set_clock_groups (::quartus::sdc)

Belongs to ::quartus::sdc 1.5

Clock groups provide a quick and convenient way to specify which
clocks are not related.  Asynchronous clocks are those that are
completely unrelated (e.g., have different ideal clock sources).
Logically exclusive clocks are not actively used in the design at
the same time (e.g., multiplexed clocks), but the clock signals may
physically exist on-chip at the same time and therefore may still
influence each other through crosstalk effects.  Physically exclusive
clocks, in contrast, cannot be physically present in the device at
the same time (e.g., multiple clocks defined on the same clock pin).

TimeQuest does not currently analyze crosstalk explicitly.  Instead,
the timing models use extra guard bands to account for any potential
crosstalk-induced delays.  As a result, TimeQuest currently treats
asynchronous, logically_exclusive, and physically_exclusive clock
groups the same.

The result of set_clock_groups is that all clocks in any group are cut
from all clocks in every other group.  This command is equivalent to
calling set_false_path from each clock in every group to each clock in
every other group and vice versa, making set_clock_groups easier to
specify for cutting clock domains.  The use of a single -group option
tells TimeQuest to cut this group of clocks from all other clocks in
the design, including clocks that are created in the future.

project_open top
create_timing_netlist
create_clock -period 10.000 -name clkA [get_ports sysclk[0]]
create_clock -period 10.000 -name clkB [get_ports sysclk[1]]

# Set clkA and clkB to be mutually exclusive clocks.
set_clock_groups -logically_exclusive -group {clkA} -group {clkB}

# The previous line is equivalent to the following two commands.
set_false_path -from [get_clocks clkA] -to [get_clocks clkB]
set_false_path -from [get_clocks clkB] -to [get_clocks clkA]