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CDC functional checks are not validated for design.

vaizguy

Hello everyone, I was recently required to perform both structural CDC checks and functional CDC checks on a design but when I go through the reports I noticed that the structural checks are performed fine but the functional reports simply say that the paths are not validated. I would like to know why these functional checks aren't being performed as there are no warnings in the log indicating why. Even the GUI has a question mark next to the functional checks tab. while the structural checks has a green/red dot next to it indicating pass/fail resp.

The tool is unable to detect direct bus synchronization instances like the following example and I was hoping that performing functional checks especially the single_bit_change check would highlight all such paths.

Eg.
input [3:0] A; // In clkA domain.
reg [3:0] B_r;
output reg [3:0] B_rr; // In clkB domain.

always @(posedge clkB) begin
  B_r <= A;
  B_rr <= B_r; // This is fine when A is a single bit.
end

Thanks in advance.

Parents

  •  Thanks for the example Clay, I was missing the validate statement after adding the functional checks, the problem was solved on adding the statement. I had removed it due to an error i was getting ealier with Clock analysis failure but now the flow seems to work just fine.

     

    Thanks again.

    Regards,

Reply

  •  Thanks for the example Clay, I was missing the validate statement after adding the functional checks, the problem was solved on adding the statement. I had removed it due to an error i was getting ealier with Clock analysis failure but now the flow seems to work just fine.

     

    Thanks again.

    Regards,

Children
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