Understanding VLSI Design Flow: RTL to GDS

Oct 1, 2024

VLSI Design Flow: RTL to GDS Lecture 3 Notes

Overview

  • Focus on understanding VLSI design flow.
  • Importance of linkages between design tasks.
  • Aim: Optimization of design tasks to benefit subsequent tasks.

Design Flow Structure

Top Level Problem

  • Start with an idea for a system (e.g., processing, computation, control).
  • Goal: Manufacture a profitable chip that fulfills the system's task.
  • Complexity in achieving the design due to various approaches.

Design Steps and Milestones

  1. Idea to RTL (Register Transfer Level)
    • High-level representation of the product concept.
    • Typically written in Verilog or VHDL.
  2. RTL to GDS (Graphic Database System)
    • Involves logical and physical design transformations.
    • Ends with layout ready for fabrication.
  3. GDS to Chip Process
    • Fabrication of the chip and preparation for market.

Abstraction in VLSI Design Flow

  • Definition: Hiding lower-level details in design description.
  • Abstraction decreases as the design progresses:
    • High abstraction in idea to RTL flow.
    • Lower abstraction in RTL to GDS flow.
  • Importance of abstraction:
    • Facilitates easier exploration of design space.
    • Higher scope for optimization at higher abstraction levels.

Considerations for Design Tasks

  1. Optimization: Finding the right combination of design parameters for better quality results.
  2. Turnaround Time: The time taken to make changes in design.
    • Short turnaround time is critical in semiconductor industry.

Levels of Abstraction

  • Example: Functionality represented in logic formulas vs. layout.
  • Higher abstraction means fewer details:
    • Easier changes and quicker turnaround.
    • Lower abstraction allows for more accurate performance evaluations.

Pre-RTL Methodologies

  • Deciding system components (hardware/software) and their interactions.
  • Steps involved in pre-RTL methodologies:
    1. Idea Evaluation: Assess market and technical feasibility.
    2. Specification Creation: Define product features and performance metrics.
    3. Hardware/Software Partitioning: Determine which components are implemented in hardware vs. software.

Hardware-Software Partitioning

  • Purpose: Exploit the advantages of both hardware (high performance) and software (ease of development and flexibility).
  • Example: Video compression algorithm.
    • DCT Calculation: Implemented in hardware for efficiency.
    • Frame Handling: Handled by software for flexibility.

Challenges in Hardware-Software Partitioning

  1. Performance Estimation: Non-existence of hardware makes performance evaluation difficult.
    • Approaches: Use FPGA emulation or quick design flow for estimation.
  2. Verification of Combined Systems: Ensuring integrated system functions as required.
    • Approaches: Co-simulation of hardware and software models.

Conclusion

  • Reviewed abstraction and its role in VLSI design flow.
  • Discussed idea to RTL flow and hardware-software partitioning.
  • Next lecture will cover behavior-level synthesis.