How to Enhance Traceability for Semiconductor Design

Key takeaways:

• Ensuring integrated circuit (IC) design traceability can eliminate potential risks introduced by technical, organizational, and supply chain complexities.
• Since most modern ICs are assemblies of heterogeneous intellectual property (IP) blocks, IP management software with built-in traceability capabilities provides a compelling solution for enhancing design performance and quality.
• IC design traceability is crucial in meeting functional safety standards of mission-critical applications for automotive and aerospace.

Designing integrated circuits (ICs) is a long and complex process that can stretch into years for complex chips in the automotive, defense, aerospace, and semiconductor industries. It requires collaboration across hundreds of designers from distributed teams. During this time, design requirements may change. Employees who designed key elements may quit or retire.

Through all this, how can a semiconductor design company ensure that all the requirements, change requests, and design decisions over the years become part of its organizational memory? If catastrophic failures of a car or airplane model are traced to an IC designed and released a decade ago, how can its manufacturer identify and correct the fault? How can it prove that it had taken all reasonable safety precautions a decade ago?

These are the kinds of real-life problems that emphasize the importance of design traceability. This article gives an overview of IC design traceability, essential practices, and useful tools to simplify it.

What is IC design traceability?

IC design traceability is a process property that ensures every design decision and change is:

• systematically recorded and documented over the entire product lifecycle
• traceable to the original requirement or subsequent change request that led to the decision or change

The traceability must be end to end, from the requirements stage till the final decommissioning of the device, including all the intermediate stages, releases, and design iterations. Traceability must also be possible in both forward and backward directions through the stages. This means every decision or change must be traceable from any stage to any other stage among the following:

• requirements gathering
• system specifications
• system architecture and design
• subsystem and module design
• implementation using electronic design automation (EDA) tools
• unit testing
• integration testing
• system testing
• acceptance testing
• device and associated software releases
• multiple iterations of the above stages after each change request
• final decommissioning

These stages are shown below as V-model illustrations of the semiconductor design process. The illustrations emphasize that traceability is required both along the V and across the V.

The two-way arrows along the V below imply that traceability must be possible in either direction from any stage.

Fig 1. Traceability along the V-model of the IC design process in both directions

The two-way arrows across the V emphasize mutual traceability between each pre-implementation stage and its corresponding post-implementation stage.

Fig 2. Traceability across the V-model of the IC design process

Why is IC design traceability necessary?

Traceability addresses the problems created by these three aspects of IC design:

1. Technical complexities
2. Organizational complexities
3. Supply chain complexities

Technical complexities

A modern IC, like a smartphone system-on-chip (SoC), is a complex device consisting of dozens of intellectual property (IP) blocks (like digital interface, analog radio frequency, camera controller, and more). Since each subsystem has unique requirements, design challenges, and verification steps, the process has inherent technical complexities.

Each IP block encapsulates a reusable set of functionalities and associated circuitry. These blocks are present in a hierarchy of dependencies with more complex IP blocks relying on simpler IP blocks. Many IP blocks are shared by multiple projects in the organization. Due to these dependencies, a small design change in a common lower-level IP block impacts all the higher-level IP blocks and devices that depend on it across various projects.

Traceability provides control over this technical complexity by identifying all these dependencies, systematically tracking changes at all levels, and notifying all affected stakeholders. Traceability also promotes automated verification suites that run whenever there's a change anywhere in the hierarchy.

Organizational complexities

Due to acquisitions or investments, teams in the semiconductor industry are often distributed across the world with each team specializing in a different aspect of IC design. They may be using different tools and workflows that are incompatible and add technical complexity. Such organizational problems prevent the efficient exchange of critical information between design stages and can result in subtle problems and incompatibilities in the design.

Traceability alleviates these issues by insisting on strong connections between design stages regardless of organizational aspects. Companies are forced to set up collaboration and shared data platforms that facilitate strong traceability.

Supply chain complexities

Another plane of complexity is introduced by semiconductor supply chain practices. Many device companies nowadays are pure integrators. They may outsource some or all subsystem designs to more specialized companies and then integrate those finished designs into a very large-scale integration (VLSI) device like an SoC. Some are fabless and outsource manufacturing to third-party foundries. Others are integrated device manufacturers that handle both design and manufacturing.

In such supply chains with many companies, communication between teams across different companies can be poor and infrequent.

Traceability addresses this aspect by again insisting on strong connections between design stages regardless of organizational boundaries. These supply chains are forced to set up shared collaboration and data exchange problems that facilitate strong traceability.

What are the benefits of strong IC design traceability?

Fig 3. Keysight HUB's IP catalog browser

Strong IC design traceability brings several benefits for semiconductor products and teams. They include:

• Inherent consistency: Traceability aims for strong consistency between requirements, specifications, implementation, and verification at all times. This automatically avoids the incompatibilities and misunderstandings that are common in the design process.
• Cross-team Organizational Memory: It facilitates a deep understanding of all aspects of the design across teams and over time. Engineers can discover the thinking behind past design decisions, making it easier to change a design.
• Streamlined fault analysis: Related to the previous point, traceability facilitates fault identification and root cause analyses.
• Efficient change management and impact analysis: Because traceability leaves few unknowns, engineers can be confident about changing the design without worrying about introducing invisible faults that may cause major failures down the line. Traceability itself identifies all the impacted teams and projects without anyone having to analyze such impacts manually.
• Greater design reuse: Traceability facilitates the reuse of existing IC designs. This has long-term reliability and cost benefits.
• Improved functional safety: IC design traceability increases the functional safety of safety-critical systems in which the ICs are used.
• Higher reliability: Traceability automatically improves the reliability of ICs and the systems they are used in over their operational lifetimes.
• Improved supply chain security: Malicious actors and state-sponsored attackers are known to target hardware vulnerabilities in critical industries. Traceability forces the design process to include hardware security verifications for potentially risky hardware dependency trees.

