1;------------------------------------------------------------------------------
2;HAVE INTERRUPT 15h DO THIS EVERY TIME IT OCCURS
3;Inputs : AH = 84h (Joystick support)
4;           DX = -1 (Installed & Enabled?) - Returns CF=Clear, DX=0
5;           DX = 0  (Get buttons) - Returns high nibble of AL, CF=Clear
6;           DX = 1  (Get Coordinates) - Returns AX,BX,CX,DX, CF=Clear
7;Outputs: Depends on DX input
8;Changes: Buff
9;------------------------------------------------------------------------------
10Int15:
11  PUSH BP            ;Save used register
12  MOV  BP,SP         ;Point at the stack
13                     ;  [BP]=BP,[BP+2]=IP,[BP+4]=CS,[BP+6]=Flags
14  PUSHF              ;Save flags
15  STI                ;Enable interrupts
16  PUSH DS,ES         ;Save used registers
17  MOV  DS,CS         ;Point DS and ES
18  MOV  ES,CS         ;  at our data area
19  CLD                ;Go forward with string functions
20  CMP  AH,84h        ;Is it the joystick function?
21  JNE  Int15Old      ;If not, just the the old routine handle it
22  CMP  Enabled,Yes   ;Are we enabled right now?
23  JNE  Int15Old      ;If not, just the the old routine handle it
24  CMP  DX,-1         ;Is it our special "is it installed" function?
25  JNE >I10           ;If not, try the next possibility
26  INC  DX            ;If so, set DX=0 (the "it's installed" flag)
27  JMP >I90           ;And we're done
28I10:                 ;Test for function 0
29  OR   DX,DX         ;Is it function 0?
30  JNZ >I40           ;If not, see if it's function 1
31  CALL DoButtons     ;If so, calculate the status of the buttons
32  JMP >I90           ;And we're done
33I40:                 ;Test for function 1
34  CMP  DX,1          ;Is it function 1?
35  JNE  Int15Old      ;If not, let the old routine handle it
36  CALL DoCoords      ;If so, calculate the coordinates
37I90:                 ;We're done
38  POP  ES,DS         ;Restore used registers
39  POPF               ;Restore flags
40  AND  B [BP+6],0FEh ;Clear the carry flag for the return
41  POP  BP            ;Restore used register
42  IRET

1;------------------------------------------------------------------------------
2;CHANGE INTERRUPTS TO OUR CODE
3;Inputs :
4;Outputs:
5;Changes: Several Interupt vectors
6;------------------------------------------------------------------------------
7ChangeInts:
8  PUSH AX,DX,DI            ;Save used registers
9  MOV  AL,08h              ;Need to change Int 08h to our code
10  MOV  DX,Int08            ;Point at our code
11  MOV  DI,OFFSET Int08Vect ;Place to store the old vector
12  CALL ChangeInt           ;Change it
13  MOV  AL,15h              ;Need to change Int 08h to our code
14  MOV  DX,Int15            ;Point at our code
15  MOV  DI,OFFSET Int15Vect ;Place to store the old vector
16  CALL ChangeInt           ;Change it
17  MOV  AL,2Fh              ;Need to change Int 2Fh to our code
18  MOV  DX,Int2F            ;Point at our code
19  MOV  DI,OFFSET Int2FVect ;Place to store the old vector
20  CALL ChangeInt           ;Change it
21  POP  DI,DX,AX            ;Restore used registers
22  RET