: Defines the rise and fall edges within the period. Generated Clocks
: Added to the required hold time, forcing the tool to insert extra delay if paths are too fast. Clock Transition and Latency
When logic takes more than one clock cycle to stabilize before being sampled, you must configure a multicycle path exception.
: As the official documentation for the creators of the SDC format, it provides the most accurate definitions of command syntax and tool behavior. Structured Methodology synopsys timing constraints and optimization user guide 2021
# Check for unconstrained paths, missing clocks, or bad syntax check_timing # Generate a summary of the worst violations in the design report_constraint -all_violators # Output a highly detailed path report for analysis report_timing -delay_type max -max_paths 10 -transition_time -capacitance Use code with caution. Analyzing a Timing Report
By internalizing the principles of this guide—especially the proper use of multi-cycle paths, clock groups, and retiming—design teams can reduce their timing closure iterations by 40% or more. As the industry moves toward even more complex heterogeneous designs, the foundational lessons of the 2021 TCO guide remain as relevant as ever.
: Used for setup analysis. It tells the tool that the external device takes up to 0.6 ns to drive the data, leaving less time for internal logic. -min : Used for hold analysis. Output Delay : Defines the rise and fall edges within the period
This command defines the setup and hold requirements of the external device receiving signals from your chip's output ports.
Real-world clock networks suffer from physical imperfections. You must model these characteristics explicitly during synthesis before physical layout occurs:
The Ultimate Guide to Synopsys Timing Constraints and Optimization : As the official documentation for the creators
Instead, the guide recommends using set_clock_sense to fix specific false paths without breaking the global timing engine.
# Create a divide-by-2 clock generated from SYS_CLK at register output 'clk_div_reg/Q' create_generated_clock -name DIV_CLK \ -source [get_ports clk_in] \ -divide_by 2 \ [get_pins clk_div_reg/Q] Use code with caution. Clock Properties: Skew, Jitter, and Latency
Based on best practices in 2021, a "garbage in, garbage out" philosophy applies to timing constraints.