From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.perfora.net (mout.perfora.net [74.208.4.194]) by huchra.bufferbloat.net (Postfix) with ESMTP id 17810200A20 for ; Sat, 17 Mar 2012 07:59:00 -0700 (PDT) Received: from [192.168.83.5] (c-76-97-152-51.hsd1.ga.comcast.net [76.97.152.51]) by mrelay.perfora.net (node=mrus1) with ESMTP (Nemesis) id 0MStht-1RhjC03IDF-00RaE0; Sat, 17 Mar 2012 10:58:59 -0400 Message-ID: <4F64A6B0.6010509@c3energy.com> Date: Sat, 17 Mar 2012 10:58:56 -0400 From: "Ron Frazier (NTP)" User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.9) Gecko/20100722 Eudora/3.0.4 MIME-Version: 1.0 CC: thumbgps-devel@lists.bufferbloat.net References: <20111025095801.C9A9D800037@ip-64-139-1-69.sjc.megapath.net> <4F64A2EC.1020805@c3energy.com> In-Reply-To: <4F64A2EC.1020805@c3energy.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V02:K0:6aSxdgzQjGKP+VPfB5Us/ovlU/fE49fOh3LYgbEkWmN 7p/DqudBQ3Mvg+QIRZjh4yOrlt6g8xigJUXnmGTfNDeJ9/Oa6N h0FY44m204QD07VUr9vdDx6kAMbnZIXyb8YcLW/cWIf/JTHiho /1GEVYV/EG84LnC+4wn5jB4ROskp9y2Bx/H7Z14uXtFGLAkOIq TziduOKtwKpRpzkPdSg/AGcw57ez8b8tiyZ41zXE/L6cPxR4w3 DdINfk/Vl3hkU8JwVTcBp0XZ5yhV0G/6jNKNnrpQU3vOyTV5fw HDowm5HG+9QTupr3jkC4atqeiAu7uvunNBXcxIizDDc07CPE4V qvhvvNOAhJqaHrNax7Jr2xmqwnWGupN3nsY6g9G0+ Subject: Re: [Thumbgps-devel] Fwd: Long term SiRF data X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 17 Mar 2012 14:59:00 -0000 PS to my prior message. The following should reset the GPS's NMEA offset from UTC to it's initial point. I don't know how varying satellite view affects this. Shut down NTP, unplug the GPS for 30 seconds, replug the GPS, wait 30 seconds, restart NTP. Sincerely, Ron > Hi all, > > (I'd like to cross post this message, including the original message > below to the NTP questions list since we've been discussing this nmea > wandering effect. Let me know if there are any objections.) > (Please forward this to the original sender of the first message if > needed.) > > I've been seeing similar wandering of the NMEA output on my BU-353. > This graph shows what looks like the internet servers (colored lines) > wandering off while my pc is locked to gps time (dark jaggy baseline). > I suppose it's actually the GPS wandering off. > > http://dl.dropbox.com/u/9879631/drifting01-peerstats.20120312.jpg > > Can someone please tell me, if known, why this happens? I've been > discussing this a good bit on the NTP questions list. On my > particular home network / internet connection, my offsets to internet > servers with NTP running run about + / - 50 ms. I've decided to use > the BU-353 GPS anyway, since in the short term, my offsets are + / - 6 > ms or so, even if over days, my time varies + / - 70 ms from UTC. At > least the variations are not every 15 minutes like they would be if I > was polling the internet. I hope to shortly have a Sure Electronics > GPS board and will be testing that. David Taylor, on the NTP > questions list says the same NMEA wandering has been observed on the > Garmin 18 ??. I'm not sure which model that was. > > Here's how to reprogram th BU-353. Lots of the support stuff is here: > > http://www.usglobalsat.com/s-122-bu-353-support.aspx > > However, the program we need is not. To program the unit, you need > SirfDemo. > > First check out the FAQ here: > > http://www.usglobalsat.com/store/gpsfacts/bu353_gps_facts.html > > And you can find a link to SirfDemo here: > > http://www.usglobalsat.com/downloads/setupSiRFDemoV387.zip > > Unzip and install SirfDemo. Do the following to reprogram the BU-353. > I assume other SirfIII units are similar. SirfDemo gives you access > to a HUGE number of internal GPS functions, probably enough to really > screw up the device if you're not careful. You can also do factory > restarts, etc., from the menus. > > a) Shut down NTP, GPSD, or any other thing attached to the GPS virtual > com port. > b) Start SirfDemo. > c) A Data Source window will pop up. Select the com port and data > rate that the GPS is currently set to. If the baud rate is unknown, > try 4800 then try to connect, then 9600, etc. If the com port is > unknown, look in the Windows control panel, system, device manager > under ports com and lpt to determine which com port is active. > d) Under the view menu, turn on the Signal, Radar, Map, Messages > Response, Messages Error, and Messages Debug windows if not on already. > e) Click the 5th toolbar button, which is connect to data source. > f) If the unit is outputting NMEA