
+         ldx   #<@MUSECallback
+         ldy   #>@MUSECallback
+         cmp   #$76
          bne   @jmpdos
 
 @hookhybrid
+         lda   #$0C
+         sta   $300 ;Sensible Software page-wraparound fix
          lda   #$4C
          sta   $33C
          stx   $33D
@@ -315,6 +323,16 @@ IDBroderbund
          beq   @skip2a
          inc   $3D60
 @skip2a
++        ldy   $371D
+         cpy   $371F   
+         bne   +
+         dey
+         bne   +
+         lda   $371E
+         ora   $3720
+         ora   $3721
+         bne   +
+         inc   $371F                 ; select drive 2
 +        jmp   $3700                 ; let it goooo...
 
 @SpaceEggsCallback3 !pseudopc $300 {
@@ -427,6 +445,24 @@ IDBroderbund
          ldx   #$60
          jmp   $B700
 
+@MUSECallback
+         lda   $85FF
+         beq   @skip2f
+         lda   #$7D
+         ldx   #$5F
+         ldy   #8
+         jsr   CompareMemory
+         !byte $BD,$8A,$C0 ;LDA $C08A,X
+         !byte $B0,$03     ;BCS *+5
+         !byte $BD,$8B,$C0 ;LDA $C08B,X
+         bcs   @notmuse
+         inc   $7D60
+
+@notmuse
+@skip2f
+         ldx   #$60
+         jmp   $7700
+
 @StarThiefCallback2 !pseudopc $110 {
 @StarThiefCallback2x
          lda   #$4C

src/ididsi.a

@@ -29,6 +29,7 @@ IDIDSI
          rts
 
 @callback1
+         ldx   #$DF
          lda   $1057
          cmp   #$84
          bne   @hook2b
@@ -37,22 +38,14 @@ IDIDSI
          sta   $10D4
          lda   #$2C
          sta   $1088
-         lda   #<@callback2
-         sta   $10F9
-         lda   #>@callback2
-         sta   $10FA
-         lda   #$33
-         bne   @patch3
+         ldx   #$F9
 
 @hook2b
          lda   #<@callback2
-         sta   $10DF
+         sta   $1000,X
          lda   #>@callback2
-         sta   $10E0
-         lda   #$3A
+         sta   $1001,X
 
-@patch3
-         sta   @tracer2+(@tracer3-@tracer2x)+(@cb3patch+1-@tracer3x)
          jmp   $1000
 
 @callback2
@@ -84,30 +77,51 @@ IDIDSI
 @tracer3
 !pseudopc $BF00 {
 @tracer3x
+         lda   $196
+         sta   @cb3patch1+1
+         sta   @cb3patch2+1
+         sta   @cb3patch3+1
+         sta   @cb3patch4+1
+         ldx   $197
+         stx   @cb3patch3+2
+         stx   @cb3patch4+2
+         dex
+         stx   @cb3patch1+2
+         stx   @cb3patch2+2
          lda   #<@callback3
          sta   $196
          lda   #>@callback3
          sta   $197
          jmp   $100
 @callback3
+
 @cb3patch
-         lda   #$D1 ;SMC
-         sta   @cb3jump+1
-         cmp   #$3A
-         lda   #0
-         ldx   #$18
-         ldy   #$BF
-         bcs   +
-         sta   $66A
-         stx   $675
-         sty   $62E
-         bne   ++
-+        sta   $671
-         stx   $67C
-         sty   $635
-++
+         ldx   #$FB
+@cb3patch1
+         lda   $d1d1,X ;SMC
+         cmp   #$c0
+         bne   @cb3jump
+         ldy   #<((@cb3_end + 1) & -2)
+-        tya
+         eor   $bf00,y
+         sta   $bf00,y
+         iny
+         iny
+         bne   -
+         lda   #$BF
+@cb3patch2
+         sta   $d1d1,X ;SMC
+         ldx   #$37
+         lda   #$00
+@cb3patch3
+         sta   $d1d1,X ;SMC
+         ldx   #$42
+         lda   #$18
+@cb3patch4
+         sta   $d1d1,X ;SMC
 @cb3jump
-         jmp   $6D1 ;SMC
+         jmp   (@cb3patch3+1)
+@cb3_end
 }
 @tracer3_e
 }

