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    UNIT asytimer;
    {Purpose  : High resolution timer which runs asynchronous to the     }
    {           rest of the program                                      }
    {Author   : Kai Rohrbacher, kai.rohrbacher@logo.ka.sub.org           }
    {Language : BorlandPascal 7.0 }
    {Date     : 26.06.1994        }
    {Remarks  : - Runs both in real- and protected mode.                 }
    {           - Only available on AT-style machines or better (uses    }
    {             real time clock services)                              }
    {           - Will "fall through" on PC's transparently: behaves as  }
    {             if time ran off immediately}

    INTERFACE

    VAR TimeFlag:^BYTE;

    FUNCTION ATClockAvailable:BOOLEAN;
    PROCEDURE SetCycleTime(microseconds:LONGINT);
    FUNCTION TimeOver:BOOLEAN;
      INLINE($C4/$1E/TimeFlag/   {LES BX,TimeFlag}
             $26/$8A/$07/        {MOV AL,ES:[BX] }
             $B1/$07/            {MOV CL,7 }
             $D2/$E8);           {SHR AL,CL}
    PROCEDURE Trigger;

    IMPLEMENTATION

    USES CRT;

    {$IFDEF DPMI}
    TYPE Treg=RECORD  {stuff for that dumb DPMI-server}
               CASE BYTE OF
                0:(LoLo,LoHi,HiLo,HiHi:BYTE);
                1:(Lo16,Hi16:WORD);
              END;
         Tregisters32=
           RECORD
             EDI,ESI,EBP,junk32,EBX,EDX,ECX,EAX:Treg;
             Flags32,ES,DS,FS,GS,IP,CS,SP,SS:WORD
           END;
    VAR regs32:Tregisters32;

     FUNCTION EmulateInt(IntNr:BYTE; VAR regs32:Tregisters32):BOOLEAN;
     ASSEMBLER; {emulate real mode interrupt IntNr with registers regs32}
     ASM
       MOV AX,300h   {emulate INT}
       XOR BH,BH     {no A20 gate reset, please}
       MOV BL,IntNr  {INT to emulate}
       XOR CX,CX     {no parameter passing via PM stack}
       LES DI,regs32 {pointer to register set}
       INT 31h       {go for it}
       CMC           {carry flag set if error, reflect this}
       MOV AX,0      {as a BOOLEAN value: return TRUE if C=0}
       ADC AX,AX     {and FALES otherwise}
     END;
    {$ENDIF}

    VAR CycleTimeLo16,CycleTimeHi16:WORD;
        IsAT:BYTE;

    {$IFDEF DPMI}
    FUNCTION ATClockAvailable:BOOLEAN; {protected mode function}
    BEGIN
     TimeFlag^:=0;             {reset flag}
     FillChar(regs32,SizeOf(regs32),0);
     regs32.ECX.Lo16:=0;
     regs32.EDX.Lo16:=1;       {trigger flag after 1us}
     regs32.ES      :=$40;     {_segment_ address of Timeflag}
     regs32.EBX.Lo16:=Ofs(TimeFlag^); {offset part = $F0}
     regs32.EAX.Lo16:=$8300;

     IF NOT EmulateInt($15,regs32)
      THEN WRITELN('Something went wrong in the INT-emulation!?');

     Delay(1); {INT-emulation went ok, look for timer event:}
               {wait 1000us, so event must have happened:}
     {Flag now should have been set to $80:}
     ATClockAvailable:=TimeFlag^=$80;
    END;

    {$ELSE}

    FUNCTION ATClockAvailable:BOOLEAN; {real mode function}
    BEGIN
     TimeFlag^:=0;             {reset flag}
     IF Test8086<>0  {is it at least an AT?}
      THEN ASM {yes, have a closer look:}
             STI
             XOR CX,CX       {trigger after 1us}
             MOV DX,1
             LES BX,TimeFlag {set Flag to $80 after this time}
             MOV AX,8300h    {run asynchron to rest of program}
             INT 15h         {go!}
           END;
     Delay(1);               {wait a 1000us}
     ATClockAvailable:=TimeFlag^=$80 {Flag=$80, if it worked}
    END;
    {$ENDIF}

    PROCEDURE SetCycleTime(microseconds:LONGINT);
    BEGIN
     TimeFlag^:=$80;
     CycleTimeHi16:=microseconds SHR 16;
     CycleTimeLo16:=microseconds AND $FFFF;
     IF (microseconds<>0) AND ATClockAvailable
      THEN IsAT:=0     {ja, Zeit�berwachung soll benutzt werden  }
      ELSE IsAT:=$80   {nein, keine m�glich oder nicht gew�nscht }
    END;

    PROCEDURE Trigger;
    {starts timer, which must have previously been set by SetCycleTime()}
    BEGIN
     IF IsAT<>0 THEN EXIT; {jmp out, if timer services unavailable}
     TimeFlag^:=0;
    {$IFDEF DPMI}
     regs32.ECX.Lo16:=CycleTimeHi16;
     regs32.EDX.Lo16:=CycleTimeLo16;  {trigger flag after t us}
     regs32.ES      :=$40;            {_segment_ address of Timeflag}
     regs32.EBX.Lo16:=Ofs(TimeFlag^); {offset part = $F0}
     regs32.EAX.Lo16:=$8300;

     IF NOT EmulateInt($15,regs32)
      THEN WRITELN('Something went wrong in the INT-emulation!?');
    {$ELSE}
    ASM
      MOV CX,CycleTimeHi16
      MOV DX,CycleTimeLo16
      LES BX,TimeFlag {set Flag to $80 after this time}
      MOV AX,8300h    {run asynchron to rest of program}
      INT 15h         {go!}
    END;
    {$ENDIF}
    END;

    BEGIN
     TimeFlag:=Ptr(Seg0040,$F0); {available byte in 1st MB}
     SetCycleTime(0)
    END.

    ____

    PROGRAM TestUnit_asytimer;
    {Kai Rohrbacher, kai.rohrbacher@logo.ka.sub.org}
    USES asytimer;
    CONST wait:LONGINT=5000000; {trigger time in us -> 5sec}

     PROCEDURE SomeThing;
     CONST s:ARRAY[0..3] OF CHAR='\|/-';
           help:BYTE=0;
     BEGIN WRITE(s[help]+^H); help:=(help+1) AND 3 END;

    BEGIN
     IF ATClockAvailable
      THEN WRITELN('INT15h-timer-routine available!')
      ELSE WRITELN('INT15h-timer-routine doesn''t work!');

     SetCycleTime(wait);
     WRITELN('Between the following 2 bells, there should be a delay of ',
             wait,' microseconds');
     Trigger;    {wait 5s = 5000ms}
     WRITE(#7);
     WHILE NOT TimeOver DO SomeThing;
     WRITELN(#7'Done!');
    END.

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