IEEE Standard VHDL Language Reference Manual - VHDL Language ...

[Pages:299]IEEE Std 1076, 2000 Edition

(Incorporates IEEE Std 1076-1993 and IEEE Std 1076a-2000)

IEEE Standard VHDL Language Reference Manual

Cosponsors Design Automation Standards Committee (DASC) of the IEEE Computer Society and Automatic Test Program Generation Subcommittee of the IEEE Standards Coordinating Committee 20 (SCC 20)

Approved 30 January 2000 IEEE-SA Standards Board

Abstract: VHSIC Hardware Description Language (VHDL) is defined. VHDL is a formal notation intended for use in all phases of the creation of electronic systems. Because it is both machine readable and human readable, it supports the development, verification, synthesis, and testing of hardware designs; the communication of hardware design data; and the maintenance, modification, and procurement of hardware. Its primary audiences are the implementors of tools supporting the language and the advanced users of the language. Keywords: computer languages, electronic systems, hardware, hardware design, VHDL

The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, New York, NY 10016-5997, USA Copyright ? 2000 by the Institute of Electrical and Electronics Engineers, Inc. All rights reserved. Published 29 December 2000. Printed in the United States of America. Print: ISBN 0-7381-1948-2 SH94817 PDF: ISBN 0-7381-1949-0 SS94817 No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.

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Introduction

(This introduction is not part of IEEE Std 1076, 2000 Edition, IEEE Standards VHDL Language Reference Manual.)

The VHSIC Hardware Description Language (VHDL) is a formal notation intended for use in all phases of the creation of electronic systems. Because it is both machine readable and human readable, it supports the development, verification, synthesis, and testing of hardware designs; the communication of hardware design data; and the maintenance, modification, and procurement of hardware.

This document specifies IEEE Std 1076, 2000 Edition, which incorporates IEEE Std 1076-1993 and IEEE Std 1076a-2000.

Participants

The following individuals participated in the development of this standard: Stephen A. Bailey, Chair

Peter J. Ashenden David L. Barton Victor Berman Alain Fonkoua Andrew Guyler John Hillawi

Serge Maginot Paul J. Menchini Jean Mermet Rob Newshutz William R. Paulsen

The following members of the balloting committee voted on this standard:

Peter J. Ashenden Stephen A. Bailey David L. Barton Victor Berman J. Bhasker Dominique Borrione Todd P. Carpenter Allen Dewey Douglas D. Dunlop Wayne P. Fischer Rita A. Glover Kenji Goto Brian S. Griffin Andrew Guyler M. M. Kamal Hashmi

Rich Hatcher Carl E. Hein John Hillawi John Hines Osamu Karatsu Jake Karrfalt Michael D. McKinney Paul J. Menchini John T. Montague Gabe Moretti Gerald Musgrave Zainalabedin Navabi Kevin O'Brien Serafin Olcoz Vincent Olive

Gregory D. Peterson Jacques Rouillard Ron Werner John Willis Phil Wilsey Alex Zamfirescu

Gregory D. Peterson Markus Pfaff Steffen Rochel Jacques Rouillard Quentin G. Schmierer Steven E. Schulz Moe Shahdad Charles F. Shelor Hiroshi Shinkai Joseph J. Stanco Atsushi Takahara David Tester Peter Trajmar J. Richard Weger John Willis

Copyright ? 2000 IEEE. All rights reserved.

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When the IEEE-SA Standards Board approved this standard on 30 January 2000, it had the following membership:

Richard J. Holleman, Chair Donald N. Heirman, Vice Chair

Judith Gorman, Secretary

Satish K. Aggarwal Dennis Bodson Mark D. Bowman James T. Carlo Gary R. Engmann Harold E. Epstein Jay Forster* Ruben D. Garzon

James H. Gurney Lowell G. Johnson Robert J. Kennelly E. G. "Al" Kiener Joseph L. Koepfinger* L. Bruce McClung Daleep C. Mohla Robert F. Munzner

Louis-Fran?ois Pau Ronald C. Petersen Gerald H. Peterson John B. Posey Gary S. Robinson Akio Tojo Hans E. Weinrich Donald W. Zipse

*Member Emeritus

Also included is the following nonvoting IEEE-SA Standards Board liaison: Robert E. Hebner

Andrew D. Ickowicz IEEE Standards Project Editor

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Copyright ? 2000 IEEE. All rights reserved.

