Hi all, I have been looking for a PPS GPS for quite some time. Most of them are expensive and on AliExpress none of them have PPS. However, after a long search I found one that is really cheap, about 50~60 Euro/USD depending on shipping. But beware, when they ship to Europe you will probably cha…

PPS/serial or GPIO will be superior, agreed. However, the PPS/USB may be better than relying on remote NTP servers. My Rpi4 has both a Navisys/USB and a Uputronics Raspberry Pi+ GPS Expansion Board (PPS/GPIO). I can compare the two. Running under chrony the Navisys has an average offset of ~670 …

oh guys. ANY USB device use “packet data exchange” over usb bus may give an unpredictable delay and not so accurate as “analog/diginal” interface. Many cheap “chinese” recievers on Aliexpress/eBay builded on uBlox GNSS. uBlox chip have many interfaces - RS232,USB, GPIO and separate PPS. If you use …

But the Navisys isn’t an very cheap no-name Chinese USB device. Steven measured it and came to the conclusion that NTP-clients will not notice any wobble. Whereas they do notice with other non-PPS USB devices. It gives very predictable time and works very well. I do not have RS-232 in my Intel I…

Trouble in usb bus. It’s not analog/digital and very complex. Data pack to "packets’ and packets goes throught bus. Bus transit times are unpredictable and unwarranted. So, If any device (theoretically even mouse or keyboard or external HDD) overload bus we can get any result. But if you don’t overl…

It’s connected to USB3. USB3 is a different animal then previous USB-versions. It can trigger interrupts instead of polling. The only thing I do not know if the trigger is also used for older devices. For USB-ports 1.x-2.x you are right, they are unpredictable. USB3.x changed all that. …

[image] umike: Trouble in usb bus. It’s not analog/digital and very complex. Data pack to "packets’ and packets goes throught bus. Bus transit times are unpredictable and unwarranted. So, If any device (theoretically even mouse or keyboard or external HDD) overload bus we can get any result. But…

[image] Bas: System time : 0.000008806 seconds fast of NTP time NTP time is the software time loop inside the chronyd daemon based on the external clocks (PPS, NTP packets etc). System time is the time of the operating system. This measure mainly tells that the operating system clock has sync…

Yes it can be very accurate, just read the protocol: NTP provides the protocol mechanisms to synchronize time in principle to precisions in the order of nanoseconds while preserving a non-ambiguous date, at least for this century. The protocol includes provisions to specify the precision and e…

Yes, the protocol allows this high precision, it is designed that way. When you have in practice only millisecond accuracy and not microsecond, the imprecision is due to the underlying infrastructure, not the NTP protocol itself.

So how come Chrony is able to present these? .-- Source mode ‘^’ = server, ‘=’ = peer, ‘#’ = local clock. / .- Source state '’ = current synced, ‘+’ = combined , ‘-’ = not combined, | / ‘?’ = unreachable, ‘x’ = time may be in error, ‘~’ = time too variable. || …

USB GPS with PPS and pretty cheap too

Server operators

jos1264 November 24, 2020, 12:18am 22

Here it is available from what I see.

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USB GPS with PPS and pretty cheap too

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