{ints.inc by K.Lammassaari 1998}

{Source must be compiled with start addr $3000 or higher.
 In old TP 3.0 you can (to save memory !) use startaddress $2200. Remember 
 to change values of Hooked and addr of _IntTbl ! Also If You use DOSPLAY 
 services, you must change address  of MBHook to $2100 and SeeHook to $2120 
 MBHook amd SeeHook are in dosplay.inc; }

{ Contains following procedures and functions:
	
 Function SetInterrupt(ProcAddr:Integer):Byte;
  - Sets an interrupt. ProcAddr := Addr(MyInterrupt procedure);
  - Returns a number for the interrupt service routine (1... )
  - REM !!Interrupt service routine MUST NOT contain any entries to DOS.
    Otherwise the internal stack of dos will be overwritten.
    Most of the standard TurboPascal I/O routines contain DOS entry.
    You must use rewritten direct code to do I/O. For example FastWrite..
  - SetInterrupt returns the required IntNumber. 
  - Discards ROM interrupt services. To obtain them use function SetRomInterrupt.
  - REM some TP standard routines access ROM, thus rom interrupt is occasionally
    accessed. 

Procedure DisableInterrupt(IntNumber:Byte);
  - SetInterrupt returns the required IntNumber. 

Procedure EnableInterrupt(IntNumber:Byte);
  - SetInterrupt returns the required IntNumber. 

Function SetRomInterrupt:Byte;
  - Reconnects the standard DOS/ROM interrupt services.
  - Returns a number of interrupt (1...)

Procedure RemoveInterrupts;
  - Well,,, removes all user interrupt services. Back to normal state.
  - IF YOU FORGET TO SE THIS AT THE END OF YOUR PROGRAM, the computer
    will crash :-)
}

Const PushAll :Array[0..14] Of Byte =($f3,$f5,$c5,$d5,$e5, $d9,
					 $f5,$c5,$d5,$e5, $dd,$e5,$fd,$e5,0);
Const PopAll :Array[0..16] Of Byte =($db,$99, $fd,$e1,$dd,$e1,
				     $e1,$d1,$c1,$f1,$d9,
				     $e1,$d1,$c1,$f1,$fb,  $c9);

	Hooked :Integer = $2ea0 ;    {In TP3.0 this value can be $20f0 } 

Var     IntJmp   :Integer Absolute $39;
        _IntTbl	:Array[0..20,0..2] Of Byte Absolute $2ea0; {In TP 3.0 this can be $20f0 }
        IntTbl	:Array[0..20] Of Integer; {Stores set interrupts }
        Int38 	:Array[0..2] Of Byte Absolute $0038;
	StoreInt:Array[0..2] Of Byte;
	FirstFreeIntTableEntry :Byte;

Function SetInterrupt(ProcAddr:Integer):Byte;
   {Returns the nbr of interrupt 1..20}

 {The parameter 'ProcAddr' contains address of the interrupt service routine}
 {It MUST not contain any entries to DOS. Otherwise the internal stack of dos
  would be overwritten. REM ! Most of the standard I/O routines contain
  DOS entry , You must use rewritten direct code to do I/O.}

Var Temp :Integer;
Begin
   Inline($f3); {DI}
   Temp := ProcAddr;
   If IntJmp <> Hooked Then
    Begin
       FillChar(_IntTbl,SizeOf(_IntTbl),0); {Clear interrupt table } 
       FillChar(IntTbl,SizeOf(IntTbl),0);   {Clear mirror table }

       Move(Int38,StoreInt,3);
       Move(PushAll,_IntTbl[0,0],SizeOf(PushAll));
	{15 bytes = 0..4 items of _IntTbl}
       _IntTbl[5,0] := $cd; Move(Temp,_IntTbl[5,1],2); 
       Move(PopAll,_IntTbl[6,0],SizeOf(PopAll));
       FirstFreeIntTableEntry := 6;
       IntJmp := Hooked; 
       IntTbl[0] := 1;IntTbl[IntTbl[0]] := ProcAddr;
       SetInterrupt := 1;
    End

   Else
    Begin
      _IntTbl[FirstFreeIntTableEntry,0] := $cd;
      Move(Temp,_IntTbl[FirstFreeIntTableEntry,1],2);
      FirstFreeIntTableEntry := FirstFreeIntTableEntry +1;
      Move(PopAll,_IntTbl[FirstFreeIntTableEntry,0],SizeOf(PopAll));
      IntTbl[0] := IntTbl[0]+1;IntTbl[IntTbl[0]] := ProcAddr;
      SetInterrupt := IntTbl[0];
    End;
   Inline($FB);
End;

Procedure DisableInterrupt(IntNumber:Byte);
  Var i :Byte;
  Begin
      Inline($f3);
      If (IntNumber < 1) Or (IntNumber > IntTbl[0]) Then Exit; {Illegal value} 
      FillChar(_IntTbl[4+IntNumber,0],3,0);
      Inline($fb);
  End;

Procedure EnableInterrupt(IntNumber:Byte);
  Var i :Byte;
  Begin
      Inline($f3);
      If (IntNumber < 1) Or (IntNumber > IntTbl[0]) Then Exit; {Illegal value} 
      _IntTbl[4+IntNumber,0] := $cd;
      Move(IntTbl[IntNumber],_IntTbl[4+IntNumber,1],2);
      Inline($fb);
  End;


Function SetRomInterrupt:Byte;
 Begin
  SetRomInterrupt := SetInterrupt(Storeint[1]+StoreInt[2]*256);
 End;

Procedure RemoveInterrupts;
Begin
 Inline($f3);
 Move(StoreInt,Int38,3);
 Inline($fb);
End;