[ntp:questions] Performance?

Unruh unruh-spam at physics.ubc.ca
Tue Dec 30 17:28:29 UTC 2008


oberman at es.net (Kevin Oberman) writes:

>> From: dhavey <dhavey at gmail.com>
>> Date: Mon, 29 Dec 2008 12:07:25 -0800 (PST)
>> Sender: questions-bounces+oberman=es.net at lists.ntp.org
>> 
>> Garmin specs say:  The rising edge of the signal is aligned to the
>> start of each GPS second.  This means edge on assert right?  So flag2
>> should be 0?
>> 
>> What is going on here?

>On my clock (EndRun, not Garmin) the PPS is low true, so the rising edge
>is NOT the assert, but the rising edge at the end of the pulse. There is
>a difference between leading and rising. (I had to talk to an engineer at
>EndRun to confirm this was the case and it may not be for the Garmin.)

Garmin defines the leading edge as the transition from 0V to 5V on the PPS
line. Now serial has two levels -12V and +12V. with capacitive coupling,
the garmin signal would be something like -2.5V to 2.5 V which really is
way out of spec for the serial port. (Or with the typicallysmall duty
cycle, more like -1V to 4V) 



>For EndRun, flag2 is 1.
>-- 
>R. Kevin Oberman, Network Engineer
>Energy Sciences Network (ESnet)
>Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
>E-mail: oberman at es.net			Phone: +1 510 486-8634
>Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751




More information about the questions mailing list