[LinuxPPS] Fwd: Fw: [ntp:hackers] u-blox reference clock driver

[Udo van den Heuvel]

Hello,

Below is a message from ntp.org with an interesting set of ideas related 
to the u-blox gps's.

There are links to a refclock implementation for u-blox.
There are kernel patches for Linux and FreeBSD.

Additionally we like the possibility to send a pulse (via strobe pin on 
LPT) on x86*.


Please implement the kernel changes!

Kind regards,
Udo

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Begin forwarded message:

Date: Fri, 10 Aug 2018 13:03:19 +0200
From: Lukas Senger <lukas at fridolin.com>
To: hackers at lists.ntp.org
Subject: [ntp:hackers] u-blox reference clock driver


Hi,

I've been writing a reference driver for u-blox GPS receivers as part
of my master's thesis and thought ntp hackers might be interested in it.
Additionally to normal PPS operation this driver can make use of the
u-blox's "Timemark" functionality.

It does this by enabling the PPSAPI echo, which generates an echo pulse
right after receiving a PPS pulse. This echo is connected to EXTINT0 on
the u-blox, where it is timestamped. So now I have the PPS timestamp as
a local time and the timemark as the receiver time to calculate an
offset. The cool thing about this is, that the offset does not include
the local interrupt latency anymore, which leads to less jitter.

Here's the driver:
https://gitlab.cs.fau.de/luksen/ntp-ubx/blob/ubx/ntpd/refclock_ubx.c

The echo/timemark feature requires kernel patches on Linux (with gpio
pins) and FreeBSD (parallel port). It's probably easiest to test on a
Raspberry Pi with the Linux patch and via GPIO pins.

Linux patch: https://gitlab.cs.fau.de/snippets/28
FreeBSD patch: https://gitlab.cs.fau.de/snippets/29

I originally tried to send this message some time ago but it seems like
there were some problems with the mailing list. By now the thesis is
finished and you can find it here:
https://wwwcip.informatik.uni-erlangen.de/~in18otin/thesis.pdf

--Lukas
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RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

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     "If you can’t measure it, you can’t improve it." - Lord Kelvin

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