Failed to receive the answer (from Suunto Vyper Air)

[Jef Driesen]

On 06/19/2012 07:57 PM, Linus Torvalds wrote:
> On Tue, Jun 19, 2012 at 12:39 AM, Amit Chaudhuri
> <amit.k.chaudhuri at gmail.com>  wrote:
>>
>> I get the followiing error report from the command line when attempting Log,
>> Import on my Suunto Vyper Air.
>>
>> Device name is /dev/ttyUSB0 and it reports permissions crw-rw---- 1 root
>> dialout 188, 0<date here>
>>
>> Error message is:
>>
>> suunto_vyper2.c:193: Failed to receive the answer.
>> <same>
>> <same>
>> suunto_common2.c:252: Cannot read memory header.
>
> This is the normal Suunto "I can't connect" message from
> libdivecomputer and doesn't mean anything very specific. It's what you
> get whenever the dive computer is even slightly wet, but it's also
> what you get when your communication cable is totally broken (as I
> found out six weeks ago - I was fighting this error forever).

The most common error is that people forget to activate the PC mode on the dive 
computer. But let's assume that's not the case here :-)

> I don't know exactly what SDM does differently, but the suunto
> protocols seem to be very timing-sensitive, and sensitive to noise.
> It's a two-wire setup, so it's simplex serial communication and
> apparently very sensitive to grounding issues etc.

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!

Jef