🚀 go-pugleaf

In article <678@bgsuvax.UUCP> denbeste@bgsuvax.UUCP (William C. DenBesten) writes:
>I have run across an interesting, but apparently not uncommon, problem.  In
>a program that I am writing, I have found a way to freeze my mouse pointer.
>...
>I suspect that the problem involves the vertical retrace interupt becoming
>disabled, but I haven't yet delved into that chapter of Inside Macintosh.
>...
Since the mouse is connected through the SCC, mouse freezing is almost always
a result of a wild memory reference.  The Zilog SCC is very sensitive, and
almost any read or write to one of its registers will disable it.  Since
the Macintosh only looks at a few of the address lines for I/O references,
it's quite easy for a wild reference to wind up hitting the SCC.

Check your program for access to NIL handles or pointers, or uninitialized
pointer variables.  If you have access to a Macintosh XL (Lisa), running
your program on it is a good way to find such errors, as wild memory
references tend to cause bus errors or other problems because of the XL's
different hardware (the mouse is handled in a totally different fashion,
so mouse freezing shouldn't be a danger).


-- 
David Goldsmith
Apple Computer, Inc.
MacApp Group

AppleLink: GOLDSMITH1
UUCP:  {nsc,dual,sun,voder,ucbvax!mtxinu}!apple!dgold
CSNET: dgold@apple.CSNET, dgold%apple@CSNET-RELAY