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AR# 64044

Vivado Synthesis - WARNING: [Synth 8-152] case item 2'bx1 overlaps with previous case item(s)

Description

Vivado Synthesis generates the following warning whenever there are case items which are getting overlapped with other listed case items.

WARNING: [Synth 8-152] case item 2'bx1 overlaps with previous case item(s)


Example of a code snippet:
 
module test (sel, din, dout);
output reg dout;
input [1:0] sel, din;
always @(*)
begin
dout = 0;    
(* parallel_case *) casex(sel) 
2'b1x : dout = din[0];
2'bx1 : dout = din[1];
endcase
end
endmodule

Solution

In the above code snippet, 2'b11 combination is present in 2'b1x as well as 2'bx1.

In order to avoid this particular warning, Ensure that you avoid overlapping case items.

This can be done similarly to the following example, by changing it to 2'b01 instead of 2'bx1:

module test (sel, din, dout);
output reg dout;
input [1:0] sel, din;
always @(*)
begin
dout = 0;    
(* parallel_case *) casex(sel) 
2'b1x : dout = din[0];
2'b01 : dout = din[1];
endcase
end
endmodule
AR# 64044
Date Created 03/25/2015
Last Updated 04/30/2015
Status Active
Type Known Issues
Tools
  • Vivado Design Suite