Rsync for program loading on embedded platforms

[Donovan Baarda]

On Wed, 2004-06-16 at 18:01, Greger Cronquist wrote:
> Hi again,
> 
> This issue solved itself rather annoyingly since we use flash memory in 
> our newer devices (which had slipped my mind). So we must erase the 
> memory first and then load.

Last time I played with flash, you could erase a block at a time. The
flash erase and write times are quite long, and flash has a limited
number of write cycles, so avoiding any re-writing is a good idea.

The simple solution here is a flash block aligned signature, and do a
block by block compare/transfer, so only blocks that are changed are
transfered/erased/written. There is no benefit to a byte-aligned rolling
window/checksum, unless you do some fancy partial-in-RAM updating tricks
before erasing/writing the blocks.

Another complicated variant that might be useful if your data size is
significantly larger than the flash block-size would be an rsync-like
algorithm that "rolls" a flash-block-aligned (instead of byte aligned)
window (rsync-block) through the flash. This would only be worth it if
the window was at least 8 times the size of the flash-blocks.

If you want to experiment with these kinds of algorithms, I thoroughly
recommend pysync... it would be easy to implement and test all these
variants using it.

-- 
Donovan Baarda <abo at minkirri.apana.org.au>
http://minkirri.apana.org.au/~abo/