Streamlining DO-254 Compliance: The Power Of Automated Clock-Domain Crossing Verification

In the realm of safety-critical electronic hardware, particularly those governed by DO-254 compliance directives, ensuring design integrity is paramount. One of the most insidious challenges designers face is clock-domain crossing (CDC) violations. When data moves between asynchronous clock domains, it can lead to metastability issues, causing unpredictable behavior, data loss or corruption, and even catastrophic system failures. Traditional verification methods often fall short, leaving critical bugs undetected until the hardware is deployed in the field.

Fig. 1: Potential CDC errors.

This is where automated solutions like Questa CDC become indispensable. Providing comprehensive CDC verification, Questa CDC bridges the knowledge gap between design and verification teams, offering a robust approach to prevent these complex problems in DO-254 projects and other safety-critical designs.

The unseen threat: Why manual CDC verification falls short

Manual CDC verification is notoriously difficult and prone to error. Designers might miss signals crossing domains, choose inappropriate synchronization schemes, or incorrectly implement synchronizers. Even meticulous code reviews often fail to uncover reconvergence issues — one of the more dangerous types of CDC problems. These issues are highly data-dependent and may only manifest in rare, specific corner cases, making them nearly impossible to catch without targeted analysis.

Furthermore, changes introduced during the implementation process, such as logic optimization or DFT logic, can inadvertently create new CDC paths or introduce glitches on existing ones. Such problems will be bypassed by standard RTL verification.

Fig. 2: Synthesis introduces glitches on CDC paths.

A comprehensive solution for robust designs

A truly comprehensive CDC verification solution, Questa CDC goes beyond basic checks to ensure the highest level of design assurance. It performs four distinct and crucial functions:

1. Structural Analysis: Questa CDC performs a thorough analysis of the RTL code to identify all signals crossing clock domains. It then determines if synchronization structures are present and correctly implemented for each path.
2. Verification of Transfer Protocols: Beyond just identifying synchronizers, the tool monitors and verifies that the synchronization structures are being used correctly, ensuring that established protocols are followed through simulation or formal analysis.
3. Global Reconvergence Checking: This is a critical capability, as reconvergence issues are particularly challenging to detect manually. Questa CDC globally checks for reconvergence, preventing situations where synchronized signals combine in downstream logic to create unexpected and erroneous behavior.
4. Identification of Glitchy Logic: The tool can identify glitchy logic introduced during synthesis or other implementation steps, ensuring that these anomalies do not compromise CDC paths.

Real-world impact

The value of Questa CDC is best illustrated by its impact on real-world projects. Companies developing safety-critical systems have discovered critical CDC bugs that would have been costly and potentially catastrophic if left undetected.

For instance, one company discovered over 60 errors using Questa CDC, some of which were deemed critical. This led to a company-wide mandate: a clean Questa CDC run is a prerequisite for releasing any design block.

In another engagement, a military space systems maker, having previously suffered from CDC bugs, used Questa CDC to uncover a real bug involving multiple independently synchronized signals feeding next-state logic — a problem that management recognized would have otherwise jeopardized the safe operation of their systems.

As one engineer noted, “The Questa CDC tool does a fantastic job identifying CDC violations and helps us eliminate these potential problems long before we enter the lab. This has long been a difficult design problem, but now we finally have a tool that can formally prove that our designs are completely free of hidden CDC issues.”

Integrating Questa CDC into your DO-254 workflow

While DO-254 does not explicitly mandate CDC verification (a reflection of its origins before multi-clock designs were prevalent), it strongly advocates thorough verification and design assurance. Questa CDC provides that added assurance, helping designs function correctly within their intended systems — a core intent of DO-254.

For projects with specific customer requirements to verify CDC paths, Questa CDC can be used to formally qualify them. Even without an explicit mandate, running Questa CDC significantly enhances the reliability of multi-clock, safety-critical designs and minimizes the risk of costly late-stage bugs.

Unlock the full details

For a deeper dive into the intricacies of clock-domain crossing verification, the challenges it presents, and how Questa CDC provides an unparalleled solution for DO-254 and other safety-critical designs, we encourage you to read the full whitepaper: Automating clock-domain crossing verification for DO-254 (and other safety-critical) designs.