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AR# 57299

2013.3 Vivado - The set_external_delay command incorrectly propagates to the routed DCP for an mmcm IP synthesized out of context (OOC)


The following critical warning appears when opening an implemented design which has MMCM with clkfb_in:

[Common 17-163] Missing value for option 'from', please type 'set_external_delay -help' for usage info. ["C:/../mmcm_proj/project_2/project_2.srcs/sources_1/ip/mmcm_wrap_fix_5/mmcm_wrap_fix.xdc":58]
[Common 17-163] Missing value for option 'from', please type 'set_external_delay -help' for usage info. ["C:/../mmcm_proj/project_2/project_2.srcs/sources_1/ip/mmcm_wrap_fix_5/mmcm_wrap_fix.xdc":59]

The referenced lines in the message are in MMCM xdc.

set_external_delay -from [get_ports o_clkfb_out] -to [get_ports i_clkfb_in] -min 0.1 
set_external_delay -from [get_ports o_clkfb_out] -to [get_ports i_clkfb_in] -max 0.11


The constraints from the MMCM xdc file propagate and are included in routed DCP. However, in the DCP file the constraints lose the -from/-to (see below) and therefore, cause the warnings.

set_external_delay -min 0.100
set_external_delay -max 0.110

In Vivado Design Suite 2013.4, synthesis will ignore this constraint and leave it for implementation only. The set_external_delay is not supported by synthesis.

AR# 57299
Date Created 08/29/2013
Last Updated 12/16/2013
Status Active
Type Known Issues
  • Vivado Design Suite - 2013.2
  • Vivado Design Suite - 2013.3