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Pure dos keyboard remapping for games?

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First post, by kin

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Anyone know a TSR that allows you to remap specific keys?
For example a,w,s,d > arrow left, arrow up, arrow down, arrow right.

Only thing I found was using ansi.sys, but I'm not sure if a dos application will overrule that.
Also, I found some flat assembly code, but I'm not quite a programmer... and uh you need to compile that to 16-bit .exe?:

; Modified Keyboard Entry - 13/10/2009 
ORG     256 
mov     ax,cs 
mov     ss,ax 
mov     sp,MyStack+64*2 
mov     ds,ax 
mov     es,ax 
; Some arbitrary modification 
mov     byte [Table+"a"],"z" 
mov     byte [Table+"z"],"a" 
; Save existing Keyboard Interrupt Vector 
push    es 
mov     ax,3509h 
int     21h     ;DOS 'Get Interrupt Vector' 
mov     [Old_09h],bx 
mov     [Old_09h+2],es 
pop     es 
; Setup new Keyboard Interrupt Vector 
mov     dx,New_09h 
mov     ax,2509h 
int     21h     ;DOS 'Set Interrupt Vector' 
; Prompt user action 
mov     dx,Msg1 
mov     ah,09h 
int     21h     ;DOS 'Display String' 
MainLoop:
mov     ah,01h 
int     21h     ;DOS 'Keyboard Input & Echo' 
cmp     al,27   ;<ESC> ? 
jne     MainLoop 
; Restore old Keyboard Interrupt Vector 
push    ds 
lds     dx,[Old_09h] 
mov     ax,2509h 
int     21h     ;DOS 'Set Interrupt Vector' 
pop     ds 
; Terminate 
mov     dx,Msg2 
mov     ah,09h 
int     21h     ;DOS 'Display String' 
mov     ax,4C00h 
int     21h     ;DOS 'Terminate/ReturnCode' 
; ---------------------------------------------- 
New_09h:
push    ax bx si ds 
mov     ax,40h  ;BIOS_DataSegment 
mov     ds,ax 
mov     si,[001Ch]  ;BIOS_KeyboardBufferTailPointer 
; Let BIOS take care of the hardware 
pushf 
call far dword [cs:Old_09h] 
cmp     si,[001Ch]      ;BIOS_KeyboardBufferTailPointer 
je      .t1     ;No new key in buffer 
mov     al,[si] ;ASCII (SCAN in [si+1]) 
mov     bx,Table 
xlat    [cs:bx] 
mov     [si],al ;Updated ASCII 
.t1:
pop     ds si bx ax 
iret
…Show last 16 lines
; ---------------------------------------------- 
ALIGN   4 
Old_09h:
dd      0 
Table:
times 256 db %-1 
MyStack:
dw      64 dup (0) 
Msg1:
db      'Watch <a> and <z> being swapped...',13,10 
db      'Please press some keys. <ESC> exits!',13,10,'$' 
Msg2:
db      "-- That's all folks",13,10,'$' 
; -----------------------------------------------

Reply 2 of 5, by NewRisingSun

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I think the "pure DOS" part of the topic precludes the use of DOSBox.

What games should that TSR be used with? That would determine how the TSR would have to be set up and whether it is possible at all.

Reply 3 of 5, by kin

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NewRisingSun wrote:

I think the "pure DOS" part of the topic precludes the use of DOSBox.

What games should that TSR be used with? That would determine how the TSR would have to be set up and whether it is possible at all.

I was hoping for one that is for all games. The reason is that I try to avoid modding my new keyboard, which has strange arrowkeys arrangement.
Quick edit, I have tried to compile this into an executable, though with slight modification. It did swap the a and z keys, but since this is not a TSR I can't really test it. Though it is possible to make it TSR.

format MZ
; Modified Keyboard Entry - 13/10/2009
mov     ax,cs
mov     ss,ax
mov     sp,MyStack+64*2
mov     ds,ax
mov     es,ax
; Some arbitrary modification
mov     byte [Table+"a"],"z"
mov     byte [Table+"z"],"a"
; Save existing Keyboard Interrupt Vector
push    es
mov     ax,3509h
int     21h     ;DOS 'Get Interrupt Vector'
mov     [Old_09h],bx
mov     [Old_09h+2],es
pop     es
; Setup new Keyboard Interrupt Vector
mov     dx,New_09h
mov     ax,2509h
int     21h     ;DOS 'Set Interrupt Vector'
; Prompt user action
mov     dx,Msg1
mov     ah,09h
int     21h     ;DOS 'Display String'
MainLoop:
mov     ah,01h
int     21h     ;DOS 'Keyboard Input & Echo'
cmp     al,27   ;<ESC> ?
jne     MainLoop
; Restore old Keyboard Interrupt Vector
push    ds
lds     dx,[Old_09h]
mov     ax,2509h
int     21h     ;DOS 'Set Interrupt Vector'
pop     ds
; Terminate
mov     dx,Msg2
mov     ah,09h
int     21h     ;DOS 'Display String'
mov     ax,4C00h
int     21h     ;DOS 'Terminate/ReturnCode'
; ----------------------------------------------
New_09h:
push    ax bx si ds
mov     ax,40h  ;BIOS_DataSegment
mov     ds,ax
mov     si,[001Ch]  ;BIOS_KeyboardBufferTailPointer
; Let BIOS take care of the hardware
pushf
call far dword [cs:Old_09h]
cmp     si,[001Ch]      ;BIOS_KeyboardBufferTailPointer
je      .t1     ;No new key in buffer
mov     al,[si] ;ASCII (SCAN in [si+1])
mov     bx,Table
xlat    [cs:bx]
mov     [si],al ;Updated ASCII
.t1:
pop     ds si bx ax
iret
…Show last 15 lines
; ----------------------------------------------
ALIGN   4
Old_09h:
dd      0
Table:
times 256 db %-1
MyStack:
dw      64 dup (0)
Msg1:
db      'Watch <a> and <z> being swapped...',13,10
db      'Please press some keys. <ESC> exits!',13,10,'$'
Msg2:
db      "-- That's all folks",13,10,'$'
; -----------------------------------------------

Reply 4 of 5, by Jepael

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What interface your keyboard has (USB, PS/2, AT, XT)?

But no there is no easy way to do that, or it would be done already.

The code you posted hooks the keyboard hardware interrupt, and after the BIOS has determined what scan code & character it is, the key press is modified in the keyboard buffer.

So this will only work if a program uses BIOS keyboard interrupt to read keyboard (or at least if it uses the buffer directly to read keys if not through BIOS).

This won't work with programs that install their own keyboard interrupt handler, and most games do this.

Some keyboard controllers (in PS/2 machines I recall) used to have a command to inject whatever you like so it looks like the data came from keyboard. But it never worked in my PCs.

Modern USB keyboards need to be emulated somehow to look like the data is coming from a keyboard controller, I have no idea how that is done, but maybe someone knows if you can make some software that intercepts the keyboard data there. It could use the system management mode which I also don't know about.

If you are good with microcontrollers, you can easily build a small box that goes between your PC and keyboard and it has PS/2 connectors. Then the microcontroller software can convert certain buttons to other buttons.

Reply 5 of 5, by kin

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It's PS/2 AT. I couldn't skip cause of the cheap price.
It's rubberdome and the overal buildquality is quite nice.
BTC5100_01.JPG

Thanks for the info. I think I might choose for the rewiring option.

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