Does anyone ever meet the (SPECTRE-18) segmentation fault ?
I try to write a detector as follow to help me print the output data. and when i run the simulation in spretre, a fatal error:
"Encountered a critical error during simulation. Please run  `mmsipack" to pack the test case... FATAL(SPECTRE-18):Segmentation fault."
I found some explanation that the segmentation fault is due to the wrong usage of memory. but i am still confused in my case...

Andrew Beckett wrote on Mar 5^th, 2020, 6:54am:



Thank you Andrew, your advice is realy nice to me (as a newbie). and I will remember that.
in my testbench, i set the trans. simulation time to 800p, and set the parameter "peiod" to 10p; The input "data" is a square wave with a period of 10p;  
Code:

module datadet(data);
input data;
electrical data;
parameter real vh =1 from [0:inf);
parameter real vl = 0 from [0:inf);
parameter real vth = (vh+vl)/2;
parameter real start_time = 0 from [0:inf);
parameter real period = 10p from (0:inf);
integer cmp;
string data_flow,a;
analog begin
    @(initial_step)
	  data_flow="";
    @(timer(start_time, period)) begin
	  cmp = (V(data)>vth);
	  $sscanf(a,"%d",cmp);
	  data_flow = {data_flow,a};
	  $strobe("the data in %M is %s", data_flow);
    end
end
endmodule
 

I'd hypothesised that the problem was caused by repeatedly extending the string data_flow and this was triggering a bug in Spectre (a segmentation fault is a clear indication of a simulator bug - but of course it's triggered by something specific in the code).

From doing some debugging, I found that the issue is not with the string concatenation but the $sscanf. In fact you really don't want $sscanf here, because that would be parsing the string a, trying to find an integer within that, and putting the result in the integer variable cmp. Instead, you want to go the other way, so you should be using $swrite rather than $sscanf:

$swrite(a,"%d",cmp);

If you do that, the code runs with no problems. The crash is actually a problem if sscanf tries to parse an uninitialised string (if a is set to "" or "1" beforehand it runs without the crash, but then the code doesn't do what you want).

I filed a Cadence Change Request, 2233969, to get the crash fixed (because it makes it hard to diagnose the true problem, which is the incorrect function being used). Hopefully everything works for you with $swrite instead of $sscanf.

Regards,

Andrew.