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Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Appendix B:
Core Latency
R
Latency for 1000BASE-X PCS and PMA Using a RocketIO Transceiver
These measurements are for the core only–they do not include the latency through the
Virtex-II Pro or Virtex-4 MGT, Virtex-5 GTP transceiver, or the Transmitter Elastic Buffer
added in the example design.
Transmit Path Latency
As measured from a data octet input into
gmii_txd[7:0]
of the transmitter side GMII
(until that data appears on
txdata[7:0]
on the MGT interface), the latency through the
core in the transmit direction is 4 clock periods of
userclk2
.
Receive Path Latency
As measured from a data octet input into the core on
rxdata[7:0]
from the MGT
interface (until that data appears on
gmii_rxd[7:0]
of the receiver side GMII), the
latency through the core in the receive direction is 6 clock periods of
userclk2
.
Latency for SGMII
When performing the SGMII standard, the core latency figures are identical to the Latency
for 1000BASE-X PCS and PMA using the MGT. Again these figures do not include the
latency through the MGT or any Elastic Buffers added in the example design.
