Synopsys Timing Constraints And Optimization User Guide 2021

The bedrock of Synopsys timing closure is the Synopsys Design Constraints (SDC) language. Written in a Tcl-based syntax, SDC communicates your design's physical and electrical intent directly to synthesis, placement, and routing engines. The Timing Engine's Perspective

During pre-layout synthesis (Design Compiler), clocks are modeled as , meaning they distribute to all registers with zero delay. During post-layout implementation (IC Compiler II), after the clock tree is physically built, clocks are switched to propagated to calculate actual network delays.

Once the design is fully constrained, Synopsys engines run cost-function optimization loops to resolve setup and hold violations.

With the release of the , Synopsys has updated its definitive manual to address modern design challenges, including increasingly complex clocking schemes, advanced low-power requirements, and the nuances of next-generation geometry nodes. synopsys timing constraints and optimization user guide 2021

Clocks are the heartbeat of any synchronous digital system. Accurately defining them is the most critical step in creating a valid constraint file. Primary Clock Definitions

Operates at the HDL/RTL level. The tool performs high-level transformations like resource sharing, re-timing, and selecting optimized macro architectures (e.g., choosing a Carry-Lookahead Adder over a Ripple-Carry Adder).

To push the engine to explore maximum logical restructuring, use the -map_effort high switch during synthesis: compile_ultra -map_effort high -retime Use code with caution. The bedrock of Synopsys timing closure is the

: Register clock pin to the data pin of the next sequential element. Reg2Out : Register clock pin to an output port.

# Create a divide-by-2 clock generated by a flip-flop 'clk_div_reg' create_generated_clock -name gen_clk -source [get_ports clk] -divide_by 2 [get_pins clk_div_reg/Q] Use code with caution. Virtual Clocks

# Pre-layout: Assume ideal clock behavior with estimated jitter set_clock_uncertainty 0.1 [get_clocks SYS_CLK] # Post-layout: Switch to real clock tree delays set_propagated_clock [get_clocks SYS_CLK] Use code with caution. Creating Base Clocks Clocks are the heartbeat of any synchronous digital system

A data pin of a sequential element or an output port. Setup vs. Hold Constraints

Generated clocks are derived from primary clocks via internal design logic like clock dividers, phase-locked loops (PLLs), or multiplexers. They must be explicitly declared so the timing engine can maintain phase relationships.

Moving registers across logic blocks to balance path delays.