Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!rutgers!rochester!cornell!vax5.cit.cornell.edu!q4kx
From: q4kx@vax5.cit.cornell.edu (Joel Sumner)
Newsgroups: comp.sys.apple2
Subject: PIF/TIF Sample
Message-ID: <1990Oct14.141319.381@vax5.cit.cornell.edu>
Date: 14 Oct 90 18:13:19 GMT
Distribution: comp
Lines: 78

Actually, there really is nothing mysterious about writing a PIF or TIF file.
I wrote BlankINIT in TML Pascal v1.5 with no problems.  A PIF is no more
than a program that gets executed at boot time and then stays in memory.  A
TIF is the same but it gets dumped from memory when it is finished.

Sample PIF

Program MyPIF;

type TaskRecord = Record
                nextTask:=longint;
		interval:=integer;
		signature:=integer;
		somecode:=array[1..3] of byte;
		myProcPtr:=ProcPtr;
		end;

var MyMemoryID:integer;
    TaskRec:TaskRecord;
		

Function CheckSomething:Boolean;
begin
end;

Procedure DoSomething;
begin
end;

Procedure TheInterrupt;
begin
if CheckSomething then DoSomething;
TaskRec.interval:=1; {Reset the interval}
end;

begin {main program, gets executed at boot time}
MyMemoryID:=MMStartUp;
MTStartup;
with TaskRec do
  	interval:=1; {1/60th of a sec, 60:=1 sec, etc..}
	signature:=$a55a;
	someCode[1]:=$C2;  {REP}
	someCode[2]:=$30; 
	someCode[3]:=$5c;  {JMP Long}
	myProcPtr:=@TheInterrupt;
	end;
SetHeartBeat(@TaskRec);
MTShutDown;
MMShutDown(MyMemoryID);
end;

The TaskRec/SetHeartBeat code is courtesy of Dave Lyons.  I have not had
success with this using ORCA/Pascal and I cannot determine why.  It may
have to do with the range checking.  It tends to trash the stack.  But it
may just be me (more likely <grin>).

Now, you are probably saying to yourself, "This looks just like a regular
application, what is the difference?"  Exactly, there isn't much difference.
There are three things you MUST do.
  1 - Change the filetype to PIF (STR)
  2 - Move it to the */SYSTEM/SYSTEM.SETUP subdir
  3 - Use Block Warden, etc.. to change the QUIT command to an RTL.  When this
      code is compiled with TML, it seems to consistently be placed at $54 
      but this may not be 100% certain.  

That's all there is to it.  For a TIF, you DON'T want to install an interrupt
(because the Interrupt procedure will be dumped from memory) but it is just
like a regular application.  Again, you have to change the filetype to
TIF, copy the file, and change the QUIT to an RTL.

Have I missed anything? 

-- 
Joel Sumner                     GENIE:JOEL.SUMNER     These opinions are 
q4kx@cornella.ccs.cornell.edu   q4kx@cornella         warranted for 90 days or
q4kx@vax5.cit.cornell.edu       q4kx@crnlvax5         60,000 miles.  Whichever
....................................................  comes first.
Never test for an error condition that you can't handle.