Question

By default, a value or transition bin definition can specify 4-state values. When a bin definition includes an X or Z, it indicates that the bin count should only be incremented when the sampled value has an X or Z in the same bit positions, i.e., the comparison is done using ===. The wildcard bins definition causes all X, Z, or ? to be treated as wildcards for 0 or 1 (similar to the =?= operator). For example:

wildcard bins g12_16 = { 4’b11?? };

The count of bin g12_16 is incremented when the sampled variable is between 12 and 16:

1100 1101 1110 1111

Similarly, transition bins can define wildcard bins. For example:

wildcard bins T0_3 = (2’b0x => 2’b1x);

The count of transition bin T0_3 is incremented for the following transitions (as if by (0,1=>2,3)):

00 => 10 00 => 11 01 => 10 01 => 11

A wildcard bin definition only consider 2-state values; sampled values containing X or Z are excluded. Thus, the range of values covered by a wildcard bin is established by replacing every wildcard digit by 0 to compute the low bound and 1 to compute the high bound.