Chap' 1 Overview of Digital Design with Verilog

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Chap. 1 Overview of Digital Design with Verilog
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Overview of Digital Design with Verilog HDL

• Evolution of computer aided digital circuit
  design
• Emergence of HDLs
• Typical design flow
• Importance of HDLs
• Popularity of Verilog HDL
• Trends in HDLs

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Evolution of Computer Aided DigitalDesign

• Digital circuits were designed with
• Vacuum tubes
• Transistors
• Integrated circuits (ICs)
• SSI
• MSI hundreds of gates
• LSI thousands of gates
• CAD techniques began to evolve
• circuit and Logic simulation about 100
  transistors
• VLSI more than 100,000 transistors
• ULSI Ultra Large Scale Integration

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Overview of Digital Design with Verilog HDL

• Evolution of computer aided digital circuit
  design
• Emergence of HDLs
• Typical design flow
• Importance of HDLs
• Popularity of Verilog HDL
• Trends in HDLs

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Emergence of HDLs

• Hardware Description Language (HDL)
• Allowed designed to model the concurrency of
  processes found in hardware elements
• Verilog HDL originated in 1983
• VHDL was developed under contract from DARPA
• Could be used to describe digital circuits at a
  register transfer level (RTL)
• Specify how the data flows between registers and
  how the design processes the data
• Logic synthesis tools can be used to produce
  gate-level netlist from the RTL description
  automatically

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Different Levels of Abstraction

• Architecture / Algorithm Level
• Describe the functionality (behavior) of a
  circuit
• Register Transfer Logic (RTL) Level
• Describe the data flow of a circuit
• Gate Level
• Describe the connectivity (structure) of a
  circuit
• Switch Level

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An Example of Verilog HDL
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Overview of Digital Design with Verilog HDL

• Evolution of computer aided digital circuit
  design
• Emergence of HDLs
• Typical design flow
• Importance of HDLs
• Popularity of Verilog HDL
• Trends in HDLs

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1.3
Typical Design Flow
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Design Flow of using HDL
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Overview of Digital Design with Verilog HDL

• Evolution of computer aided digital circuit
  design
• Emergence of HDLs
• Typical design flow
• Importance of HDLs
• Popularity of Verilog HDL
• Trends in HDLs

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Why use the HDL ?

• Difficult to design directly on hardware
• Mixed-level modeling and simulation
• Easier to explore different design options
• Reduce design time and cost

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Advantages of HDLs

• Advantages compared to traditional
  schematic-based design
• Design with RTL description logic synthesis
  tool
• Abstract level
• Independent to fabrication technology
• Reuse when fabrication technology changing
• Functional verification can be done early
• Optimized to meet the desired functionality
• Analogous to computer programming
• Textual description with comments

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Overview of Digital Design with Verilog HDL

• Evolution of computer aided digital circuit
  design
• Emergence of HDLs
• Typical design flow
• Importance of HDLs
• Popularity of Verilog HDL
• Trends in HDLs

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History of the Verilog HDL

• 1984 Gateway Design Automation introduced the
  Verilog-XL digital logic simulator
• The Verilog language was part of the Verilog-XL
  simulator
• The language was mostly created by 1 person, Phil
  Moorby
• The language was intended to be used with only 1
  product
• 1989 Gateway merged into Cadence Design Systems
• 1990 Cadence made the Verilog HDL public domain
• Open Verilog International (OVI) controlled the
  language

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History of the Verilog HDL (Contd)

• 1995 The IEEE standardized the Verilog HDL (IEEE
  1364)
• 2001 The IEEE enhanced the Verilog HDL for
  modeling scalable designs, deep sub-micron
  accuracy, etc.

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Useful Features of the Verilog HDL

• A general-purpose HDL
• Easy to learn and use
• Syntax is similar to C (VHDL is similar to
  PASCAL)
• Allows different levels of abstraction to be
  mixed in the same model
• In terms of switches, gates, RTL, or behavioral
  code
• Need to learn only for stimulus and hierarchical
  design
• Most popular logic synthesis tools support
  Verilog
• Rich of Verilog HDL libraries
• Provided by fabrication vendors for postlogic
  synthesis simulation
• Allows the widest choice of vendors while
  designing a chip
• With powerful PLI (Programming Language
  Interface)
• Write custom C code to interact with internal
  data structure

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Overview of Digital Design with Verilog HDL

• Evolution of computer aided digital circuit
  design
• Emergence of HDLs
• Typical design flow
• Importance of HDLs
• Popularity of Verilog HDL
• Trends in HDLs

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Trends in HDLs

• Higher levels of abstraction
• Think only in terms of functionality for
  designers
• CAD tools take care of the implementation details
• Behavioral modeling
• Design directly in terms of algorithms and
• the behavior of the circuit
• Formal verification
• Supports for Mixed-level design
• Ex very high speed and timing-critical circuits
  like µPs
• Mix gate-level description directly into the RTL
  description
• System-level design in a mixed bottom-up
  methodology
• Use either existing Verilog modules, basic
  building blocks, or IPs
• Ex SystemC for SoC designs