IEEE Std 1076-2008：权威VHDL语言参考手册

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"IEEE Std 1076™-2008是VHDL语言的最新标准参考手册，由IEEE Computer Society的Design Automation Standards Committee赞助并批准，对2002年的版本进行了修订。该手册是VHDL使用者的重要参考资料，提供详细的语言规范和用法指南。" VHDL（VHSIC Hardware Description Language）是一种硬件描述语言，用于设计和建模数字系统，特别是在电子工程和计算机科学领域广泛应用。IEEE Std 1076-2008是VHDL的标准参考文档，它定义了语言的语法、语义以及使用规则，确保不同开发者和工具之间的兼容性。此手册的核心内容可能包括以下几个方面： 1. **语言结构**：VHDL的语法基础，如实体、结构体、包、配置、过程、函数等基本元素的定义和使用方式。 2. **数据类型**：包括基本数据类型（如位、布尔、整数、实数、字符等）和用户自定义数据类型，如记录、数组和枚举类型。 3. **运算符和表达式**：涵盖算术、关系、逻辑、位操作等各种运算符，以及如何组合这些运算符形成表达式。 4. **进程和时序控制**：描述设计中的时间行为，如并发进程、等待语句、敏感列表和时钟边沿检测。 5. **库和包**：VHDL库的管理，包括标准库（如STD库和WORK库）以及用户自定义库的创建和使用，包的定义用于封装常量、类型、子程序等。 6. **模拟和综合**：解释VHDL代码如何在仿真环境中运行，以及如何转换为可实现的硬件描述，包括综合过程和约束的处理。 7. **实体与架构**：实体描述了硬件接口，而架构则定义了其内部逻辑，这两部分结合构成完整的VHDL设计。 8. **子程序**：函数和过程的声明和实现，用于复用和抽象设计中的模块化功能。 9. **接口对象**：信号、变量和常量的定义和使用，以及它们在设计中的通信作用。 10. **模式和约束**：用于指定设计参数和限制，提高设计的灵活性和可重用性。 11. **错误处理和注释**：关于错误报告和诊断，以及如何在代码中添加有意义的注释以提高可读性。通过这个标准手册，开发者可以深入理解VHDL的各个方面，学习如何编写清晰、有效且符合标准的代码，从而在设计复杂的数字系统时能够得心应手。由于VHDL语言的广泛使用和标准化，该手册对于教育、研究和工业界的专业人士来说都是必不可少的工具。

IEEE

Std 1076-2008 IEEE STANDARD VHDL LANGUAGE REFERENCE MANUAL

1.3 Structure and terminology of this standard

1.3.1 General

This standard is organized into clauses, each of which focuses on some particular area of the language.

Within each clause, individual constructs or concepts are discussed in each subclause.

Each subclause describing a specific construct begins with an introductory paragraph. Next, the syntax of

the construct is described using one or more grammatical productions.

A set of paragraphs describing the meaning and restrictions of the construct in narrative form then follow.

In this document, the word shall is used to indicate a mandatory requirement. The word should is used to

indicate a recommendation. The word may is used to indicate a permissible action. The word can is used for

statements of possibility and capability.

Finally, each clause may end with examples, notes, and references to other pertinent clauses.

1.3.2 Syntactic description

The form of a VHDL description is described by means of context-free syntax using a simple variant of the

Backus-Naur form (BNF); in particular:

a) Lowercase words in roman font, some containing embedded underlines, are used to denote syntactic

categories, for example:

formal_port_list

Whenever the name of a syntactic category is used, apart from the syntax rules themselves, spaces

take the place of underlines [thus, “formal port list” would appear in the narrative description when

referring to the syntactic category in item a)].

b) Boldface words are used to denote reserved words, for example:

array

Reserved words shall be used only in those places indicated by the syntax.

c) A production consists of a left-hand side, the symbol “::=” (which is read as “can be replaced by”),

and a right-hand side. The left-hand side of a production is always a syntactic category; the right-

hand side is a replacement rule. The meaning of a production is a textual-replacement rule: any

occurrence of the left-hand side may be replaced by an instance of the right-hand side.

d) A vertical bar (|) separates alternative items on the right-hand side of a production unless it occurs

immediately after an opening brace, in which case it stands for itself, as follows:

letter_or_digit ::= letter | digit

choices ::= choice { | choice }

In the first instance, an occurrence of “letter_or_digit” can be replaced by either “letter” or “digit.”

In the second case, “choices” can be replaced by a list of “choice,” separated by vertical bars [see

item f) for the meaning of braces].

e) Square brackets [ ] enclose optional items on the right-hand side of a production; thus, the following

two productions are equivalent:

return_statement ::= return [ expression ] ;

return_statement ::= return ; | return expression ;

Note, however, that the initial and terminal square brackets in the right-hand side of the production

for signatures (see 4.5.3) are part of the syntax of signatures and do not indicate that the entire right-

hand side is optional.

