Re: Crc16 on power failure
- From: "Robert Adsett" <sub2@xxxxxxxxxxxxxxxxxxxxx>
- Date: 19 Jan 2007 07:08:02 -0800
Mr. C wrote:
On Thu, 18 Jan 2007 17:54:38 +0100, "Ignacio G.T."
<igtorque.remove@xxxxxxxxxxxxxxx> wrote:
I'd suggest using a simple checksum (perhaps complemented), instead of a
CRC. Usually, a checksum is faster to calculate than a CRC by software.
True, they are faster, but they are not nearly as good at detecting
errors. 8-bit checksum, XOR-ing, or whatever can allow for a 1/256
chance of not detecting an error. A 16-bit checksum is better than an
8-bit, but not nearly as good at detecting single bit errors as a
CRC-16. Jack Crenshaw states that a 16-bit CRC will detect:
It's clear CRC are much better at burst error detection. But since
both methods contain the same number of possible check digits they have
the same probability of any given random sequence matching a given
check (1 in 64K for a 16bit check) it follows that a simple check
should be better in non-burst conditions. It only remains to determine
what kind of errors your memory system can give you ;)
As well as a CRC and check sum you can also consider a Fletcher
checksum. Also for storing backup values of operating parameters
coonsider running an EEC on each parameter instead of a block check.
National had an app note on a straightforward one I can look up. The
EEC has the advantage of being per item and so likely faster if you
only change an item or two, it will take up more room though. You
could combine it with a simple checksum over a block to give a dual
layer check.
Robert
.
- References:
- Re: Crc16 on power failure
- From: Ignacio G.T.
- Re: Crc16 on power failure
- From: Mr . C
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