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From: | Reinhard Arlt |
Subject: | Re: ✘n2k and issue #176 |
Date: | Tue, 14 Dec 2021 01:26:01 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 |
Hello,i have learned quite a bit, since i have written the n2K code for gpsd many years ago.
And feel, that i was (at least a bit) pushed out of this group, as "my" data structures for attitude are removed from gpsd.
First a few comments:1.) A solution to respect only n2k gps and ais messages is absolutely the wrong way. On a boat, you want to see as much info from the nmea2000 bus as possible, and convert them into JSON and nmea0183 messages.
2.) The source address a of a n2k device is static. It is only allowed to change the own address, if you lose an address claim, or your device gets a new address during an ISO address assignment.
On a proper working n2k bus, you can only lose the address claim, if a new device is added. As the address claim is broken by design (it violate a basic can rule), a restart of the bus and all devices is always a good idea, as you never know, if an other device is off bus afterwards!
I have no experience with the ISO bus, but i assume, that changing the devices on the bus will happen here more frequently.
The central problem comes form the nmea. A "normal" device on a n2k bus can always get the info of the devices on the bus with a dummy address claim. But you need a vendor id and a device id for that purpose, and the nmea charge you quite a bit for it. And even more worse, you will lose the device id, if your device is not certified after a few month.
My suggestion is: Tracking of the (j1939) address claim is not a big thing. And adding a timeout for devices, that do not send messages any longer also not.
I can write this code, but i still think, that it is not needed.I have never seen an iso address assignment on a boat in the wild, even it is mentioned in the n2k standard as a possibility.
Kind regards Reinhard On 12/13/21 8:20 PM, Gary E. Miller wrote:
Yo All! Any NMEA2000 folks around? There is a new issue with the NMEA2000 driver, and I have no idea how that driver works. The issue is: https://gitlab.com/gpsd/gpsd/-/issues/176 If you care about the NMEA2000 driver, please jump in to #176. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 gem@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can't measure it, you can't improve it." - Lord Kelvin
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