Most UVM testbenches fail coverage closure for one reason nobody talks about — and it's not your constraints.

After reviewing 20+ verification projects, I see the same pattern:

5 well-written sequences
All of them exercising the “happy path”
Corner cases added as an afterthought at week 8
By then, coverage holes require surgical constrained-random surgery that takes 2x as long as getting it right in week 1.

The fix is boring but it works:

Before you write a single line of driver code, define your sequence taxonomy:

baseline_seq — protocol-compliant, valid stimulus
stress_seq — back-to-back transactions, max burst length
error_inject_seq — bad addr, illegal burst, protocol violations
mixed_seq — interleaved read/write with randomized gaps
Map each to a functional coverage bin. If your sequence can’t hit a bin, the sequence is incomplete — not your coverage model.

This one habit saves 3–4 weeks of closure pain at tape-out.

Hashtags: #SystemVerilog #UVM #HardwareVerification #ASIC #ChipDesign #EDA