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Re: [gpsd-dev] RFC: Patch tp prevent call to ntpd_link _* for driver_nme

From: address@hidden
Subject: Re: [gpsd-dev] RFC: Patch tp prevent call to ntpd_link _* for driver_nmea2000
Date: Wed, 30 May 2012 09:13:54 +0200



i know, that i disable ntp support for nmea2000 now. This several two reasons:


-- the usage of ntp with gpsd on the boat has no top priority for me, the support of more then one GPS device, the AIS transmitter, and other instruments come first.


-- i see no way to test it, i have only one linux machine on the boat, perhaps you can tell me how to compare the ntp results of a gpsd using a conventional usb gps (u-blox 5) reciever, and a ntpd on the gpsd using the information from the nmea2000 bus.


-- as nmea2000 is a CAN bus (network), you need support in the CAN driver and perhaps even in the CAN interface hardware, to get a good timestamps. There are own time protocols for CAN, but not part ofnmea2000 as far as i know.


-- i have spend some time trying to understand the interaction of the pps daemon and the other ntp stuff, but my understanding of the subsystem is not good enough to make a change here. My understanding is, the the ntp_link_activate() and ntpd_link_deactivate() only allocate/free the the shared memory segment for ntp, and then starts the pps subsystem, that is unusable for nmea2000 as it is today.


Question: Does the ntp subsystem (without pps support) work, if there is only the shared memory segment present? then it is a nice option, to move my patches into ´╗┐ntp_link_activate() and ntpd_link_deactivate() after allocating/freeing the ntp shared memory segment. If this works, it will be for shure a far better solution!





Von: "Gary E. Miller" <address@hidden>

An: "address@hidden" <address@hidden>

Cc: address@hidden, "Eric S. Raymond" <address@hidden>

Betreff: Re: [gpsd-dev] RFC: Patch tp prevent call to ntpd_link_* for driver_nmea2000

Datum: Tue, 29 May 2012 20:49:38 +0200


Yo address@hidden


On Mon, 28 May 2012 11:38:18 +0200

"address@hidden" <address@hidden> wrote:


> here is patch, that keeps the pps thread away from the nmea2000

> socket, it do not start the ntpd stuff.


I finally got a look at your patch. Looks to me like it goes too far,

so I would revert it. This turns off not only PPS but basic ntpd

functionality. There is no PPS on nmea2000, but there are time

stamps and ntpd can use those.





Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701

address@hidden Tel:+1(541)382-8588



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