Contents

0. Overview of this standard .................................................................................................................... 1

0.1 Intent and scope of this standard.................................................................................................. 1 0.2 Structure and terminology of this standard.................................................................................. 1 0.2.1 Syntactic description................................................................................................................. 2 0.2.2 Semantic description ................................................................................................................. 3 0.2.3 Front matter, examples, notes, references, and annexes ........................................................... 3

1. Design entities and configurations....................................................................................................... 5

1.1 Entity declarations ....................................................................................................................... 5 1.1.1 Entity header ............................................................................................................................. 5 1.1.1.1 Generics ................................................................................................................................. 6 1.1.1.2 Ports ....................................................................................................................................... 7 1.1.2 Entity declarative part ............................................................................................................... 8 1.1.3 Entity statement part ................................................................................................................. 9 1.2 Architecture bodies ...................................................................................................................... 9 1.2.1 Architecture declarative part ................................................................................................... 10 1.2.2 Architecture statement part ..................................................................................................... 10 1.3 Configuration declarations......................................................................................................... 12 1.3.1 Block configuration ................................................................................................................ 13 1.3.2 Component configuration ....................................................................................................... 15

2. Subprograms and packages................................................................................................................ 19

2.1 Subprogram declarations ........................................................................................................... 19 2.1.1 Formal parameters .................................................................................................................. 20 2.1.1.1 Constant and variable parameters ........................................................................................ 20 2.1.1.2 Signal parameter .................................................................................................................. 21 2.1.1.3 File parameters ..................................................................................................................... 22 2.2 Subprogram bodies .................................................................................................................... 22 2.3 Subprogram overloading............................................................................................................ 25 2.3.1 Operator overloading .............................................................................................................. 26 2.3.2 Signatures ................................................................................................................................ 26 2.4 Resolution functions .................................................................................................................. 27 2.5 Package declarations.................................................................................................................. 28 2.6 Package bodies........................................................................................................................... 29 2.7 Conformance rules ..................................................................................................................... 31

3. Types.................................................................................................................................................. 33

3.1 Scalar types ................................................................................................................................ 34 3.1.1 Enumeration types .................................................................................................................. 34 3.1.1.1 Predefined enumeration types .............................................................................................. 35 3.1.2 Integer types ............................................................................................................................ 36 3.1.2.1 Predefined integer types ....................................................................................................... 36 3.1.3 Physical types .......................................................................................................................... 36 3.1.3.1 Predefined physical types .................................................................................................... 38 3.1.4 Floating point types ................................................................................................................. 39 3.1.4.1 Predefined floating point types ............................................................................................ 40 3.2 Composite types......................................................................................................................... 40

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3.2.1 Array types .............................................................................................................................. 40 3.2.1.1 Index constraints and discrete ranges .................................................................................. 42 3.2.1.2 Predefined array types .......................................................................................................... 44 3.2.2 Record types ............................................................................................................................ 44 3.3 Access types............................................................................................................................... 45 3.3.1 Incomplete type declarations .................................................................................................. 46 3.3.2 Allocation and deallocation of objects .................................................................................... 47 3.4 File types.................................................................................................................................... 47 3.4.1 File operations ......................................................................................................................... 48 3.5 Protected types ........................................................................................................................... 50 3.5.1 Protected type declarations ..................................................................................................... 50 3.5.2 Protected type bodies .............................................................................................................. 51

4. Declarations ....................................................................................................................................... 55

4.1 Type declarations ....................................................................................................................... 55 4.2 Subtype declarations .................................................................................................................. 56 4.3 Objects ....................................................................................................................................... 57 4.3.1 Object declarations .................................................................................................................. 58 4.3.1.1 Constant declarations ........................................................................................................... 58 4.3.1.2 Signal declarations ............................................................................................................... 59 4.3.1.3 Variable declarations ........................................................................................................... 60 4.3.1.4 File declarations ................................................................................................................... 62 4.3.2 Interface declarations .............................................................................................................. 63 4.3.2.1 Interface lists ........................................................................................................................ 65 4.3.2.2 Association lists ................................................................................................................... 66 4.3.3 Alias declarations .................................................................................................................... 68 4.3.3.1 Object aliases ....................................................................................................................... 69 4.3.3.2 Nonobject aliases ................................................................................................................. 70 4.4 Attribute declarations................................................................................................................. 71 4.5 Component declarations............................................................................................................. 72 4.6 Group template declarations ...................................................................................................... 72 4.7 Group declarations ..................................................................................................................... 73

5. Specifications..................................................................................................................................... 75

5.1 Attribute specification................................................................................................................ 75 5.2 Configuration specification........................................................................................................ 77 5.2.1 Binding indication ................................................................................................................... 78 5.2.1.1 Entity aspect ......................................................................................................................... 80 5.2.1.2 Generic map and port map aspects ...................................................................................... 81 5.2.2 Default binding indication ...................................................................................................... 83 5.3 Disconnection specification ....................................................................................................... 84

6. Names ................................................................................................................................................ 87

6.1 Names ........................................................................................................................................ 87 6.2 Simple names ............................................................................................................................. 88 6.3 Selected names........................................................................................................................... 89 6.4 Indexed names ........................................................................................................................... 91 6.5 Slice names ................................................................................................................................ 92 6.6 Attribute names.......................................................................................................................... 92

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Copyright ? 2000 IEEE. All rights reserved.

