VLSI DV Interview Puzzles · All levels

type_option.auto_bin_max bin grouping

Find the denominator and percentage for a wide coverpoint constrained by type_option.auto_bin_max.

Puzzle

Difficulty: Medium · Puzzle 5 of 6 · Topic: Coverage Options Puzzles

Find the denominator and percentage for a wide coverpoint constrained by type_option.auto_bin_max.

Code

systemverilog

covergroup cg with function sample(bit [5:0] addr);
  cp_addr: coverpoint addr {
    type_option.auto_bin_max = 8;
  }
endgroup

initial begin
  cg c = new();
  c.sample(0);
  c.sample(7);
  c.sample(9);
  c.sample(17);
  c.sample(34);
end

Hint

6-bit space has 64 values. auto_bin_max=8 groups values into 8 bins.

Step-by-step solution

diagram

1) Denominator is 8 auto bins.
2) With roughly 8-value groups, samples map to groups: 0..7, 8..15, 16..23, 32..39.
3) Unique groups hit are four bins.
4) Coverage = 4/8 = 50%.

Answer

Answer: Scored bins = 8 and coverage = 50%.

Why candidates get it wrong

People sometimes still assume one bin per value and incorrectly report 5/64 instead of grouped-bin coverage.

Interviewer follow-up

Why might you prefer explicit semantic bins over auto grouping for signoff reviews?

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