data, that should appear in the > debug window. If it is outputting satellite data, you'll get that in > the signal and radar windows. > g) Under the Action menu, select switch to SIRF protocol. The NMEA > data will stop and the response window will start outputting data. > h) Under the Action menu, select switch to NMEA protocol. > i) A parameter selection window will pop up. This allows the sentence > output to be customized. Using the drop down boxes, put a 1 in every > sentence you want to occur once per second. Put a 2 for once every 2 > seconds, etc. Put a 0 if you don't want the sentence to appear at > all. You can click in the first number field, type a number, and tab > to the rest if you like. I leave checksums turned on. Select your > baud rate, then click send. > j) The response view windows should stop updating and the debug view > should start up again with NMEA sentences. > k) Click the 5th toolbar button again which will disconnect you from > the GPS. > l) Close SirfDemo. > m) You are now ready to resume using the GPS with NTP as normal. > > There are many many other options you can choose from the menu options > of SirfDemo, including a factory reset, should you need it. > > Hope this helps. > > Sincerely, > > Ron > > >> I can't remember if I had shared this already. >> >> >> ---------- Forwarded message ---------- >> From: Hal Murray >> Date: Tue, Oct 25, 2011 at 2:58 AM >> Subject: Long term SiRF data >> To: Eric Raymond >> Cc: Hal Murray, Dave Taht >> , Jim Getty, Gary Miller >> >> >> >> >> I've been collecting data from 2 SiRF units. I'm up to about 12 days >> now. >> >> Quick summary: both suck. >> >> Both are located inside my house, poor conditions. >> >> >> The first is a Holux GR-213. It's setup to only send GPRMC sentences. >> That's what I would use with ntpd. >> >> Here is the startup: >> http://www.megapathdsl.net/~hmurray/bb/gps/Holux-1.png >> >> The green marks are "good" sentences. The Y offset is the difference >> between >> the actual arrival time and the time stamp in the sentence. The blue >> marks >> are the fraction part of the time stamp in the sentence. The red >> marks are >> invalid sentences. >> >> At about -2.94 (hours) the reported time jumped by 1 second. My >> guess is >> that it learned about the latest leap second or something like that. >> >> At about -2.82 hours, the fractional part of the report switched to >> 0. I >> have no idea what caused that. It doesn't really matter much. It >> wasn't >> useful anyway. >> >> Here is the big picture: >> http://www.megapathdsl.net/~hmurray/bb/gps/Holux-2.png >> There is a mode shift every 1-3 days. What's the right term? >> >> For reference, here is an old graph with the mode shift every 8-12 >> hours. >> http://www.megapathdsl.net/~hmurray/bb/gps/SiRF-GPRMC-4800.png >> >> This is the previous 2 pictures glued together: >> http://www.megapathdsl.net/~hmurray/bb/gps/Holux-3.png >> >> Here is one day: >> http://www.megapathdsl.net/~hmurray/bb/gps/Holux-4.png >> >> ------------- >> >> The second unit is a Global Sat BU-353. It ignored my attempts to >> change the >> configuration, so I let it run in the default setup. Normally it sends >> GPGGA, GPGSA, and GPRMC. Every 5 seconds it includes 3 GPGSV sentences >> before the GPRMC. I think that fits in 1 second at 4800 baud, but >> the GPRMC >> gets pushed over to the next second. >> >> Here is the graph for the GPGGA sentences: >> http://www.megapathdsl.net/~hmurray/bb/gps/BU-353-gpgga.png >> The long term cycle time is 8-10 days. >> >> Here is the graph for the GPRMC sentences: >> http://www.megapathdsl.net/~hmurray/bb/gps/BU-353-gprmc.png >> The top band of green is the data that gets pushed over to the next >> second. >> The blue and purple are the number of satellites. (They are scaled >> up by >> 100.) I don't see any pattern. >> >> This unit doesn't always return 000 for the fraction part of the time >> stamp. >> Sometimes it's 998 or 999 with the previous second. >> http://www.megapathdsl.net/~hmurray/bb/gps/BU-353-gpgga-off.png >> >> >> >> -- >> These are my opinions, not necessarily my employer's. I hate spam. >> >> >> >> >> > -- (PS - If you email me and don't get a quick response, don't be concerned. I get about 300 emails per day from alternate energy mailing lists and such. I don't always see new messages very quickly. If you need a reply and have not heard from me in 1 - 2 weeks, send your message again.) Ron Frazier timekeepingdude AT c3energy.com