Failed to receive the answer (from Suunto Vyper Air)

[Jef Driesen]

On 2012-06-20 14:45, Amit Chaudhuri wrote:
>> If the failure is during the first data packet, then this is a known
>> problem
>> with the vyper2 class devices. For some unknown reason the 
>> communication
>> fails
>> to startup properly the first time you try, but if you retry 
>> immediately
>> again
>> it usually works. Unfortunately we don't know what the underlying 
>> problem
>> is. It
>> might indeed be some timing issue. If anyone has some suggestions, 
>> let me
>> know!
>>
> Tried the immediate retry idea (thanks) and it consistently fails.
>
> I will add some diagnostics to libdivecomputer and recompile & 
> re-test.
> I'll update in a few days with any results.
>
> If you have any suggestions for other things I might try I'm open to 
> having
> a tinker.  I've no experience of reverse engineering protocols but I 
> am not
> afraid of a bit of research and some C/C++.

If you need additional diagnostics, apply this patch [1] to log the 
serial communication. This will allow you to see what is going on. The 
same patch is also used in the pre-compiled test applications on the 
libdivecomputer website.

If you need some info on the protocol look here [2].

[1] http://www.divesoftware.org/libdc/tmp/serial.patch
[2] http://www.sarnau.info/papers:suunto_d9

Possible areas of interest are the serial_sleep calls (especially the 
one at startup, try to make it larger) and the half-duplex emulation 
(which is basically a variable length sleep).

Jef