6986840c0d
When the fingerprint feature isn't used (or with a timestamp of zero),
the response to the SIZE (0xC6) and DATA (0xC4) commands is received
almost instantly:
[0.302704] W: C60000000010270000
[0.366727] R: DCF90F00
[0.367829] W: C40000000010270000
[0.394812] R: E0F90F00
But when the fingerprint feature is used (with a non-zero timestamp),
there is a noticable delay:
[0.341218] W: C64CEB204D10270000
[1.927905] R: FE0B0000
[1.931610] W: C44CEB204D10270000
[5.092081] R: 020C0000
In this particular case, the total amount of dive data was close to 1M
bytes, which pushed the delay over the 3 second timeout, and caused the
download to fail. Increasing the timeout to 5 seconds fixed the problem.
The most likely explanation is that the dive computer needs to scan its
internal logbook to determine which dives and how many bytes to send.
Because that involves reading relative slow flash memory, this can take
up to a few seconds, especially if there are many dives present.
The duration of the delay also depends on the value of the fingerprint
timestamp: the less dives we try to download, the longer the delay! I
suspect that's because the most recent dives are located near the end of
the logbook. Hence, the less dives we request, the more dives the dive
computer needs to skip.
Below are some timings for downloading espectively 792410, 531856 and
270850 bytes from the same dive computer, but with a different
fingerprint value:
[0.216305] W: C6F8D5C84510270000
[0.373511] R: 56170C00
[0.378929] W: C4F8D5C84510270000
[0.661388] R: 5A170C00
[0.236246] W: C620D80F4810270000
[0.559608] R: 8C1D0800
[0.563755] W: C420D80F4810270000
[1.171631] R: 901D0800
[0.246193] W: C654E6434A10270000
[0.826365] R: FE210400
[0.831760] W: C454E6434A10270000
[1.974351] R: 02220400
Overview ======== Libdivecomputer is a cross-platform and open source library for communication with dive computers from various manufacturers. The official web site is: http://www.libdivecomputer.org/ The sourceforge project page is: http://sourceforge.net/projects/libdivecomputer/ Installation ============ On UNIX-like systems (including Linux, Mac OS X, MinGW), use the autotools based build system. Run the following commands from the top directory (containing this file) to configure, build and install the library and utilities: $ ./configure $ make $ make install If you downloaded the libdivecomputer source code directly from the git source code repository, then you need to create the configure script as the first step: $ autoreconf --install To uninstall libdivecomputer again, run: $ make uninstall Support ======= Please send bug reports, feedback or questions to the mailing list: http://libdivecomputer.org/cgi-bin/mailman/listinfo/devel or contact me directly: jef@libdivecomputer.org License ======= Libdivecomputer is free software, released under the terms of the GNU Lesser General Public License (LGPL). You can find a copy of the license in the file COPYING.