Re: [SystemSafety] Statistical Assessment of SW ......

From: Matthew Squair < >
Date: Sat, 24 Jan 2015 18:38:22 +1100


I can't speak for the entire hardware engineering community Peter, but I'd say that across industry the 'knowing there's a solution' mileage may vary :)

Back to how hardware can affect deterministic behaviour though, I have another example (not mine) of how hardware issues can affect determinism. In this one the read/write to a 12 bit register was assumed to be an atomic action. All good you might think, but the register was built from two 6 bit registers so that read/write turned out to not be so atomic after all. Problem found after reading the hardware spec in detail and (as it was told to me) asking some clarifying questions of the manufacturer.

On Sat, Jan 24, 2015 at 3:51 PM, Peter Bernard Ladkin < ladkin_at_xxxxxx

> On 2015-01-24 00:12 , Matthew Squair wrote:
> > Another non-trivial hardware problem is how to ensure a shared concept
> of time in a distributed
> > system in the presence of clock drift. Said drift can lead to quite
> different responses to inputs
> > from redundant identical components, based on their hitting a time gate
> at slightly different moments.
>
> I thought Leslie Lamport and Fred Schneider essentially solved this
> problem thirty years ago. Are
> you saying the HW people haven't get got it on board? The original problem
> came from the SIFT
> verification attempt at SRI, along with the Byzantine Generals problem.
>
> See for example item #62 on Lamport's publications list, a JACM paper:
> http://research.microsoft.com/en-us/um/people/lamport/pubs/pubs.html#clocks
>
> Schneider, for example:
> https://www.cs.cornell.edu/fbs/publications/byzClockBandol.ps
>
> Here's a survey paper from 1990 from Barbara Simons, Jennifer Welch and
> Nancy Lynch which I didn't
> know about until I looked:
> http://groups.csail.mit.edu/tds/papers/Lynch/lncs90-asilomar.pdf
>
> Ulrich Schmid did a lot of work on it in the 1990's, but I don't know it
> well. Here's a keynote talk
> he gave in 2007
> https://ti.tuwien.ac.at/ecs/people/schmid/Mypapers/ispcs.pdf and a list
> of selected
> papers, which is unhelpfully presented without titles and with a somewhat
> inefficient window
> generation: https://ti.tuwien.ac.at/ecs/people/schmid/Mypapers
>
> PBL
>
>
> Prof. Peter Bernard Ladkin, Faculty of Technology, University of
> Bielefeld, 33594 Bielefeld, Germany
> Je suis Charlie
> Tel+msg +49 (0)521 880 7319 www.rvs.uni-bielefeld.de
>
>
>
>
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-- 
*Matthew Squair*
MIEAust CPEng

Mob: +61 488770655
Email: MattSquair_at_xxxxxx
Website: www.criticaluncertainties.com <http://criticaluncertainties.com/>



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