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Open-sourcing a more precise time appliance

engineering.fb.com

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Re: Open-sourcing a more precise time appliance

#81

Post by reportingsjr »

mFixman wrote: post #62
michaelt wrote: post #18

A few years back I was interested in microsecond-precise timekeeping. My experience was GPS-backed network clocks were surprisingly cheap - but PTP-aware network switches were surprisingly expensive. And though I thought I could cut the cost of a grandmaster clock from $2000 down to $200, I figured there'd be no point if I then have to connect it to a $20,000 network switch. I wonder how Facebook are connecting their…

I'm curious: what's the use case for microsecond-precise timekeeping?

There are plenty of practical applications for it.

Imagine super high speed, high precision robotics, maybe a synthetic fiber layup machine or an exotic milling machine, that moves at 10m/s. If you have 1us of precision and accuracy then you can send movement commands that are precise down to 10um.

Re: Open-sourcing a more precise time appliance

#82

Post by zinekeller »

michaelt wrote: post #49
delayclose2 wrote: post #38

> The offset is practically 0 ranging within nanoseconds range. Uhm, no, the graph clearly shows that the offset is varying between 0-2 microseconds, which is 0 - 2,000 nanoseconds. 2,000 nanoseconds is not "practically zero". PTP precision is supposed to be in the 10ns range. Also, how did they get 40us precision on (what I assume to be) a normal kernel on a normal x86 box? I would have assumed that in a datacenter…

PTP is a standard feature on a lot of Intel chipsets so a lot of servers have it 'for free' and aren't using it. It timestamps packets at the network card - independently of any kernel timing.

Addenda: Intel networking chips, so even in AMD or ARM systems this actually works (assuming that you have the correct OS and drivers/modules/support software).

Also, this isn't exclusive to Intel: most modern (server) NICs at least support TCXO-based timings, and some built for precision uses OCXO for even better precision.

Re: Open-sourcing a more precise time appliance

#83

Post by nullc »

michaelt wrote: post #39
rkangel wrote: post #4

I'm still unclear why they need the MAC on top of the GNSS reception. I can understand if it's just to provide holdover in event of GNSS signal loss, but they seem to be saying that it provides better precision when you've got both.

Although clock holdover might seem like a pointless feature - GPS outages are very unusual* - what holdover is mostly for is giving you time to respond if someone clumsily knocks your antenna over, or crushes your coax cable, or it gets damage that makes it fill with water, or something like that. A lot of the demand for high-precision clocks is for cell phone base stations, where there's no guarantee there'll be som…

In downtown mountain view I saw brief GPS outages a couple times a week, presumably due to people driving around with GPS jammers (e.g. to knock out GPS tracking of their own cars).

Re: Open-sourcing a more precise time appliance

#84

Post by nullc »

jeffbee wrote: post #56

Slaving your clocks to GPS seems like it just gives the USAF space command a way to, eventually, wreck your operations. If you don’t have requirements for accuracy referenced to civil time (such as mifid 2) why wouldn’t you just go with the atomic clocks alone, with gps as an advisory-only monitoring reference?

Long term drift on these inexpensive secondary atomic clocks isn't that amazing, sadly.

Re: Open-sourcing a more precise time appliance

#85

Post by Shish2k »

nonameiguess wrote: post #40

> Now, as long as printing the PCB and soldering tiny components does not sound scary, anyone can build their own Time Card for a fraction of the cost of a regular time appliance. Doesn't sound scary, but not a lot of research labs and data centers are going to want to build their expansion cards from parts, even given free access to instructions. I understand if there isn't enough of a market for this to make it a v…

From https://github.com/opencomputeproject/Time-Appliance-Project...

> Where can I get one?

> […] we are currently working with several suppliers and will have their contact info soon available to allow you to puchase an out-of-the-box ready Time Card.

Re: Open-sourcing a more precise time appliance

#86

Post by gjvc »

judge2020 wrote: post #74
toomuchtodo wrote: post #67

Earlier quoted context omitted.

I am torn. I absolutely love the technical blog post and the effort that went into open sourcing everything needed to build these devices, but, you know, Facebook. Compliments and respect to the engineers involved for really well done engineering.

Amazing people at Facebook make amazing things, but it does seem like only the worst of them (FB, Google) have the cash to burn to hire teams of engineers for projects outside of ones that directly contribute to generating revenue.

fundamental foundations like this is money well spent

Re: Open-sourcing a more precise time appliance

#88

Post by latchkey »

BonoboIO wrote: post #73
latchkey wrote: post #58

A very long time ago , HP made a GPS time card just like this, encased in glass and filled with an inert gas such that if the card was tampered with, it was rendered useless. This prevented someone from faking the time signal.

Can you show us a picture. Did not find anything on google beside HP Laptop spam.

I'm not sure it was ever sold to the public.

Buddy of mine owns timestamp.com and we were building a service where you could hash/timestamp emails (we would take over the MX for a domain and become a forwarding service). All of this was long before we had blockchains.

Sadly, it never really took off so we abandoned the idea (what is up there now is currently another half attempt at the idea).

Others have tried, but it isn't really a huge demand despite the apparent need.

Re: Open-sourcing a more precise time appliance

#89

Post by unsui »

mFixman wrote: post #62
michaelt wrote: post #18

A few years back I was interested in microsecond-precise timekeeping. My experience was GPS-backed network clocks were surprisingly cheap - but PTP-aware network switches were surprisingly expensive. And though I thought I could cut the cost of a grandmaster clock from $2000 down to $200, I figured there'd be no point if I then have to connect it to a $20,000 network switch. I wonder how Facebook are connecting their…

I'm curious: what's the use case for microsecond-precise timekeeping?

The question I'm interested in a corrollary of the above question:

What's the use case for microsecond-precise timekeeping, that is of interest to (i.e., benefits) FB?

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