Syntax of the set_bus_skew Command - 2023.2 English

Vivado Design Suite User Guide: Using Constraints (UG903)

Document ID
UG903
Release Date
2023-11-01
Version
2023.2 English

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.

Note: Both the -from and -to options must be specified when specifying a bus skew constraint.
Note: AMD recommends setting a bus skew constraint on paths with a fanout of 1 (single load). Also, each bus skew constraint must cover at least two startpoints and two endpoints.

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.