Category : Windows 3.X Files
Archive   : HANDLER.ZIP
Filename : HANDLER.ASM

TITLE HANDLER.ASM -- Sample Windows DLL ISR
;****************************************************************************
;
; PROGRAM: handler.asm
;
; PURPOSE:
;
; FUNCTIONS:
;
;
;****************************************************************************

.286
memM EQU 1 ;Medium memory model

.xlist
include windows.inc
include cmacros.inc
include handler.inc
.list


nHookVector EQU 09h
DOS_SetVector EQU 2500h
DOS_GetVector EQU 3500h

sBegin Data
staticD dOldVector,0
staticW nCount,0
staticW hWndApp,0
sEnd

sBegin Code
assumes cs,Code
assumes ds,Data
;****************************************************************************
; FUNCTION: LibMain(HANDLE, WORD, WORD, LPSTR)
;
; PURPOSE: Is called by LibEntry. LibEntry is called by Windows when
; the DLL is loaded. The LibEntry routine is provided in
; the LIBENTRY.OBJ in the SDK Link Libraries disk. (The
; source LIBENTRY.ASM is also provided.)
;
; LibEntry initializes the DLL's heap, if a HEAPSIZE value is
; specified in the DLL's DEF file. Then LibEntry calls
; LibMain. The LibMain function below satisfies that call.
;
; The LibMain function should perform additional initialization
; tasks required by the DLL. LibMain should return a value of 1
; if the initialization is successful.
;
;****************************************************************************
cProc LibMain, ,
parmW hModule;
parmW wDataSeg;
parmW cbHeapSize;
parmD lpszCmdLine;

cBegin LibMain
cCall Install_Handler,<>
mov ax,1
cEnd LibMain


;****************************************************************************
; FUNCTION: WEP(int)
;
; PURPOSE: Performs cleanup tasks when the DLL is unloaded. WEP() is
; called automatically by Windows when the DLL is unloaded (no
; remaining tasks still have the DLL loaded).
;
;******************************************************************************/
cProc WEP, ,
parmW bSystemExit

cBegin WEP
int 1
cCall De_Install_Handler,<>
mov ax,1
cEnd WEP


;****************************************************************************
; FUNCTION: SetISRWindow(HWND)
;
; PURPOSE: This routine receives the handle to the window that should
; receive ISRM_RUPT messages.
;
;****************************************************************************
cProc SetISRWindow, ,
parmW hWnd
cBegin SetISRWindow
int 1
mov ax,hWnd
mov hWndApp,ax
cEnd SetISRWindow



;****************************************************************************
; FUNCTION: GetISRCount()
;
; PURPOSE: This function simply returns the value of nCount to the
; caller.
;
;****************************************************************************
cProc GetISRCount, ,
cBegin GetISRCount
mov ax,nCount
cEnd GetISRCount


;****************************************************************************
; FUNCTION: Do_Int()
;
; PURPOSE: This routine is called by the ISR in the Install_Handler
; routine. Note that this routine is EXPORTED, so when it
; is called, DS is loaded with the default data segment of
; this DLL. Thus, the routine has access to dOldVector, so
; it can call the next interrupt handler in the chain.
;
;
;****************************************************************************
cProc Do_Int, ,
cBegin Do_Int

pushf
call DWORD PTR dOldVector ; do DOS timer

inc nCount
cmp hWndApp,0
jz doiexit

mov bx,ISRM_RUPT
sub ax,ax
cCall PostMessage,
jmp doiexit

xor ax,ax
mov hWndApp,ax
doiexit:

cEnd Do_Int


;****************************************************************************
; FUNCTION: Install_Handler()
;
; PURPOSE: This routine saves the interrupt vector "nHookVector" in
; the global variable "dOldVector". Then, it installs a small
; ISR at that vector which calls the routine "Do_Int()" when
; the interrupt occurs.
;
;
;****************************************************************************
cProc Install_Handler, NEAR,
cBegin Install_Handler

push bx ;Save previous handler
push es
mov ax,DOS_GetVector + nHookVector
int 21h
mov WORD PTR dOldVector,bx
mov WORD PTR dOldVector+2,es
pop es
pop bx


push ds ;Install handle
push dx ;
push cs
pop ds
mov dx,OFFSET MyISR
mov ax,DOS_SetVector + nHookVector
int 21h
pop dx ;
pop ds ;

jmp set_exit

MyISR: ;Our ISR
pusha
push ds
push es

cCall Do_Int ;Do Interrupt Handling

pop es
pop ds
popa
iret ;exit MyISR

set_exit: ;exit Install_Handler

cEnd Install_Handler


;****************************************************************************
; FUNCTION: De_Install_Handler()
;
; PURPOSE: Restores the interrupt vector "nHookVector" with the address
; at "dOldVector".
;
;****************************************************************************
cProc De_Install_Handler, NEAR,
cBegin De_Install_Handler

push ds ;
push dx ;
mov dx,WORD PTR dOldVector
mov ax,WORD PTR dOldVector+2
cmp dx,0 ;were we installed?
jnz dih_go
cmp ax,0
jz dih_skip
dih_go:
mov ds,ax
mov ax,DOS_SetVector + nHookVector
int 21h
dih_skip:
pop dx ;
pop ds ;

cEnd De_Install_Handler



sEnd
end