[ntp:questions] How to determin hardware latency for PPS offset given simple tools.

David Taylor david-taylor at blueyonder.co.uk.invalid
Fri Jun 7 08:23:13 UTC 2013


On 06/06/2013 20:17, Doug Calvert wrote:
> unruh has a nice page about interrupt coalescing:
>
> http://axion.physics.ubc.ca/scatter/rt.html

This is a quite interesting note, unfortunately rendered rather less 
useful by the graphs, which have no axis names or units marked, and 
which appear to have inconsistent scales (although this may simply be 
lack of legibility).  For example:

   http://axion.physics.ubc.ca/scatter/rtdt1.gif

The units on the vertical axis appear to be labelled:

   -0.0001  -5x10-6  0  5x10-6  0.0001

which I interpret as -100us, -5 us, 0,  +5us  +100us, but it appears to 
be a linear axis.  Is the 5x10-6 supposed to be 5x10-5?  The character 
needs serious improvement as it looks like 5x10-6 to me.  But in any 
case, as microseconds are referred to in the text, would it not be a lot 
clearer if the graphs were also in microseconds, rather than some small 
fraction of seconds?

Similar problems in:

   http://axion.physics.ubc.ca/scatter/gps.gif

where the -5 and -6 suffices are very difficult to distinguish.  I do 
hope that Bill can re-do these graphs some time as it would enhance the 
value of this work.
-- 
Cheers,
David
Web: http://www.satsignal.eu



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