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Re: [gpsd-users] Is gpsd supposed to be filtering NMEA sentences it does

From: Eric S. Raymond
Subject: Re: [gpsd-users] Is gpsd supposed to be filtering NMEA sentences it doesn't understand?
Date: Wed, 4 Feb 2015 08:40:16 -0500
User-agent: Mutt/1.5.23 (2014-03-12)

Ed W <address@hidden>:
> I'm using GPSD 3.10.  I'm feeding it data from an airmar 200WX combined
> wind/temp/pressure/everything sensor.  The raw serial port output includes
> such sentences as:
> $YXXDR,A,9.3,D,PTCH,A,-7.5,D,ROLL*78
> However, these don't emerge from gpsd (using gpspipe -[rR])
> - Is this deliberate?

The packet getter discards these packets because the prefix YX is not in the 
list of known NMEA talker IDs:

 * The NMEA portion of the state machine allows the following talker IDs:
 *      $GP -- Global Positioning System.
 *      $GL -- GLONASS, according to IEIC 61162-1
 *      $GN -- Mixed GPS and GLONASS data, according to IEIC 61162-1
 *      $II -- Integrated Instrumentation (Raytheon's SeaTalk system).
 *      $IN -- Integrated Navigation (Garmin uses this).
 *      $WI -- Weather instrument (Airmar PB200, Radio Ocean ROWIND, Vaisala 
 *      $HC -- Heading/compass (Airmar PB200).
 *      $TI -- Turn indicator (Airmar PB200).
 *      $EC -- Electronic Chart Display & Information System (ECDIS)
 *      $SD -- Depth Sounder
 *      $P  -- Vendor-specific sentence
 *      !AB -- NMEA 4.0 Base AIS station
 *      !AD -- MMEA 4.0 Dependent AIS Base Station 
 *      !AI -- Mobile AIS station
 *      !AN -- NMEA 4.0 Aid to Navigation AIS station
 *      !AR -- NMEA 4.0 AIS Receiving Station
 *      !AX -- NMEA 4.0 Repeater AIS station
 *      !AS -- NMEA 4.0 Limited Base Station
 *      !AT -- NMEA 4.0 AIS Transmitting Station
 *      !BS -- Base AIS station (deprecated in NMEA 4.0)
 *      !SA -- NMEA 4.0 Physical Shore AIS Station

> - Would it be possible to introduce an option to allow all unknown NMEA
> sentences to pass through (ie to use gpsd as a NMEA multiplexer)

No. That would be an extremely bad idea for several reasons, including:

1. Options are evil - they blow up the test complexity of the software
and conflict with the goal of zero configuration.

2. GPSD's job is not to reveal NMEA quirks, it's to hide them.  Those sentences
are a case in point; obviously XDR ought to be translated to a JSON ATT report.

The right question for you to be asking would be "Can we add YXXDR to the
set of accepted and parsed sentences?"  Possibly.  Full documentation, please.
                <a href="";>Eric S. Raymond</a>

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