Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!dewey.soe.berkeley.edu!oster
From: oster@dewey.soe.berkeley.edu (David Phillip Oster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Think C 4.0 questions
Message-ID: <34256@ucbvax.BERKELEY.EDU>
Date: 12 Feb 90 15:50:33 GMT
References: <10682@bsu-cs.bsu.edu> <1968@cbnewsk.ATT.COM> <10111@hoptoad.uucp> <90039.151841CXT105@PSUVM.BITNET> <10160@hoptoad.uucp> <34242@ucbvax.BERKELEY.EDU> <10194@hoptoad.uucp>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: oster@dewey.soe.berkeley.edu.UUCP (David Phillip Oster)
Organization: School of Education, UC-Berkeley
Lines: 27

tim@hoptoad.UUCP (Tim Maroney) replies to me:
_>>2.) TickCount is one of the calls that is part of the Journaling system.
_>>If Journaling is on, then TickCount will make a Control() call on the
_>>journaling driver, which may do anything it wants, including i/o (such as
_>>writing the journal log out to disk.)  (Many versions of Apple's
_>>Imagewriter driver assume that TickCount() will not clobber A0. And it
_>>won't, unless journaling is on.)
_>
_>Interesting point.  This is in fact what IM says (I-261-2), but I just
_>disassembled the TickCount routine in my SE's RAM and it doesn't take
_>any side trips under any circumstances; there is simply no way for it
_>ever to call Control.  Journaling is activated by setting a flag in low
_>memory, so TickCount doesn't get patched when journaling recording mode
_>is turned on.  Perhaps this implementation of the routine is part of
_>the replacement of the old journaling system by MacroMaker.

_>Journaling drivers *can* do i/o, but i/o doesn't move memory.
If you disassemble the MacPlus ROMs, you'll see the Control call that
TickCount makes if Journaling is turned on.


_>>3.) PBWrite to the file manager may move memory, as I just discussed in an
_>>immediately previous message.

_>Unfortunately, that discussion was incorrect.

I bow to your superior experience on this one.