Re: Martian Rover Spirit's mulitasking software reset.

[Mark Lorenzen <mark.lorenzen@surfpost.dk>]

Martin Dowie <martin.dowie@afraidof.co.uk> writes:

> ME wrote:
> > The mars rover Spirit suffered a software reset as a result of a
> > multitasking problem.
> > "The apparent cause was that the rover's central processing unit was
> > overworked as several tasks were running in parallel at the time."
> >  The rover uses VX works and I believe C. Testing obviously did not
> > catch this fault. Would the use of Ada  made any difference?
> >
> 
> My understanding is that there was a "priority inverstion", so had

That is also my understanding.

> they used "pragma Locking_Policy (Ceiling_Locking);" (RM  D.3 Priority
> Ceiling Locking) then the problem could have been avioded.
>
> Of course, they might not have used it even if they were using Ada. :-)

As far as I know, they were aware of the priority inversion problem
before launch, but did not consider it important enough to warrant a
fix. I guess that a watchdog device simply kicks in and reboots the
system, should it hang for too long.

- Mark