Re: [time-nuts] GPS for ntp
On 24/10/2014 21:33, Joseph Gray wrote: Timestamping a message to the nearest 100 ns is what I am after. If I can't do it directly with the ublox, I'll have to look at the PRU on the Beaglebone. It has a 200 Mhz clock and single cycle instructions. The BBB has no less than 8 peripherals that will do event capture at under 100ns resolution, no need to mess around with the PRU. To be fair, pretty much any microprocessor would be capable of doing this, and an arduino or pic could be a lot cheaper way to go depending on your requirements. If you need to stick to a BBB: DMTIMER's 4 to 7 will do hardware capture, but they operate at 'only' 25mhz. The SoC also contains 3 eCAP units which operate at the OCP bus speed (100mhz / 10ns resolution) and can store up to 4 events. The last unit is also an eCAP unit, but it's a PRUSS peripheral and operates at the PRUSS clock speed (200mhz / 5ns resolution). The surprise is you _don't_ actually need to write PRU code to access it, all the PRUSS peripherals can also be controlled from the main ARM core (and similarly the PRU can access all the SoC peripherals). Using two hardware capture units, you can implement a simple (or as complex as you want to make it) interval timer and follow Tom's posting from a few days ago: https://www.febo.com/pipermail/time-nuts/2014-October/087356.html Cheers Simon ___ 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] GPS for ntp
Tom, Thanks for the information and your comments as to the suitability of these units. First hand knowledge is always appreciated. I had already figured out that there were four models :-) I was reading the documentation from ublox and the time stamping interrupt caught my eye. However, it is listed as only being available on the R model. I can't find anyone selling that model. Timestamping a message to the nearest 100 ns is what I am after. If I can't do it directly with the ublox, I'll have to look at the PRU on the Beaglebone. It has a 200 Mhz clock and single cycle instructions. Joe Gray W5JG On Oct 24, 2014 1:39 PM, "Tom Van Baak" wrote: > Joe, et al. > > I put some info at: http://leapsecond.com/pages/reyax/ > > Here's what you need to know about those Reyax GPS boards: > > 1) These are simple, well-made, low-cost, tiny GPS boards. Four models are > available, based on three u-blox chips. The prices are $14 $16 $20 $27. > > 2) The 3 chips are u-blox MAX-7C, NEO-7N, NEO-M8N. See > http://www.u-blox.com for chip info. Board documentation: > http://www.reyax.com/Module/GPS/RYN25AI/RYN25AI.pdf > http://www.reyax.com/Module/GPS/RY725AI/RY725AI.pdf > http://www.reyax.com/Module/GPS/RY825AI/RY825AI.pdf > > 3) The 4 boards available: > http://www.ebay.com/itm/171493874434 > http://www.ebay.com/itm/181553452840 > http://www.ebay.com/itm/181562403752 > http://www.ebay.com/itm/181566850426 > > 4) The only difference between the $14 RYN25AI and $16 RYN25DI is that > RYN25DI adds a ±10 V RS232 transceiver. The other 3 boards have a typical > "inverted" logic-level (3.3V) serial interface, suitable for uP or SBC or > UART/USB interface chip. > > I have no affiliation with seller "reyax" but their boards seem a step > above some of the other GPS stuff on eBay. In general I gravitate to > low-cost GPS receiver breakout boards with serial I/O and clean 1PPS > output. It's amazing how well these integrated antenna boards work: a truly > "3-pin" timing solution: power, ground, 1PPS. > > Note these are not "timing receivers" in the sense of RINEX output or > external clock input or position-hold with sawtooth correction. But for > less demanding work, the ±20 ns level that many of these receivers offer > more than enough. > > 5) You can also find similar boards from US sellers such as > http://parallax.com/ , http://adafruit.com/ , http://sparkfun.com/ > > 6) All of this is grossly overkill for NTP (at the 1 ms or even 1 us > level). But if some of you are pushing NTP to sub-microsecond limits, cheap > GPS/1PPS receivers like this are of interest. > > For more details, including almost medical-grade photos of a GPS patch > antenna, see: > http://leapsecond.com/pages/reyax/ > > /tvb > > - Original Message - > From: "Joseph Gray" > To: ; "Discussion of precise time and > frequency measurement" > Sent: Thursday, October 23, 2014 9:18 PM > Subject: Re: [time-nuts] GPS for ntp > > > > OK, I see source of the confusion. There is a difference of "one" > character > > in the two part numbers. The RYN25 has the older Ublox chipset. The RY725 > > has the Neo-7N chipset. There is only a $6 difference in price. I think > > I'll get a few to play with. > > > > Joe Gray > > W5JG > > ___ > 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.
Re: [time-nuts] GPS for ntp
Joe, et al. I put some info at: http://leapsecond.com/pages/reyax/ Here's what you need to know about those Reyax GPS boards: 1) These are simple, well-made, low-cost, tiny GPS boards. Four models are available, based on three u-blox chips. The prices are $14 $16 $20 $27. 2) The 3 chips are u-blox MAX-7C, NEO-7N, NEO-M8N. See http://www.u-blox.com for chip info. Board documentation: http://www.reyax.com/Module/GPS/RYN25AI/RYN25AI.pdf http://www.reyax.com/Module/GPS/RY725AI/RY725AI.pdf http://www.reyax.com/Module/GPS/RY825AI/RY825AI.pdf 3) The 4 boards available: http://www.ebay.com/itm/171493874434 http://www.ebay.com/itm/181553452840 http://www.ebay.com/itm/181562403752 http://www.ebay.com/itm/181566850426 4) The only difference between the $14 RYN25AI and $16 RYN25DI is that RYN25DI adds a ±10 V RS232 transceiver. The other 3 boards have a typical "inverted" logic-level (3.3V) serial interface, suitable for uP or SBC or UART/USB interface chip. I have no affiliation with seller "reyax" but their boards seem a step above some of the other GPS stuff on eBay. In general I gravitate to low-cost GPS receiver breakout boards with serial I/O and clean 1PPS output. It's amazing how well these integrated antenna boards work: a truly "3-pin" timing solution: power, ground, 1PPS. Note these are not "timing receivers" in the sense of RINEX output or external clock input or position-hold with sawtooth correction. But for less demanding work, the ±20 ns level that many of these receivers offer more than enough. 5) You can also find similar boards from US sellers such as http://parallax.com/ , http://adafruit.com/ , http://sparkfun.com/ 6) All of this is grossly overkill for NTP (at the 1 ms or even 1 us level). But if some of you are pushing NTP to sub-microsecond limits, cheap GPS/1PPS receivers like this are of interest. For more details, including almost medical-grade photos of a GPS patch antenna, see: http://leapsecond.com/pages/reyax/ /tvb - Original Message - From: "Joseph Gray" To: ; "Discussion of precise time and frequency measurement" Sent: Thursday, October 23, 2014 9:18 PM Subject: Re: [time-nuts] GPS for ntp > OK, I see source of the confusion. There is a difference of "one" character > in the two part numbers. The RYN25 has the older Ublox chipset. The RY725 > has the Neo-7N chipset. There is only a $6 difference in price. I think > I'll get a few to play with. > > Joe Gray > W5JG ___ 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] GPS for ntp
OK, I see source of the confusion. There is a difference of "one" character in the two part numbers. The RYN25 has the older Ublox chipset. The RY725 has the Neo-7N chipset. There is only a $6 difference in price. I think I'll get a few to play with. Joe Gray W5JG On Thu, Oct 23, 2014 at 2:41 AM, Brian Inglis < brian.ing...@systematicsw.ab.ca> wrote: > On 2014-10-22 21:07, Joseph Gray wrote: > >> Now I'm confused. Both the ebay listing and the linked specsheet clearly >> state that the Ublox Neo-7N is used. Is this true or not? >> > > On Wed, Oct 22, 2014 at 2:50 PM, Tom Van Baak wrote: >> >>> The USB interface will give you unpredictable timing and you still have >>> to hook >>> up the PPS output somehow, so can only really be recommended for >>> navigation uses. >>> >>> No, both versions of this board have a very nice 1PPS output pin. >>> Use the serial or USB interface for NMEA sentences only; use 1PPS for >>> timing. >>> >> I managed to browse to N25 not 725 devices when I looked them up! > -- > Take care. Thanks, Brian Inglis > ___ > 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.
