Re: [fpc-pascal]Porting to Free pascal this little Turbo Pascal code

[Nelson M. Sicuro]

In my humble experience with FreePascal, I know that you cannot mess with  
segment registers as you do in 16 bits mode. This code of yours need to be  
rewrited from scratch to be in 32 bits mode, without using the segment  
registers and the inline functions (replaced with asm statements).
Anyway, this code seems unsafe to run in 32 bits anyway.
Most 32 bits environments are indeed capable of multitask programming,  
take a look at the DOS 32 bit extenders that FreePascal uses.

Best regards,
Nelson
Anybody capable of providing me an answer on how to get this working  
with Free
Pascal (under DOS) ?

The trick is that the Base Pointer and Segment Stack are saved and  
restored.
That is what I am trying to do . Note FreePascal only accepts ASM blocks.

And also I do not know what instruction $89/$2e $8c/$16 $8b/$2e $8e/$16  
$90/$90/
$90 refer to.
Regards.

================ beginning of the code =================
Unit Tasker;
{$R- ,$S- ,$N-}
{
  Non-Preemptive MultiTasking Unit
  for Turbo Pascal Version 4
  Author  : Michael Warot
  Date    : November 1987
  Purpose : Simple multi-tasking for turbo pascal 4.0
}
Interface
Const
  MaxProc   = 20;
Type
  ProcState = (Dead,Live,Pause,Sleep);
  SpaceRec  = Array[0..$1000] of Byte;
  SpacePtr  = ^SpaceRec;
  Task_Rec  = Record
                ID     : Word;        { Process Number }
                Base,                 { BP save area   }
                Stack  : Word;        { SS save area   }
                State  : ProcState;   { Is it a live process ? }
              End; { Record }
Var
  BP_save,SS_save   : Word;
  BP_load,SS_load   : Word;
  New_Ptr   : SpacePtr;
  Procs     : Array[0..MaxProc] of Task_Rec;
  LastP     : Word;
  NextP     : Word;
  ThisP     : Word;
  LiveCount : Word;                   { How many thing happening? }
{$F+}
Procedure Fork;
Procedure Yield;
Implementation
   (* PROBLEM NEXT LINE *)
Procedure SaveFrame; Inline($89/$2e/BP_save/$8c/$16/SS_save);
   (* PROBLEM NEXT LINE *)
Procedure LoadFrame; Inline($8b/$2e/BP_load/$8e/$16/SS_load);
{$F+}
Procedure Fork;
Begin
   (* PROBLEM NEXT LINE *)
  inline($90/$90/$90);
  SaveFrame;
  If (ThisP = 0) and (LastP < MaxProc) then
  begin
    Procs[ThisP].ID    := ThisP;
    Procs[ThisP].Base  := BP_Save;
    Procs[ThisP].Stack := SS_Save;
    Procs[ThisP].State := Live;
    Inc(NextP);
    Inc(LastP);
    New(New_Ptr);
    Procs[NextP].ID    := NextP;
    Procs[NextP].Base  := ofs(new_ptr^[$0f00]);
    Procs[NextP].Stack := seg(new_ptr^[$0f00]);
    Procs[NextP].State := Live;
    Move(Ptr(SS_save,BP_Save)^,new_ptr^[$0f00],$10);
    Inc(LiveCount);
  end; { if root process }
  bp_load := bp_save;
  ss_load := ss_save;
  LoadFrame;
End; { Fork }
{$F-}
{$F+}
Procedure Yield;
Begin
  SaveFrame;
  Procs[ThisP].Base  := BP_Save;
  Procs[ThisP].Stack := SS_Save;
  If LiveCount > 1 then
  begin
    repeat
      ThisP := NextP;
      NextP := Succ(NextP); If NextP > LastP then NextP := 0;
    until Procs[ThisP].State <> Dead;
  end;
  bp_load := Procs[ThisP].Base;
  ss_load := Procs[ThisP].Stack;
  LoadFrame;
End; { Yield }
{$F-}
End. { Unit }
================ end of the code =================
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