QUESTION:
What challenges did you face in using VxWorks? Is your application source
availble for public viewing?

ANSWER from Jesse Wright on October 6, 1997:
First off VxWorks was not ported to our platform (IBM RAD 6000). We paid
Wind-Rivers to do the port (big bucks). And with any new port there were
problems: some things were slow, bugs, etc. But we had a very good working
releationship with the company so it was all finally worked out. In general
our experience was very positive given the environment.

I think the worst problem we had, we did to ourself.  Something we did not
understand was that there are 2 settings to interrupts: use Floating Point
or not use Floating Point. We set all of ours to not use Floating Point
(i.e. don't save Floating Point Registers). Unfortantly some of the
interrupt routines called functions that did use Floating Point. This would
cause a completely different function to sometimes get divide by zero
faults. We got most found in testing, 2 found in cruise, and 1 found on the
surface. The surface one came about because we were told the maximum data
rate would be 1-2 kilobits / second. That is all we tested to in our
complete tests. After the first day we were running at 6-9 kilobits /
second.

The faster rate increased the chance of this happening because there were
more interrupts running at the same time to support the rate and to support
the high number of camera images. This was the cause, as I understand it, of
the rash of resets the first week. As soon as we found it, it was fixed.

We could not set all interrupts to use Floating Point because that would
slow the system down by quite a bit (we did test).

Sorry, but the application source is not available for public viewing. We
have no choice. Ronald Regan signed an executive order declaring most
functions on a spacecraft to be "munitions platforms" and thus covered under
the national security acts. Even though you can go buy books describing all
of the algorithms we use (some of our people on Pathfinder wrote the books)
it is still covered. We are covered under the "remote sensing" part of the
order in addition to the "munitions platforms".

There is no question that the software source for the flight computer is
under this act. It was a surprise to us also.

Jesse Wright