Newsgroups: comp.sys.mac.programmer
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!cec2!news
From: jyp@wucs1.wustl.edu (Jerome Yvon Plun)
Subject: Shared addresses between applications with system 7
Message-ID: <1991Jun12.204031.11225@cec1.wustl.edu>
Summary: Converting A5-based address into absolute address
Keywords: Shared data, A5, Memory Manager
Sender: news@cec1.wustl.edu (USENET News System)
Organization: Washington University, St. Louis MO
Distribution: usa
Date: Wed, 12 Jun 91 20:40:31 GMT

  I need to have a block of memory available to two applications running
concurrently (one of the applications doesn't know about the goodies of 
System 7 so I can't use either AppleEvents or raw PPC, and using a shared 
file is too slow).  
  I though of allocating a Ptr in one application, pass the address of the
Ptr to the other application (with the value of A5), and flip A5 whenever I
need to access the shared data.  This works fine if I assigne a constant to
the shared data, since the constant is not dependent on A5.  But if I want to
copy a variable from one application's A5 world into the shared data from the
other application's A5 world, I need to write a little routine in assembly
that copies the value of the source into a register (say d0), changes A5, and
writes d0 into the destination variable.  Doing that for a buffer of data is
cumbersome.
  
  So, I would like to know if it possible to convert an "Address Register
Indirect with Displacement" (i.e. A5 + offset) into an absolute address for
a global variable, thus making that variable independent of what application
is being executed.

  Thanks.  Jerome.

Jerome Plun            []  Is it a crime to want something else?
jyp@wucs1.wustl.edu    []  Is it a crime to believe in something different?
Washington University  []  
St Louis, MO           []  "Smalltown England", New Model Army, Vengeance