The syntax of the
set_bus_skew command with the basic options
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, or the clock pin of a
sequential element, such as a register or a RAM. An input (or inout) port is not
The list of nodes for the -to option should be a list of valid endpoints. A valid
set_bus_skew is a clock, or the data pin of a
sequential cell. An output (or inout) port is not supported by
The list of nodes for the
-through option should be a list of valid
pins, or nets.
-to command line options can
refer to clocks, Xilinx recommends that you be more specific and specify a limited
list of startpoints and endpoints per constraint. This will ensure that not too many
paths get covered by each constraint and that each constraint can be reasonably
-tooptions must be specified when specifying a bus skew constraint.
The bus skew value must be realistic and reasonable. Xilinx 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.