The firmware version and serial number are stored in the final block
of each dive. That makes it very tricky to support the devinfo event
correctly. For an efficient implementation of the fingerprint feature,
the devinfo event should be emitted before downloading the manifests
or the dives. Fortunately it turns out it is actually possible to
retrieve the firmware version and serial number independently, using
the special identifier command.
A shutdown command should be send to the device, before the connection
is actually closed. In the absence of this command, the device will
display an error, even if the data transfer itself was successful!
The new Petrel protocol uses a simple data compression scheme to reduce
the transfer times. The data is broken up into blocks of 32 bytes each.
Each block except the first is XOR'ed with the previous block, creating
large runs of zeros due to the similarity of the data. The zeros are
then run-length encoded (RLE) to save space.
This is done in preparation for the implementation of the new Petrel
protocol, which shares the low level communication with the existing
Predator protocol.
