EDM01-36v10 DAG_9.2X2_Card_User_Guide - Using your DAG card
©2010 - 2012 Endace Technology Ltd. Confidential - Version 10 - May 2012
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Situation 2 (Ethernet)
The ERF stream was generated with a CRC but the CRC must be corrected on the retransmitted packet.
In this case you should configure TR-TERF to strip the original 32-bit CRC and configure the MAC to add
a hardware calculated CRC as in Situation 1 above to replace it. This means even if the CRC is incorrect
in the received ERF stream, a correct CRC will be generated when the packet is retransmitted.
Example
dagconfig terf_strip32 tx_crc
Situation 3 (Ethernet)
The ERF stream was generated with a CRC, and the CRC must be retransmitted exactly even if it is
incorrect.
In this case you should configure TR-TERF
not
to strip the CRC, and configure the MAC
not
to add a
hardware-calculated CRC, so that the original CRC is retained. This allows received packets with bad
CRCs to be retransmitted which may be a useful tool for testing or diagnostic purposes.
Example
dagconfig noterf_strip notx_crc
Retransmitting errored packets
In some circumstances it may not be desirable to retransmit packets which have been incorrectly
received for any reason. To allow for this, TR-TERF can be optionally configured not to retransmit any
packets marked with the
rxerror
(receive error) flag.
For further details, refer to
EDM04-03 dagflood User Manual
.
Usage notes
The following points should be noted when using TR-TERF:
•
When using
dagflood
to transmit an ERF stream to the card you should set the "
-1
" flag (maximum
data burst length) to a value greater than the default of 1MB to achieve the highest transmit data
rate. During testing Endace found a value of 16MB (16777216) to be effective. This reduces the
possibility of a buffer under-run occurring if insufficient data is committed in a burst and the
dagflood
process is not scheduled by the OS to run in a timely manner.
•
For best accuracy when testing, you should ensure both the sending and receiving cards are
synchronized to the same time source.
TR TERF known issues
TR-TERF is less accurate when using multiple interfaces. If a large packet is transmitted to the card on a
particular interface, the transmit buffers for the other interfaces may experience a buffer under-run. This
is because data is only transferred to one interface at any one time, record by record as the input ERF
stream is interleaved between interfaces.
This may be especially noticeable where very small packets are transmitted on one interface and very
large packets transmitted on another interface.
