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 A842B208A7B for ; Tue, 27 Mar 2012 00:59:15 -0700 (PDT) Received: from [192.168.83.3] (c-76-97-152-51.hsd1.ga.comcast.net [76.97.152.51]) by mrelay.perfora.net (node=mrus0) with ESMTP (Nemesis) id 0M71H3-1SQWDF3zb3-00wKHO; Tue, 27 Mar 2012 03:59:14 -0400 Message-ID: <4F717350.7000101@c3energy.com> Date: Tue, 27 Mar 2012 03:59:12 -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 To: "thumbgps-devel@lists.bufferbloat.net" Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V02:K0:mB/bkm5avYLlDJur6CqzS8LBJwXmSPOsM1yqFp09sDf XNxoGcZS45VryPIqbhtLEML9MG+5VMobNkhO+AJQjpobkrpRxF CbhjmxLyT356cu/tuPEbOoBhQfGI1GXpD08ZweJBwef2/vFMsH cviogUR6MLHPzAqEPeUS5aEClEgoZjJMTx31I5KA57LcIx7whc hbqkrpyawlDJsM15qgi1aLN507GmybXxJZFLRVCjf+d5+WJoN5 TfhoPb34Q68APO9UJVtgyRFBDnC0cwvIU9vPDBNMlUdil1+02B 9bzxyoWLPj4OQ3vqanXXOlmGxEII5NNHLXAYso22xIXgX7LWUm PpJixaMknD6r67qxmzcWVsMpX7u34IXzPSgIB+xGv Subject: [Thumbgps-devel] performance testing sure gps board via usb serial converter 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: Tue, 27 Mar 2012 07:59:15 -0000 Hi guys, I thought you'd like to see this. I'm definitely getting performance from my GPS connecting through a Prolific based serial - USB converter that is within the specs that you proposed for your project - ie + / - 1ms offsets from GPS time. I posted this on the NTP Questions list tonight. Some parameters apply only to Windows and some apply only to Linux. The testing reported was done on Windows. Season to taste for your OS. Sincerely, Ron --------------------- I've been doing some performance testing with the Sure GPS board connected via serial - USB converter, with PPS to DCD. I'm running Win7. Performance is limited by the USB interface, but I've observed some interesting trends. I have email periodically checking for messages in the background, and I have 5 browser windows open with about 48 tabs. Acknowledgments Thanks to Alby for showing me how to use flag1 on the 20 driver to turn on pps without using the 22 driver separately. I don't know if there are any performance differences between the two. Thanks to Dave Hart for letting me know that flag3 to turn on kernel discipline doesn't apply to Windows and could cause problems. All these parameters and permutations are confusing, particularly if experimenting with Windows and Linux. Thanks to David Taylor for encouraging me to experiment with interpolation, using the environment variable NTPD_USE_INTERP_DANGEROUS=1 to turn on and NTPD_USE_SYSTEM_CLOCK=1 to turn off. Does that apply to Linux by the way? In the past, I thought realtime priority for the NTPD process was causing problems. So, I've been experimenting with both priority and interpolation. Realtime is the default priority. The most accurate time source I have is my GPS. Internet, in my case, doesn't even come close. So, I'm testing min and max offsets of my computer's clock to the GPS polling every 8 seconds. The tests weren't too scientific nor too long, but I still saw some interesting results. 1) Interpolation ON , Above Normal Priority, + 1.00 / - 0.75 ms, Total Range 1.75 ms 2) Interpolation ON , Realtime Priority, + 0.99 / - 0.67 ms, Total Range 1.66 ms 3) Interpolation OFF, Above Normal Priority, + 1.21 / - 1.19 ms, Total Range 2.40 ms 4) Interpolation OFF, Realtime Priority, + 1.13 / - 1.02 ms, Total Range 2.15 ms Comparing lines 1 and 2, going from Above Normal to Realtime priority with interpolation on reduces range by .09 ms. Comparing lines 3 and 4, going from Above Normal to Realtime priority with interpolation off reduces range by .25 ms. Comparing lines 3 and 1, in that order, turning interpolation on at Above Normal priority, reduces range by .65 ms. Comparing lines 4 and 2, in that order, turning interpolation on at Realtime priority, reduces range by .49 ms. Conclusion, I'm leaving interpolation on, and I'm leaving the process at Realtime priority. OK. It's 3:34 AM and I have to get some sleep. I really have to get UN-obsessed with this. I really do like to fully understand the technology I'm using, but GPS + NTPD has turned out to be a real challenge. Signing off for now and, if there are typos, to bad. Hopefully, someone will find this useful. Sincerely, Ron -- (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