The Worst FPGA Design I've Ever Seen

Why It Matters

Without proper clock‑domain crossing, FPGA designs become unreliable, risking costly failures in critical systems such as defense hardware.

Key Takeaways

• Multiple clock domains lacked proper synchronization mechanisms in design.
• No timing constraints between domains caused nondeterministic behavior.
• Design produced inconsistent display output across builds, showing white noise.
• Engineer repeatedly rebuilt FPGA instead of fixing clock‑domain crossing.
• Robust CDC requires FIFOs, handshakes, or synchronizers, not ad‑hoc wiring.

Summary

The video recounts a notorious FPGA project where two independent clock domains exchanged data without any proper clock‑domain crossing (CDC) strategy. Each domain had its own frequency constraints, yet the design omitted any timing relationship or synchronizer between them, violating basic digital design principles.

Because the CDC was unmanaged, the FPGA behaved unpredictably: some builds displayed a clean image while others produced white‑noise artifacts. The engineer in charge simply rebuilt and re‑programmed the device each time it failed, treating the symptom as a one‑off issue rather than addressing the root cause. The problem persisted despite being at a defense contractor, highlighting that even high‑stakes environments can suffer from elementary design oversights.

The speaker emphasizes that the solution required a complete rewrite of the data‑exchange logic, employing proven CDC techniques such as dual‑clock FIFOs, handshaking protocols, or multi‑stage synchronizers. The anecdote serves as a cautionary tale about relying on ad‑hoc wiring and neglecting timing analysis.

The broader implication is clear: robust CDC is non‑negotiable for reliable FPGA operation, especially in mission‑critical applications. Ignoring it leads to nondeterministic performance, costly rework, and potential system failures, underscoring the need for disciplined design practices.

Original Description

seriously, pay attention to clock domain crossings