Endace DAG 4.5G2 Card, Руководство пользователя

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EDM 01-17 DAG 4.5G2/G4/GF Card User Guide
Timestamps
ERF files contains a hardware generated timestamp of each packet’s arrival.
The format of this timestamp is a single little-endian 64-bit fixed point
number, representing the number of seconds since midnight on the January
1970.
The high 32-bits contain the integer number of seconds, while the lower 32-
bits contain the binary fraction of the second. This allows an ultimate
resolution of 2-32 seconds, or approximately 233 picoseconds.
The ERF timestamp allows you to find the difference between two
timestamps using a single 64-bit subtraction. You do not need to check for
overflows between the two halves of the structure as you would need to do
when comparing Unix time structures.
Different DAG cards have different actual resolutions. This is accommodated
by the lowermost bits that are not active being set to zero. In this way the
interpretation of the timestamp does not need to change when higher
resolution clock hardware is available.
Example
Below is example code showing how a 64-bit ERF timestamp (erfts) can be
converted into a
struct timeval
representation (tv):
unsigned long long lts;
struct timeval tv;
lts = erfts;
tv.tv_sec = lts >> 32;
lts = ((lts & 0xffffffffULL) * 1000 * 1000);
lts += (lts & 0x80000000ULL) << 1; /* rounding */
tv.tv_usec = lts >> 32;
if(tv.tv_usec >= 1000000) {
tv.tv_usec -= 1000000;
tv.= 1;
}
Configuration
Tools The DUCK is very flexible, and can be used with or without an external time
reference. It can accept synchronization from several input sources, and also
be made to drive its synchronization output from one of several sources.
Synchronization settings are controlled by the
dagclock
utility.
Note: You should only run
dagclock
after you have loaded the
appropriate Xilinx images. If at any stage you reload the Xilinx images
you must rerun
dagclock
to restore the configuration.
©2005-2006 26 Version 4: August 2006