Description

If targeting Spartan-6 devices with the Ethernet 1000BASE-X PCS/PMA or SGMII v11.3 in ISE 14.1 software, timing errors similar to the following might be seen when implementing the example design:

"Timing constraint: ts_tx_clk = PERIOD TIMEGRP "tx_logic" 8 ns HIGH 50%;
For more information, see Period Analysis in the Timing Closure User Guide (UG612).

3809 paths analyzed, 1863 endpoints analyzed, 49 failing endpoints
49 timing errors detected. (49 setup errors, 0 hold errors, 0 component switching limit errors)
Minimum period is 10.057ns."

Solution