Re: [time-nuts] GPS for ntp
On 2014-10-22 21:07, Joseph Gray wrote: Now I'm confused. Both the ebay listing and the linked specsheet clearly state that the Ublox Neo-7N is used. Is this true or not? On Wed, Oct 22, 2014 at 2:50 PM, Tom Van Baak wrote: The USB interface will give you unpredictable timing and you still have to hook up the PPS output somehow, so can only really be recommended for navigation uses. No, both versions of this board have a very nice 1PPS output pin. Use the serial or USB interface for NMEA sentences only; use 1PPS for timing. I managed to browse to N25 not 725 devices when I looked them up! -- Take care. Thanks, Brian Inglis ___ 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] GPS for ntp
Now I'm confused. Both the ebay listing and the linked specsheet clearly state that the Ublox Neo-7N is used. Is this true or not? Joe Gray W5JG On Wed, Oct 22, 2014 at 2:50 PM, Tom Van Baak wrote: > > The USB interface will give you unpredictable timing and you still have > to hook > > up the PPS output somehow, so can only really be recommended for > navigation uses. > > No, both versions of this board have a very nice 1PPS output pin. > Use the serial or USB interface for NMEA sentences only; use 1PPS for > timing. > > /tvb > > ___ > 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.
Re: [time-nuts] GPS for ntp
> The USB interface will give you unpredictable timing and you still have to > hook > up the PPS output somehow, so can only really be recommended for navigation > uses. No, both versions of this board have a very nice 1PPS output pin. Use the serial or USB interface for NMEA sentences only; use 1PPS for timing. /tvb ___ 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] GPS for ntp
On 2014-10-20 19:39, Joseph Gray wrote: What does everyone think of this GPS module for ntp use? According to the specsheet, it uses a Ublox Neo-7N. http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 Does anyone want to take a wild guess as to the best/worst case UTC offset I might get with such a setup? I realize that I'd have to try it to really find out, but guesses and advice from those more knowledgeable is always appreciated. RYN25AI and RYN25DI actually use a MAX-7C (Crystal), with no RTC, designed for low cost, low power, a passive antenna, and for the AI, a USB interface. The USB interface will give you unpredictable timing and you still have to hook up the PPS output somehow, so can only really be recommended for navigation uses. http://www.ebay.com/itm/RYN25DI-10Hz-RS232-interface-high-performance-GPS-Glonass-antenna-module-battery-/181553452840?pt=LH_DefaultDomain_0&hash=item2a456dd728 The DI has an RS-232 interface so you can at least hook that up with the PPS on DCD to the BB UART and get less jittery results, which will vary with temperature, as it uses only a regular crystal oscillator. -- Take care. Thanks, Brian Inglis ___ 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] GPS for ntp
Thanks for the great explanation. Is there any data on the performance ? Cheers Simon On 21/10/2014 22:29, Dennis Ferguson wrote: On 21 Oct, 2014, at 08:58 , Simon Marsh wrote: How do you map the timer counter value in to a PPS timestamp ? (that is, how do you turn the HW counter value in to what the OS thought the time was when the event occured ?) On the NetBSD prototype I have the clock adjustment system call interface is expanded to deal with multiple clocks, only one of which is the system clock. The HW counter becomes its own clock, which is the clock in which PPS measurements are expressed and which is adjusted into alignment with the PPS data. The system clock is adjusted into alignment with the HW counter clock using offset data from PIO polling of the clock pair. The IEEE1588 timestamp counter becomes a third clock, which gets adjusted into alignment with the system clock for use as a PTP server, or which is used to adjust the system clock when operating as a client. For the beaglebone this is probably overkill; since the clocks are all synchronous the system<->peripheral clock polling essentially determines a constant offset, after which you can keep them in sync by making the same relative rate adjustments to all clocks. For the general IEEE1588 case, however, the counter being sampled at the ethernet interface is often clocked by a different crystal then the clock you would prefer to use as the system clock, and the process of steering one clock into synchronization with another needs to be more complex. I should note that none of these clock adjustments really requires a PLL or other feedback control loop, nor does NTP, since no clock hardware is actually adjusted. The crystals are all free running and are unaffected by the adjustments. What is adjusted is instead a "paper clock", that is the adjustment is to the arithmetic done to convert each free running counter to a time of day, and this can be done open loop, with perfectly predictable results and with no feedback control, by just doing the adjustment arithmetic accurately and transparently. The thing the PLL does for ntpd, then, is to allow it to deal with (paper) clock adjustment interfaces which don't do the arithmetic accurately, or at least don't tell you what they actually did, so that the arithmetic done can only be determined by further measurement. This is unavoidable if you need to deal with a big variety of operating systems, I guess, but it does make the problem harder than if the adjustment interface is fixed and feedback loop eliminated, leaving just the measurement problem. Dennis Ferguson ___ 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.
