HARDWARE DESCRIPTION

LANGUAGE (HDL)

Development of digital IC technology

The following slides are adapted from “Digital Integrated Circuits - A Design Perspective,” 2003.J. M. Rabaey, A. Chandrakasan, B. Nikolic

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ENIAC - The first electronic computer (1946)

10 feet tall;1,000 square feet of floor- space; 30 tons;More than 70,000 resistors;

10,000 capacitors; 6,000 switches; 18,000 vacuum tubes;

Requires 150 kilowatts of power;

Transistor Age

1951: Shockley develops junction transistor which can be manufactured in quantity.

1947: Bardeen and Brattain create point-contact transistor

Early Integration

Jack Kilby, working at Texas Instruments, invented a monolithic “integrated circuit” in July 1959.

He had constructed the flip-flop shown in the patent drawing above.

Planar transistors

In mid 1959, Noyce develops the first true IC using planar transistors,

Practice Makes Perfect

1961: TI and Fairchild introduced first logic IC’s

1963: Densities and yields improve. This circuit has four flip-flops.

Continues development

1967: Fairchild markets the first semi-custom chip. Transistors (organized in columns) can be easily rewired to create different circuits. Circuit has ~150 logic gates.

1968: Noyce and Moore leave Fairchild to form Intel. By 1971 Intel had 500 employees;

By 2004, 80,000 employees in 55 countries and $34.2B in sales.

Continues development

1970: Intel starts selling a 1k bit RAM.

1971: Ted Hoff at Intel designed the first microprocessor. The 4004 had 4-bit busses and a clock rate of 108 KHz. It had 2300 transistors and was built in a 10 um process.

Exponential Growth

1972: 8088 introduced.

Had 3,500 transistors supporting a byte-wide data path.

1974: Introduction of the 8080.

Had 6,000 transistors in a 6 um process.

The clock rate was 2 MHz.

Today

Many disciplines have contributed to the current state-of-the-art in VLSI Design:

• Solid State Physics

• Materials Science

• Lithography and fab

• Device modeling

• Circuit design and layout

• Architecture design

• Algorithms

• CAD tools

To come up with chips like:

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Pentium 4 – 0.18 um t

0.18-micron process technology– Introduction date: November 20, 2000

(1.5, 1.4 GHz)– Level Two cache: 256 KB Advanced

Transfer Cache – System Bus Speed: 400 MHz– SSE2 SIMD Extensions– Transistors: 42 Million – Typical Use: Desktops and entry-level

workstations

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0.13-micron process technology (2.53, 2.2, 2 GHz)» Introduction date:

January 7, 2002» Level Two cache:

512 KB Advanced» Transistors: 55 Million

Pentium 4

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Pentium Pro - multichip module (MCM)

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• IBM chip has nine processor cores• 192 billion floating-point operations per second (192 G)• Typical Use: multimedia

Supercomputer for Sony's PlayStation 3

Moore’s Law

In 1965, Gordon Moore noted that the number of transistors on a chip doubled every 18 to 24 months.

He made a prediction that semiconductor technology will double its effectiveness every 18 months

Moore’s Law

161514131211109876543210

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Source: Electronics, April 19, 1965.

Technology Directions: SIA Roadmap

Year 1999 2002 2005 2008 2011 2014 Feature size (nm) 180 130 100 70 50 35 Logic trans/cm 2 6.2M 18M 39M 84M 180M 390M Cost/trans (mc) 1.735 .580 .255 .110 .049 .022 #pads/chip 1867 2553 3492 4776 6532 8935 Clock (MHz) 1250 2100 3500 6000 10000 16900 Chip size (mm 2) 340 430 520 620 750 900 Wiring levels 6-7 7 7-8 8-9 9 10 Power supply (V) 1.8 1.5 1.2 0.9 0.6 0.5 High-perf pow (W) 90 130 160 170 175 183

Integrated Circuits

Full-CustomASICs

Semi-CustomASICs(std cell)

UserProgrammable

PLD FPGA

PAL PLA PML LUT(Look-Up Table)

MUX Gates

World of Integrated Circuits

• designs must be sentfor expensive and timeconsuming fabricationin semiconductor foundry

• bought off the shelfand reconfigured bydesigners themselves

ASICApplication Specific

Integrated Circuit

FPGAField Programmable

Gate Array

• designed all the wayfrom behavioral descriptionto physical layout

• no physical layout design;design ends with a bitstream used to configure a device

ASIC versus FPGA

Off-the-shelf

Low development cost

Short time to market

Reconfigurability

High performance

ASICs FPGAs

Low power

Low cost inhigh volumes

Which Way to Go?

