The syntax of the set_bus_skew command with the basic options
is:
set_bus_skew [-from <args>] [-to <args>] [-through <args>] <value>The list of objects for the -from option should be a list of valid startpoints.
A valid startpoint for set_bus_skew is a
clock
pin of a sequential element, such as a register or a
RAM,
or the cell itself. An input (or inout) port is not supported by
set_bus_skew.
The list of nodes for the -to option should be a list of valid endpoints. A
valid endpoint for set_bus_skew is
a
data pin of a sequential
cell
or the cell itself. An output (or inout) port is not supported by
set_bus_skew.
The list of nodes for the -through option should be a list of valid
pins, or nets.
-from and
-to options must be specified when specifying a bus skew
constraint.The bus skew value must be realistic and reasonable. AMD recommends to use a value larger than half the minimum period of the source and destination clocks. The recommended value for the bus skew also depends on the CDC topology as illustrated by the following examples.