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[gpsd-dev] GPDS hand hardware fault/alarm reporting

From: Michael J. Tubby B.Sc. MIET
Subject: [gpsd-dev] GPDS hand hardware fault/alarm reporting
Date: Sun, 29 Oct 2017 09:48:15 +0000
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We have been using GPS receivers in vehicle location systems since the early 1990s and the Trimble Advanced Navigation Sensor (TANS) - if anyone remembers that - and have worked through multiple generations from SVeeSix, ACE to Lassen-iQ and have always used Timble's TSIP binary code.

We have a new product design and we've switched to Ublox MAX-M8W and I face a but of a dilemma, I could:

    a) keep our codebase and write a new UBX binary driver; or

    b) switch to using GPSD as effectively a Hardware Abstraction Layer (HAL) - our preferred route

Our platforms are ARM-based (i.MX6, Linux 4.1, Ubuntu 14.04 LTS server) and I have downloaded and built GPSD 3.19, got working with MAX-M8W on out platform, got NTPD working with shared memory and built a prototype test client - all in one evening!  While I'm impressed with the quality and ease of use of both GPSD and libgps it leaves us with a challenge for GPS receiver and antenna fault monitoring and reporting.

Our products are designed for business-critical and mission-critical users (e.g. Emergency Services and other government agencies). Equipment gets broken both accidentally and (on occasions) deliberately we need to monitor the hardware for faults as we generally need to get faulty installations fixed asap.

All of our products use an external antenna with active pre-amp and we monitor the power consumption of the pre-amp to determine whether the antenna is good or faulty, there are three conditions - "good", "open circuit" (not plugged in) and "short circuit".  These are reported via status bits in TSIP and UBX - some chips have the hardware built in while other's you have to add bits around the GPS receiver.

When using the proprietary binary interfaces, e.g. Trimble TSIP and Ublox UBX, additional instrumentation is available for faults and alarms and we use these as well.

Several receivers support 'battery backup failed' and or 'system RAM corrupt' at start-up along with 'DSP faults' and many newer GPS receivers support jamming detection by detecting the presence of in-band RF interference and flag this also.

I am only across the Trimble and Ublox GPS/GNSS receivers that we currently use but an approach for adding generic support these faults/alarms would be to add a new set of flags as a uint32_t called 'gps.fault' or similar and define a set of values:

    GPS_FAULT_DSP_FAILURE             0x00000004
    GPS_FAULT_ANTENNA_SHORT           0x00000010
    GPS_FAULT_JAMMING_DETECTED        0x00000020

that the drivers could set.

Before we go off hacking GPSD and libgps too much I thought I'd check if we're going in the right direction or overlapping with anyone else.

Does anyone else want to work on this?  Does anyone want to contribute to the list of faults/fault codes for other receivers?


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