Re: [time-nuts] Cheap jitter measurements

Hi, On 04/26/2018 12:35 AM, Tom Van Baak wrote: > Hi Gary, > >> As requested, here is my raw data: http://pi5.rellim.com/1d.log.gz > > I'm having a close look. These are quite a few bad data points and that > partly explains why your ADEV plots were off. Trim the file at, say, line > 71000

Re: [time-nuts] Cheap jitter measurements

Hi Gary, > As requested, here is my raw data: http://pi5.rellim.com/1d.log.gz I'm having a close look. These are quite a few bad data points and that partly explains why your ADEV plots were off. Trim the file at, say, line 71000 and try again; the results will be much better. I'll post an

Re: [time-nuts] Cheap jitter measurements

Tom! On Wed, 25 Apr 2018 04:01:10 -0700 "Tom Van Baak" wrote: > Hi Gary, > > > A little coding later and there are nice plots. They were compared > > to the output of tvb's adev.c program. Results are similar. > > Whoa there cowboy. That doesn't mean it's right.

[time-nuts] Cheap jitter measurements

Lady Heather v6 supports the TAPR TICC. It has most of the functionality of Timelab (but not as pretty), runs on Linux,etc, and can process both channel s(actually 4 channels if you have two TICCs). You can use it either as the main input device or as an auxiliary input device in

Re: [time-nuts] Cheap jitter measurements

nothing else, at least look at what TimeLab does. The PDF user manual is a > superb tutorial on working with time & frequency data. > > Anyway, a good start to your NTP measurement project. Thanks for posting. > > /tvb > > > - Original Message - > From: &

Re: [time-nuts] Cheap jitter measurements

age - From: "Gary E. Miller" <g...@rellim.com> To: "time-nuts" <time-nuts@febo.com> Sent: Tuesday, April 24, 2018 8:45 PM Subject: Re: [time-nuts] Cheap jitter measurements Time-nuts! I went ahead and bought the TAPR-TICC, it is a very impressive instrument. Fo

Re: [time-nuts] Cheap jitter measurements

Time-nuts! I went ahead and bought the TAPR-TICC, it is a very impressive instrument. For this setup it is combined with a Jackson Labs GPSTLXO as the 10MHz reference. The JL is a GPS disciplined temperature compensated crystal oscillator. The first setup uses the TAPR-TICC in Period mode,

Re: [time-nuts] Cheap jitter measurements

On Mon, Apr 9, 2018 at 3:36 AM, Tom Van Baak wrote: > > My mental model of a black box computer running NTP is that I should be able > to give it a pulse (e.g., via parallel, serial, GPIO) and it tells me what > time it was. Use a GPSDO / Rb / picDIV to generate precise

Re: [time-nuts] Cheap jitter measurements

It's worth noting that you can get rid of a /lot/ of the variance on a modern linux box: 1) Set the CPU to run at the same speed at all times (generally "max performance" but which way you do it doesn't really matter) 2) Set processor masks so that no processes other than your timing code

Re: [time-nuts] Cheap jitter measurements

kb...@n1k.org said: > Except that’s not the way most timers run. The silicon needed to get a > programable divider to work at 2.4 GHz is expensive. If you dig into the > hardware descriptions, the clock tree feeds something much slower to the > “top end” of the typical timer in a CPU or

Re: [time-nuts] Cheap jitter measurements

Gary E. Miller writes: > It tests the time to do two back to back clock_gettime(). Output > looks like this: > > # ./clock_test > samples 101, delay 1000 ns > min 67 ns, max 302 ns, mean 176 ns, median 197 ns, StdDev 52 ns > > You run it a few times and you will see the granularity in the >

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 11, 2018, at 4:58 AM, Hal Murray wrote: > > > g...@rellim.com said: >> It tests the time to do two back to back clock_gettime(). > > That's the time it takes to read the clock. That's not what I mean by > granularity but I think I see how you might use

