Listing 3



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Listing 3: A Skeleton Hardware Interrupt Handler

;add this extra function to the external declarations...
EXTRN POSTMESSAGE:FAR
;
.CODE
;put in the usual WINMAIN() function ...

;followed by a callback ...
   PUBLIC        DPMICALLBACK
DPMICALLBACK     PROC WINDOWS PASCAL FAR \
      hWnd:WORD,msgtype:WORD,wParam:WORD, lParam:DWORD
;put in the usual CASE structure to process messages,
;but with some additions ...
   mov   ax,msgtype
   cmp   ax,WM_CREATE
   je    xcreate
   cmp   ax,WM_DESTROY
   je    xdestroy
   cmp   ax,WM_USER
   je    xuser
   ...etc ... 
   ...
;here is the handling of the WM_CREATE case ...
xcreate: ;whatever you want, plus ...
   call   installint            ;hooks the vector.
   jmp    xexit
;here is the handling of the WM_USER case ...
xuser:
   push   ax
   push   dx
   mov    ah,2                    ;write char to scrn
   mov    dl,07                   ;beep
   int    21h
   pop    dx
   pop    ax
   jmp    xexit
xdestroy:
   call POSTQUITMESSAGE PASCAL,0
;unhook the int-51h...
     push   dx
     push   ds
     mov    dx,offsetint          ;this is the old INT-51 vector
   mov    ds,selectorint          ; /
   mov    ax,2551h               ;before quitting, we are restoring it.
   int    21h
   pop    ds
   pop    dx
   jmp    xexit
;whatever else you want here ...
 ...
xexit:
   sub    ax,ax                   ;returns 0 in DX:AX.
   cwd                            ;return a 32-bit (long) value).
   ret
DPMICALLBACK ENDP
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