Altera SDC and TimeQuest API - Manual (Page 38)

2–28 Chapter 2: SDC and TimeQuest API Package and Commands
sdc
SDC and TimeQuest API Reference Manual © December 2009 Altera Corporation
set_clock_uncertainty
Usage
set_clock_uncertainty [-add] [-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>
Options
-add: Specifies that this assignment is an addition to the clock uncertainty derived by
derive_clock_uncertainty call
-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: Specifies the uncertainty value (applies to clock hold or 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: Specifies the uncertainty value (applies to clock setup or recovery checks)
(default)
-to <to_clock>: Valid destinations (string patterns are matched using Tcl string
matching)
<uncertainty>: Uncertainty
Description
Specifies clock uncertainty or skew for clocks or clock-to-clock transfers. You can specify uncertainty
separately for setup and hold, and can specify separate rising and falling clock 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.
The values for the -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 TimeQuest-extension
substitution rules. See the help for use_timequest_style_escaping for details.
When -add option is used, clock uncertainty assignment is treated as an addition to the value calculted by
derive_clock_uncertainty command for a particular clock transfer. Note that when -add option is not used
and derive_clock_uncertainty is called, user specified clock uncertainty assignment will take priority.
When derive_clock_uncertainty command is not used, specifying -add option to set_clock_uncertainty
command will not have any effect.
Example
set_clock_uncertainty -setup -rise_from clk1 -fall_to clk2 200ps