Re: [time-nuts] GPS for ntp
On 21 Oct, 2014, at 08:58 , Simon Marsh wrote: > How do you map the timer counter value in to a PPS timestamp ? > (that is, how do you turn the HW counter value in to what the OS thought the > time was when the event occured ?) On the NetBSD prototype I have the clock adjustment system call interface is expanded to deal with multiple clocks, only one of which is the system clock. The HW counter becomes its own clock, which is the clock in which PPS measurements are expressed and which is adjusted into alignment with the PPS data. The system clock is adjusted into alignment with the HW counter clock using offset data from PIO polling of the clock pair. The IEEE1588 timestamp counter becomes a third clock, which gets adjusted into alignment with the system clock for use as a PTP server, or which is used to adjust the system clock when operating as a client. For the beaglebone this is probably overkill; since the clocks are all synchronous the system<->peripheral clock polling essentially determines a constant offset, after which you can keep them in sync by making the same relative rate adjustments to all clocks. For the general IEEE1588 case, however, the counter being sampled at the ethernet interface is often clocked by a different crystal then the clock you would prefer to use as the system clock, and the process of steering one clock into synchronization with another needs to be more complex. I should note that none of these clock adjustments really requires a PLL or other feedback control loop, nor does NTP, since no clock hardware is actually adjusted. The crystals are all free running and are unaffected by the adjustments. What is adjusted is instead a "paper clock", that is the adjustment is to the arithmetic done to convert each free running counter to a time of day, and this can be done open loop, with perfectly predictable results and with no feedback control, by just doing the adjustment arithmetic accurately and transparently. The thing the PLL does for ntpd, then, is to allow it to deal with (paper) clock adjustment interfaces which don't do the arithmetic accurately, or at least don't tell you what they actually did, so that the arithmetic done can only be determined by further measurement. This is unavoidable if you need to deal with a big variety of operating systems, I guess, but it does make the problem harder than if the adjustment interface is fixed and feedback loop eliminated, leaving just the measurement problem. Dennis Ferguson ___ 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] GPS for ntp
>> One solution to the problem is use two independent HW capture inputs. One >> for a GPS 1PPS and the other for your event. > >> In this case the system clock does not need to be synchronized -- since it >> is used only to interpolate between the two events. The event timestamp is >> little more than adding the differential of the two most recent captures, >> which is a number from 0 to 1 second. > You haven't solved the problem yet. Now you have to synchronize the HW > capture counters. Hi Hal, Nope, there's no need to synchronize HW counters (against "system time" or UTC or something). That's the beauty of time-stamping or capture counters: they are free-running (at some internal CPU frequency) and share a common clock counter register from which the capture/snapshot is taken. > You can probably do that with some simple but delicate initialization code. > Maybe copy the value from the counter used for the system time? At the > time-nut level, you have to worry about things like cache misses. (There may > be more fine print at that level depending upon the details of the hardware.) No, again that's the beauty of H/W capture counters. You completely avoid the OS or software rat's nest called system time. Only the capture registers keep perfect "system time" by virtue of their continuous h/w counting, unaffected by software, locks, interrupts, cache, TLB, or microcode latency issues. > You could also do it by calibrating out the difference: just feed the same > pulse into both input pins. You have to do that each time you (re)start > things. That's easy for a one-off project but adds another ugly step if you > want to do it in production. Collecting long term data moves a hobby project > a lot closer to production. The modern CPU's with capture/compare registers I've seen use a common N-bit timer register as the capture source, so there's no issue with intra-capture synchronization. What is still critical, to align with UTC for example, is inter-clock synchronization. And that's why two h/w capture counters are needed -- one for the event (LAN packet, for example) and one for the GPS/1PPS timestamp. /tvb ___ 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] GPS for ntp
Here's some more info Joe My Blitzortung.org station 1162 reboots daily. It is located at 42 degrees latitude. GlobalTop PA6H GPS module. The antenna is a Motorola patch in the attic, looking through wooden boards and tar shingles. I have the antenna against the underside of the roof, tipped to the South. There are power lines on the South and East sides of the house. On the North side of the house is an 17 meter high tower with guy wires and HF inverted V antennas. Lots of multi-path. My H-field loops are made from old, quad-shielded Thick-LAN cable, 3 turns, 1.5 meter diameter. The controller has been running 18 hours so far today and there is a heavy cloud cover today. Here are current stats: Availability100.00% Type Mediatek/GlobalTop with 38400baud (FW: AXN_2.10_3339_11092201,5051) Antenna External Status Active, 3D-fix Satellites 11 tracked, 11 in view Date/Time 2014-10-21 19:31:46 Position 42.996052° -82.464241° 187.7m Smoothed 42.996035° -82.464253° 188.1m (smoothed over 1d, 0h) PDOP/HDOP/VDOP1.41 / 0.83 / 1.14 Sat. Signals (SNR) 5 42dB 2 41dB 29 43dB 10 29dB 13 30dB 26 41dB 25 28dB 6 32dB 12 29dB 9 18dB 15 23dB PPS Accuracy Mean: 33.7ns, Current: 23ns On 10/21/2014 09:23 AM, Joseph Gray wrote: I missed the lightningmaps mention the first time. That is very helpful. Joe Gray W5JG On Tue, Oct 21, 2014 at 5:22 AM, Didier Juges wrote: >Check lightningmaps.org, mentioned on this list before for lightning >location via TOA using STMicro Cortex -M4 devices. > >Didier KO4BB > > ___ 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] GPS for ntp
t...@leapsecond.com said: >> You have to synchronise between the counter >> value and what the OS understands is 'system time' in order to create a >> retrospective timestamp for when the event occured. > Also true. > One solution to the problem is use two independent HW capture inputs. One > for a GPS 1PPS and the other for your event. > In this case the system clock does not need to be synchronized -- since it > is used only to interpolate between the two events. The event timestamp is > little more than adding the differential of the two most recent captures, > which is a number from 0 to 1 second. You haven't solved the problem yet. Now you have to synchronize the HW capture counters. You can probably do that with some simple but delicate initialization code. Maybe copy the value from the counter used for the system time? At the time-nut level, you have to worry about things like cache misses. (There may be more fine print at that level depending upon the details of the hardware.) You could also do it by calibrating out the difference: just feed the same pulse into both input pins. You have to do that each time you (re)start things. That's easy for a one-off project but adds another ugly step if you want to do it in production. Collecting long term data moves a hobby project a lot closer to production. -- These are my opinions. I hate spam. ___ 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] GPS for ntp
On Tue, Oct 21, 2014 at 6:58 AM, Simon Marsh > How do you map the timer counter value in to a PPS timestamp ? > (that is, how do you turn the HW counter value in to what the OS thought the > time was when the event occured ?) He is running NTP. NTP's job is it keep the system time in sync with a number of "reference clocks". The 1PPS from a GPS makes a good reference clock. It does this by adjusting the RATE of the system clock to not gain or loose vs. a set of reference clocks over time. The algorithm is not simple. The weak link is that the timing is done in software and in the real world the accuracy is a few microseconds. -- Chris Albertson Redondo Beach, California ___ 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] GPS for ntp
