Re: Using Global Variables

[crispen <@ada3.ca.boeing.com:crispen@efftoo.boeing.com>]

Victor Giddings and Lee Marden share some guilty secrets about using
shared memory.  Here's one of mine.  On a multi-board VME chassis
running VxWorks/VADSWorks, we changed the boot configuration file
so that the sysMemTop function in VxWorks thought each VME board
had 64K memory less than it actually had.  This top 64K was used
to pass data back and forth between the boards:

	for Control_Block use at System.Physical_Address (xxxxx);

It worked great, especially when the system crashed, because the
ROM monitor had the ability (under most kinds of crashes) to display
memory in a hex dump even when the OS and all the application
programs were thoroughly hosed.  We knew that 0x3f0004 contained
the service request, etc.

Of course, we had a pretty firm control: one writer, one reader for
a field, and the writer interrupted the reader when it wanted the
reader to read the field.

I really enjoyed this.  It was like the old days in microprocessors,
where you knew were everything was and you treated machines like
machines.  Those were the days...
+-------------------------------+--------------------------------------+
| Bob Crispen                   |   The owls are not what they seem    |
| crispen@foxy.boeing.com       +--------------------------------------+
| (205) 461-3296                |Opinions expressed here are mine alone|
+-------------------------------+--------------------------------------+