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[gpsd-dev] Implementing support for additional message in u-blox driver

From: Michael Pratt
Subject: [gpsd-dev] Implementing support for additional message in u-blox driver
Date: Fri, 11 May 2018 11:18:52 -0400

Hello all,

I have been working with gpsd and a u-blox M8T receiver, and I have some questions about the u-blox driver implementation and the messages that are supported. 

1) gpsd supports the NAV-TIMEGPS message, which "reports the precise GPS time of the most recent navigation solution ...". Some u-blox protocols also implement similar messages for GLONASS, Galileo, and BeiDou (NAV-TIMEGLO, NAV-TIMEGAL, and NAV-TIMEBDS, respectively), but these are not supported by gpsd. Would there be any advantage to supporting these messages? The NAV-PVT message already reports UTC time, so is there any need to parse additional timing messages? In a scenario in which only non-GPS constellations are available, would the NAV-PVT message provide sufficient timing information, or would the constellation-specific message provide better information?

2) u-blox also implements a NAV-TIMEUTC message which reports a "UTC Time Solution", which is also not supported by gpsd. However, the NAV-PVT message already reports UTC time. Would implementing support for the NAV-TIMEUTC message be redundant?

3) Why are NAV_SVINFO messages required to have a payload of at least 152 bytes? This means at least 12 channels are required to be present in the message, or else the entire message is discarded. Is there a reason for this requirement? It seems to me that the minimum valid payload size is 8 bytes, and that information about any number of channels would be useful.

Thanks very much for your time and any help with these questions.

Best regards,

Michael Pratt

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