Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ukma!husc6!ogccse!afoster
From: afoster@ogccse.ogc.edu (Allan Foster)
Newsgroups: comp.sys.mac
Subject: The REAL reason the mouse is jerkey!
Message-ID: <4254@ogccse.ogc.edu>
Date: 16 Aug 89 17:39:05 GMT
Organization: Oregon Graduate Center, Beaverton, OR
Lines: 45

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Organization: Oregon Graduate Center, Beaverton, OR
Keywords: multitasking, jerkey mouse

In article <866@bridge2.ESD.3Com.COM> ngg@bridge2.3Com.com (Norman Goodger) writes:
>>>	- While printing a background job, I often have a hard time keeping
>>	  control of the mouse pointer -- it's like using the mouse as a
>>	  slingshot.  Very annoying.
>
>The problem is disk access in the background, unless Apple includes DMA for
>SCSI in the future, mouse motions will always be jerky in some operations.
>
>
No no not true.  The disk access does indeed make the mouse a little jerky, but that
is not the reason.

The real reason is in the ADB drivers.  When Andy Hertzfeld wrote the mouse
drivers for the old mac he went to great pains to make sure that the mouse
acted RIGHT. 
The engineers who implemented the ADB just SCREWED UP.  The ADB chip collects
all the info about mouse movements and stores it as one change since the last
poll by the CPU.  If the CPU is busy then the figures stored as to how much
the mouse has moved becomes large.

OK, so what is the fix?  Simple.  Patch the ADB drivers for the mouse device
so that if the mouse has moved more than a threshold value since the last time
it was read, then ignore it.  This will make the mouse behave exactly like the
old mac plus mouse.  Some experimenting would be in order to see exactly
what should happen.

This works. (I have done the mod on my machine...) but I cannot find the
patch.  If there is demand for it I can always disassemble my resources
and find out what I did!

Regards
Allan Foster
MicroPhone II Development Team
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