VIP & Agent Architecture: Interview Drills

PROMPT
You see stimulus coverage, monitor mismatch rate, illegal sequence detection on VIP & Agent Architecture. Walk through root cause and fix.

STRONG ANSWER
1. Names the layer and transaction identity.
2. Explains VIP separates driver, monitor, sequencer, checker, and coverage so protocol intent is observable and reusable.
3. Requests UVM agent diagram, monitor transaction log, checker failure.
4. Proposes one reduced sequence and one system regression.

WEAK ANSWER
Jumps to widening the interface, increasing FIFO depth, or blaming firmware without evidence.

PROTOCOL AGENT

  sequencer --> driver --> [ DUT pins ]
                              |
  monitor <-------------------+
     |
     +--> scoreboard (expected vs actual)
     +--> coverage   (which scenarios were hit)

Active agent drives; passive agent only observes (for system reuse).

ROOT-CAUSE TREE — VIP & Agent Architecture

stimulus coverage, monitor mismatch rate, illegal sequence detection looks wrong
        |
   reproducible?
     /        \
   no          yes
   |            |
 flaky env   same first transaction every time?
 / seed         /            \
              yes             no
               |               |
        protocol rule     timing/reset/PVT
        or config bug     or load-dependent

VERIFICATION CLOSURE LOOP

spec clause -> test -> assertion -> coverage -> waiver -> signoff
                  ^                           |
                  +--------- gap found --------+

COVERAGE vs ESCAPE RATE

escapes
  |*
  | *
  |  *
  |   **  <- knee: more random helps
  |     ****
  +----------------> constrained-random depth