> With HW capture, you can get an accurate view of when the event took > place but only relative to the counter in the particular timer/capture > unit that is being used. True. > You have to synchronise between the counter > value and what the OS understands is 'system time' in order to create a > retrospective timestamp for when the event occured. Also true. One solution to the problem is use two independent HW capture inputs. One for a GPS 1PPS and the other for your event. In this case the system clock does not need to be synchronized -- since it is used only to interpolate between the two events. The event timestamp is little more than adding the differential of the two most recent captures, which is a number from 0 to 1 second. For added precision, and if your system oscillator happens to be many ppb fast or slow, you simply adjust the differential by that small rate offset. There is no need to actually set the system clock (time) or need to discipline the system clock (rate). Since you're capturing a GPS/1PPS snapshot every second, the clock rate offset is effectively measured every second for free. /tvb ___ 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] GPS for ntp
Hi Simon, Ah, slightly different question :) I'm afraid I didn't write the code, so I can't really answer that question. What I can say is that it does appear to be as good as Ian (Lepore's) ntpq output shows. To be honest, I just use the code :) Iain On 21/10/14 15:39, Simon Marsh wrote: Sorry, I wasn't clear. The /dev/pps0 devices output a timestamp corresponding to when the event happened. The GPIO driver does this very simply by waiting for an interrupt event and then asking what (current) time it is. This leads to the problem that there is a non-deterministic time between the event and when the code gets to ask 'what time is it ?' With HW capture, you can get an accurate view of when the event took place but only relative to the counter in the particular timer/capture unit that is being used. You have to synchronise between the counter value and what the OS understands is 'system time' in order to create a retrospective timestamp for when the event occured. Whilst you've solved the problem with the interrupt approach, you've created a different one of needing to synchronise counters. My question is how do you convert between the timer value and system time to get the timestamp ? Cheers Simon On 21/10/2014 15:14, Iain Young wrote: It just turns up as /dev/pps0 like any other PPS source, so you configure ntp in the same way you would for any other PPS source, or build ppsapitest to test it manually (Although be aware you -may get a Invalid argument error from ppsapitest after running it more than once. Reboot solves it, and since the BBB's don't do anything else, and I don't restart ntp too often, its not a big deal for me.) Iain On 21/10/14 14:58, Simon Marsh wrote: Iain, How do you map the timer counter value in to a PPS timestamp ? (that is, how do you turn the HW counter value in to what the OS thought the time was when the event occured ?) Cheers Simon On 21/10/2014 13:54, Iain Young wrote: It's been done on FreeBSD. See: http://lists.freebsd.org/pipermail/freebsd-arm/2013-February/004769.html Patch is now in recent FreeBSD releases/snapshots And yes, it's far superior to than using the GPIOs, or UARTS There was some work done on Linux, but I'm not sure it was ever finished or published. All of my "Timing" Beaglebones run FreeBSD, with the exception of the TIC stufff I wrote for the PRUSS's. As soon as the userspace bits of that work on FreeBSD, I'll probably switch that to FreeBSD as well. All the Best Iain On 21/10/14 13:33, Neil Schroeder wrote: Andrew- I'm actually referring to using either the eCAP function or one of the integrated dmtimer triggers - which are, from some accounts, more accurate than a gpio. Google beaglebone dmtimer pps. NS On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland wrote: On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder wrote: The one thing that hasn't yet happened is making the beaglebone timestamp on the linux side in a way that works for ntp. Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there yet. I have been working on it but if anyone has some insight its appreciated. It appears to support gpio class devices, with interrupts, so the pps-gpio driver (in-tree since 3.2) should work just fine. The only thing that's needed (other than building the driver) is a bit of code in the board support file to register the device. Various folks have done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), and I've done it for the UDOO Dual (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is probably about as easy. I'm not sure if there's other hardware that lets you do better than grabbing an interrupt, but that will get you in the microsecond range or a bit better, anyhow. ___ 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 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 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 th
Re: [time-nuts] GPS for ntp
Sorry, I wasn't clear. The /dev/pps0 devices output a timestamp corresponding to when the event happened. The GPIO driver does this very simply by waiting for an interrupt event and then asking what (current) time it is. This leads to the problem that there is a non-deterministic time between the event and when the code gets to ask 'what time is it ?' With HW capture, you can get an accurate view of when the event took place but only relative to the counter in the particular timer/capture unit that is being used. You have to synchronise between the counter value and what the OS understands is 'system time' in order to create a retrospective timestamp for when the event occured. Whilst you've solved the problem with the interrupt approach, you've created a different one of needing to synchronise counters. My question is how do you convert between the timer value and system time to get the timestamp ? Cheers Simon On 21/10/2014 15:14, Iain Young wrote: It just turns up as /dev/pps0 like any other PPS source, so you configure ntp in the same way you would for any other PPS source, or build ppsapitest to test it manually (Although be aware you -may get a Invalid argument error from ppsapitest after running it more than once. Reboot solves it, and since the BBB's don't do anything else, and I don't restart ntp too often, its not a big deal for me.) Iain On 21/10/14 14:58, Simon Marsh wrote: Iain, How do you map the timer counter value in to a PPS timestamp ? (that is, how do you turn the HW counter value in to what the OS thought the time was when the event occured ?) Cheers Simon On 21/10/2014 13:54, Iain Young wrote: It's been done on FreeBSD. See: http://lists.freebsd.org/pipermail/freebsd-arm/2013-February/004769.html Patch is now in recent FreeBSD releases/snapshots And yes, it's far superior to than using the GPIOs, or UARTS There was some work done on Linux, but I'm not sure it was ever finished or published. All of my "Timing" Beaglebones run FreeBSD, with the exception of the TIC stufff I wrote for the PRUSS's. As soon as the userspace bits of that work on FreeBSD, I'll probably switch that to FreeBSD as well. All the Best Iain On 21/10/14 13:33, Neil Schroeder wrote: Andrew- I'm actually referring to using either the eCAP function or one of the integrated dmtimer triggers - which are, from some accounts, more accurate than a gpio. Google beaglebone dmtimer pps. NS On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland wrote: On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder wrote: The one thing that hasn't yet happened is making the beaglebone timestamp on the linux side in a way that works for ntp. Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there yet. I have been working on it but if anyone has some insight its appreciated. It appears to support gpio class devices, with interrupts, so the pps-gpio driver (in-tree since 3.2) should work just fine. The only thing that's needed (other than building the driver) is a bit of code in the board support file to register the device. Various folks have done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), and I've done it for the UDOO Dual (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is probably about as easy. I'm not sure if there's other hardware that lets you do better than grabbing an interrupt, but that will get you in the microsecond range or a bit better, anyhow. ___ 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 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 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.
