Post-synthesis and post-layout verification - Verilog Tutorial

Post-synthesis and post-layout verification are essential steps in the digital design flow to ensure that the synthesized and layout designs meet the specified functionality and performance requirements. In this tutorial, we will explore post-synthesis and post-layout verification techniques in Verilog, provide examples, explain the steps in detail, and offer best practices for reliable digital designs.

Example: Post-Synthesis Verification

Here's an example of using "assert" statements for post-synthesis verification:


    module my_design(input clk, input rst, input data_in, output data_out);

      reg data_out;

      always @(posedge clk) begin

        if (rst) data_out <= 1'b0;

        else data_out <= ~data_out;

      end

      assert(data_out == data_in) else $error("Data mismatch!");

    endmodule

In this example, the "assert" statement checks if "data_out" matches the input "data_in" after synthesis. If the condition is not met, it triggers an error during simulation, indicating a potential bug in the design.

Steps for Post-Synthesis and Post-Layout Verification

Follow these steps to perform post-synthesis and post-layout verification:

Generate Netlist: Synthesize the RTL design to obtain a gate-level netlist using tools like Synopsys Design Compiler.
Timing Analysis: Perform timing analysis to ensure that the design meets the required timing constraints and setup/hold times.
Functional Verification: Verify the functionality of the synthesized design by running simulations and comparing the results with the RTL simulations.
Power Analysis: Analyze the power consumption of the synthesized design to meet the power requirements.
Layout Design: Generate the layout of the design using tools like Cadence Innovus or Synopsys IC Compiler.
Design Rule Checking (DRC): Check the layout against manufacturing design rules to ensure it is DRC clean.
Post-Layout Simulation: Perform post-layout simulations to validate the functionality of the layout design and check for any unexpected behavior.
Physical Verification: Run physical verification checks like DRC, LVS (Layout vs. Schematic), and ERC (Electrical Rule Check) to ensure the layout adheres to design rules.
Signal Integrity Analysis: Analyze the design for potential signal integrity issues like noise, crosstalk, and reflections.
Reliability Analysis: Assess the design for potential reliability concerns, such as electromigration and thermal issues.

Common Mistakes in Post-Synthesis and Post-Layout Verification

Not performing proper timing analysis after synthesis, leading to timing violations in the design.
Skipping post-layout simulation, which may result in undetected bugs in the layout design.
Ignoring physical verification checks, causing manufacturing issues and delays.

Frequently Asked Questions

Q: What is the purpose of post-synthesis verification?
A: Post-synthesis verification validates the functionality of the design after synthesis to ensure that the gate-level netlist meets the intended behavior.
Q: Why is post-layout verification important?
A: Post-layout verification ensures that the layout design matches the intended RTL design, checks for layout-related issues, and verifies signal integrity.
Q: What is the significance of timing analysis in post-synthesis verification?
A: Timing analysis checks the timing performance of the synthesized design, ensuring that it meets the required setup, hold, and propagation times.
Q: Why do we need to perform physical verification?
A: Physical verification checks ensure that the layout adheres to manufacturing rules, reducing the risk of defects in silicon and improving reliability.
Q: What is signal integrity analysis, and why is it crucial?
A: Signal integrity analysis assesses the design for potential noise and interference issues, which are critical for high-speed designs to maintain data integrity and reliability.

Summary

Post-synthesis and post-layout verification are crucial stages in the Verilog design flow to ensure that the synthesized and layout designs meet the functional, timing, and physical requirements. By following the outlined steps and avoiding common mistakes, designers can effectively verify their designs and detect and resolve any issues, leading to reliable and robust digital designs.