Path: utzoo!attcan!uunet!husc6!uwvax!tank!nucsrl!jln
From: jln@eecs.nwu.edu (John Norstad)
Newsgroups: comp.sys.mac.programmer
Subject: SlotVInstall problem
Message-ID: <10050047@eecs.nwu.edu>
Date: 16 Nov 88 22:09:39 GMT
Organization: Northwestern U, Evanston IL, USA
Lines: 37


A programmer came to me with a problem I couldn't solve.  Perhaps
one of you knows the answer.  The SlotVInstall function is returning
error code -2 (invalid queue element) even though the qType field
of the VBLTask record is properly set to vType (1).  IM V-566 states
explicitly that qType should be set to vType.  I wrote a very
simple MPW C tool that fails in this way (prints -2) when run 
on a Mac II:

#define __ALLNU__  1
#include <Types.h>
#include <OSUtils.h>
#include <Retrace.h>
VBLTask	myTask;
pascal void doit() {}
main() {
   myTask.qType = vType;
   myTask.vblAddr = doit;
   myTask.vblCount = 10;
   myTask.vblPhase = 0;
   printf("%d\n", SlotVInstall(myTask, 0));
}

I know absolutely nothing about slots or the slot manager, but it seems
to me that my little test program above should have worked.  The program
works fine if I replace the call to SlotVInstall with a call to VInstall.
Could the problem be a bad slot number in the call?

Please respond at the address below.  The address in the header of this
posting is bogus.

John Norstad
Academic Computing and Network Services
Northwestern University

Bitnet:    jln@nuacc
Internet:  jln@nuacc.acns.nwu.edu