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AR# 14546

6.1i XST - "WARNING:Xst:646 - Signal <signal_name> is assigned but never used." Is the alias construct supported?


Keywords: XST, VHDL, alias, construct, support

Urgency: Standard

General Description:
When I use the alias construct, a number of the following errors are reported:

"WARNING:Xst:646 - Signal <signal_name> is assigned but never used."
"XST 524: All outputs of the instance <instance_name> of the block <module_name> are unconnected in block <block_name>."


The alias construct is not fully supported in XST; the following alias constructs are not supported:

- An alias of an alias
- An alias declaration without subtype_indication
- Signatures on alias declarations
- An operator symbol as alias_designator
- An alias of an operator symbol
- Character literals as alias designators
- An alias to user-defined functions

Some issues with the alias construct are fixed in the latest 5.2i Service Pack available at:
The first service pack containing the fix is 5.2i Service Pack 2.
AR# 14546
Date Created 04/23/2002
Last Updated 10/20/2005
Status Archive
Type General Article