When opening a Synthesized or Implemented checkpoint in Vivado I sometimes see the following Critical Warning:
[Common 17-170] Unknown option '-default_probability', please type 'set_switching_activity -help' for usage info. ["/path_to_project/path_tst.srcs/constrs_2/imports/test/test.xdc":##]
I do not use this switch in my XDC file at the line number reported or anywhere else.
Why does this occur?
This is a known issue and has been fixed in Vivado 2014.4. When writing a DCP file out from the tools, the DCP will incorporate the designs XDC constraints. When converting the constraint referred to in the line number in the Critical Warning, it performs an incorrect switch mapping. The line in the XDC file reported is as follows:
set_switching_activity -default_static_probability 0.5
However, the corresponding line in the DCP XDC file is as follows:
set_switching_activity -default_probability 0.500
This mapping causes the tools to report the Critical Warning, however, this is safe to ignore as the power analysis of the checkpoint is not affected. This is because the original constraint in this case was set to the default value which can be seen by running "report_switching_activity" on the open DCP file.
default static probability = 0.5 However, if the original constraint was not set to the default of 0.5, then this would cause an issue when running power analysis on the checkpoint. It would be necessary to reapply the constraint directly on the open checkpoint as follows to work around this issue:
set_switching_activity -default_static_probability 0.25
After doing so, if report_switching_activity is re-written then it will report the newly set default. Power analysis can then be done.
default static probability = 0.25
Was this Answer Record helpful?