On Fri, 12 Jun 2015 18:29:29 -0400
Ed Armstrong eds_equipm...@verizon.net wrote:
The Ethernet on the Raspberry Pi is on the USB bus. That adds about a 1/2
ms
of jitter.
Is it possible to modify the kernel so the USB is polled more often, and
would that significantly reduce the jitter?
Hal, what stopped me from going down the BBB path was the reports of RF
noise, they supposedly create a lot of noise. Not acceptable in an HF
environment. Google around about the RF noise with the BBB. mg NG7M
On Sat, Jun 13, 2015 at 12:02 AM, Hal Murray hmur...@megapathdsl.net
wrote:
Several time-nuts have asked about my setup, here are some details of what
I changed in the kernel and in the NTP build... Make sure and use the
default config for the Pi 2 CPU when setting up .config for the Linux
kernel. Make sure you are actually seeing your new kernel after you copy
it to
eds_equipm...@verizon.net said:
Is it possible to modify the kernel so the USB is polled more often, and
would that significantly reduce the jitter?
Modifying the kernel may not be enough if the timing parameters are in the
microcode for the USB device.
Whether any improvement is
m.matthew.geo...@gmail.com said:
As you can see, the PPM frequency on this Pi is still showing -7.742. I
assume that is if it was undisciplined? I have wondered about that.
That's the fudge factor needed to make that box keep reasonable time.
At one level, it's the difference between the
On 6/10/2015 5:00 AM, Hal Murray wrote:
eds_equipm...@verizon.net said:
OK, here is the actual question. Do you think it is OK to consider a pulse
which arise 250 ns early to be close enough? And no, I am not forgetting
about that 3 ns, there is about 3 ns of delay added by the output
).
Cheers!
-Randal r3
-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Ed Armstrong
Sent: Tuesday, 09 June, 2015 22:30
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] PPS for NTP Server - How Close Is Good Enough?
Hi
Hi
Be careful of “single source” comparisons. When running with one reference,
NTP is really measuring the reference against it’s self. It’s analogous to
using a
frequency counter to check it’s own reference. It *does* indeed check a number
of things.
It’s not really checking everything.
An
Hi Ed,
I have started another thread under the name NTG550AA 1 PPS mod for
finding the subject easier and I include here my thoughts about this
modification.
I am the one who discovered the 1PPS pulse while troubleshooting a
NTG550AA. For me I don't imagine any future use of the X8 Chip
Hi Bob, yes I'm including several other sources and usually about 3 are
getting included in the discipline of the local clock. Here is my ntpq
-pcrl output at the time I wrote this message.
pi@raspi2 ~ $ ntpq -pcrl
remote refid st t when poll reach delay offset
jitter
Here is what I have been able to do with a Motorola Oncore UT+ that I got
from Bob Stewart awhile back. This is with a Raspberry PI 2 with a number
of tweaks and a custom compiled kernel. Nothing too drastic... plus the
current Dev version of NTP compile on the Raspberry PI. I'm getting better
Hi
Comparing a GPS to a series of “over the net” sources will always make the GPS
look
good. NTP is usually smart enough to figure out that the GPS is the one it
wants and lock
in on it.
The ppm’s at the bottom are talking about the software PLL and how it’s offset
from your
computer’s
Hi, this is my first post ever to a mailing list, so if I'm doing
anything wrong please be gentle with your corrections :-)
A short time ago I purchased a Nortel/Trimble NTGS50AA GPSTM, I'm sure
many on this list are familiar with it. At the time of purchase, my only
interest was the 10 MHz
Do you think it is OK to consider a pulse which arise 250 ns early to be close
enough?
For NTP usage that will be no problem whatsoever.
Dave
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On Wed, Jun 10, 2015 at 6:30 AM, Ed Armstrong eds_equipm...@verizon.net wrote:
Hi, this is my first post ever to a mailing list, so if I'm doing anything
wrong please be gentle with your corrections :-)
Welcome!
[snip]
My next step was to find out where the even second pulse entered the
From: Ed Armstrong
[]
OK, here is the actual question. Do you think it is OK to consider a
pulse which arise 250 ns early to be close enough? And no, I am not
forgetting about that 3 ns, there is about 3 ns of delay added by the
output circuitry.
Hope you didn't mind the long-winded post, and I
For driving NTP..
1) NTP works in microseconds and your networked clients will see accuracy
in the range of a few milliseconds.
2) There is a way to fix this in NTP's configuration file, you can specify
what the delay is.
On Tue, Jun 9, 2015 at 9:30 PM, Ed Armstrong eds_equipm...@verizon.net
Hi Ed --
For standard PC hardware, 250ns is way under the interrupt granularity
of the computer, and will never be noticed. Some specialized
configurations (https://www.febo.com/pages/soekris/) have timer
resolution to a few hundred nanoseconds, but that takes hacking.
I know there have
).
Cheers!
-Randal r3
-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Ed Armstrong
Sent: Tuesday, 09 June, 2015 22:30
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] PPS for NTP Server - How Close Is Good Enough?
Hi
On Wed, Jun 10, 2015 at 12:30 PM, Ed Armstrong eds_equipm...@verizon.net
wrote:
OK, here is the actual question. Do you think it is OK to consider a pulse
which arise 250 ns early to be close enough? And no, I am not forgetting
about that 3 ns, there is about 3 ns of delay added by the output
Hi
Welcome!
At best your NTP setup will be good to a few microseconds. By the time you get
the time delivered (even over a LAN) it will be good to a few hundred
microseconds at best. The ~ 250 ns error should not be a big deal.
This being Time Nuts, you might take a look at the options on
On Tue, June 9, 2015 11:30 pm, Ed Armstrong wrote:
OK, here is the actual question. Do you think it is OK to consider a
pulse which arise 250 ns early to be close enough?
It is only 250ns early relative to the even second output. What is the
even second output referenced to?
What most people
eds_equipm...@verizon.net said:
OK, here is the actual question. Do you think it is OK to consider a pulse
which arise 250 ns early to be close enough? And no, I am not forgetting
about that 3 ns, there is about 3 ns of delay added by the output
circuitry.
If you want to earn your
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