[ntp:questions] YEA! My Sure Electronics GPS just arrived.

Gom gom at gom.invalid
Mon Mar 26 18:15:33 UTC 2012

Even with multimedia timer on its smallest resolution, you will run into 
the 1 ms barrier under windows.

To do better you need to enable interpolation, this simple operation 
will improve your jitter by at least 10x.

Le 25/03/2012 23:06, Ron Frazier (NTP) a écrit :
> On 3/24/2012 12:46 PM, unruh wrote:
>> On 2012-03-24, Ron Frazier (NTP)<timekeepingntplist at c3energy.com> wrote:
>>> I now have the PPS circuit working on the Sure board. I have not
>>> soldered it yet. I just taped a jumper wire between the PPS test point
>>> at the edge of the board and the DCD pin 1 on the RS-232 port. The
>>> serial data is coming in through the Trendnet TU-S9 serial - USB
>>> converter, which is passing DCD. I'm getting + .5 / - 1.5 ms offsets.
>>> The PPS is nowhere to be seen on the statistics screen, but it is
>>> obviously working. I don't know why it's not more centered around zero,
>> Peaked around zero in comparison with what? Remember that the serial to
>> usb of dcd and then the decoding of that interrupt is going to
>> institute delays. It should always be later than "true time".
> I just meant that the offsets were shifted more toward the positive on
> the graph rather than being centered around zero. They seem to be
> centered around zero now.
>>> and maybe that will change. However, my total peak to peak range of
>>> offset variance is 2 ms, and that's coming through USB. If I can
>>> maintain that level of accuracy, and it's consistent with UTC, then I'm
>>> very happy. That's plenty good for my purposes. I still may try to run
>>> it through a real serial port on another machine just for kicks.
>> You can get 1us, not 1ms that way. But if a factor of 1000 is irrelevant
>> for you, then what you have is fine.
> I don't have to have 1 us. I just want the computer's clocks to be right
> and to be doing better than I can with internet servers. In that regard,
> any offsets better than 50 ms are good. I plan to test this GPS for a
> while and and make sure it's stable. Then, I want to set up every
> computer so it can use the GPS if it's attached. Then, I'll try the real
> serial thing on the PC that has a port. Eventually, I want to make
> probably that one a server for all the rest. I'll probably have to give
> the server a fixed IP address in my router since those can change when
> DHCP assigns them.
>>> Sincerely,
>>> Ron

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