Summary of "Overview of VLSI Design Flow - I"

Summary of "Overview of VLSI Design Flow - I"

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Main Ideas and Concepts

1. Introduction to VLSI Design Flow
   • The course covers the flow from RTL (Register Transfer Level) to GDS (Graphic Database System).
   • Initial lectures provide an overview of the entire VLSI Design Flow to understand the interconnections and optimization opportunities among various design tasks.
   • The ultimate goal: transform a high-level idea into a manufacturable chip that performs the intended task profitably.
2. High-Level Structure of VLSI Design Flow
   • The design flow is divided into three main parts:
     1. Idea to RTL (System-level design): Converting a conceptual product idea into RTL code (Verilog/VHDL).
     2. RTL to GDS: Logical and physical design stages transforming RTL into a layout represented by GDS.
     3. GDS to Chip: Fabrication, testing, packaging, and final chip production.
   • This lecture focuses primarily on the first part (Idea to RTL) and system-level design concepts.
3. Concept of Abstraction in VLSI Design
   • Abstraction means hiding lower-level details to manage complexity.
   • As the design progresses from idea to chip, abstraction decreases because more implementation details are added.
   • High abstraction (e.g., system behavior or logic formulas) allows faster exploration of design options and quicker turnaround time but with less accuracy in performance estimation.
   • Low abstraction (e.g., layouts, transistor-level) offers more accurate evaluation of parameters like delay and area but increases turnaround time and limits optimization scope.
   • Trade-off between abstraction, optimization scope, turnaround time, and accuracy:
     • High abstraction → high optimization scope, low turnaround time, low accuracy.
     • Low abstraction → low optimization scope, high turnaround time, high accuracy.
4. Pre-RTL Methodologies and System-Level Design
   • Pre-RTL design involves defining system components (hardware/software), their interaction, and overall system architecture.
   • Steps in system-level design:
     • Idea evaluation: Market need, financial viability, technical feasibility.
     • Specification creation: Define features, PPA (Power, Performance, Area) targets, schedule, and time to market.
     • Hardware-Software Partitioning: Decide which functions/components are implemented in hardware and which in software.
     • IC design & manufacture (hardware) and software development proceed in parallel.
     • System integration and validation/testing finalize the product.
5. Hardware-Software Partitioning
   • Motivation: Exploit strengths of both hardware and software to achieve high-quality products.
   • Advantages of Hardware:
     • High performance via parallelism.
     • Better energy efficiency and speed.
   • Advantages of Software:
     • Easier development and debugging.
     • Greater flexibility and easier customization.
     • Shorter development time.
   • Typical system example:
     • Software runs sequentially on a general-purpose processor.
     • Dedicated hardware accelerators perform critical, computationally heavy tasks in parallel.
   • Example: Video compression algorithm partitioning
     • Bottleneck function (e.g., Discrete Cosine Transform) implemented in hardware accelerator.
     • Other functions (e.g., frame handling) implemented in software for flexibility.
6. Methodology for Hardware-Software Partitioning
   • Objective: Find a minimal set of functions to move from software to hardware to meet performance targets.
   • Initial state: All functions in software (set S), hardware set (H) empty.
   • Given performance threshold P.
   • Iterative process:
     • Measure current performance.
     • If performance < P, profile functions to identify bottlenecks.
     • Move the most critical bottleneck function(s) from S to H.
     • Re-evaluate performance.
     • Repeat until performance meets P or no further improvement.
   • Challenges:
     • Performance estimation without actual hardware: use FPGA prototyping or quick synthesis to estimate gains.
     • Verification of combined hardware/software system: use co-simulation with hardware models to validate functionality.

Detailed Bullet Points: Hardware-Software Partitioning Algorithm

• Input:
  • Set S: All functions currently implemented in software.
  • Set H: Initially empty (hardware functions).
  • Performance threshold P.
  • Parameter n: Maximum functions to move per iteration.
• Process:
  1. Evaluate current system performance.
  2. If performance ≥ P, stop (no partitioning needed).
  3. Else, profile software functions to measure execution time per function.
  4. Identify the most time-consuming (bottleneck) function f_i.
  5. Move f_i from S to H (i.e., implement in hardware).
  6. Re-evaluate performance.
  7. Repeat steps

Category

Educational

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