General Description:
When running PAR on a Virtex-4 design containing MGTs, PAR might error out due to unfeasible MGT nets routing.
For MGT resources to be placed and routed correctly, the MGT instance, the GT11CLK instance, and the MGTCLK input pads have to be explicitly LOC'd.
BUFG's connected to the MGTCLK pins have to also be explicitly LOC'd.
Example - 4Vfx60 FF1152 - Locking down the MGTCLK pins, MGT, and GT11CLK instances in a UCF file.
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#Begin Example UCF file - Please consult current Virtex4 MGT User Guide and Virtex4 data sheet for placement information
# Lock down the REFCLK pins:
NET "MGTCLKN_IN" LOC = "AP28" ;
NET "MGTCLKP_IN" LOC = "AP29" ;
# Lock down the MGT:
INST "INST_GT11" LOC = GT11_X0Y2;
# Lock down the GT11CLK
INST "INST_GT11CLK_MGT" LOC = GT11CLK_X0Y1;
#Lock down the BUFG
# Note that in all BUFG primitives, the location constraint is the same
# BUFG
INST "INST_BUFG" LOC = BUFGCTRL_X0Y1;
# BUFGCTRL
INST "INST_BUFGCTRL" LOC = BUFGCTRL_X0Y2;
# BUFGCE
INST "INST_BUFGCE" LOC = BUFGCTRL_X0Y3;
#End Example UCF file
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