can't download Oceanic VT3 on linux

[Jef Driesen]

On 2014-03-07 03:20, Hamish Moffatt wrote:
> I'm trying to download from my VT3. I've built libdivecomputer 0.4.2
> on Linux (64-bit) but downloading is very slow and eventually fails.
> I've tested with both Subsurface and using the "universal" example. It
> does retrieve some dive data ok though.
> 
> Downloading my VT3 does work on Windows though, using Diving Log 5.0
> (includes libdivecomputer 0.4.2, 32-bit) or the "universal" app binary
> which I downloaded directly from the libdivecomputer.org site.

I'm a bit surprised it works on Windows, but not on Linux. Because the 
code is the same, except for the low-level serial code, that might 
indicate a problem with the driver rather than the dive computer.

> I've included a bit of the output log from "universal" on linux below.
> I checked that nothing else has the port open with lsof - earlier
> modem-manager was running but I've killed and removed that now.

Normally, if modem-manager has the port open, you wouldn't even be able 
to open the serial port, because we try to get exclusive access. So I 
assume you fixed that problem correctly. To applications talking to the 
same serial port results in all kinds of weird problems.

> [0.209269] INFO: Write: size=4, data=B1000000
> [3.212314] INFO: Read: size=0, data=
> [3.212333] ERROR: Failed to receive the answer. [in oceanic_atom2.c:331 
> (oceanic_atom2_send)]
> [3.212341] INFO: Sleep: value=100
> [3.312423] INFO: Flush: queue=1, input=0, output=0
> [3.312656] INFO: Write: size=4, data=B1000000
> [3.314042] INFO: Read: size=1, data=5A
> [3.324885] INFO: Read: size=17, data=0416041120081001425800730000000075

> [6.441357] INFO: Write: size=4, data=B1005400
> [6.443109] INFO: Read: size=1, data=A5
> [6.443125] ERROR: Unexpected answer start byte(s). [in 
> oceanic_atom2.c:337 (oceanic_atom2_send)]
> [6.443133] INFO: Sleep: value=100
> [6.543215] INFO: Flush: queue=1, input=0, output=0
> [6.543519] INFO: Write: size=4, data=B1005400
> [6.544642] INFO: Read: size=1, data=5A
> [6.555511] INFO: Read: size=17, data=39111F172E0CABB4258302172E4B7BB785

What happens here is that the first time we send a command to the dive 
computer, we either don't get a reply back (first case above), or the 
dive computer replies with a negative answer (second case above). In 
such case, libdivecomputer will automatically retry sending the command, 
and that appears to work.

Usually such errors are rare, and you shouldn't even notice them. But 
you seem to get an error on every single packet. That also explains why 
the download is terribly slow. If there is no response from the dive 
computer, the timeout (3 seconds) will expire. Thus every packet will 
take 3 seconds instead of a few milleseconds. You can easily see this 
from the timings in the first case above.

If you've bad luck and the retrying fails too, then eventually 
libdivecomputer will give up and fail with an error.

> Any suggestions?

Does your dive computer have a low battery? It's pretty common reason 
for failing downloads. Typically the PC interface requires more power 
than during diving. Another thing is to avoid using USB hubs and connect 
directly to a USB port on the PC.

Jef