What are the best practices for setting up timing constraints and exceptions for STA?

2 Use a standard format and syntax

One of the most common sources of errors and confusion in STA is the format and syntax of the timing constraints and exceptions. Different STA tools may have different formats and syntaxes, but it is advisable to use a standard and widely accepted format, such as the Synopsys Design Constraints (SDC) format. SDC is a text-based format that uses commands and attributes to specify the timing constraints and exceptions. Using a standard format and syntax will make your constraints and exceptions easier to read, write, debug, and port across different tools and platforms.

3 Group and organize the constraints and exceptions

Another best practice for setting up timing constraints and exceptions for STA is to group and organize them logically and hierarchically. This will help you avoid duplication, inconsistency, and conflicts among the constraints and exceptions. You can group and organize the constraints and exceptions by using categories, such as clock definitions, input/output delays, false paths, multicycle paths, clock domain crossings, mode-specific constraints, and power-aware constraints. You can also use sub-files, libraries, variables, and macros to modularize and reuse the constraints and exceptions.

4 Validate and verify the constraints and exceptions

Once you have written the timing constraints and exceptions, you need to validate and verify them to ensure that they are correct and complete. You can use various methods and tools to validate and verify the constraints and exceptions, such as syntax checking, consistency checking, coverage checking, cross-checking, and simulation. Validation and verification will help you detect and fix any errors, gaps, or mismatches in the constraints and exceptions, and improve the quality and reliability of the STA results.

5 Review and update the constraints and exceptions

Finally, you need to review and update the timing constraints and exceptions regularly and iteratively throughout the design cycle. As the design evolves and changes, so do the timing requirements and scenarios. You need to review and update the constraints and exceptions to reflect the latest design changes and feedback, and to optimize the timing performance and efficiency of the circuit. You also need to document and communicate the changes and the rationale behind them to the relevant stakeholders and team members.

6 Follow the best practices and guidelines

Setting up timing constraints and exceptions for STA is not a trivial task, and it requires careful planning, execution, and management. To avoid common mistakes and pitfalls, you should follow the best practices and guidelines that are recommended by the industry experts, the STA tool vendors, and the design community. You can also refer to some of the useful resources and references that are available online, such as books, blogs, forums, webinars, and tutorials.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?