Re: [time-nuts] Designing an embedded precision GPS time server

On Thu, October 26, 2017 7:38 pm, Denny Page wrote: > If you are going to do PTP with ptp4l, or NTP with Chrony, you are going > to want hardware timestamping support on the ethernet phy. Or the MAC. The processor used on BeagleBone Black has timestamping in the MAC. Not quite as accurate as

Re: [time-nuts] Designing an embedded precision GPS time server

On Thu, October 26, 2017 5:58 pm, Bob kb8tq wrote: > Why go to the green? Cheaper. > Just go with one of these Pocket Beagles I have > sitting here wondering what to do with them. Pocket Beagles do not have Ethernet. How are you going to make a network time server from a board with no network?

Re: [time-nuts] Phase noise measurement experiment by Andrew Holme

The 16 bit ADCs (at least the LTC lower sample rate ones ) tend to be a few dBc/Hz quieter. However the difference is < 12 dBc/Hz. Bruce > > On 27 October 2017 at 14:35 Li Ang <379...@qq.com> wrote: > > Hi > I just found Andrew recently post a phase noise measruement page on >

Re: [time-nuts] Designing an embedded precision GPS time server

Hi I suspect that once you find a group of chips that do have 1588 embedded in them that digging into all the nasty details will take a bit. Time stamping to a 1 ms resolution might not be a very helpful thing ….. There are ex-Freescale / now NXP devices that do have pretty good 1588 in them.

Re: [time-nuts] Designing an embedded precision GPS time server

If you are going to do PTP with ptp4l, or NTP with Chrony, you are going to want hardware timestamping support on the ethernet phy. I would view this as one of the principal concerns in choosing a system. I’m not sufficiently familiar with Beagles… do any of them support hardware timestamping?

[time-nuts] Phase noise measurement experiment by Andrew Holme

Hi I just found Andrew recently post a phase noise measruement page on www.aholme.co.uk/PhaseNoise/Main.htm . He uses 4-channel 14bit ADC to do the sampling work. -170dBc noise floor seems not bad for me. Since the cross correlation could reduce noise a lot, I am wondering what the

[time-nuts] I've been thinking about a GPS receiver experiment

The Thunderbolt, Star-4, Trueposition, and HP GPSDOs/Smartclocks are all known to do this. Typically the learning period is around 24 hours before the compensation is allowed to run. My HP GPSDO seems to take a week for best performance. Separating tempco and aging drift seems to me to be a

Re: [time-nuts] Designing an embedded precision GPS time server

Hi Why go to the green? Just go with one of these Pocket Beagle’s I have sitting here wondering what to do with them. They were just a bit under $20 when I picked them up. I doubt the price will climb over time …… Indeed you could get two Pi Zero W’s for the pice of the Pocket Beagle. Lash an

Re: [time-nuts] Designing an embedded precision GPS time server

On 26/10/17 22:11, Chris Caudle wrote: The processor you mentioned has a Cortex-M7 at 300MHz. has a Cortex-A8 running at 1GHz plus a Cortex-M processor available as a coprocessor. Peripheral set is pretty comparable, and you can buy BBB at retail for $50 which gets you the faster higher

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Terrific points. There are so many levels of sophistication. My own experience is with catastrophic signal loss on the reference. Determining degradation on your primary reference can present challenges. I once designed a device that compared three Cesiums and switched the reference within

Re: [time-nuts] Designing an embedded precision GPS time server

On Wed, October 25, 2017 7:53 pm, Nick Sayer via time-nuts wrote: > I am considering a new project based on its cousin, the ATSAME70. What is a reasonable cost target for that at the volumes you could produce? Coming up with something that is a better value than BeagleBone Black at any kind of

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi You get into all sorts of issues trying to estimate tempco. You have time lags and gradients that make it a very messy process. Toss in measurement based on small range temperature swings (like from a HVAC system) …. it’s a mess. If the OCXO is a typical modern part and it’s been on power

[time-nuts] I've been thinking about a GPS receiver experiment

Many years ago I tried to add some code to Lady Heather to calculate the tempco and aging of the oscillator in a normally running Tbolt. Although the equations would theoretically work (using SVD decomposition) it seldom worked properly. Failure seemed to be caused by noise in the small

Re: [time-nuts] Designing an embedded precision GPS time server

Hi So, get it up and running on the 1588 hardware built into one of these “all in one” MCU’s should be possible. Note the absence of words like easy or straightforward :) Bob > On Oct 26, 2017, at 12:45 PM, Chris Caudle wrote: > > On Thu, October 26, 2017 9:40 am,

Re: [time-nuts] Designing an embedded precision GPS time server

On Thu, October 26, 2017 9:40 am, Bob kb8tq wrote: > Since time stamping hardware does exist for 1588, why not simply put the > effort into folding that into NTP? According to the Chrony project web page chronyd already includes support for that. See "NTP timestamping" section:

Re: [time-nuts] Designing an embedded precision GPS time server

Hi Since time stamping hardware does exist for 1588, why not simply put the effort into folding that into NTP? Then you have a “generic” solution that addresses a lot of the ambiguity a wide range of cases. It shows up in many of the low end micro’s so it’s not just a “big box only” solution.

Re: [time-nuts] I've been thinking about a GPS receiver experiment

Hi Most GPSDO’s do some sort of “slew” to an average DAC value when they go into holdover. Freezing at the last value is not (in general) a good idea. Often things degrade before there is a dropout. Your final DAC value may not be a good one to maximize holdover duration. Some setups try to