Re: [time-nuts] GPS for ntp
It just turns up as /dev/pps0 like any other PPS source, so you configure ntp in the same way you would for any other PPS source, or build ppsapitest to test it manually (Although be aware you -may get a Invalid argument error from ppsapitest after running it more than once. Reboot solves it, and since the BBB's don't do anything else, and I don't restart ntp too often, its not a big deal for me.) Iain On 21/10/14 14:58, Simon Marsh wrote: Iain, How do you map the timer counter value in to a PPS timestamp ? (that is, how do you turn the HW counter value in to what the OS thought the time was when the event occured ?) Cheers Simon On 21/10/2014 13:54, Iain Young wrote: It's been done on FreeBSD. See: http://lists.freebsd.org/pipermail/freebsd-arm/2013-February/004769.html Patch is now in recent FreeBSD releases/snapshots And yes, it's far superior to than using the GPIOs, or UARTS There was some work done on Linux, but I'm not sure it was ever finished or published. All of my "Timing" Beaglebones run FreeBSD, with the exception of the TIC stufff I wrote for the PRUSS's. As soon as the userspace bits of that work on FreeBSD, I'll probably switch that to FreeBSD as well. All the Best Iain On 21/10/14 13:33, Neil Schroeder wrote: Andrew- I'm actually referring to using either the eCAP function or one of the integrated dmtimer triggers - which are, from some accounts, more accurate than a gpio. Google beaglebone dmtimer pps. NS On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland wrote: On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder wrote: The one thing that hasn't yet happened is making the beaglebone timestamp on the linux side in a way that works for ntp. Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there yet. I have been working on it but if anyone has some insight its appreciated. It appears to support gpio class devices, with interrupts, so the pps-gpio driver (in-tree since 3.2) should work just fine. The only thing that's needed (other than building the driver) is a bit of code in the board support file to register the device. Various folks have done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), and I've done it for the UDOO Dual (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is probably about as easy. I'm not sure if there's other hardware that lets you do better than grabbing an interrupt, but that will get you in the microsecond range or a bit better, anyhow. ___ 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 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 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] GPS for ntp
Iain, How do you map the timer counter value in to a PPS timestamp ? (that is, how do you turn the HW counter value in to what the OS thought the time was when the event occured ?) Cheers Simon On 21/10/2014 13:54, Iain Young wrote: It's been done on FreeBSD. See: http://lists.freebsd.org/pipermail/freebsd-arm/2013-February/004769.html Patch is now in recent FreeBSD releases/snapshots And yes, it's far superior to than using the GPIOs, or UARTS There was some work done on Linux, but I'm not sure it was ever finished or published. All of my "Timing" Beaglebones run FreeBSD, with the exception of the TIC stufff I wrote for the PRUSS's. As soon as the userspace bits of that work on FreeBSD, I'll probably switch that to FreeBSD as well. All the Best Iain On 21/10/14 13:33, Neil Schroeder wrote: Andrew- I'm actually referring to using either the eCAP function or one of the integrated dmtimer triggers - which are, from some accounts, more accurate than a gpio. Google beaglebone dmtimer pps. NS On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland wrote: On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder wrote: The one thing that hasn't yet happened is making the beaglebone timestamp on the linux side in a way that works for ntp. Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there yet. I have been working on it but if anyone has some insight its appreciated. It appears to support gpio class devices, with interrupts, so the pps-gpio driver (in-tree since 3.2) should work just fine. The only thing that's needed (other than building the driver) is a bit of code in the board support file to register the device. Various folks have done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), and I've done it for the UDOO Dual (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is probably about as easy. I'm not sure if there's other hardware that lets you do better than grabbing an interrupt, but that will get you in the microsecond range or a bit better, anyhow. ___ 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 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.
Re: [time-nuts] GPS for ntp
I wasn't sure if ntp would be the way to go or not. OTOH, wasn't PHK getting nanosecond accuracy with FreeBSD on the Net4501, or is my memory faulty? Joe Gray W5JG On Mon, Oct 20, 2014 at 11:03 PM, Chris Albertson wrote: > NTP is not nearly good enough to use for measuring speed of light > delays. It works at the microsecond level at best. I think what you > want is each station to have a local oscillator that runs in phase > with the 1PPS signal that comes from GPS receivers. Then you measure > the incoming signal relative to the phase of the local oscillator. > > On Mon, Oct 20, 2014 at 6:39 PM, Joseph Gray wrote: > > What does everyone think of this GPS module for ntp use? According to the > > specsheet, it uses a Ublox Neo-7N. > > > > > http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 > > > > I'm thinking about using it for a Beaglebone ntp server. I know there was > > some discussion about Beaglebones a while back. Has anyone gotten ntpd > with > > PPS and time stamping running on a Beaglebone yet (like on the Soekris > > Net4501)? > > > > Does anyone want to take a wild guess as to the best/worst case UTC > offset > > I might get with such a setup? I realize that I'd have to try it to > really > > find out, but guesses and advice from those more knowledgeable is always > > appreciated. > > > > What I'm really after is to eventually have several Beaglebones scattered > > around the area as part of a TDOA DF network. I have spare radios to > > dedicate to the task. Each fixed node will timestamp incoming > transmissions > > and then relay that information to a central location. The central system > > will use the data to calculate the location of the transmitter. > > > > Does anyone here have any experience with this sort of thing? Would you > > recommend a better way of accurately timing the transmissions vs using > ntp > > on each Beaglebone? > > > > I know that TDOA is used by the cellular companies. Is anyone aware of > some > > "user level" projects or source code for this? I've Googled a bit, but > > haven't turned up much. There was one thesis about an Amateur doing part > of > > this, but he didn't have much detail on the satellite nodes and didn't > > describe anything about the centralized processing part. > > > > I have one Beaglebone White that I got cheap, so I have something to get > > started with. Later, as I figure out things, I'll buy a few Beaglebone > > Blacks. > > > > Joe Gray > > W5JG > > ___ > > 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. > > > > -- > > Chris Albertson > Redondo Beach, California > ___ > 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.
