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AR# 44521

XST - Severity Change for XST message "WARNING:HDLCompiler:1511" Beginning in ISE 13.3 Software

Description

The message "WARNING:HDLCompiler:1511" produced by Verific XST prior to 13.3 will change to "ERROR:HDLCompiler:1511" beginning with version 13.3 of XST for cases where both a blocking and non-blocking statement are used for a signal within an always block.

Solution

Example:

module top (d, clk, rst, q);
output q;
input d;
input clk,rst;
reg q;
always @(posedge clk)
begin
if (rst)
q <= 1'b0; // non-blocking statement
else
q = d; // blocking statement
end
endmodule
---

The Verific XST (prior to version 13.3) would have given the following warning message for the above piece of code:

WARNING:HDLCompiler:1511 - "top.v" Line 2: Mix of blocking and non-blocking assignments to variable <q> is not a recommended coding practice.

Starting from 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:1511 - "top.v" Line 2: Mix of blocking and non-blocking assignments to variable <q> is not a recommended coding practice.

In the above example,both a blocking statement and a non-blocking statement are used for the registered output signal q within an always block, which causes the compiler to error out with "HDLCompiler:1511."

AR# 44521
Date Created 10/13/2011
Last Updated 05/19/2012
Status Active
Type Error Message
Tools
  • ISE Design Suite - 13.3