THE WORLD OF VLSI &

VHDL

Yesterday, Today

&Tomorrow

The World of VLSI• History of the Integrated Circuit

(IC) design

• The IC Technologies

History of the IC designIn 1947 Transistor was invented & demonstrated @ Bell Labs

The first IC appeared in the market in 1961 ~14 years after the transistorFlip-flop:

2 transistors & resistorsCost ~$100

• The Silicon Technology is Growing...•Now on the same amount of Silica

~500 times faster operations 10 million transistors, 1/2 mile of interconnectCost few cents!!!

The Technology changes compared to the IC Design cycle

Moore’s Law

In 1965, GardonMoore stated that the silicon technology will double the number of transistors on a chip every 2 years!!!

And it is happening !!!!!!

The Search of products

“How to reduce the high designing cost for future success of this technology ??? ”:

1968 Noyce Reduce the cost of design process Find product with large market-

Regular structure, Many applications1968 :Noyce, Moore & Grove Forms Intel

!!SemiconductorMemory Chip

Microprocessor Technology

Microprocessor = IC Tech +SoftwareProcessor

Power+Memory capacity Software market

Advantages of VLSI ? Less AREA (compactness at system

levels) Less POWERConsumption Less TESTING(more complex testing) Higher RELIABILITY (due to improved on-chip

interconnects) Higher SPEED(due to reduced

interconnect length) Significant COST SAVINGS

The goal of the IC designer Meet the market requirements

Satisfying customers need Beating the competition

Increasing performance or functionality of the product Reducing cost compared to the available solutions

Achieved by: Using next generation Silicon technologies New design concepts & tools High level of integration

The Design is an optimization problem with parameters as Technology, Time, Cost and Customer requirements

Design Approaches

Custom full control of design best results, slowest design time.

Semi-custom (std cell) use Cell libraries from vendor cad tools, faster design time

EPLA/EPLD -FPGA Electrically Programmable (in the Field)

ASIC(Application Specific Integrated Circuit)

Implements custom functions according to description Not off-the-shelf

Can be described in HDL (Verilog,VHDL) in an abstract technology Independent fashion

Verified using a simulator Analogous to software debugger

Constructed out of logical function cells (AND,OR) and Re-Usable Macro

Building blocks (ADDERs, REGISTERs) Mapped or translated using Synthesis products

Implemented in Field Programmable, Standard Cell or Gate Array families

For high volume production Designers pay CAD vendors ~$50K -$500K for Design tools Designer pay foundry( ~ $200K -.5M) and per part

agreement

Field Programmable Gate Array

A chip that can be configured by a user to implement different digital logic circuits

Invented in 1984

FPGA building blocks: Programmable logic blocks Programmable interconnectField

INTRODUCTION…!!!VHDL

STANDS FOR..??ERYARDIFFICULTANGUAGE

REALLY..??HSICARDWAREESCRIPTION

OUR MOTIVE…!!!

To compress the digital world.To explore the hidden perfection

and create the brain of a machine.

*The above two are considered as a very difficult tasks in the field of electronics engineering, where in fact it’s a very simple technology.

Modeling digital systems..!! VHDL is for coding models of a digital

system. Reasons for modeling:

◦ Requirements specification◦ Documentation◦ Testing using simulation◦ Formal verification◦ Synthesis

Goal:◦ Most ‘reliable’ design process, with

minimum cost and time◦ Avoid design errors!

What is VHDL??VHDL is a programming language that

allows one to model and develop complex digital systems in a dynamic environment.

Object Oriented methodology for you C people can be observed -- modules can be used and reused.

Allows you to designate in/out ports (bits) and specify behavior or response of the system.

C/VHDL Comparison…!!! C is procedural language whereas VHDL

is semi concurrent & semi sequential language.

C is Case Sensitive whereas VHDL is case insensitive.

There are some similarities, as with any programming language, but syntax and logic are quite different.

