Re: [gpsd-dev] [PATCH] Fix on NMEA driver 2D mode

[José Miguel Gonçalves]

On 12-04-2012 16:59, Eric S. Raymond wrote:
> José Miguel Gonçalves<address@hidden>:
> > The problem does not occur with the full set of NMEA messages.
> > Moreover, it does not happen if I add the GLL message to the set of
> > messages that the device sends.
> Good.
>
> > A device that behaves like you describe is not really following the
> > standard. I understand that you want to support the biggest set of
> > receivers that you can, but I think that you should privilege the
> > ones that behave correctly.
> Sadly, attempting that would be a disaster. The NMEA standard is
> proprietary and complex; additionally, while I've never seen it, I
> have good reason to believe that it is vague about edge cases and
> exceptional conditions.  Thus, "behave correctly" is not necessarily
> well-defined even if one can see NMEA 0813 - and I think mamy GPS
> implementors never have seen it.  Instead they emulate the behaviors they've
> seen in other devices, along with the mutations that arose during
> previous folk transmission.

My company has a copy of the standard and I don't think it's vague, at least in 
the point we are discussing. But I agree with you that, because of its proprietary 
nature, many (if not the majority) of the implementations were made without 
reading the standard, with the implied problems of that.

> Under these circumstances, you basically need to code to cope with maximum
> perversity in what comes up the pipe.
>
> What's your expected gain from reducing the sentence set?  You haven't
> given me a good reason to support that yet at the cost of
> reduced bulletproofing, but perhaps there is one.

I mainly work with low power and low processing embeded systems, so I normally 
need to spare every CPU resource that I can. Because of that I normally set my GPS 
receivers to output only the messages that I need to process.

I think that we can yet be on the safe side and solve this problem aroused with 
PolaRx2 if we change the test to;

((session->newdata.mode < MODE_NO_FIX) || (session->newdata.mode > MODE_2D))

Best regards,
José Gonçalves