Re: [time-nuts] Cheap jitter measurements

g...@rellim.com said: > It tests the time to do two back to back clock_gettime(). That's the time it takes to read the clock. That's not what I mean by granularity but I think I see how you might use that word. The comment at the top of the code says "latency". When I hear "granularity", I

Re: [time-nuts] Cheap jitter measurements

Yo Hal! On Tue, 10 Apr 2018 15:41:41 -0700 Hal Murray wrote: > > Yeah, but the granularity is much worse. > > Do you have code that demonstrates that? (or tell me how and I'll > try it) Look in gpsd git head. In the contrib directory here is a program:

Re: [time-nuts] Cheap jitter measurements

Gary said: >> The API for the kernel clock can be read to a ns. I don't see ntpd >> having much use for finer grain than that. I should look at the >> source to see what the internal details look like. > Yeah, but the granularity is much worse. Do you have code that demonstrates that? (or

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 10, 2018, at 5:05 PM, Dan Kemppainen wrote: > > Hi Bob, > > The performance counter does not use the system time calls, NTP, etc. It's an > independent counter clocked from raw CPU clock. So you have a ~300pS > Timestamping counter in the processor. Why

Re: [time-nuts] Cheap jitter measurements

Hi Bob, The performance counter does not use the system time calls, NTP, etc. It's an independent counter clocked from raw CPU clock. So you have a ~300pS Timestamping counter in the processor. Why not use that hardware to do the measurement? Does the signal have to exit the PC to measure it?

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 10, 2018, at 2:59 PM, Hal Murray wrote: > > > kb...@n1k.org said: >> Yes, but looping back to the start of this thread, the intent is to actually >> measure the jitter directly. That’s where the whole need for a stamped >> pulse comes from. To paraphrase

Re: [time-nuts] Cheap jitter measurements

kb...@n1k.org said: > Yes, but looping back to the start of this thread, the intent is to actually > measure the jitter directly. That’s where the whole need for a stamped > pulse comes from. To paraphrase the earlier comments, the intent is to get > away from a “self reported” result and

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 10, 2018, at 12:23 PM, David J Taylor via time-nuts > wrote: > > Hi, > > Yes, but isn't generating pulses OUT of a PC with low latency/jitter one > of the difficult issues? > > If we (somebody smarter than me...) flip this around and modify a copy > NTP to

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 10, 2018, at 11:56 AM, Dan Kemppainen wrote: > > Hi, > > Yes, but isn't generating pulses OUT of a PC with low latency/jitter one of > the difficult issues? > > If we (somebody smarter than me...) flip this around and modify a copy NTP to > grab the

Re: [time-nuts] Cheap jitter measurements

Hi, Yes, but isn't generating pulses OUT of a PC with low latency/jitter one of the difficult issues? If we (somebody smarter than me...) flip this around and modify a copy NTP to grab the QueryPerformanceCounter value when it gets a PPS pulse and log that count, don't we now have a way to

Re: [time-nuts] Cheap jitter measurements

Hi, Yes, but isn't generating pulses OUT of a PC with low latency/jitter one of the difficult issues? If we (somebody smarter than me...) flip this around and modify a copy NTP to grab the QueryPerformanceCounter value when it gets a PPS pulse and log that count, don't we now have a way to

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 10, 2018, at 9:59 AM, Dan Kemppainen wrote: > > Hi, > > Don't know how good they are, but there are two functions in the kernel32 lib > in windows that are related to a cpu performance counter, > QueryPerformanceCounter and QueryPerformanceFrequency.

Re: [time-nuts] Cheap jitter measurements

lemetrics.com> To: <time-nuts@febo.com> Sent: Tuesday, April 10, 2018 6:59 AM Subject: Re: [time-nuts] Cheap jitter measurements Hi, Don't know how good they are, but there are two functions in the kernel32 lib in windows that are related to a cpu performance counter, Q

Re: [time-nuts] Cheap jitter measurements

Hi, Don't know how good they are, but there are two functions in the kernel32 lib in windows that are related to a cpu performance counter, QueryPerformanceCounter and QueryPerformanceFrequency. (Maybe Linux has similar?) Anyway, on most systems the frequency reported is the raw cpu clock.

