Stratix V Device Handbook: Volume 2: Transceivers

ID 683779
Date 11/23/2021
Document Table of Contents

6.7. Dynamic Reconfiguration of Loopback Modes

You can enable the pre- and post-CDR reverse serial loopback modes by writing the appropriate bits of the Transceiver Reconfiguration Controller.

The following loopback paths are available:

  • Serial loopback path— The output from the serializer is fed back to the CDR. While in this mode, the serializer also feeds the data to the TX output port. Enabling or disabling serial loopback mode is done through the PHY management interface.
  • Post-CDR reverse serial loopback path— The RX captures the input data and feeds it into the CDR. The recovered data from the CDR output feeds into the TX driver and sends to the TX pins through the TX driver. For this path, the RX and CDR can be tested. For this path, the TX driver can be programmed to use either the main tap only or the main tap and the pre-emphasis first post-tap. Enabling or disabling the post-CDR reverse serial loopback modes is done through the PMA Analog Reconfiguration IP in the Transceiver Reconfiguration PHY IP.
  • Pre-CDR reverse serial loopback path— The RX captures the input data and feeds it back to the TX driver through a buffer. With this path, you can perform a quick check for the quality of the RX and TX buffers. Enabling or disabling the pre-CDR reverse serial loopback mode.
Note: Serial loopback can be implemented with the transceiver PHY IP directly using the Avalon interface or a control port.