keep Verilog HDL Synthesis Attribute

A Verilog HDL synthesis attribute that directs Analysis & Synthesis to keep a particular wire intact. You can use this synthesis attribute to keep a combinational node so you can observe the node during simulation or with the Signal Tap Logic Analyzer.

Note: Analysis & Synthesis also recognizes the synonymous synthesis attribute syn_keep. This synthesis attribute behaves identically to the keep synthesis attribute.

You cannot use this synthesis attribute for nodes that have no fan-out.

To use the keep synthesis attribute, you can specify the keep synthesis attribute in a comment that is on the same line as the combinational node you want Analysis & Synthesis to keep. In the comment, precede the synthesis attribute with the synthesis keyword.

For example, in the following code, the comment /* synthesis keep */ directs Analysis & Synthesis to not minimize the keep_wire combinational node:


wire keep_wire /* synthesis keep */;