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 10, 2018, at 6:58 AM, Hal Murray wrote: > > > kb...@n1k.org said: >> The kernel clock comes from the CPU clock. That CPU clock is phase locked to >> a crystal. If you have a CPU that is driven by a VCXO that is a *very* >> unusual CPU board. The crystal

Re: [time-nuts] Cheap jitter measurements

kb...@n1k.org said: > The kernel clock comes from the CPU clock. That CPU clock is phase locked to > a crystal. If you have a CPU that is driven by a VCXO that is a *very* > unusual CPU board. The crystal runs at an arbitrary frequency. That gives > you edges that are unlikely to happen “right

Re: [time-nuts] Cheap jitter measurements

There's a "realtime" kernel available for Linux that improves timing - no idea if this would help in this situation. See: linux-image-rt-amd64 in debian, for instance ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to

Re: [time-nuts] Cheap jitter measurements

Am 10.04.2018 um 01:03 schrieb Gary E. Miller: Yo Hal! On Mon, 09 Apr 2018 13:53:21 -0700 Hal Murray wrote: The API for the kernel clock can be read to a ns. I don't see ntpd having much use for finer grain than that. I should look at the source to see what the

Re: [time-nuts] Cheap jitter measurements

Yo Hal! On Mon, 09 Apr 2018 13:53:21 -0700 Hal Murray wrote: > The API for the kernel clock can be read to a ns. I don't see ntpd > having much use for finer grain than that. I should look at the > source to see what the internal details look like. Yeah, but the

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 9, 2018, at 4:53 PM, Hal Murray wrote: > > > kb...@n1k.org said: >> Somewhere in the NTP algorithm, there is a “zero error” estimate. GPS >> modules have the same thing buried in them. A GPS module (like NTP as >> described above) can only *express* a PPS

Re: [time-nuts] Cheap jitter measurements

kb...@n1k.org said: > Somewhere in the NTP algorithm, there is a “zero error” estimate. GPS > modules have the same thing buried in them. A GPS module (like NTP as > described above) can only *express* a PPS modulo some clock rate. GPS > modules get around this with a firmware hack. They

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 9, 2018, at 2:19 PM, Achim Gratz wrote: > > Bob kb8tq writes: >>> Similarly, the box should be able to give me a pulse at a known time. >> >> how do you set up NTP to do that? > > Not at all, that must be done in the kernel if you want any accuracy at > all.

Re: [time-nuts] Cheap jitter measurements

Bob kb8tq writes: >> Similarly, the box should be able to give me a pulse at a known time. > > how do you set up NTP to do that? Not at all, that must be done in the kernel if you want any accuracy at all. But you could modify an existing device driver (for the LPT port) to use GPIO instead to

Re: [time-nuts] Cheap jitter measurements

Hi > On Apr 9, 2018, at 2:53 AM, Trevor N. wrote: > > Bob kb8tq wrote: >> Hi >> >> Without the ability to put out a “known good” time pulse there is no quick >> way to >> check NTP. GPS modules suffer a similar issue. They put out a pulse and a >> “correction” (sawtooth

Re: [time-nuts] Cheap jitter measurements

There is a program for the RPi which handles the PPS input for NTP and can produce an output on a GPIO pin here: https://vanheusden.com/time/rpi_gpio_ntp/ but it's user-mode so of limited use. Perhaps the OP could adapt it? Cheers, David -- SatSignal Software - Quality software written to

[time-nuts] Cheap jitter measurements

Bob kb8tq wrote: >Hi > >Without the ability to put out a “known good” time pulse there is no quick way >to >check NTP. GPS modules suffer a similar issue. They put out a pulse and a >“correction” (sawtooth error) to tell you what they just told you. Doing the >same >sort of thing with NTP may

Re: [time-nuts] Cheap jitter measurements

" I appreciate that the clock-blessed may have doubts about the truth of his sources. But the fact is, you need a larger sample size to better estimate error. The man who is happy in his ignorance has not considered that calibrated doubt can be more satisfying than unjustified certainty."