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IEEE STANDARD VHDL LANGUAGE REFERENCE MANUAL Std 1076-2008

f) Braces { } enclose a repeated item or items on the right-hand side of a production. The items may

appear zero or more times; the repetitions occur from left to right as with an equivalent left-recursive

rule. Thus, the following two productions are equivalent:

term ::= factor { multiplying_operator factor }

term ::= factor | term multiplying_operator factor

g) If the name of any syntactic category starts with an italicized part, it is equivalent to the category

name without the italicized part. The italicized part is intended to convey some semantic informa-

tion. For example, type_name and subtype_name are both syntactically equivalent to name alone.

h) The term simple_name is used for any occurrence of an identifier that already denotes some

declared entity.

1.3.3 Semantic description

The meaning and restrictions of a particular construct are described with a set of narrative rules immediately

following the syntactic productions. In these rules, an italicized term indicates the definition of that term,

and identifiers appearing entirely in uppercase letters refer to definitions in package STANDARD (see

16.3).

The following terms are used in these semantic descriptions with the following meanings:

erroneous: The condition described represents an ill-formed description; however, implementations are not

required to detect and report this condition. Conditions are deemed erroneous only when it is impossible in

general to detect the condition during the processing of the language.

error: The condition described represents an ill-formed description; implementations are required to detect

the condition and report an error to the user of the tool.

illegal: A synonym for “error.”

legal: The condition described represents a well-formed description.

1.3.4 Front matter, examples, notes, references, and annexes

Prior to this subclause are several pieces of introductory material; following Clause 24 are some annexes and

an index. The front matter, annexes (except Annex B), and index serve to orient and otherwise aid the user

of this standard, but are not part of the definition of VHDL; Annex B, however, is normative.

Some clauses of this standard contain examples, notes, and cross-references to other clauses of the standard;

these parts always appear at the end of a clause. Examples are meant to illustrate the possible forms of the

construct described. Illegal examples are italicized. Notes are meant to emphasize consequences of the rules

described in the clause or elsewhere. In order to distinguish notes from the other narrative portions of this

standard, notes are set as enumerated paragraphs in a font smaller than the rest of the text. Cross-references

are meant to guide the user to other relevant clauses of the standard. Examples, notes, and cross-references

are not part of the definition of the language.

1.3.5 Incorporation of Property Specification Language

VHDL incorporates the simple subset of the Property Specification Language (PSL) as an embedded

language for formal specification of the behavior of a VHDL description. PSL is defined by

IEEE Std 1850

-2005.

All PSL constructs that appear in a VHDL description shall conform to the

Information on references can be found in Clause 2.

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IEEE STANDARD VHDL LANGUAGE REFERENCE MANUAL Std 1076-2008

2. Normative references

The following referenced documents are indispensable for the application of this document (i.e., they must

be understood and used, so each referenced document is cited in text and its relationship to this document is

explained). For dated references, only the edition cited applies. For undated references, the latest edition of

the referenced document (including any amendments or corrigenda) applies.

IEEE Std 754

-1985 (Reaff 1990), IEEE Standard for Binary Floating-Point Arithmetic.

IEEE Std 854

-1987 (Reaff 1994), IEEE Standard for Radix-Independent Floating-Point Arithmetic.

IEEE Std 1850

-2005, IEEE Standard for Property Specification Language (PSL).

ISO/IEC 8859-1:1998, Information technology—8-bit single-byte coded graphic character sets—Part 1:

Latin alphabet No. 1.

ISO/IEC 9899:1999, Programming languages—C.

ISO/IEC 9899:1999/Cor 1:2001, Programming languages—C, Technical Corrigendum 1.

ISO/IEC 9899:1999/Cor 2:2004, Programming languages—C, Technical Corrigendum 2.

ISO/IEC 19501:2005, Information technology—Open Distributed Processing—Unified Modeling Language

(UML) Version 1.4.2.

IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, P.O. Box 1331, Piscataway,

NJ 08855-1331, USA (http://standards.ieee.org/).

The IEEE standards or products referred to in this clause are trademarks of the Institute of Electrical and Electronics Engineers, Inc.

ISO/IEC publications are available from the ISO Central Secretariat, Case Postale 56, 1 rue de Varembé, CH-1211, Genève 20, Swit-

zerland/Suisse (http://www.iso.ch/). ISO/IEC publications are also available in the United States from Global Engineering Documents,

15 Inverness Way East, Englewood, Colorado 80112, USA (http://global.ihs.com/). Electronic copies are available in the United States

from the American National Standards Institute, 25 West 43rd Street, 4th Floor, New York, NY 10036, USA (http://www.ansi.org/).

Authorized licensed use limited to: East China Normal University. Downloaded on September 13, 2009 at 22:51 from IEEE Xplore. Restrictions apply.

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