Date: Thu, 16 Feb 1995 19:24:44 -0500 (EST)
From: Kimberley Burchett <OKRA AT max DOT tiac DOT net>
Sender: Kimberley Burchett <OKRA AT max DOT tiac DOT net>
Reply-To: Kimberley Burchett <OKRA AT max DOT tiac DOT net>
Subject: interrupt handlers
To: DJGPP Mailing List <djgpp AT sun DOT soe DOT clarkson DOT edu>


  I have a kind of interrupt handler.  It's for the mouse so what happens 
is the mouse driver is called (in real mode) and then it calls my handler 
(via a real mode callback).  All of this works just fine until I call 
another function from inside my handler.
  This is my function.


static void MouseHandler(_go32_dpmi_registers *regs) {
 
  event Event;
 
  // set event fields
  Event.info.mouse.Pos.x = regs->x.cx;
  Event.info.mouse.Pos.y = regs->x.dx;
  Event.info.mouse.lb = regs->x.bx & 1;
  Event.info.mouse.rb = (regs->x.bx >> 1) & 1;
 
  // did mouse change position?
  if ( (regs->x.ax & 1) != 0) {
    Event.Type = MouseMove;
    AddEvent(Event);
  }
  // did the buttons do anything?
  if ( (regs->x.ax >> 1) > 0) {
    Event.Type = MouseButton;
    AddEvent(Event);
  }
}


  This works just fine if I call it directly from the main program (not in
an interrupt) or if I don't call AddEvent() or if I don't pass anything to
AddEvent().  As it is, it crashes with a stack retrace pointing to either
where I called AddEvent or to AddEvent itself.  This happens even if
AddEvent doesn't do anything (I commented out all the internals and it
crashed the same way).
  When it prints out the stack retrace, the first retrace points to
AddEvent or MouseHandler, then it SIGSEGVs and ends up pointing to a
different function I have.  I have a feeling this is the result of it
being in an interrupt, though. 
  There is no paging going on - this is just a test prog and it only uses
76k according to topline.
  This is pretty urgent - I really need it to continue with my project.

  btw: is it okay to call malloc from an interrupt?  AddEvent() calls 
malloc.  (but that's not the problem since I can comment it out and still 
crash...)
							Kim
						... job hunting ...