Re: [time-nuts] GPS for ntp
I missed the lightningmaps mention the first time. That is very helpful. Joe Gray W5JG On Tue, Oct 21, 2014 at 5:22 AM, Didier Juges wrote: > Check lightningmaps.org, mentioned on this list before for lightning > location via TOA using STMicro Cortex -M4 devices. > > Didier KO4BB > > > On October 20, 2014 8:39:16 PM CDT, Joseph Gray wrote: > >What does everyone think of this GPS module for ntp use? According to > >the > >specsheet, it uses a Ublox Neo-7N. > > > > > http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 > > > >I'm thinking about using it for a Beaglebone ntp server. I know there > >was > >some discussion about Beaglebones a while back. Has anyone gotten ntpd > >with > >PPS and time stamping running on a Beaglebone yet (like on the Soekris > >Net4501)? > > > >Does anyone want to take a wild guess as to the best/worst case UTC > >offset > >I might get with such a setup? I realize that I'd have to try it to > >really > >find out, but guesses and advice from those more knowledgeable is > >always > >appreciated. > > > >What I'm really after is to eventually have several Beaglebones > >scattered > >around the area as part of a TDOA DF network. I have spare radios to > >dedicate to the task. Each fixed node will timestamp incoming > >transmissions > >and then relay that information to a central location. The central > >system > >will use the data to calculate the location of the transmitter. > > > >Does anyone here have any experience with this sort of thing? Would you > >recommend a better way of accurately timing the transmissions vs using > >ntp > >on each Beaglebone? > > > >I know that TDOA is used by the cellular companies. Is anyone aware of > >some > >"user level" projects or source code for this? I've Googled a bit, but > >haven't turned up much. There was one thesis about an Amateur doing > >part of > >this, but he didn't have much detail on the satellite nodes and didn't > >describe anything about the centralized processing part. > > > >I have one Beaglebone White that I got cheap, so I have something to > >get > >started with. Later, as I figure out things, I'll buy a few Beaglebone > >Blacks. > > > >Joe Gray > >W5JG > >___ > >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. > > -- > Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do > other things. > ___ > 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.
Re: [time-nuts] GPS for ntp
It's been done on FreeBSD. See: http://lists.freebsd.org/pipermail/freebsd-arm/2013-February/004769.html Patch is now in recent FreeBSD releases/snapshots And yes, it's far superior to than using the GPIOs, or UARTS There was some work done on Linux, but I'm not sure it was ever finished or published. All of my "Timing" Beaglebones run FreeBSD, with the exception of the TIC stufff I wrote for the PRUSS's. As soon as the userspace bits of that work on FreeBSD, I'll probably switch that to FreeBSD as well. All the Best Iain On 21/10/14 13:33, Neil Schroeder wrote: Andrew- I'm actually referring to using either the eCAP function or one of the integrated dmtimer triggers - which are, from some accounts, more accurate than a gpio. Google beaglebone dmtimer pps. NS On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland wrote: On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder wrote: The one thing that hasn't yet happened is making the beaglebone timestamp on the linux side in a way that works for ntp. Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there yet. I have been working on it but if anyone has some insight its appreciated. It appears to support gpio class devices, with interrupts, so the pps-gpio driver (in-tree since 3.2) should work just fine. The only thing that's needed (other than building the driver) is a bit of code in the board support file to register the device. Various folks have done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), and I've done it for the UDOO Dual (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is probably about as easy. I'm not sure if there's other hardware that lets you do better than grabbing an interrupt, but that will get you in the microsecond range or a bit better, anyhow. ___ 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 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] GPS for ntp
Perhaps the programmable realtime unit (PRU) is what you're looking for. It's used in the 5370 CPU replacement. -- Paul On Tue, Oct 21, 2014 at 8:33 AM, Neil Schroeder wrote: > Andrew- > I'm actually referring to using either the eCAP function or one of the > integrated dmtimer triggers - which are, from some accounts, more accurate > than a gpio. > > Google beaglebone dmtimer pps. > > NS > > On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland > wrote: > >> On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder >> wrote: >> > The one thing that hasn't yet happened is making the beaglebone timestamp >> > on the linux side in a way that works for ntp. >> > >> > Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there >> > yet. >> > >> > I have been working on it but if anyone has some insight its appreciated. >> > >> >> It appears to support gpio class devices, with interrupts, so the >> pps-gpio driver (in-tree since 3.2) should work just fine. The only >> thing that's needed (other than building the driver) is a bit of code >> in the board support file to register the device. Various folks have >> done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), >> and I've done it for the UDOO Dual >> (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is >> probably about as easy. >> >> I'm not sure if there's other hardware that lets you do better than >> grabbing an interrupt, but that will get you in the microsecond range >> or a bit better, anyhow. >> ___ >> 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 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] GPS for ntp
Andrew- I'm actually referring to using either the eCAP function or one of the integrated dmtimer triggers - which are, from some accounts, more accurate than a gpio. Google beaglebone dmtimer pps. NS On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland wrote: > On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder > wrote: > > The one thing that hasn't yet happened is making the beaglebone timestamp > > on the linux side in a way that works for ntp. > > > > Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there > > yet. > > > > I have been working on it but if anyone has some insight its appreciated. > > > > It appears to support gpio class devices, with interrupts, so the > pps-gpio driver (in-tree since 3.2) should work just fine. The only > thing that's needed (other than building the driver) is a bit of code > in the board support file to register the device. Various folks have > done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), > and I've done it for the UDOO Dual > (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is > probably about as easy. > > I'm not sure if there's other hardware that lets you do better than > grabbing an interrupt, but that will get you in the microsecond range > or a bit better, anyhow. > ___ > 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.
