In message  <1BD1B35E65@firga.sun.ac.za> PICLIST@MITVMA.MIT.EDU writes:
> Hi,
>
> > Another problem with periodic saving is that if power fails during a save
> > the data may be garbled.  One solution to this would be to save two
> > copies with a scheme such as CRC applied to each copy to check if it is
> > valid.  If upon turning the power back on, a copy fails the CRC the other
> > one would be used.  The bad copy would be fixed by rewriting it from the
> > good one.  (If both copies fail CRC, obviously this is a problem.  This
> > shouldn't happen if it is just power on/off causing garbled data to be
> > written)
>
> A method I have used keeps two copies of the data and a pointer byte.
> I write alternately to the one or the other.  I first write the data and
> then write the single pointer byte to indicate which of the entries
> contain the most recent info.  This method makes sure that the data you
> read is always valid (although it might not be the newest data).
>
Niki,

Is there not a danger with this method that the pointer location
could get corrupted if it is being written at the same time that
the power is being removed?

Have you a mechanism to deal with that?


Best regards,

Mike Watson