module top(input sel, d0, d1, output reg out);
1'b0: out = d0;
1'b1: out = d1;
The Verific XST (prior to the version 13.3 software) would have given the following warning message for the above piece of code:
WARNING:HDLCompiler:1419 - "top.v" Line 9: Case statement with no case item violates IEEE 1800 syntax
Beginning with the version 13.3 of XST, this warning is modified to an error without any change to the actual information or message as follows:
ERROR:HDLCompiler:1419 - "top.v" Line 9: Case statement with no case item violates IEEE 1800 syntax
In the above example, because all ofthe case items are commented out from the case statement, it leaves the case statement empty, which violates the IEEE 1800 syntax. Therefore, it is to your benefit to avoid using an empty case statement.