Low Phase Drift Calibration is a new feature added in release v6.0 that improves phase stability between WR switch restarts to <10ps. Due to FPGA limitations this functionality is present only on ports 1-12. The LPDC requires an additional, automated calibration procedure to run for Tx and Rx path of each affected FPGA transceiver. The Tx calibration is performed once for all ports at startup of the WR switch. The Rx calibration is performed each time a link goes up on a port. Both Tx and Rx calibration is indicated by blinking of Link/WR Mode LED (left). The downside is that the calibration makes startup of the WR switch longer. Similarly, the time between connecting a fiber and the link going up (e.g. as observed in wr_mon) is noticeably longer.