Re: [time-nuts] GPS for ntp
Check lightningmaps.org, mentioned on this list before for lightning location via TOA using STMicro Cortex -M4 devices. Didier KO4BB On October 20, 2014 8:39:16 PM CDT, Joseph Gray wrote: >What does everyone think of this GPS module for ntp use? According to >the >specsheet, it uses a Ublox Neo-7N. > >http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 > >I'm thinking about using it for a Beaglebone ntp server. I know there >was >some discussion about Beaglebones a while back. Has anyone gotten ntpd >with >PPS and time stamping running on a Beaglebone yet (like on the Soekris >Net4501)? > >Does anyone want to take a wild guess as to the best/worst case UTC >offset >I might get with such a setup? I realize that I'd have to try it to >really >find out, but guesses and advice from those more knowledgeable is >always >appreciated. > >What I'm really after is to eventually have several Beaglebones >scattered >around the area as part of a TDOA DF network. I have spare radios to >dedicate to the task. Each fixed node will timestamp incoming >transmissions >and then relay that information to a central location. The central >system >will use the data to calculate the location of the transmitter. > >Does anyone here have any experience with this sort of thing? Would you >recommend a better way of accurately timing the transmissions vs using >ntp >on each Beaglebone? > >I know that TDOA is used by the cellular companies. Is anyone aware of >some >"user level" projects or source code for this? I've Googled a bit, but >haven't turned up much. There was one thesis about an Amateur doing >part of >this, but he didn't have much detail on the satellite nodes and didn't >describe anything about the centralized processing part. > >I have one Beaglebone White that I got cheap, so I have something to >get >started with. Later, as I figure out things, I'll buy a few Beaglebone >Blacks. > >Joe Gray >W5JG >___ >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. -- Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do other things. ___ 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] GPS for ntp
From: Simon Marsh [] No claims are any good without being backed by data, so attached are a couple of plots showing my NTP performance from the past 4 hours. 'Sheliak' is the BBB with the PCI-5S and 'Albali' is a Pi with an adafruit ultimate GPS breakout (MTK3339). It's easy to see the heating coming on at ~6:20, as both servers are out in the open and it's interesting to see how they both respond to the temperature change. The scale is in milliseconds, so 5m is showing 5us. Cheers Simon === .. and for comparison, plots from seven Raspberry Pi NTP servers running various GPS/PPS modules all with indoor antennas, some better located than others. Raspberry Pi #7 is user-mode PPS, not kernel-mode. I can supply loopstats if anyone want them. These are the offset values reported by NTP and sampled by MRTG at 5-minute intervals. Now the omitted URL for the plots: http://www.satsignal.eu/mrtg/performance_ntp.php Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] GPS for ntp
On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder wrote: > The one thing that hasn't yet happened is making the beaglebone timestamp > on the linux side in a way that works for ntp. > > Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there > yet. > > I have been working on it but if anyone has some insight its appreciated. > It appears to support gpio class devices, with interrupts, so the pps-gpio driver (in-tree since 3.2) should work just fine. The only thing that's needed (other than building the driver) is a bit of code in the board support file to register the device. Various folks have done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example), and I've done it for the UDOO Dual (https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is probably about as easy. I'm not sure if there's other hardware that lets you do better than grabbing an interrupt, but that will get you in the microsecond range or a bit better, anyhow. ___ 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] GPS for ntp
From: Simon Marsh No claims are any good without being backed by data, so attached are a couple of plots showing my NTP performance from the past 4 hours. 'Sheliak' is the BBB with the PCI-5S and 'Albali' is a Pi with an adafruit ultimate GPS breakout (MTK3339). It's easy to see the heating coming on at ~6:20, as both servers are out in the open and it's interesting to see how they both respond to the temperature change. The scale is in milliseconds, so 5m is showing 5us. Cheers Simon .. and for comparison, plots from seven Raspberry Pi NTP servers running various GPS/PPS modules all with indoor antennas, some better located than others. Raspberry Pi #7 is user-mode PPS, not kernel-mode. I can supply loopstats if anyone want them. These are the offset values reported by NTP and sampled by MRTG at 5-minute intervals. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] GPS for ntp
Running the BBB as an NTP server is a breeze and has a couple of advantages over the Pi. Specifically, on the BBB, the kernel module is pre-built and configuring the PPS driver is done at runtime using the device tree. No kernel re-compilation is required to get up and running, just plug and go on any of the available GPIO. The ethernet interface on the BBB is also a SoC peripheral so gives much better latency than the USB ethernet on the Pi. This gives a big improvement if you are using it to serve time for other NTP clients. I have one of the Reyax u-blox 8 modules and it works as described, _but_ be aware that they do not have an external antenna connector. I found the reception indoors was poor to the point of making it unuseable, so depending on your circumstances, this could be a major problem. E-bay is riddled with GPS modules and pretty much any of them will be fine for NTP use. For a more off the wall suggestion, I currently have a BBB hooked up to one of these: http://www.ebay.com/itm/Mini-U-blox-B39-PCI-5S-1-500-PCI-E-Express-Wireless-Card-GPS-Module-for-MID-Lapt-/201172829176?pt=Radio_Control_Parts_Accessories&hash=item2ed6d5c3f8 A little bit of soldering is required (see here: http://emerythacks.blogspot.co.uk/2013/01/u-blox-pci-5s-cheap-gps-module-for-your.html), but what you get is a dirt cheap u-blox 5 module powered at 3.3v directly by the BBB. It's not cutting edge, and I'm not going to suggest using one of these to discipline your frequency standard, but for simple NTP use it works a treat. No claims are any good without being backed by data, so attached are a couple of plots showing my NTP performance from the past 4 hours. 'Sheliak' is the BBB with the PCI-5S and 'Albali' is a Pi with an adafruit ultimate GPS breakout (MTK3339). It's easy to see the heating coming on at ~6:20, as both servers are out in the open and it's interesting to see how they both respond to the temperature change. The scale is in milliseconds, so 5m is showing 5us. Cheers Simon What does everyone think of this GPS module for ntp use? According to the specsheet, it uses a Ublox Neo-7N. http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 I'm thinking about using it for a Beaglebone ntp server. I know there was some discussion about Beaglebones a while back. Has anyone gotten ntpd with PPS and time stamping running on a Beaglebone yet (like on the Soekris Net4501)? [] I have one Beaglebone White that I got cheap, so I have something to get started with. Later, as I figure out things, I'll buy a few Beaglebone Blacks. Joe Gray W5JG Joe, You might also consider the Raspberry Pi as an NTP server using PPS: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html You can get the ublox 7Q in a ready-to-go no=-soldering board here: http://ava.upuaut.net/store/index.php?route=product/product&path=59_60&product_id=95 I would reckon on sub-100 microsecond timing accuracy with the Raspberry Pi and kernel-mode PPS, but I've not done any comparison with the BB. Cheers, David ___ 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] GPS for ntp
What does everyone think of this GPS module for ntp use? According to the specsheet, it uses a Ublox Neo-7N. http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 I'm thinking about using it for a Beaglebone ntp server. I know there was some discussion about Beaglebones a while back. Has anyone gotten ntpd with PPS and time stamping running on a Beaglebone yet (like on the Soekris Net4501)? [] I have one Beaglebone White that I got cheap, so I have something to get started with. Later, as I figure out things, I'll buy a few Beaglebone Blacks. Joe Gray W5JG Joe, You might also consider the Raspberry Pi as an NTP server using PPS: http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html You can get the ublox 7Q in a ready-to-go no=-soldering board here: http://ava.upuaut.net/store/index.php?route=product/product&path=59_60&product_id=95 I would reckon on sub-100 microsecond timing accuracy with the Raspberry Pi and kernel-mode PPS, but I've not done any comparison with the BB. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] GPS for ntp