What is an ASIC Chip ?

• Application Specific Integrated Circuit

• A chip that is produced to perform a specific function i.e. microcontroller

• Limited interconnect layers, dedicated routing channels

• Intellectual Properties for timing and performance. DLLs, PLLs, DDRs, RAMs

• Fabricated System-On-Chip

ASIC Design Flow (Overview)

Source: [Brown99]

What is an FPGA Chip ?

• Field Programmable Gate Array

• A chip that can be configured by user to implement different digital hardware

• Configurable Logic Blocks (CLB) and Programmable Switch Matrices. Sea-of-gates

• Bitstream to configure: function of each block & the interconnection between logic blocks

I/O Block

I/O B

lock

I/O Block

I/O B

lock

FPGA Design Flow (Overview)

HDL SOURCE

LOGIC SYNTHESISTO GATES

MAPPINGPLACEMENTROUTING

BITSTREAMGENERATIONAND PROGRAMMING(UNIQUE TO FPGAs)

FPGA Chips

HDL DESIGN SOFTWARES

What is HDL?• Hardware Description Language : A type of

programming language for sampling and modeling of electronic & logic circuit designs

• It can describe the circuit’s operation, design and organization

• By using CAD tools, it can be used for test and verify through simulations

• Also used to model the intended piece of device like ASICs, FPGAs, CPLDs and others

• Various kinds : VHDL, Verilog HDL, AHDL etc

Why HDL?• Software solution due to :

– Limits in hardware solutions – Increasing design complexity– Increasing cost in time and investment– Increasing knowledge requirement– Inadequacy of other existing languages

• Text-based rather than schematic design– Easier development– faster time-to-market– synthesis and analysis– Documentation

• Programming languages such as C or Java cannot serve as HDLs (unless modified significantly).

• Programming languages are modeled after a sequential process, where operations are performed in a sequential order (order matters).– This is amenable to the human thinking process, in which an algorithm is

unfolded into a recipe or step-by-step process– This process matches the basic operation of a hardware computing platform.

• HDLs such as VHDL (VHSIC (Very High Speed Integrated Circuit) HDL) and Verilog were developed to support the underlying characteristics of hardware– Connections of parts– Concurrent operations– Concept of propagation delay and timing

These characteristics cannot be captured by traditional PLs

Programming Language (PL) vs Hardware Description Language (HDL)

A Dataflow Language

DATAFLOWCONTROLFLOW

EX: C language assignment EX: VHDL signal assignment

X = A & B; X <= A and B;

X is computed out of A and B ONLY each time this assignment is executed

A PERMANENT link is created between A, B, and X

X is computed out of A and B WHENEVER A or B changes

A Dataflow Language (cont’d)

DATAFLOWCONTROLFLOW

EX: C language assignment EX: VHDL signal assignment

X = A & B;------X = C & D;

X <= A and B;------X <= C and D;

YES YES NO NO

Introduction toVHDL

(part 1)

• VHSIC Hardware Description Language– VHSIC stands for Very High Speed Integrated

Circuit

• Jointly developed in 1983 by Intermetrics, IBM & Texas Instruments

• Initially used by the US Dept. of Defense

• IEEE Standard in 1987 then enhanced and restandardized in 1993

What is VHDL?

• Near-approach to industry– High density electronic design– Multidisciplinary – electronics, microelectronics,

communications, instrumentations and control

• Technology related– Reconfigurable– Actual implementation

• System Design– System throughput recognition– problem solving ability– debugging techniques

Using VHDL as UniMAP’sOBE and PBL

VHDL CAD tool in this subject

VHDL Main Features

TimingDataflow

Structure

Behavior

VHDL Main Features

• Supports the whole design process from high to low abstraction levels :

• System and algorithmic level• Register Transfer Level• Logic level• Circuit level (to some extent)

• Suitable for specifications either in behavioral or structural domain

• Precise simulation semantics is associated with the language definition :• Timing simulations specified• Output simulation is uniquely identified and independent of the

VHDL implementation

VHDL specifications are accepted by hardware synthesis tools

Case Sensitivity

• VHDL is not case sensitiveExample:

Names or labelsdatabusDatabusDataBusDATABUS

are all equivalent

Free Format• VHDL is a “free format” language No formatting conventions, such as spacing

or indentation imposed by VHDL compilers. Space and carriage return treated the same way.Example:

if (a=b) then

orif (a=b) then

orif (a =b) then

are all equivalent

Comments

• Comments in VHDL are indicated with a “double dash”, i.e., “--”

