Altera SDC and TimeQuest API - Manual (Page 66)

2–56 Chapter 2: SDC and TimeQuest API Package and Commands
sdc_ext
SDC and TimeQuest API Reference Manual © December 2009 Altera Corporation
set_active_clocks
Usage
set_active_clocks <clocks>
Options
<clocks>: List or collection of clocks
Description
Sets the list of active clocks for timing analysis. All other clocks not in the list or collection are considered
inactive.
Timing analysis is only performed on active clocks. All clocks are active by default. Generated clocks that
are generated from inactive clocks are considered inactive. Therefore, to make a generated clock active,
specify both the parent and generated clock when calling set_active_clocks.
To reset all clocks to active, call "set_active_clocks *" or "set_active_clocks [all_clocks]".
set_active_clocks does not affect all reports. For example, inactive clocks are still reported by
report_clocks, report_clock_transfers, and similar commands.
Example
# Only analyze clk1
set_active_clocks [get_clocks clk1]
# Only analyze clk2
set_active_clocks [get_clocks clk2]
# Analyze all clocks
set_active_clocks [all_clocks]