CDC / RDC · All levels
Async FIFO CDC: Comparison Matrix
Comparison Matrix for Async FIFO CDC.
Comparison matrix
FIFO, handshake, and pulse strategies trade throughput and complexity.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | safe | extra latency | high-risk crossings |
| Balanced | practical | more setup | most production paths |
| Aggressive | fast schedule | escape risk | late-stage crunch |
| Refactor | structural gain | long cycle | recurring failures |
+------------------+----------------+----------------+----------------+When to choose each approach
Select approach by silicon risk, not only schedule urgency
Interview traps
Global waiver spray
Unproven protocol assumptions
Evidence comparison
CDC/RDC EVIDENCE MATRIX — Async FIFO CDC
+-----------------------+----------------------------+----------------------------+---------------------------+
| Evidence | Tells you | Does not prove | Next action |
+-----------------------+----------------------------+----------------------------+---------------------------+
| structural report | crossing topology class | protocol liveness | add assertions/formal |
| reset map | release dependencies | dynamic startup behavior | run reset stress tests |
| formal proof | bounded safety/liveness | real firmware sequence | correlate with simulation |
| simulation stress | observed mode behavior | full state-space closure | target unhit corners |
| waiver log | accepted residual risk | technical correctness | periodic revalidation |
+-----------------------+----------------------------+----------------------------+---------------------------+CDC/RDC deep dive
Protocol correctness is the bridge between structural clean and functional safe.
Concept diagram
PROTOCOL FLOW
intent -> transport protocol -> synchronization -> destination acceptanceMetric graph
PROTOCOL ISSUE BURNDOWN
open issues: 20 -> 11 -> 5 -> 0Reports and artifacts
FIFO pointer proofs
req/ack liveness
pulse miss checks
protocol assertions
Mini case study
Async FIFO empty/full logic looked correct until gray decode mismatch appeared during reset overlap.
Debug branches
Pointer sync audit
formal liveness checks
reset interaction review
Senior review question
Ask: what evidence proves this risk is closed for silicon, not just tool-clean?
Key takeaways
State crossing class, assumptions, and owner with every issue.
Run structural and dynamic regressions after each fix.
Common pitfalls
Treating all warnings as equivalent risk.
Waiving issues without containment evidence.
Skipping reset and reconvergence stress after CDC fixes.
Principal CDC/RDC review addendum
Async FIFOs decouple domains with gray-coded pointers and synchronized status logic; correctness depends on pointer math, full/empty rules, and reset behavior.
Metric: overflow/underflow risk, pointer synchronization integrity, latency throughput