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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

  • Hi Chrystian, Thanks for the quick reply,
    When you say "enabled" do you mean added , as I added the CDC structural checks, validated them and only then did I add the functional checks with the following command;
    add cdc check -functional... (and then reported them)
    If this is not enough to enable functional checks would you please tell me about the functional checks flow. Also when you mean structural checks cleaned up, does it mean that until I get zero path failures on structural checks I cannot perform functional checks or will functional checks be performed on the CDC paths that passed the structural checks and failed CDC paths ignored. Thanks,

Reply

  • Hi Chrystian, Thanks for the quick reply,
    When you say "enabled" do you mean added , as I added the CDC structural checks, validated them and only then did I add the functional checks with the following command;
    add cdc check -functional... (and then reported them)
    If this is not enough to enable functional checks would you please tell me about the functional checks flow. Also when you mean structural checks cleaned up, does it mean that until I get zero path failures on structural checks I cannot perform functional checks or will functional checks be performed on the CDC paths that passed the structural checks and failed CDC paths ignored. Thanks,

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