Basic VHDL concepts...!!!• Interfaces (PORTS)• Behavior• Structure• Test Benches• Simulation• Synthesis

3 Ways to do it..the VHDL way..

DataflowBehavioralStructural

Kind of BORING sounding huh??Well, it gets more exciting with the details !!

:)

The DATAFLOW modeling…!!!

Uses statements that defines the actual flow of data.....such as,

x <= y -- this is NOT less than equal to

-- told you its not C

this assigns the Boolean signal x to the value of Boolean signal y... i.e. x = y this will occur whenever y changes....

Modeling PORTS!!!Entity declaration…(Describes the input/output ports of a module)

entity reg4 isport ( d0, d1, d2, d3, en, clk : in bit;

q0, q1, q2, q3 : out bit );end entity reg4;

entity name port names port mode (direction)

port typereserved words

punctuation

Modeling the behavioral way..!! Architecture body

Describes an implementation of an entity May be several per entity

Behavioral architecture Describes the algorithm performed by the

module Contains

Process statements, each containingSequential statements, including

Signal assignment statements andWait statements

Some SYNTAX to know…!!! Omit entity at end of entity declaration. Omit architecture at end of architecture

body. Omit is in process statement header.

architecture behav of reg4 isbegin

process (d0, ... )...

begin...

end process ;end behav;

entity reg4 isport ( d0, d1, d2 : in bit d3, en, clk : in bit;

q0, q1, q2, q3 : out bit );end reg4;

Modeling the STRUCTURAL way…!!! Structural architecture

implements the module as a composition of subsystems

contains○ signal declarations, for internal

interconnectionsthe entity ports are also treated as signals

○ component instancesinstances of previously declared

entity/architecture pairs○ port maps in component instances

connect signals to component ports

Mixed behavior & structure…!!! An architecture can contain both

behavioral and structural partsProcess statements and component

instances○ Collectively called concurrent statements

Processes can read and assign to signals Example: register-transfer-level (RTL)

modelData path described structurallyControl section described behaviorally

Mixed examples…!!!

shift_reg

reg

shift_adder

control_section

multiplier multiplicand

product

Test bench your model…!!! Testing a design by simulation Use a test bench model

A model that uses your model Apply test sequences to your inputs Monitors values on output signals

Either using simulator. Or with a process that verifies correct

operation Or logic analyzer.

Simulation…!!! Discrete event simulation

Time advances in discrete steps.When signal values change—events occur.

A processes is sensitive to events on input signalsSpecified in wait statements.Resumes and schedules new values on

output signals.○ Schedules transactions.○ Event on a signal if value changes.

FPGA design flow…!!!Initial Design Entry

Logic Optimization

Technology Mapping

Placement

Routing

Programming Unit

VHDL, Schematic, State Diagram

Minimized Blocks- To minimize area

Optimize Boolean Expression into a standard form- To optimize area or speed

Where the logic block is placed ?- With optimum routing wire Connection between cells- To minimize area.

Used to configure the final circuit

Some FPGA to know..!!!

Some FPGA to know..!!!

Skills that you will gain…!!! Implement the VHDL portion of coding for

synthesis. Identify the differences between behavioral

and structural coding styles. Distinguish coding for synthesis versus

coding for simulation. Use scalar and composite data types to

represent information. Use concurrent and sequential control

structure to regulate information flow. Implement common VHDL constructs (Finite

State Machines [FSMs], RAM/ROM data structures).

Benefits Of VHDL• Executable specification.• Functionality separated from implementation.• Simulate early and fast (Manage complexity)• Explore design alternatives.• Get feedback (Produce better designs)• Automatic synthesis and test generation (ATPG for

ASICs)• Increase productivity (Shorten time-to-market)• Technology and tool independence.• Portable design data (Protect investment)

VHDL Applications & SCOPE Digital Signal Processing. IC Testing & Analysis. FPGA Design Verification. FPGA Development. Hardware Design. IC designing. ASIC Development.

• THANK YOUE-Mail

Gaurav_rai@live.com

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