[ntp:hackers] Solaris serial port jitter

Brian Utterback brian.utterback at sun.com
Fri Oct 22 06:00:52 PDT 2004

This is fascinating. I have been looking into the driver code for this
problem, and I can tell you that the drivers do nothing different when
PPS is turned on unless the DCD signal changes. The TIOCSPPS ioctl merely
sets a bit flag, and this flag is not even looked at unless there is a
DCD event, in which case hardpps is called. And that is it.

This suggests that there is a difference in ntpd when PPS is turned on.
Could it force a higher priority? I would like to track this down, and
to do that, I would still suggest using Solaris 10. The diagnosibility
of these types of problems is orders of magnitude easier with the
dtrace facility available in 10.

David L. Mills wrote:
> Guys,
> Apparently, the serial port driver on both Ultra 1 and Blade 1500 are 
> jiggered so that, if you enable the PPSAPI, the jitter goes away, even 
> if the PPS is not actually connected. Away means a couple of hundred 
> microseconds, but that is expected. It was several tens of milliseconds 
> to over a second. With PPS the Ultra 1 (pogo) is nominally 20 
> microseconds jitter.
> That's a relief.
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> hackers at support.ntp.org
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Power corrupts. PowerPoint corrupts absolutely.
Brian Utterback - OP/N1 Revenue Product Engineering, Sun Microsystems, Inc.
Ph/VM: 877-259-7345, Em:brian.utterback-at-ess-you-enn-dot-kom

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