Difficulty: Medium · Puzzle 1 of 6 · Topic: Cross Coverage Puzzles
How many cross bins are actually scored, and what is final cross coverage?
covergroup cg with function sample(bit [2:0] len, bit [1:0] burst);
cp_len: coverpoint len {
bins short = {[0:3]};
bins long = {[4:5]};
bins xlong = {[6:7]};
}
cp_burst: coverpoint burst {
bins incr = {0};
bins wrap = {1};
bins fixed = {2};
}
x_len_burst: cross cp_len, cp_burst {
bins smoke = binsof(cp_len.short) && binsof(cp_burst.incr);
bins stress = binsof(cp_len) intersect {[6:7]} && binsof(cp_burst.wrap);
ignore_bins everything_else = default;
}
endgroup
initial begin
cg c = new();
c.sample(1,0);
c.sample(7,1);
c.sample(5,2);
enddefault ignore removes all unnamed auto cross tuples from scoring.
1) Scored bins are only smoke and stress -> denominator 2.
2) sample(1,0) hits smoke.
3) sample(7,1) hits stress.
4) sample(5,2) falls in ignored default space.
5) Cross coverage = 2/2 = 100%.Answer: Scored cross bins = 2 and final cross coverage = 100%.
Without checking default ignore, engineers often assume a full 3x3 cross denominator of 9 bins.
If ignore_bins everything_else is removed, what would coverage be with the same three samples?