Some Veo devices never respond to the initialization command, but have
no problem to continue the communication. Therefore a timeout with no
data received is ignored. If there happens to be a real problem, it will
be catched when sending one of the other commands afterwards.
The "\\.\" prefix allows to access the Win32 device namespace directly,
without going through the file system. This is required to support
non-standard port names, and COMx ports with a number greater than 9.
The Aeris Elite T3 appears to update the global logbook pointer
incorrectly when overwriting old dives. As a result there can be logbook
entries pointing to profile data that has already been overwritten with
newer dives, and those cause problems when calculating the total amount
of bytes in the profile ringbuffer.
As a workaround we validate the logbook pointers immediately after
downloading. At this early stage we can check manually for ringbuffer
overflows without having to rely on the values stored in the data.
Because the user needs to initiate the transfer on the device itself, we
have to wait for an unknown amount of time. The infinite timeout works,
but causes problems if the data never arrives. By polling the serial
line, an application can at least cancel the operation.
With the knowledge of the end of profile pointer and the number of
samples, the ringbuffer can be traversed backwards and the start of the
ringbuffer doesn't have to be fixed anymore.
Especially the version commands seems to be sensitive to errors. Once
the initialization phase is over, a delay is usually not necessary, but
it should cause a noticable slowdown either because errors are supposed
to be rare.
If a logbook entry contains an invalid ringbuffer pointer, the error is
not returned immediately, but delayed until the end of the download.
With this approach we can download at least the dives before the
problematic logbook entry.
