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Re: [gpsd-dev] gpspipe improvement proposal for hi-res timestamps -2-
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From: |
Gary E. Miller |
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Subject: |
Re: [gpsd-dev] gpspipe improvement proposal for hi-res timestamps -2- |
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Date: |
Fri, 3 May 2013 16:26:16 -0700 |
Yo Andreas!
On Sat, 4 May 2013 01:17:05 +0200
"Andreas Merz" <address@hidden> wrote:
> One GPS is a Navilock NL303 with a SiRF chip. It is interesting
> to see that the RMC messages (derived from MID2) are not
> equidistant in time but follow a pattern with a 3 sec period. [1]
>
> The other GPS is a good old Garmin GPS12 attached to the RS232 port.
> Its behaviour is even more strange.
> The RMC messages step around within a one second interval.
> This will make it tricky to synchronize a local clock. [2]
Yup, that is why we never bothered with high resolution time tagging.
The sentences are just all over the place.
Some GPS are hard to get better than +/-500mSec time over RS-232.
You can get down to around +/-50mSec using USB or even down to
+/-1mSec is some special cases.
Basically, if you need good time, you need PPS. Then you can get sub
mSec or better.
RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
address@hidden Tel:+1(541)382-8588
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