Re: [time-nuts] PC clock generator without 14.318MHz
Chris, I agree with you that additional HW to avoid interrupt latency is necessary. My NTP servers with stable oscillator and HW card processing PPS (still in use but some mainboards failed after 10 years of reliable service) are described here: http://archiv.cesnet.cz/doc/techzpravy/2007/ntp-server/ Vladimir On 10/20/2016 04:38 AM, Chris Albertson wrote: The last time I read about this it was on an ARM based board. They clocked it with a GPSDO. I think the problem is MUCH easier if you can abandon the PC platform. The other story I read solved to problem by adding even more hardware and some software changes. They moved the nanosecond counter out of the CPU chip to a hardware counter and then the PPS signal connected to a latch. This avoids the interrupt latency. In most normal NTP servers the interrupt causes the CPU to snapshot its internal nanosecond counter and store the snapshot in memory and set a flag so the user space task can then read the value stated in RAM. This gets you only microsecond resolution. With special hardware the counter is latched with external hardware then then on the interrupt handler only has read the latch and place that valuer in RAM and set the same flag. The trouble is that EVERY routine that reads the internal counters has to by modified to read the eternal counter. As I remember these system ran BSD UNIX. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] PC clock generator without 14.318MHz
On 10/18/2016 11:23 PM, Mike Cook wrote: Le 18 oct. 2016 à 16:53, Vladimir Smotlacha<v...@cesnet.cz> a écrit : Hello, I have operated own NTP servers with stable system clock for many years. The principle is quite simple - I replaced 14.318 MHz quartz with OCXO based circuit. Now I have to build few more servers with modern mini-ITX motherboards, however on many of them (e.g. from ASUS) I can’t find any 14.317 MHz quartz. Such frequency is a relic of original PC design and I wonder if it is used any other basic frequency in recent clock generators? The 14.317MHz xtal was connected to the south bridge controller chip, but for recent CPUs this has gone away as has northbridge and the system clock has been integrated into the PCH (Platform Controller Hub) chip according to Wikipedia, so I suspect that if you find the clock feeding that , then you could stabilize it in that same way. Thank you Mike, PCH will be object of my experiments. I wonder than probably nobody solved stable clock source in "post 14.318" mainboards. Vladimir thanks, Vladimir ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. "The power of accurate observation is commonly called cynicism by those who have not got it. » George Bernard Shaw ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] PC clock generator without 14.318MHz
Hello, I have operated own NTP servers with stable system clock for many years. The principle is quite simple - I replaced 14.318 MHz quartz with OCXO based circuit. Now I have to build few more servers with modern mini-ITX motherboards, however on many of them (e.g. from ASUS) I can’t find any 14.317 MHz quartz. Such frequency is a relic of original PC design and I wonder if it is used any other basic frequency in recent clock generators? thanks, Vladimir ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] wrong date on Trimble ACUTIME 2000
Hi, today (29 February] failed several my NTP servers during first few minutes of the day. The reason was wrong date reported by our Trimble ACUTIME 2000 - it forgot the leap year: $GPGGA,004848.0,5006.106,N,01423.494,E,0,08,0.00,00249,M,045,M,,*52 $GPGSV,2,1,8,18,55,087,42,21,42,070,39,26,26,186,40,15,15,057,38*48 $GPGSV,2,2,8,16,49,209,43,08,34,298,41,27,68,298,44,10,54,156,44*44 $GPRMC,004848.0,A,5006.106,N,01423.494,E,000.00,000.0,010316,00.3,E*67 $GPGGA,004856.0,5006.106,N,01423.494,E,0,08,0.00,00249,M,045,M,,*5D $GPGSV,2,1,8,18,55,087,43,21,42,070,39,26,25,186,40,15,15,057,37*45 $GPGSV,2,2,8,16,49,209,43,08,35,298,41,27,68,298,43,10,54,155,44*41 $GPRMC,004856.0,A,5006.106,N,01423.494,E,000.00,000.0,010316,00.3,E*68 This particular GPS receiver works reliable for 15 years, so three leap years already passed without problem. Does anybody else observed similar behaviour? thanks, Vladimir Smotlacha ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