src/idpersonal.a

@@ -0,0 +1,58 @@
+; Personal Software tracer
+; written by qkumba
+;
+; tested on
+; - MicroChess
+; - Gammon Gambler
+; - Checker King
+
+IDPersonal
+         lda   #3
+         ldx   #$3C
+         ldy   #7
+         jsr   CompareMemory
+         !byte $AD,$CC,$03 ;LDA $03CC
+         !byte $EA         ;NOP
+         !byte $4C,$A5,$03 ;JMP $03A5
+         bcs   @not_microchess
+
+; patch code to regain control after decryption
+         lda   #<@callback_microchess
+         sta   $3bf
+         lda   #>@callback_microchess
+         sta   $3c0
+@exit
+         rts
+
+@callback_microchess
+         lda   $85ff
+         beq   +
+         inc   $35c1
++        jmp   $3500
+
+@not_microchess
+         lda   #3
+         ldx   #$46
+         ldy   #9
+         jsr   CompareMemory
+         !byte $AD,$BB,$03 ;LDA $03BB
+         !byte $85,$3F     ;STA $3F
+         !byte $E6,$3F     ;INC $3F
+         !byte $A0,$4E     ;LDY #$4E
+         bcs   @exit2
+
+; patch code to regain control after decryption
+         lda   #$4c
+         sta   $346
+         lda   #<@callback_gammon
+         sta   $347
+         lda   #>@callback_gammon
+         sta   $348
+@exit2
+         rts
+
+@callback_gammon
+         lda   $85ff
+         beq   +
+         inc   $ba2
++        jmp   $b00

src/idprodos.a

@@ -12,17 +12,37 @@ IDProDOS
          !byte $86,$43     ;STA $43
          !byte $C9,$03     ;CMP #$03
          bcs   @exit
+         ldx   #$60
+         stx   $801
+         inc   $3D
+         jsr   $C65C
+         dec   $27
+         dec   $3D
+         dec   $3D
+         lda   #$38
+         sta   $801
+         lda   #9
+         ldx   #$48
+         ldy   #7
+         jsr   CompareMemory
+         !byte $C9,$E7     ;CMP #$E7
+         !byte $D0,$F4     ;BCS *-$0B
+         !byte $BD,$8C,$C0 ;LDA $C08C,X
+         bcc   @exit
+
          ldy   #@ProDOSCallback_e-@ProDOSCallback
 -        lda   @ProDOSCallback-1,y
          sta   @ProDOSCallbackx-1,y
          dey
          bne   -
+
          lda   #$4C
          sta   $8FC
          lda   #<@ProDOSCallbackx
          sta   $8FD
          lda   #>@ProDOSCallbackx
          sta   $8FE
+         clc
 @exit
          rts
 

src/idsensible.a

@@ -0,0 +1,42 @@
+; Sensible Software tracer
+; written by qkumba
+;
+; tested on
+; - Sensible Speller
+;
+IDSensible
+         lda   #3
+         ldx   #1
+         ldy   #6
+         jsr   CompareMemory
+         !byte $29,$00 ;AND #$00
+         !byte $85,$3A ;STA $3A
+         !byte $9A     ;TXS
+         !byte $08     ;PHP
+         bcs   @exit
+
+; patch encoded code to regain control after it loads sectors into $400+
+         lda   #(<@pcallback) xor $99
+         sta   $03A3
+         lda   #(>@pcallback) xor $99
+         sta   $03A4
+
+@exit
+         rts
+
+@pcallback
+         !word @callback
+
+@callback
+
+; disable ROM checksum-failure branching
+         lda   $6CE
+         cmp   #$4C
+         bne   +
+         lda   #$60
+         sta   $6CE
+
+; and nibble check which fails occasionally
+         lda   #$2C
+         sta   $79B
++        jmp   ($0026)