Intel® Cyclone® 10 GX Transceiver PHY User Guide

ID 683054
Date 4/14/2023
Document Table of Contents

4.7. Timing Constraints for Bonded PCS and PMA Channels

For designs that use TX PMA and PCS Bonding, the digital reset signal (tx_digitalreset) to all TX channels within a bonded group must meet a maximum skew tolerance imposed by physical routing. This skew tolerance is one-half the TX parallel clock cycle (tx_clkout). This requirement is not necessary for TX PMA Bonding or for RX PCS channels.
Note: If the design is not able to meet the maximum skew tolerance requirement with a positive margin, Intel® recommends reassigning the channels’ locations that are not adjacent to the PCIe Hard IP block.
Figure 166. Physical Routing Delay Skew in Bonded Channels

You must provide a Synopsys Design Constraint (SDC) for the reset signals to guarantee that your design meets timing requirements. The Quartus Prime software generates an .sdc file when you generate the Transceiver Native PHY IP core.

This .sdc contains basic false paths for most asynchronous signals, including resets. In the case of bonded designs, this file contains examples for maximum skew on bonded designs. This .sdc file contains an example false_path and an example max_skew constraint for the tx_digitalreset signals.

All modified IP constraints from a generated .sdc file must be moved to the project’s main .sdc file, because changes are lost if the IP is regenerated.

This skew is present whether you tie all tx_digitalresets together, or you control them separately. If your design includes the Transceiver PHY Reset Controller IP core, you can substitute your instance and interface names for the generic names shown in the example.

SDC Constraint for TX Digital Reset When Bonded Clocks Are Used

set_max_skew -from *<IP_INSTANCE_NAME> *tx_digitalreset*r_reset 
-to *pld_pcs_interface* <1/2 coreclk period in ps>

In the above example, you must make the following substitutions:

  • <IP_INSTANCE_NAME>—substitute the name of your reset controller IP instance or PHY IP instance
  • <½ coreclk period in ps>—substitute half of the clock period of your design in picoseconds

If your design has custom reset logic, replace the *<IP_INSTANCE_NAME>*tx_digitalreset*r_reset with the source register for the TX PCS reset signal, tx_digitalreset.

For more information about the set_max_skew constraint, refer to the SDC and Timing Analyzer API Reference Manual.