Chap. 1 Overview of Digital Design with Verilog

2

Overview of Digital Design with Verilog HDL Evolution of computer aided digital circuit des

ign Emergence of HDLs Typical design flow Importance of HDLs Popularity of Verilog HDL Trends in HDLs

3

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

4

Overview of Digital Design with Verilog HDL Evolution of computer aided digital circuit des

ign Emergence of HDLs Typical design flow Importance of HDLs Popularity of Verilog HDL Trends in HDLs

5

Emergence of HDLs

Hardware Description Language (HDL) Allowed designed to model the concurrency of pro

cesses found in hardware elements Verilog HDL originated in 1983 VHDL was developed under contract from DARP

A Could be used to describe digital circuits at a regis

ter transfer level (RTL) Specify how the data flows between registers and how t

he design processes the data Logic synthesis tools can be used to produce gate-level

netlist from the RTL description automatically

6

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

7

An Example of Verilog HDL

8

Overview of Digital Design with Verilog HDL Evolution of computer aided digital circuit des

ign Emergence of HDLs Typical design flow Importance of HDLs Popularity of Verilog HDL Trends in HDLs

9

Typical Design Flow

10

Design Flow of using HDL

11

Overview of Digital Design with Verilog HDL Evolution of computer aided digital circuit des

ign Emergence of HDLs Typical design flow Importance of HDLs Popularity of Verilog HDL Trends in HDLs

12

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

13

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

14

Overview of Digital Design with Verilog HDL Evolution of computer aided digital circuit des

ign Emergence of HDLs Typical design flow Importance of HDLs Popularity of Verilog HDL Trends in HDLs

15

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

16

History of the Verilog HDL (Cont’d) 1995: The IEEE standardized the Verilog HD

L (IEEE 1364) 2001: The IEEE enhanced the Verilog HDL fo

r modeling scalable designs, deep sub-micron accuracy, etc.

17

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

18

Overview of Digital Design with Verilog HDL Evolution of computer aided digital circuit des

ign Emergence of HDLs Typical design flow Importance of HDLs Popularity of Verilog HDL Trends in HDLs

19

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