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Re: [gpsd-dev] A detail in your ntpoffset script
From: |
Hal Murray |
Subject: |
Re: [gpsd-dev] A detail in your ntpoffset script |
Date: |
Wed, 23 Oct 2013 12:52:38 -0700 |
address@hidden said:
> On one host I have two GPS/PPS. They differ by a consistent 1.5 uSec.
Is that just the expected synchronization?
What would happen if both PPS pulses happened at exactly the same time? The
interrupts would get merged into one. The interrupt processing would
consistently check one first. How much time would you expect between first
check and the second? 1.5 uSec seems like a reasonable ballpark to me,
depending on your CPU.
It's slightly more complicated with USB. The hardware will go through a
polling cycle every time the clock ticks. It will test one first, then the
second. I'd expect a bit more than 1.5 uSec in that case, and occasionally
the PPS pulses will happen after the hardware has checked the first and
before the second, so the first will be one polling cycle later than the
second.
--
These are my opinions. I hate spam.
- Re: [gpsd-dev] A detail in your ntpoffset script, (continued)
Re: [gpsd-dev] A detail in your ntpoffset script, Gary E. Miller, 2013/10/22
Re: [gpsd-dev] A detail in your ntpoffset script, Eric S. Raymond, 2013/10/22
Re: [gpsd-dev] A detail in your ntpoffset script,
Hal Murray <=
Re: [gpsd-dev] A detail in your ntpoffset script, Gary E. Miller, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Dave Platt, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Gary E. Miller, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Eric S. Raymond, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Harlan Stenn, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Harlan Stenn, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Gary E. Miller, 2013/10/23
Re: [gpsd-dev] A detail in your ntpoffset script, Sanjeev Gupta, 2013/10/24
Re: [gpsd-dev] A detail in your ntpoffset script, Andy Walls, 2013/10/22