Comment indicator can be placed anywhere in the line Any text that follows in the same line is treated as a comment Carriage return terminates a comment No method for commenting a block extending over a

couple of linesExamples:-- main subcircuitData_in <= Data_bus; -- reading data from the input FIFO

VHDL Architectures

• Does not allow a layout description

Behavioral

Structural

Algorithmic

FSM

RTL

Gate

Layout

Abstraction Levels VHDL Architectures

How it works

How it is connected

VHDL WRITTEN FORMAT

Library / Package Declaration

Entity Declaration

Architecture Flow

Example VHDL Code• 3 sections to a piece of VHDL code• File extension for a VHDL file is .vhd• Name of the file is usually the entity name

(nand_gate.vhd)LIBRARY DECLARATION

ENTITY

ARCHITECTURE

LIBRARY ieee;USE ieee.std_logic_1164.all;

ENTITY nand_gate ISPORT( a : IN STD_LOGIC;

b : IN STD_LOGIC; z : OUT STD_LOGIC);

END nand_gate;

ARCHITECTURE model OF nand_gate ISBEGIN

z <= a NAND b;END model;

LIBRARY / PACKAGE DECLARATIONLibrary ieee;Use ieee.std_logic_1164.all;Use ieee.std_logic_signed.all;Use ieee.std_logic_unsigned.all;Use ieee.std_logic_arith.all;

Library work;Use work.my_package.entity_name;Use work.my_package.function_name;

Library Declarations

Use all definitions from the package

std_logic_1164

LIBRARY ieee;USE ieee.std_logic_1164.all;

ENTITY nand_gate ISPORT( a : IN STD_LOGIC;

b : IN STD_LOGIC; z : OUT STD_LOGIC);

END nand_gate;

ARCHITECTURE model OF nand_gate ISBEGIN

z <= a NAND b;END model;

Library declaration

Library Declarations - Syntax

LIBRARY library_name;

USE library_name.package_name.package_parts;

Commonly Used Libraries• ieee

– Specifies multi-level logic system including STD_LOGIC, and STD_LOGIC_VECTOR data types

• std– Specifies pre-defined data types

(BIT, BOOLEAN, INTEGER, REAL, SIGNED, UNSIGNED, etc.), arithmetic operations, basic type conversion functions, basic text i/o functions, etc.

• work– User-created designs after

compilation

Needs to be explicitly declared

Visible by default

Design Entity

Design Entity - most basic building block of a design.

One entity can have many different architectures.

entity declaration

architecture 1

architecture 2

architecture 3

design entity

ENTITY DECLARATION

• Specifies the input and output signals of the entity

• Format :Entity entity_name isport (port_names : mode data_type);End entity_name;

1

2

3

(1) Rules for Entity NameGeneral rules of thumb (according to VHDL-87)

1. All names should start with an alphabet character (a-z or A-Z)

2. Use only alphabet characters (a-z or A-Z) digits (0-9) and underscore (_)

3. Do not use any punctuation or reserved characters within a name (!, ?, ., &, +, -, etc.)

4. Do not use two or more consecutive underscore characters (__) within a name (e.g., Sel__A is invalid)

5. All names and labels in a given entity and architecture must be unique

6. Cannot end with an ‘_’ underscore7. Cannot have a blank space to separate words

(2) Common Data Type

• Std_logic data– bit logic– std_logic– std_logic_vector (b downto a) or std_logic_vector (a to b) :

array of bit logic• Signed, Unsigned• Integer• Boolean• Legal values for std_logic : 0,1,Z,-,L,H,U,X,W

– Only the first 4 are used in synthesis

(3) Port Modes: SummaryThe Port Mode of the interface describes the direction in which data travels with respect to the component

– In: Data comes in this port and can only be read within the entity. It can appear only on the right side of a signal or variable assignment.

– Out: The value of an output port can only be updated within the entity. It cannot be read. It can only appear on the left side of a signal assignment.

– Inout: The value of a bi-directional port can be read and updated within the entity model. It can appear on both sides of a signal assignment.

