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Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 12:
Constraining the Core
R
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 GTX Transceiver Attributes
The Virtex-5 GTX 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_gtx_tile.vhd
file (for VHDL design entry) or the
rocketio_wrapper_gtx_tile.v
file (for Verilog design entry): these files were
generated using the GTX Transceiver Wizard - to change the attributes, re-run the Wizard.
See
“Virtex-5 RocketIO GTX Wizard” in Chapter 7
.
Virtex-5 RocketIO GTX Transceivers for SGMII or Dynamic Standards
Switching Constraints
If the core is generated to use the GTX Rx Elastic Buffer, then all of the constraints
documented in
“Clock Period Constraints,” page 167
, apply.
However, if the FPGA Fabric Rx Elastic Buffer is selected, then an extra clock period
constraint of 16 ns is required for
rxrecclk
: with the GTX Rx Elastic Buffer bypassed,
rxrecclk
is provided by the GTX transceiver 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-5 FXT Devices for SGMII or
Dynamic Standards Switching,” page 105
for more information about this logic.
The following UCF syntax shows the necessary constraint being applied to the
rxrecclk
signal sourced from GTX 0.
#***********************************************************
# PCS/PMA Clock period Constraints for the GTP/X 0 *
# recovered clock: please do not relax *
#***********************************************************
NET "core_wrapper/rocketio/rxrecclk0" TNM_NET = "rxrecclk0";
TIMESPEC "ts_rxrecclk0" = PERIOD "rxrecclk0" 16 ns;
Setting GTX Transceiver Attributes
Additionally, if the FPGA Fabric Rx Elastic Buffer is selected, then the attributes of the
Virtex-5 GTX transceiver which are set directly from HDL source code do differ from the
standard case. These can be found in the
rocketio_wrapper_gtx_tile.vhd
file (for
VHDL design entry) or the
rocketio_wrapper_gtx_tile.v
file (for Verilog design
entry): these files were generated using the GTX RocketIO Wizard - to change the
attributes, re-run the Wizard. See
“Virtex-5 RocketIO GTX Wizard” in Chapter 8
.
Ten-Bit Interface Constraints
The constraints defined in this section are implemented in the UCF for the example
designs delivered with the core. Sections from this UCF have been copied into the
descriptions in this section to serve as examples, and should be studied with the HDL
source code for the example design. See also
Chapter 6, “The Ten-Bit Interface.”
