Xilinx 1000BASE-X - Manual (Page 166)

166 www.xilinx.com Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 12: Constraining the Core R
Virtex-4 RocketIO MGTs for SGMII or Dynamic Standards Switching
Constraints
All the constraints described in the section “Virtex-4 RocketIO MGTs for 1000BASE-X
Constraints.” In addition, if the FPGA Fabric Rx Elastic Buffer is selected, an extra clock
period constraint of 16 ns is required for rxrecclk1.
With the MGT Rx Elastic Buffer bypassed, rxrecclk1 is provided by the MGT to the
FPGA fabric for the recovered receiver data signals leaving the transceiver. This data is
then written into the replacement Rx Elastic Buffer implemented in the FPGA fabric. See
“Virtex-4 Devices for SGMII or Dynamic Standards Switching,” page 101 .
The following UCF syntax shows the necessary constraint being applied to GT11 A.
#***********************************************************
# PCS/PMA Clock period Constraints for the GT11 A *
# recovered clock: please do not relax *
#***********************************************************
NET "core_wrapper/rocketio/rxrecclk10" TNM_NET = "rxrecclk10";
TIMESPEC "ts_rxrecclk10" = PERIOD "rxrecclk10" 16 ns;
Virtex-5 RocketIO GTP Transceivers for 1000BASE-X Constraints
The constraints defined in this section are implemented in the UCF for the example
designs delivered with the core. Sections from the UCF are copied into the following
descriptions to serve as examples, and should be studied with the HDL source code for the
example design. See also
“Virtex-5 LXT and SXT Devices” in Chapter 7 .
Clock Period Constraints
The clkin clock is provided to the GTP transceiver. It is a high-quality reference clock
with a frequency of 125 MHz and should be constrained.
The refclkout clock is provided by the GTP for use in the FPGA fabric, which is then
connected to global clock routing to produce the usrclk2 signal. This is the main 125
MHz clock used by all core logic and must be constrained.
The following UCF syntax shows these constraints being applied.
#***********************************************************
# PCS/PMA Clock period Constraints: please do not relax *
#***********************************************************
NET "*clkin" TNM_NET = "clkin";
TIMESPEC "TS_clkin" = PERIOD "clkin" 8 ns HIGH 50 %;
NET "*refclkout" TNM_NET = "refclkout";
TIMESPEC "TS_refclkout" = PERIOD "refclkout" 8 ns HIGH 50 %;
Setting GTP Transceiver Attributes
The Virtex-5 GTP transceiver has many attributes that are set directly from HDL source
code for the transceiver wrapper file delivered with the example design. These can be
found in the rocketio_wrapper_gtp_tile.vhd file (for VHDL design entry) or the
rocketio_wrapper_gtp_tile.v
file (for Verilog design entry): these files were
generated using the GTP Transceiver Wizard - to change the attributes, re-run the Wizard.
See
“Virtex-5 RocketIO GTP Wizard” in Chapter 7 .