NTP is not nearly good enough to use for measuring speed of light delays. It works at the microsecond level at best. I think what you want is each station to have a local oscillator that runs in phase with the 1PPS signal that comes from GPS receivers. Then you measure the incoming signal relative to the phase of the local oscillator. On Mon, Oct 20, 2014 at 6:39 PM, Joseph Gray wrote: > What does everyone think of this GPS module for ntp use? According to the > specsheet, it uses a Ublox Neo-7N. > > http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 > > I'm thinking about using it for a Beaglebone ntp server. I know there was > some discussion about Beaglebones a while back. Has anyone gotten ntpd with > PPS and time stamping running on a Beaglebone yet (like on the Soekris > Net4501)? > > Does anyone want to take a wild guess as to the best/worst case UTC offset > I might get with such a setup? I realize that I'd have to try it to really > find out, but guesses and advice from those more knowledgeable is always > appreciated. > > What I'm really after is to eventually have several Beaglebones scattered > around the area as part of a TDOA DF network. I have spare radios to > dedicate to the task. Each fixed node will timestamp incoming transmissions > and then relay that information to a central location. The central system > will use the data to calculate the location of the transmitter. > > Does anyone here have any experience with this sort of thing? Would you > recommend a better way of accurately timing the transmissions vs using ntp > on each Beaglebone? > > I know that TDOA is used by the cellular companies. Is anyone aware of some > "user level" projects or source code for this? I've Googled a bit, but > haven't turned up much. There was one thesis about an Amateur doing part of > this, but he didn't have much detail on the satellite nodes and didn't > describe anything about the centralized processing part. > > I have one Beaglebone White that I got cheap, so I have something to get > started with. Later, as I figure out things, I'll buy a few Beaglebone > Blacks. > > Joe Gray > W5JG > ___ > 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. -- Chris Albertson Redondo Beach, California ___ 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] GPS for ntp
The one thing that hasn't yet happened is making the beaglebone timestamp on the linux side in a way that works for ntp. Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there yet. I have been working on it but if anyone has some insight its appreciated. On Monday, October 20, 2014, Bob Camp wrote: > Hi > > There is a *lot* of detail on this in the archives. > > Quick rundown - the Soekris has some custom code and “stuff” that makes it > better for NTP than any of the other boards. > > For any normal use, a couple of microseconds is likely “good enough. For > that, many boards and GPS’s will do just fine. Yes people have gotten NTP > running on just about every board that will run Linux. > > Bob > > > On Oct 20, 2014, at 9:39 PM, Joseph Gray > wrote: > > > > What does everyone think of this GPS module for ntp use? According to the > > specsheet, it uses a Ublox Neo-7N. > > > > > http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 > > > > I'm thinking about using it for a Beaglebone ntp server. I know there was > > some discussion about Beaglebones a while back. Has anyone gotten ntpd > with > > PPS and time stamping running on a Beaglebone yet (like on the Soekris > > Net4501)? > > > > Does anyone want to take a wild guess as to the best/worst case UTC > offset > > I might get with such a setup? I realize that I'd have to try it to > really > > find out, but guesses and advice from those more knowledgeable is always > > appreciated. > > > > What I'm really after is to eventually have several Beaglebones scattered > > around the area as part of a TDOA DF network. I have spare radios to > > dedicate to the task. Each fixed node will timestamp incoming > transmissions > > and then relay that information to a central location. The central system > > will use the data to calculate the location of the transmitter. > > > > Does anyone here have any experience with this sort of thing? Would you > > recommend a better way of accurately timing the transmissions vs using > ntp > > on each Beaglebone? > > > > I know that TDOA is used by the cellular companies. Is anyone aware of > some > > "user level" projects or source code for this? I've Googled a bit, but > > haven't turned up much. There was one thesis about an Amateur doing part > of > > this, but he didn't have much detail on the satellite nodes and didn't > > describe anything about the centralized processing part. > > > > I have one Beaglebone White that I got cheap, so I have something to get > > started with. Later, as I figure out things, I'll buy a few Beaglebone > > Blacks. > > > > Joe Gray > > W5JG > > ___ > > 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 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] GPS for ntp
Hi There is a *lot* of detail on this in the archives. Quick rundown - the Soekris has some custom code and “stuff” that makes it better for NTP than any of the other boards. For any normal use, a couple of microseconds is likely “good enough. For that, many boards and GPS’s will do just fine. Yes people have gotten NTP running on just about every board that will run Linux. Bob > On Oct 20, 2014, at 9:39 PM, Joseph Gray wrote: > > What does everyone think of this GPS module for ntp use? According to the > specsheet, it uses a Ublox Neo-7N. > > http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 > > I'm thinking about using it for a Beaglebone ntp server. I know there was > some discussion about Beaglebones a while back. Has anyone gotten ntpd with > PPS and time stamping running on a Beaglebone yet (like on the Soekris > Net4501)? > > Does anyone want to take a wild guess as to the best/worst case UTC offset > I might get with such a setup? I realize that I'd have to try it to really > find out, but guesses and advice from those more knowledgeable is always > appreciated. > > What I'm really after is to eventually have several Beaglebones scattered > around the area as part of a TDOA DF network. I have spare radios to > dedicate to the task. Each fixed node will timestamp incoming transmissions > and then relay that information to a central location. The central system > will use the data to calculate the location of the transmitter. > > Does anyone here have any experience with this sort of thing? Would you > recommend a better way of accurately timing the transmissions vs using ntp > on each Beaglebone? > > I know that TDOA is used by the cellular companies. Is anyone aware of some > "user level" projects or source code for this? I've Googled a bit, but > haven't turned up much. There was one thesis about an Amateur doing part of > this, but he didn't have much detail on the satellite nodes and didn't > describe anything about the centralized processing part. > > I have one Beaglebone White that I got cheap, so I have something to get > started with. Later, as I figure out things, I'll buy a few Beaglebone > Blacks. > > Joe Gray > W5JG > ___ > 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] GPS for ntp
What does everyone think of this GPS module for ntp use? According to the specsheet, it uses a Ublox Neo-7N. http://www.ebay.com/itm/RY725AI-10Hz-UART-USB-interface-GPS-Glonass-QZSS-antenna-module-flash-memory-/181562403752 I'm thinking about using it for a Beaglebone ntp server. I know there was some discussion about Beaglebones a while back. Has anyone gotten ntpd with PPS and time stamping running on a Beaglebone yet (like on the Soekris Net4501)? Does anyone want to take a wild guess as to the best/worst case UTC offset I might get with such a setup? I realize that I'd have to try it to really find out, but guesses and advice from those more knowledgeable is always appreciated. What I'm really after is to eventually have several Beaglebones scattered around the area as part of a TDOA DF network. I have spare radios to dedicate to the task. Each fixed node will timestamp incoming transmissions and then relay that information to a central location. The central system will use the data to calculate the location of the transmitter. Does anyone here have any experience with this sort of thing? Would you recommend a better way of accurately timing the transmissions vs using ntp on each Beaglebone? I know that TDOA is used by the cellular companies. Is anyone aware of some "user level" projects or source code for this? I've Googled a bit, but haven't turned up much. There was one thesis about an Amateur doing part of this, but he didn't have much detail on the satellite nodes and didn't describe anything about the centralized processing part. I have one Beaglebone White that I got cheap, so I have something to get started with. Later, as I figure out things, I'll buy a few Beaglebone Blacks. Joe Gray W5JG ___ 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.