Additionally, traceability is recommended or mandatory best practice of the regulations that govern the various critical industries:

• Compliance with automotive standards: The International Organization for Standardization (ISO) 26262 standard for automotive functional safety requires traceability between hardware safety requirements and semiconductor designs. Traceability is critical for SoC makers of automotive electronic systems like advanced driver assistance systems (ADAS) and machine learning-based autonomous vehicles.
• Compliance with other industry standards: IC design traceability is a key demand of safety standards like the DO-254 for aviation ICs, International Electrotechnical Commission (IEC) 62304 for medical devices, and IEC61508 for general electronic components like industrial internet-of-things (IoT) devices.

What are some common challenges of IC design traceability?

Implementing good IC design traceability involves overcoming challenges like:

• Siloed data: The data required for traceability is often siloed in disparate systems either within or across organizational boundaries. Integrating these disparate systems with a centralized traceability system can be challenging.
• Version control: IC designs undergo frequent changes to cater to different applications. Maintaining consistent integration at the system level can be challenging. Traceability requires effective version control of all design artifacts to avoid problems like inadvertent selection of the wrong design variant.
• Real-time actions: Traceability brings both short-term and long-term benefits. In the short term, traceability can be very useful if it can detect a minute change made in one subsystem and immediately trigger automated verification runs for all the impacted subsystems and projects. However, this requires reliable change detection and real-time alerting, which is a challenge when the data is siloed.
• Dependency tracking: Identifying dependency hierarchies is a challenge because without the proper tools, manually tracking thousands of interdependent files is a labor-intensive task.
• Variety of tools: Traceability is most effective when seamlessly integrated into the day-to-day tool ecosystem preferred by engineers. However, each design stage uses specialized proprietary tools whose vendors often prefer lock-in over interoperability. As a result, integrating traceability into other tools can be a challenge.
• Storage demands: Traceability involves storing massive amounts of design data (both text and binary formats) along with all their version metadata.
• Adherence to legal agreements: The goals of traceability and IP reuse can sometimes conflict with licensing and intellectual property protection agreements signed with third parties. Traceability implementations must address these aspects by providing mitigations like access controls so that only authorized personnel can access those IPs.

In the sections that follow, we explore aspects of an effective IC design traceability process that overcome the above challenges.

The role of IP management in IC design traceability

Fig 4. Keysight HUB's comparison tools for easy IP selection

Most modern IC designs are built on third-party and outsourced IP blocks to speed up development and reduce costs. So traceability too is best implemented at the same IP block level. Effective traceability requires effective IP management as well.

An effective IP lifecycle management system for traceability requires the following capabilities:

• IP designers must be able to easily create, manage, and share IP. The IP management system must facilitate them to promote a deep understanding of all aspects of their designs and also facilitate reuse.
• IP consumers must have visibility into all the internal and third-party IP blocks available across the enterprise. However, this visibility must be limited to only the licensed information and only for authorized engineers. For others, a request and approval workflow must be available.
• Managers must get clear IP traceability across the full design hierarchy, with access to change reviews, conflict analysis, and release approvals.

7 best practices for IC design traceability

For effective IC design traceability, implement the following best practices:

1. Centralized platform: An enterprise-wide centralized platform for IP management and traceability addresses multiple challenges and complexities. Siloed data can be more easily integrated. Real-time change detection and actions are possible.
2. Integrate with commonly used tools: Integrate the traceability features with all the design and development tools used in the design process. This integration ensures that all tools are working with the most current data, streamlines workflows, and reduces the risk of errors due to data mismatches or outdated information.
3. Implement security controls: Implement robust data security and access controls through defined roles and permissions for each user. This is critical for protecting sensitive and valuable intellectual property (IP) from unauthorized access or theft.
4. Full design hierarchy tracking: Implement traceability for the full design hierarchy. The platform must be capable of managing very deep dependencies, detecting even small changes at any level of this hierarchy, and bubbling up the change to all the impacted IP blocks and projects.
5. Long-term version control: Effective and long-term version control of IP artifacts is crucial. All the design documents, register transfer level (RTL) files, verification data, device modeling data, product development kits, and files required for the manufacturing process must be under version control. Even years after a release, engineers must be able to trace back exactly which version went to tape-out.
6. Systematic versioning policies: Implement structured versioning policies, such as semantic versioning. Structured versioning helps to manage engineering change orders (ECOs) more efficiently and facilitates design traceability to comply with standards like ISO 26262.
7. Change visualization: The traceability platform must provide convenient visual tools that enable engineers to get a deep understanding of the changes. For example, it's faster to visualize a change in a design schematic when shown as an image rather than a text-format netlist.

Use Keysight IP Management (HUB) for best-in-class IC design traceability

Fig 5. Keysight HUB's IP details page

The Keysight IP Management (HUB) is an enterprise-grade IP management solution with powerful IC design traceability features:

• IPs can include documents, user experiences, scripts, methodologies, libraries, and even ideas.
• It provides clear IP traceability across the full design hierarchy, with access to change reviews, conflict analysis, and release approvals.
• It also integrates most of the popular design tools including Cadence Virtuoso Studio, Siemens EDA (Pyxis), and Silvaco Expert.

Additionally, Keysight Visual Design Diff provides visual comparisons of the differences between two versions of a design and enhances the quality of traceability.

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