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Re: [gpsd-users] 1PPS works on CH340G based usb-serial converter
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From: |
Gary E. Miller |
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Subject: |
Re: [gpsd-users] 1PPS works on CH340G based usb-serial converter |
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Date: |
Tue, 24 Mar 2015 11:48:19 -0700 |
Yo Chen!
On Tue, 24 Mar 2015 16:10:58 +0800
Chen Wei <address@hidden> wrote:
> The GPS is a ublox-5 module. The 1PPS wire is soldered to CH340G's DCD
> pin:
>
> https://dl.dropboxusercontent.com/u/509097/CH340G-usb-gps-1PPS.png
I do not understand your setup. Can you explain a bit more?
> NTP only works with PPS from gpsd shared memory.
No, there is the new ntpd gpsd-json driver, as well as the ATOM
driver.
> The Type 22 reference
> clock of NTP is not working,
That would be an ntpd problem, not a gpsd problem.
> probably because the 1PPS from this
> USB-GPS combination is not good enough, which indicated by the kernel
> error message "hardpps: PPSJITTER: bad pulse".
Garbage in, garbage out. Any idea why? Have you put a scope on it?
In any case, I am not familiar with the hardpps driver, it is not used
by gpsd.
> The kernel accept 1PPS
> from the same GPS module when it connected to GPIO though.
With some limitations. The pps-gpio driver only timestamps the
asser edge, not the clear edge. I jsut reported that bug to the
maintainters, they are still in denial.
> The jitter of this USB-GPS is around 300-700 micro-seconds.
Which jitter, the serial time jitter or the PPS jitter? I assume you
mean the PPS jitter?
How long did you let the system run? I find it takes days for a RasPi
clock to settle down.
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