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AR# 60855

PC-CFR v5.0 : Recommended usage of XDC constraint files for better timing closure.

Description

In order to obtain better timing closure with the PC-CFR v5.0 IP core, it is recommended to use the <ip_inst_name>.xdc  file during implementation.


Solution

The PC-CFR v5.0 IP core delivers two xdc files, <ip_inst_name>_ooc.xdc  and <ip_inst_name>.xdc.

The <ip_inst_name>_ooc.xdc  file is intended to be used only during synthesis with out of context mode.

In order to  obtain better timing closure with the PC-CFR v5.0 IP core, it is recommended to use the <ip_inst_name>.xdc  file during implementation.

BRAMs operate at the maximum frequency in WRITE_FIRST mode and this xdc file converts all BRAM primitives to WRITE_FIRST mode.

Specifically, this is done by the following lines:

set_property WRITE_MODE_A WRITE_FIRST [get_cells -hierarchical -filter { PRIMITIVE_TYPE =~ BMEM.bram.* || PRIMITIVE_TYPE =~ BLOCKRAM.BRAM.* } ]

set_property WRITE_MODE_B WRITE_FIRST [get_cells -hierarchical -filter { PRIMITIVE_TYPE =~ BMEM.bram.* || PRIMITIVE_TYPE =~ BLOCKRAM.BRAM.* } ]


The set_property commands can be applied only after synthesis (during implementation) when the BRAM primitives become accessible.

If used during synthesis, these commands result in a warning message as no cells would match the BRAM primitives.

After adding the <ip_inst_name>.xdc constraint file, follow the steps below to make it implementation only:

  • Right click on the <ip_inst_name>.xdc constraint file.
  • Click "Set Used In"
  • Ensure that the Implementation checkbox is selected & the Synthesis checkbox is unchecked.
AR# 60855
Date Created 05/27/2014
Last Updated 07/28/2014
Status Active
Type General Article
IP
  • Peak Cancellation Crest Factor Reduction (PC-CFR)