GTS Transceiver PHY User Guide

ID 817660
Date 7/08/2024
Public
Document Table of Contents

2.5.1. FEC Loopback Mode

Both Firecode and RS-FEC support a loopback mode, offering various debugging options.
You can enable the FEC loopback mode parameter in the IP Parameter Editor GUI. When you enable the FEC loopback mode, the output of the TX FEC block is looped back to the RX FEC as shown in the following figure. For more information about enabling the FEC loopback mode refer to FEC Options. You can also enable the FEC loopback mode by configuring the fec_lpbk_en register (0x70000[1]).
Figure 20. FEC Loopback Mode
Note: The FEC loopback mode requires an additional step since the o_rx_is_lockedtodata signal is deasserted if the i_rx_serial_data is not toggling. This causes the hard IP blocks such as the TX/RX PMA Interface, PCS, FEC into a reset state and prevents any loopback in these digital blocks to function correctly. You must perform a write to the rx_ignore_lock2data register (0x10018 bit[0]) to override the RX PMA status signals (refer to RX PMA Status Signals table for more information) so that these hard IP blocks can come out of reset and the FEC loopback mode can function.