Data stable for maximum 40 clocks

SystemVerilog
1

I try to write an assertion with this request:
when enable fell,
data should be stable for maximum 40 clocks.
[*40] - is at least 40…
how can I do the maximum?

Thanks!

2

That would be same as saying data must change within 40 cycles.

$fell(enable) |-> ##[1:40] $changed(data);
3

Thank you.
it works to me when I wrote this code using $past, when use $changed it is not seem well, the assertion finish before data change:

image
image1785×274 13.8 KB

Should I write with $changed in other way?

Thanks

4

$fell(enable) |->
##[1:40] $stable(data) ##1 $changed(data);

5

$changed(v) is defined as ($past(v) !== v). That means $change to/from an unknown is true.

6

So it better using $changed(), because in this way it not fail when data going from X to valid value, Yes?

thank a lot.