Coverage - SVA: The Power of Assertions in SystemVerilog - page 409

Example 18.6.

covergroup cover_delay @( posedge clk);
dl_pt: coverpoint delay {
bins delays [100]: {[10:110]};

}
dt_pt: coverpoint data;
dlXdt: cross dt_pt, dl_pt;
endgroup
cover_delay cover_delay_inst = new ();

t

The covergroup definition is named cover_delay .The covergroup tracks two
variables, delay and data . They are identified by using the keyword coverpoint
and by labeling them dl_pt and dt_pt , respectively. The variable values are
read whenever the clocking event @( posedge clk) occurs and are recorded into
individual bins according to their values.
For dl_pt , there is an array delays of 100 bins into which the occurrence counts
of values of delay in the range [10:110] are maintained. In other words, when the
recorded value of delay is 10 the bin delays[0] is incremented; if it is, say, 100
then the bin delays[90] is incremented; etc.
For dt_pt , the bins are allocated automatically. By default, there are at
most 64 bins, but that value can be changed by an optional specification
auto_bin_max=number of the covergroup . If the value range of the sampled
variable is less than the specified maximum, the number of bins is that of the
variable range. If the range is larger than the maximum, then the variable values are
uniformly distributed over the bins.
The cross correlation dlXdt of the values of delay and data is specified using
the keyword cross . This defines a set of pairs of values consisting of the Cartesian
product of the sets of bins of coverpoint sof dl_pt and dt_pt . In this way, the
user can observe the correlated pairs of values of data and delay that occurred
during the simulation.
The clocking event can be replaced by an interface definition of the sample
method as follows:

covergroup cover_delay
with function sample( int unsigned delay, logic [7:0] data);
In this case, the coverage is triggered when the method sample is called. The
actual arguments must be type-compatible with the formal arguments of the method.
Note that the formal argument names match exactly those of the coverpoint
variables delay and data . In this way, the same covergroup instance can read
different variables passed as actuals to instances of the sample function and collect
the coverage information in the same bins. Using the method is especially helpful
when new instances of the variables are created over and over, as in the example
in the following section where local variables are passed to a covergroup instance.
When no clocking event or sample method is explicitly specified, the default sample
method is available to trigger sampling of coverpoint variable values.