Using Synopsys Design Compiler: A Practical Guide
Synopsys Design Compiler (DC) is one of the most widely used tools for RTL synthesis in digital ASIC design. It converts RTL (Verilog/VHDL) into a gate-level netlist optimized for area, power, and timing based on technology libraries and constraints.
This guide explains how Design Compiler works, how to use it step by step, and what hiring managers expect you to understand.
1. What Is Synopsys Design Compiler?
Design Compiler is a logic synthesis tool that:
Reads RTL code (Verilog/VHDL)
Applies timing, area, and power constraints
Maps logic to standard-cell libraries
Produces an optimized gate-level netlist
Typical Inputs
RTL files
Technology libraries (.lib)
Design constraints (.sdc)
Typical Outputs
Gate-level netlist (.v)
Timing reports
Area and power reports
2. Design Compiler Flow Overview
The standard DC flow looks like this:
Setup libraries
Read RTL
Define constraints
Elaborate design
Compile (synthesize)
Analyze reports
Write outputs
Understanding this flow is critical for both interviews and real projects.
3. Setting Up Libraries
Design Compiler needs technology libraries to map logic to real gates.
Common Libraries
Target library → Used for synthesis
Link library → Used to resolve references
Symbol library → Used for schematic viewing (optional)
Example:
set target_library "slow.lib"
set link_library "* slow.lib"
📌 Hiring managers expect you to understand why libraries matter, not just how to load them.
4. Reading and Elaborating RTL
Read RTL files:
read_verilog alu.v
Elaborate the design:
elaborate alu
Check for errors:
check_design
This step ensures:
No missing modules
No unresolved references
Correct hierarchy
5. Applying Design Constraints (SDC)
Constraints guide optimization.
Clock Definition
create_clock -period 10 [get_ports clk]
Input/Output Delays
set_input_delay 2 -clock clk [all_inputs]
set_output_delay 2 -clock clk [all_outputs]
Timing Exceptions (example)
set_false_path -from [get_ports reset]
🎯 Strong candidates know that bad constraints = bad silicon.
6. Compiling the Design
Basic compile:
compile
Advanced optimization:
compile_ultra
What DC optimizes:
Logic depth
Gate sizing
Register placement
Boolean simplification
Trade-offs:
Faster timing → larger area
Smaller area → slower timing
7. Analyzing Reports
After synthesis, reports are crucial.
Timing Report
report_timing
Area Report
report_area
Power Report
report_power
Hiring managers care more about how you interpret these reports than how you generate them.
8. Writing Output Files
Gate-Level Netlist
write -format verilog -hierarchy -output alu_netlist.v
Constraints
write_sdc alu.sdc
Design Database
write -format ddc -hierarchy -output alu.ddc
These outputs are used in place-and-route tools like IC Compiler or Fusion Compiler.
9. Common Design Compiler Commands to Know
Command Purpose
check_design Validate RTL
compile_ultra High-effort synthesis
report_timing Analyze timing
set_max_area Control area
set_dont_touch Protect logic
get_cells Query objects
Knowing these commands helps you debug faster.
10. Common Interview Questions
Be prepared to answer:
What is the difference between compile and compile_ultra?
What happens if timing constraints are missing?
How does DC optimize timing?
What is the role of target vs link library?
How do you fix negative slack?
Clear answers here strongly impress hiring managers.
11. Best Practices
✔ Always check reports after synthesis
✔ Use meaningful constraints
✔ Avoid over-constraining
✔ Fix RTL issues before synthesis
✔ Document assumptions
Design Compiler rewards clean RTL and clear intent.
Final Thoughts
Synopsys Design Compiler is not just a tool—it’s a decision engine that transforms RTL into real hardware. Mastering it means understanding:
Digital logic
Timing
Constraints
Optimization trade-offs
If you can explain what DC is doing and why, you’re already ahead of many candidates.
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