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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

  • Okay, I understand that the functional checks will not be performed for CDC paths that have failed structural checks but in this case there seems to be functionally unvalidated CDC paths which cleared structural checks, shouldn't these paths be validated for functional checks?
    The problem I'm facing is that even though there are a lot of CDC paths that cleared structural checks there seem to be no paths that are Put through functional checks, when I get the functional checks reports they contain all the paths, under which the different functional checks are reported with the phrase "Not validated" next to them, and the final validated data summary just mentions the path totals which are fine, and the path fails/passes which are both 0.

    Thanks, PS: yes I am using Conformal lec
Reply

  • Okay, I understand that the functional checks will not be performed for CDC paths that have failed structural checks but in this case there seems to be functionally unvalidated CDC paths which cleared structural checks, shouldn't these paths be validated for functional checks?
    The problem I'm facing is that even though there are a lot of CDC paths that cleared structural checks there seem to be no paths that are Put through functional checks, when I get the functional checks reports they contain all the paths, under which the different functional checks are reported with the phrase "Not validated" next to them, and the final validated data summary just mentions the path totals which are fine, and the path fails/passes which are both 0.

    Thanks, PS: yes I am using Conformal lec
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