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)<timekeepingntpl...@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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