7. Expressions ........................................................................................................................................ 95

7.1 Rules for expressions ................................................................................................................. 95 7.2 Operators.................................................................................................................................... 96 7.2.1 Logical operators .................................................................................................................... 96 7.2.2 Relational operators ................................................................................................................ 97 7.2.3 Shift operators ......................................................................................................................... 98 7.2.4 Adding operators ................................................................................................................... 100 7.2.5 Sign operators ....................................................................................................................... 102 7.2.6 Multiplying operators ............................................................................................................ 102 7.2.7 Miscellaneous operators ........................................................................................................ 104 7.3 Operands .................................................................................................................................. 104 7.3.1 Literals .................................................................................................................................. 105 7.3.2 Aggregates ............................................................................................................................. 106 7.3.2.1 Record aggregates .............................................................................................................. 106 7.3.2.2 Array aggregates ................................................................................................................ 107 7.3.3 Function calls ........................................................................................................................ 108 7.3.4 Qualified expressions ............................................................................................................ 108 7.3.5 Type conversions .................................................................................................................. 109 7.3.6 Allocators .............................................................................................................................. 110 7.4 Static expressions..................................................................................................................... 111 7.4.1 Locally static primaries ......................................................................................................... 111 7.4.2 Globally static primaries ....................................................................................................... 112 7.5 Universal expressions .............................................................................................................. 113

8. Sequential statements....................................................................................................................... 115

8.1 Wait statement ......................................................................................................................... 115 8.2 Assertion statement.................................................................................................................. 117 8.3 Report statement ...................................................................................................................... 118 8.4 Signal assignment statement .................................................................................................... 118 8.4.1 Updating a projected output waveform ................................................................................. 120 8.5 Variable assignment statement ................................................................................................ 123 8.5.1 Array variable assignments................................................................................................... 124 8.6 Procedure call statement .......................................................................................................... 124 8.7 If statement............................................................................................................................... 125 8.8 Case statement ......................................................................................................................... 125 8.9 Loop statement......................................................................................................................... 126 8.10 Next statement ......................................................................................................................... 127 8.11 Exit statement........................................................................................................................... 127 8.12 Return statement ...................................................................................................................... 128 8.13 Null statement .......................................................................................................................... 128

9. Concurrent statements...................................................................................................................... 129

9.1 Block statement........................................................................................................................ 129 9.2 Process statement ..................................................................................................................... 130 9.3 Concurrent procedure call statements...................................................................................... 131 9.4 Concurrent assertion statements .............................................................................................. 132 9.5 Concurrent signal assignment statements ................................................................................ 133 9.5.1 Conditional signal assignments ............................................................................................. 135 9.5.2 Selected signal assignments .................................................................................................. 137 9.6 Component instantiation statements ........................................................................................ 138 9.6.1 Instantiation of a component ................................................................................................. 139

Copyright ? 2000 IEEE. All rights reserved.

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9.6.2 Instantiation of a design entity .............................................................................................. 141 9.7 Generate statements ................................................................................................................. 144

10. Scope and visibility.......................................................................................................................... 145

10.1 Declarative region.................................................................................................................... 145 10.2 Scope of declarations ............................................................................................................... 145 10.3 Visibility .................................................................................................................................. 146 10.4 Use clauses............................................................................................................................... 150 10.5 The context of overload resolution .......................................................................................... 150

11. Design units and their analysis ........................................................................................................ 153

11.1 Design units ............................................................................................................................. 153 11.2 Design libraries ........................................................................................................................ 153 11.3 Context clauses ........................................................................................................................ 154 11.4 Order of analysis ...................................................................................................................... 155

12. Elaboration and execution................................................................................................................ 157

12.1 Elaboration of a design hierarchy ............................................................................................ 157 12.2 Elaboration of a block header .................................................................................................. 159 12.2.1 The generic clause ............................................................................................................... 159 12.2.2 The generic map aspect ....................................................................................................... 159 12.2.3 The port clause .................................................................................................................... 159 12.2.4 The port map aspect ............................................................................................................ 159 12.3 Elaboration of a declarative part .............................................................................................. 160 12.3.1 Elaboration of a declaration ................................................................................................ 161 12.3.1.1 Subprogram declarations and bodies ............................................................................... 161 12.3.1.2 Type declarations ............................................................................................................. 161 12.3.1.3 Subtype declarations ........................................................................................................ 162 12.3.1.4 Object declarations ........................................................................................................... 162 12.3.1.5 Alias declarations ............................................................................................................. 163 12.3.1.6 Attribute declarations ....................................................................................................... 163 12.3.1.7 Component declarations ................................................................................................... 163 12.3.2 Elaboration of a specification ............................................................................................. 163 12.3.2.1 Attribute specifications .................................................................................................... 163 12.3.2.2 Configuration specifications ............................................................................................ 163 12.3.2.3 Disconnection specifications ........................................................................................... 164 12.4 Elaboration of a statement part ................................................................................................ 164 12.4.1 Block statements ................................................................................................................. 164 12.4.2 Generate statements ............................................................................................................ 164 12.4.3 Component instantiation statements ................................................................................... 166 12.4.4 Other concurrent statements ............................................................................................... 166 12.5 Dynamic elaboration................................................................................................................ 167 12.6 Execution of a model ............................................................................................................... 167 12.6.1 Drivers ................................................................................................................................. 168 12.6.2 Propagation of signal values ............................................................................................... 168 12.6.3 Updating implicit signals .................................................................................................... 171 12.6.4 The simulation cycle ........................................................................................................... 172

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