– Buffer: Used for a signal that is an output from an entity. The value of the signal can be used inside the entity, which means that in an assignment statement the signal can appear on the left and right sides of the <= operator

Example 1

Full AdderA

B

Cin

SUM

Cout

Entity Full_Adder isPort ( A,B,Cin : in std_logic;

SUM, Cout : out std_logic);

End Full_Adder;

Example 2

4 bit Full Adder

A[3..0]

Cin

SUM[3..0]

Cout

B[3..0]

Entity Full_Adder isPort ( A,B : in std_logic_vector(3 downto 0);

Cin : in std_logic;SUM : out std_logic_vector(3 downto 0);Cout : out std_logic);

End Full_Adder;

ARCHITECTURE• The Internal Aspect of a Design Unit• Can be behavioral (RTL) or structural• Always associated with single entity• Single entity can have multiple architectures

architecture architecture_name of entity_name is{architecture_declarative_part}

begin{architecture_descriptive_part}

end [architecture_name];

architecture architecture_name of entity_name is{architecture_declarative_part}

begin{architecture_descriptive_part}

end [architecture_name];

ARCHITECTURE DATA OBJECTS3 kinds of data object declared and used in architecture:

1. Signal – variable data used to connect internal modulesExample signal cnt : std_logic_vector(2 downto 0);

2. Constant – fixed value throughout the design Example constant length : std_logic_vector(3 downto 0) := “0101”;

3. Variable – internal representations not physically visible and declared within a process.

Example variable cnt : std_logic_vector(2 downto 0);

Architecture Examples

Architecture ex1 of system isBegin

y <= A and (not B);z <= not a xnor (b xor c);

End ex1;

Architecture ex2 of another_system isSignal x1, x2 : std_logic_vector(2 downto 0);

Beginx1 <= A and (not B);z <= x1 + x2;

End ex2;

• Two architecture flavors: Behavioral & Structural

architecture TWO of MUX2 is component MX2 -- a macro from a library port (A, B, S:in std_logic; Y :out std_logic); end component;begin-- instantiate MX2 U1: MX2 port map(A=>AIN, B=>BIN, S=>SIN, Y=>YOUT); end TWO;

architecture TWO of MUX2 is component MX2 -- a macro from a library port (A, B, S:in std_logic; Y :out std_logic); end component;begin-- instantiate MX2 U1: MX2 port map(A=>AIN, B=>BIN, S=>SIN, Y=>YOUT); end TWO;

architecture ONE of MUX2 isbegin YOUT <= (AIN and not SIN) or (BIN and SIN);end ONE;

architecture ONE of MUX2 isbegin YOUT <= (AIN and not SIN) or (BIN and SIN);end ONE;

Declarative part

BehavioralBehavioral

StructuralStructural

Descriptive part

Operators

Single Wire Versus Bus

wire

a

bus

b

1

8

SIGNAL a : STD_LOGIC;

SIGNAL b : STD_LOGIC_VECTOR(7 downto 0);

Single versus Double Quote

• Use single quote to hold a single bit signal– a <= ‘0’, a <=‘Z’

• Use double quote to hold a multi-bit signal– b <= "00", b <= "11"

Standard Logic VectorsSIGNAL a: STD_LOGIC;SIGNAL b: STD_LOGIC_VECTOR(3 DOWNTO 0);SIGNAL c: STD_LOGIC_VECTOR(3 DOWNTO 0);SIGNAL d: STD_LOGIC_VECTOR(7 DOWNTO 0);SIGNAL e: STD_LOGIC_VECTOR(15 DOWNTO 0);SIGNAL f: STD_LOGIC_VECTOR(8 DOWNTO 0); ……….a <= '1';b <= "0000"; -- Binary base assumed by defaultc <= B"0000"; -- Binary base explicitly specifiedd <= "0110_0111"; -- You can use '_' to increase readabilitye <= X"AF67"; -- Hexadecimal basef <= O"723"; -- Octal base

Priority Dataflow

position of parenthesis

RTL netlist layout

Vectors and ConcatenationSIGNAL a: STD_LOGIC_VECTOR(3 DOWNTO 0);SIGNAL b: STD_LOGIC_VECTOR(3 DOWNTO 0);SIGNAL c, d, e: STD_LOGIC_VECTOR(7 DOWNTO 0);

a <= "0000"; b <= "1111"; c <= a & b; -- c = "00001111"

d <= '0' & "0001111"; -- d <= "00001111"

e <= '0' & '0' & '0' & '0' & '1' & '1' & '1' & '1'; -- e <= "00001111"

Exercise

1. Generate the VHDL code for a logic circuit of a Half Adder and simulate in Quartus II

2. Using the Half Adder in Question 1, generate and simulate the VHDL code for a logic circuit of a Full Adder.

3. What do you think a VHDL code representation for a 4-bit logic circuit of a 2-to-1 Multiplexer looks like? Simulate your VHDL code in Quartus II to show the dataflow operation.

Next Chapter

• VHDL Architecture writing design styles– Concurrent Statements– Sequential Statements– Behavioral vs Structural