Endace DAG 4.5G2 Card, Руководство пользователя

Страница: 35 / 46

EDM 01-18 DAG 4.5G2/G4/GF Card User Guide
Single Card No
Reference
When a single card is used with no external reference, the card can be
synchronized to the host PC clock. Most PC clocks are not very accurate by
themselves, but the DUCK drifts smoothly at the same rate as the PC clock.
If a PC is running NTP to synchronize its own clock, then the DUCK clock is
not as smooth because the PC clock is adjusted in small jumps. However the
DUCK clock does not drift away from UTC.
The synchronization achieved with this method is not as accurate as using an
external reference source such as GPS.
The DUCK clock is synchronized to a PC clock by setting input
synchronization selector to overflow as follows:
dagclock –d0 none overin
muxin overin
muxout none
status Synchronized Threshold 11921ns Failures 0 Resyncs 0
error Freq 1836ppb Phase 605ns Worst Freq 143377ppb Worst
Phase 88424ns
crystal Actual 49999347Hz Synthesized 16777216Hz
input Total 87039 Bad 0 Singles Missed 0 Longest Sequence
Missed 0
start Wed Apr 27 14:27:41 2005
host Thu Apr 28 14:38:20 2005
dag Thu Apr 28 14:38:20 2005
Two Cards No
Reference
Overview
If you are using two DAG cards in a single host PC with no reference clock,
you must synchronize the cards using the same method if you wish to
compare the timestamps between the two cards. You may wish to do this for
example if the two cards monitor different directions of a single full-duplex
link. You can synchronize the cards in two ways:
•
One card can be a clock master for the second. This is useful if you want
both cards to be accurately synchronized with each other, but not so for
absolute time of packet time-stamps, or
•
One card can synchronize to the host and also act as a master for the
second card
©2005-2006 29 Version 4: August 2006