How to binary patch that uses input.device?

[gurksallad]

The title is vague so let me explain further. A system friendly game (written for KS2.x) uses input.device to grab key presses from the user. Arrow keys and keypad 1, 2, 3, 5 have the same function, but the function for keypad 7, 8, 9 exist only there. This makes it difficult on Amiga 600 that does not have a keypad, so I want to binary patch the code to "remap" they keys, sort of.


If $BFEC01 was used, that would have been easy to find where the keys are read and simply patch it. However, now input.device, with a horrible mess of events and handlers and what-not, are involved which makes it impossible to straight up find where in the disassembled code the actual key handling routine is.


In the reference manual for Devices I know for a fact that the raw codes for NP 7-9 is 0x3D, 0x3E, 0x3F, but there is no hit for these bytes anywhere in the code so there must be some other kind of pointer magic involved and I don't know how to untangle this mess. If I just managed to find the actual key handling code things would be simpler, but I cannot navigate to it because I don't know what I should look fore.


My best guess is this part, but I'm completely confused and I think I'm on the wrong track to even remotely find anything.

CODE:00021408               loc_21408:                              ; CODE XREF: IORequestAndMaskEtc+68?j
CODE:00021408                                                       ; IORequestAndMaskEtc+8C?j ...
CODE:00021408 044 0C46 00B8                 cmpi.w  #$B8,d6
CODE:0002140C 044 6E2E                      bgt.s   loc_2143C
CODE:0002140E 044 0C46 00B0                 cmpi.w  #$B0,d6
CODE:00021412 044 6D28                      blt.s   loc_2143C
CODE:00021414 044 0C46 00B5                 cmpi.w  #$B5,d6
CODE:00021418 044 6604                      bne.s   loc_2141E
CODE:0002141A 044 3C3C 00B5                 move.w  #$B5,d6
CODE:0002141E
CODE:0002141E               loc_2141E:                              ; CODE XREF: IORequestAndMaskEtc+F6?j
CODE:0002141E 044 0C46 00B8                 cmpi.w  #$B8,d6
CODE:00021422 044 6604                      bne.s   loc_21428
CODE:00021424 044 3C3C 00B8                 move.w  #$B8,d6
CODE:00021428
CODE:00021428               loc_21428:                              ; CODE XREF: IORequestAndMaskEtc+100?j
CODE:00021428 044 0C46 00B3                 cmpi.w  #$B3,d6
CODE:0002142C 044 6604                      bne.s   loc_21432
CODE:0002142E 044 3C3C 00B3                 move.w  #$B3,d6
CODE:00021432
CODE:00021432               loc_21432:                              ; CODE XREF: IORequestAndMaskEtc+10A?j
CODE:00021432 044 0C46 00B0                 cmpi.w  #$B0,d6
CODE:00021436 044 6604                      bne.s   loc_2143C
CODE:00021438 044 3C3C 00B0                 move.w  #$B0,d6
CODE:0002143C
CODE:0002143C               loc_2143C:                              ; CODE XREF: IORequestAndMaskEtc+EA?j
CODE:0002143C                                                       ; IORequestAndMaskEtc+F0?j ...
CODE:0002143C 044 4A46                      tst.w   d6
CODE:0002143E 044 6740                      beq.s   loc_21480
CODE:00021440 044 2004                      move.l  d4,d0
CODE:00021442 044 0240 0003                 andi.w  #3,d0
CODE:00021446 044 6704                      beq.s   loc_2144C
CODE:00021448 044 0646 0100                 addi.w  #$100,d6
CODE:0002144C
CODE:0002144C               loc_2144C:                              ; CODE XREF: IORequestAndMaskEtc+124?j
CODE:0002144C 044 0804 0003                 btst    #3,d4
CODE:00021450 044 6704                      beq.s   loc_21456
CODE:00021452 044 0646 0200                 addi.w  #$200,d6
CODE:00021456
CODE:00021456               loc_21456:                              ; CODE XREF: IORequestAndMaskEtc+12E?j
CODE:00021456 044 2004                      move.l  d4,d0
CODE:00021458 044 0240 0030                 andi.w  #$30,d0 ; '0'
CODE:0002145C 044 6704                      beq.s   loc_21462
CODE:0002145E 044 0646 0400                 addi.w  #$400,d6
CODE:00021462
CODE:00021462               loc_21462:                              ; CODE XREF: IORequestAndMaskEtc+13A?j
CODE:00021462 044 0804 0006                 btst    #6,d4
CODE:00021466 044 6704                      beq.s   loc_2146C
CODE:00021468 044 0646 1000                 addi.w  #$1000,d6
CODE:0002146C
CODE:0002146C               loc_2146C:                              ; CODE XREF: IORequestAndMaskEtc+144?j
CODE:0002146C 044 0804 0007                 btst    #7,d4
CODE:00021470 044 6704                      beq.s   loc_21476
CODE:00021472 044 0646 2000                 addi.w  #$2000,d6
CODE:00021476
CODE:00021476               loc_21476:                              ; CODE XREF: IORequestAndMaskEtc+14E?j
CODE:00021476 044 0807 0007                 btst    #7,d7
CODE:0002147A 044 6704                      beq.s   loc_21480
CODE:0002147C 044 0646 0800                 addi.w  #$800,d6
CODE:00021480

So my question is: what strategy should I use to be able to find the key handling code? I have a full disassembly (by IDA) but I cannot set any breakpoints and investigate anything in realtime, so I have to figure it out only by using the disassembly.


(I have read https://eab.abime.net/showthread.php?t=62322 which is an interesting and related thread, but my head hurts even more. Classes in assembly is horrible)

[Galahad/FLT]

Any particular game?

[Thomas Richter]

If the game uses the input device, then there should be commodities that generate the key events for the numeric keypad for you, emulating it. Thus, there is no patch required.

[gurksallad]

Originally Posted by Galahad/FLT

Any particular game?

Hi. It's a game called Eye of the Beholder made by Strategic Simulations Inc.