Re: [time-nuts] Cheap jitter measurements

That may be an article of faith for those who haven't experienced the delights of time-nuttery, but to be fair, the man with n<2 clocks doesn't know what time it is either. Even if n=1, he only believes he knows what time it is. I appreciate that the clock-blessed may have doubts about the truth

Re: [time-nuts] Cheap jitter measurements

Hi Without the ability to put out a “known good” time pulse there is no quick way to check NTP. GPS modules suffer a similar issue. They put out a pulse and a “correction” (sawtooth error) to tell you what they just told you. Doing the same sort of thing with NTP may be possible. Indeed

Re: [time-nuts] Cheap jitter measurements

Pity the poor man who has (n>1) clocks, for he knows not what time it is. Dana On Sun, Apr 8, 2018 at 4:29 PM, John Ackermann N8UR wrote: > I want to jump on Tom's post, and Bob's note at 1:14 on Saturday (that > begins with "Just to be very clear..." They both raise an

Re: [time-nuts] Cheap jitter measurements

Tom Van Baak wrote on Sun, 8 Apr 2018 at 12:36:52 -0700 in <55EB8D26CCDC4B1ABFBC53F95E4C0557@pc52>: > My mental model of a black box computer running NTP ... > Imagine the black box has two BNC connectors; one accepts an input > pulse to be timed; one outputs a pulse at

Re: [time-nuts] Cheap jitter measurements

kb...@n1k.org said: > In both cases (pulse in and pulse out) the first step is to ask NTP “when > was that?”. You still have a pretty big chunk of NTP in the middle of the > process …. If NTP only “knows” what is happening (or can control what is > happening) to +/- 300 ns. The guts

Re: [time-nuts] Cheap jitter measurements

I want to jump on Tom's post, and Bob's note at 1:14 on Saturday (that begins with "Just to be very clear..." They both raise an important point about measurements. With both NTP and GPSDO measurements a lot of folks focus heavily on what the "black box" is reporting about itself. But

Re: [time-nuts] Cheap jitter measurements

>> Similarly, the box should be able to give me a pulse at a known time. > > how do you set up NTP to do that? Don't know. That's not NTP's job. Any process that can query system time and get/set a GPIO bit will do. The question to be answered is how close to the real time (as in UTC(k), atomic

Re: [time-nuts] Cheap jitter measurements

Hi Ok, I’ll bite …. > On Apr 8, 2018, at 3:36 PM, Tom Van Baak wrote: > What do you mean by "jitter" and what do you really want to do? >>> I mean jitter as NTP defines jitter. Whatever that is. >> >> I think you need to figure out what you want to do so you don't

Re: [time-nuts] Cheap jitter measurements

>>> What do you mean by "jitter" and what do you really want to do? >> I mean jitter as NTP defines jitter. Whatever that is. > > I think you need to figure out what you want to do so you don't fool yourself. > > ntpd is a PLL. There is a low pass filter in the control loop. It will > track

Re: [time-nuts] Cheap jitter measurements

Hi Whatever you want to call it (jitter / wander / noise / crud ), an Rb in a stable temperature environment ( a few degrees C per hour) will have “stuff” with the dimensions of nanoseconds when compared to a good GPS. A “normal” NTP setup with a crystal on the motherboard as it’s main

Re: [time-nuts] Cheap jitter measurements

>> What do you mean by "jitter" and what do you really want to do? > I mean jitter as NTP defines jitter. Whatever that is. I think you need to figure out what you want to do so you don't fool yourself. ntpd is a PLL. There is a low pass filter in the control loop. It will track the low

[time-nuts] Cheap jitter measurements

The TICC is a very nice device. A LOT of bang for the buck.Highly recommended. Lady Heather supports it (you can actually connect two for 4 channel operation) and can run under Linux. It provides most of the basic functionality of Timelab (with less pretty plots).

