Intel® Quartus® Prime Pro Edition User Guide: Scripting

ID 683432
Date 10/04/2021
Public

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3.1.27.22. set_clock_uncertainty (::quartus::sdc)

The following table displays information for the set_clock_uncertainty Tcl command:

Tcl Package and Version

Belongs to ::quartus::sdc

Syntax set_clock_uncertainty [-h | -help] [-long_help] [-add] [-enable_same_physical_edge] [-fall_from <fall_from_clock> ] [-fall_to <fall_to_clock> ] [-from <from_clock> ] [-hold] [-rise_from <rise_from_clock> ] [-rise_to <rise_to_clock> ] [-setup] [-to <to_clock> ] <uncertainty>
Arguments -h | -help Short help
-long_help Long help with examples and possible return values
-add Specifies that this assignment is an addition to the clock uncertainty derived by derive_clock_uncertainty call
-enable_same_physical_edge Enable setting uncertainty value for same physical clock edge
-fall_from <fall_from_clock> Valid destinations (string patterns are matched using Tcl string matching)
-fall_to <fall_to_clock> Valid destinations (string patterns are matched using Tcl string matching)
-from <from_clock> Valid destinations (string patterns are matched using Tcl string matching)
-hold Only apply the uncertainty value to hold and removal checks
-rise_from <rise_from_clock> Valid destinations (string patterns are matched using Tcl string matching)
-rise_to <rise_to_clock> Valid destinations (string patterns are matched using Tcl string matching)
-setup Only apply the uncertainty value to setup and recovery checks
-to <to_clock> Valid destinations (string patterns are matched using Tcl string matching)
<uncertainty> Uncertainty
Description

Specifies clock uncertainty or skew for clocks for clock-to-clock transfers. You can specify uncertainty separately for setup and hold, and you can specify separate rising and falling clock transitions. If you omit to specify -setup or -hold, the uncertainty value will be applied to both analysis types. Similarly, if you omit to specify rising or falling clock transitions, the uncertainty value will be applied to both transitions. The setup uncertainty is subtracted from the data required time for each applicable path, and the hold uncertainty is added to the data required time for each applicable path. Intel Quartus Prime software computes clock uncertainty for every clock transfer. For particular transfers, you can use the set_clock_uncertainty assignment to override the automatically derived value, or you can specify the -add option to add to the automatically derived value. Note that the -add option is only relative to the automatically derived value. If multiple set_clock_uncertainty assignments apply to the same clock transfer, the later value overrides the earlier ones, regardless of whether the -add option was used. Note: The Timing Analyzer does not apply clock uncertainty to transfers involving the same physical launch and latch edge (that is, the latch and launch edges are the same edge of a clock source and occur at the same time) by default. Such transfers typically occur in hold analysis, but may also occur in setup analysis with a multicycle value of 0. You can use the -enable_same_physical_edge option to override this behavior. The values for -from, -to, and similar options are either collections or a Tcl list of wildcards used to create collections of appropriate types. The values used must follow standard Tcl or Timing Analyzer-extension substitution rules. See the help for use_timing_analyzer_style_escaping for details.

Example Usage
set_clock_uncertainty -setup -rise_from clk1 -fall_to clk2 200ps
Return Value Code Name Code String Return
TCL_OK 0 INFO: Operation successful

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