Fwd: Re: Purposeful Parity control

[Alan Deikman <Alan.Deikman@znyx.com>]

> >> Why was the parity control necessary for a chip-to-chip bus?
> >
> >For the same reason it's necessary in other reliable, high-speed data
> >transfer mechanisms - it is very easy for single bit errors to sneak in, be
> >they due to design margin, bad components, external influence, or whatever,
> >and without some bandwidth-efficient, cost-effective detection method, a
> >single bit error could easily run undetected for a while and worm its way
> >into causing system instability.
>
>Do you believe parity check could measurably compensate for
>"design margin, bad components, external influence, or whatever" ?
>The systems I have seen either work and make no errors so
>parity control has nothing to do all the time
>or make too many errors and parity control is useless.
>
>Which chip-to-chip PCI based device do you know to recover
>from parity error and continue?
>
>What is the typical system behaviour today upon parity error?

Consumer-grade products incorporating PCI probably do not
need parity.  Most of us have been using PCI for years on
our desktop systems and have never seen a single parity
error.  Certainly more reliable than the typical operating
system which is run on the same hardware.

On the other hand there are plenty of specifications I have
seen that would require at least parity protection.  For
example, airborne applications typically see a fairly high
incidence of bit-errors induced by cosmic rays.  Telco
applications also want some error detection.

If a network hub/bridge/router device re-frames a data
packet (re-calculates its CRC), the system architects are
very happy to see parity protection along as many data
paths as possible inside that box.

I can't say the PCI designers had all these applications
in mind, but the fact that they added parity makes PCI
more useful than it would have been otherwise.  These
designs often do not include a connector.

Regards,

----------------------------------------
Alan Deikman        | 510 249 0800 Voice
ZNYX Networks, Inc. | 603 843 5867 FAX