On-Chip Variation (OCV) is a critical factor in modern integrated circuit (IC) design, accounting for the inevitable variations that occur during the manufacturing process. These variations can significantly impact the timing performance of a chip. Synopsys PrimeTime is a widely used tool for static timing analysis (STA) that allows designers to report and analyze timing considering OCV. This comprehensive guide provides detailed instructions and commands to effectively report timing OCV in PrimeTime.
OCV refers to the deviations in the manufacturing process that cause variations in transistor characteristics across a chip. These variations can be categorized into several types, including:
OCV can lead to variations in signal propagation delays, which directly impact the timing performance of the circuit. Accurate reporting and analysis of timing OCV are essential to ensure that the design meets its performance specifications under all possible variations.
Before reporting timing OCV, it is essential to set up your design environment correctly. This involves:
set_operating_conditions
command to specify variations in process parameters.Process corners represent different combinations of variations in manufacturing parameters. Defining accurate corners is crucial for meaningful OCV analysis. Use the set_operating_conditions
command to define these corners.
set_operating_conditions -process_derate <value>
Replace <value>
with the specific derate factor that corresponds to your OCV model.
OCV analysis is inherently statistical, requiring the use of PrimeTime's SSTA capabilities. The report_timing
command plays a pivotal role in this process.
To report timing with OCV, use the following command:
report_timing -ocv
This command generates timing reports that incorporate OCV effects, providing insights into how variations impact your design's timing.
report_timing
Command with OCV OptionsThe report_timing
command can be customized with various options to tailor the OCV analysis to your specific needs.
report_timing -ocv
This command provides a basic timing report that includes OCV considerations.
For a more comprehensive analysis, include additional parameters:
report_timing -ocv -path_type full_clock
This command extends the report to include full clock path types, offering a more detailed view of timing under OCV.
To further refine the timing report, you can limit the number of paths and control the precision of the report:
report_timing -ocv -path_type full_clock -max_paths 10 -significant_digits 3
This command limits the report to the top 10 paths with the most significant timing impacts and sets the decimal precision to three digits.
Tuning timing derates can help simulate the impact of OCV on your design's timing performance. The set_timing_derate
command is used for this purpose.
set_timing_derate -late 1.1
This command sets the derate factor for late paths to 1.1, making them 10% slower. Adjusting derate values allows for fine-tuning based on specific OCV scenarios.
Similarly, you can adjust early paths:
set_timing_derate -early 0.9
This sets the derate factor for early paths to 0.9, making them 10% faster.
After setting the derate values, generate the timing report to see the adjusted timing metrics:
report_timing -derate
This command provides a detailed report of the timing derate values applied to various paths, helping you understand the impact of OCV on your design's timing.
To comprehensively assess OCV impacts, it's advisable to analyze timing across multiple defined corners. This involves running the report_timing
command for each corner and aggregating the results.
report_timing -delay min -max_paths 10 -significant_digits 4 -nosplit -sort_by worst_slack -corner <corner_name>
Replace <corner_name>
with each defined OCV corner name. This approach provides a statistical overview of timing performance under varying OCV conditions.
Ensure that your process corners accurately reflect the expected variations in the manufacturing process. Misdefined corners can lead to misleading timing reports.
Maintain consistency in operating conditions across different analysis runs to ensure comparability of timing reports.
Analyze critical paths comprehensively, as these are the most likely to be affected by OCV and can significantly impact overall design performance.
Utilize PrimeTime's Statistical Static Timing Analysis (SSTA) features to gain a deeper understanding of timing variations and their impacts.
Stay updated with the latest PrimeTime documentation and Synopsys resources to utilize new features and best practices for OCV analysis.
Below is an example workflow demonstrating the steps and commands used to report timing OCV in PrimeTime:
set_operating_conditions -process_derate 1.05
set_operating_conditions -process_derate 0.95
This defines two process derate factors representing upper and lower bounds of process variations.
report_timing -ocv
Generates a baseline timing report incorporating OCV effects based on the defined corners.
set_timing_derate -late 1.1
Adjusts late path timing derates to simulate OCV impact.
report_timing -ocv -path_type full_clock -max_paths 10 -significant_digits 3
Produces a detailed timing report with specific constraints for comprehensive analysis.
report_timing -delay min -max_paths 10 -significant_digits 4 -nosplit -sort_by worst_slack -corner high_variation
report_timing -delay min -max_paths 10 -significant_digits 4 -nosplit -sort_by worst_slack -corner low_variation
Generates timing reports for high and low variation corners to compare performance metrics.
If your timing reports do not accurately reflect OCV impacts, ensure that:
PrimeTime commands are sensitive to syntax. Double-check command structures and options to avoid errors.
OCV analysis, especially when dealing with multiple corners and detailed reports, can be computationally intensive. Optimize your analysis by limiting the number of paths and controlling the precision where possible.
For more detailed information and advanced configurations, refer to the official Synopsys PrimeTime documentation:
Access to some documentation may require a valid Synopsys account.
Reporting timing OCV in Synopsys PrimeTime is a multifaceted process that involves defining accurate process corners, leveraging statistical timing analysis, and utilizing specific commands to generate comprehensive reports. By following the outlined steps and best practices, designers can ensure that their ICs meet performance requirements even in the presence of manufacturing variations. Regularly consulting Synopsys documentation and staying updated with tool enhancements will further enhance the effectiveness of OCV analysis in your design workflow.