Re: [time-nuts] Cheap jitter measurements

Time Nuts! TL:DR: I decided to go with the Rb and TAPR-TICC. Long story: Thank you to all that made such good suggestions. I think you pretty much covered the spectrum of options to measuring PPS very nicely. I'm tempted by the used 5370/5371 idea. It has 150 ps resolution and does a ton of

Re: [time-nuts] Cheap jitter measurements

Hal! On Tue, 03 Apr 2018 13:06:43 -0700 Hal Murray wrote: > > What would you guys suggest as the cheapest way to see jitter down > > to around 1 nano second? > > What do you mean by "jitter" and what do you really want to do? I mean jitter as NTP defines jitter.

Re: [time-nuts] Cheap jitter measurements

I would say my implementation is simpler than Nick’s: https://www.eevblog.com/forum/projects/lars-diy-gpsdo-with-arduino-and-1ns-resolution-tic/?all . It is just an Arduino+ two HCMOS and a few passive components. >From the beginning Nick copied my interpolator. Later he added a FET that >might

Re: [time-nuts] Cheap jitter measurements

o it is not the right tool > for your nanosecond needs. I do have a 10 ns version that I use, but that's > still a bit coarse for GPS work. > > > > I have spare FEI Rb here; I'll send it if you want it. That way you can > afford a TICC. > > > > /tvb > > > >

Re: [time-nuts] Cheap jitter measurements

oarse for GPS work. > > I have spare FEI Rb here; I'll send it if you want it. That way you can > afford a TICC. > > /tvb > > > - Original Message ----- > From: "Gary E. Miller" <g...@rellim.com> > To: "time-nuts" <time-nuts@febo.com>

Re: [time-nuts] Cheap jitter measurements

Gary There is a Blast from the past the PIC TIC. Richard McCorkle did it and in its time was widely popular. He helped me on many projects so I included his boards with my board orders. Not being a time nut I never took a closer look at his board. Having recently revisited the subject for

Re: [time-nuts] Cheap jitter measurements

g...@rellim.com said: > With care I can measure GPS jitter on a RasPi to a bit over 300 nano sec > resolution. That is the smallest increment of the RasPi 3B clock with a > 64-bit kernel. That is clearly not time-nuts accuracy. > What would you guys suggest as the cheapest way to see jitter

Re: [time-nuts] Cheap jitter measurements

al Message - From: "Gary E. Miller" <g...@rellim.com> To: "time-nuts" <time-nuts@febo.com> Sent: Tuesday, April 03, 2018 10:47 AM Subject: [time-nuts] Cheap jitter measurements Time-nuts! With care I can measure GPS jitter on a RasPi to a bit over 300 nano sec r

Re: [time-nuts] Cheap jitter measurements

Find a nice used 5370/5371? :) There is a 5371 on ebay for $250 at the moment. On Tue, Apr 3, 2018 at 1:47 PM, Gary E. Miller wrote: > Time-nuts! > > With care I can measure GPS jitter on a RasPi to a bit over 300 nano sec > resolution. That is the smallest increment of the

Re: [time-nuts] Cheap jitter measurements

On Tue, 3 Apr 2018 10:47:37 -0700 "Gary E. Miller" wrote: > What would you guys suggest as the cheapest way to see jitter down to > around 1 nano second? Look at Nick Sayers GPSDO and his interpolator. You wont get any cheaper than that. Next best thing is to use a TDC7200

[time-nuts] Cheap jitter measurements

Time-nuts! With care I can measure GPS jitter on a RasPi to a bit over 300 nano sec resolution. That is the smallest increment of the RasPi 3B clock with a 64-bit kernel. That is clearly not time-nuts accuracy. What would you guys suggest as the cheapest way to see jitter down to around 1 nano