Synopsys Timing Constraints And Optimization User Guide 2021 [verified] Jun 2026

set_output_delay -max 0.5 -clock SYS_CLK [get_ports data_out] set_output_delay -min -0.2 -clock SYS_CLK [get_ports data_out] Use code with caution. 4. Advanced Timing Exceptions

While standard clock and I/O constraints handle many cases, complex designs require advanced constructs. The guide covers these in detail.

Converts HDL code into a generic technology-independent netlist (GTECH).

# Prioritize timing over area considerations during compile set_max_area 0 # Fix hold time violations automatically during synthesis (compile_ultra) set_fix_hold [all_clocks] # Enable high-effort optimization for aggressive timing closure compile_ultra -retime -gate_clock Use code with caution. synopsys timing constraints and optimization user guide 2021

At the heart of the guide lies the principle of . Unlike dynamic simulation, which tests functionality using specific input vectors, STA is a much faster and more thorough method that mathematically verifies the timing performance of a design. It breaks the design into all possible timing paths, calculates the signal propagation delay along each path, and checks for violations of timing constraints.

Use set_max_fanout constraints or manually insert buffers to distribute the load.

The content in this article is based on notes and summaries from that version. It is important for engineers to always refer to the latest official documentation for their specific tool version, as features and commands are continuously updated. Later versions, like the release used in some community resources, may include changes that supersede the 2021 guide. set_output_delay -max 0

Do not use the default settings. The 2021 guide explicitly warns against using compile_ultra without the -timing_high_effort flag. The default is "balanced," which leaves 5-7% performance on the table.

Duplicating a heavily loaded gate to split its fanout load across two identical driving sources, significantly reducing propagation delay. Summary Checklist for Timing Closure Constraint Category Crucial Command Examples Primary Engineering Objective Clock Setup create_clock , create_generated_clock

The guide stresses that an improperly defined clock is the root of 90% of timing violations. The guide covers these in detail

# Creates a 200MHz clock (5ns period) with a 50% duty cycle on the 'sys_clk' port create_clock -name SYS_CLK -period 5.0 [get_ports sys_clk] Use code with caution. Generated Clocks

In early synthesis stages, clocks are treated as "ideal," meaning they arrive at every register simultaneously with zero edge distortion. To make synthesis realistic, engineers must model physical clock constraints: