Re: Martian Rover Spirit's mulitasking software reset.

["ME" <abcdefg@nonodock.net>]

"Mark Lorenzen" <mark.lorenzen@surfpost.dk> wrote in message 
news:m34pvkobtg.fsf@localhost.localdomain...
> 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.
>

But one of the original problems with Spirit was that it was that it had 
reset itself once every hour until it almost ran out of power. This was 
originally due to a flash memory management error which in turn was due to a 
complication due to new software uploaded to it because the system was 
launched with a serious flaw that was identified later.  I recall a JPL 
scientist admitting that the software was written last because they could 
upload it. The entire mission was on a very tight schedule and as is far too 
often the case the software comes last.
> - Mark