IEEE 2008年VHDL语言标准参考手册

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IEEE Std 1076-2008是针对VHDL（VHSIC Hardware Description Language，超大规模集成电路硬件描述语言）的标准文档，由设计自动化标准委员会（Design Automation Standards Committee, DAC）赞助并由IEEE计算机协会发布。该标准修订了先前的IEEE Std 1076-2002版本，于2008年9月26日获得批准，反映了VHDL语言的最新发展和规范。 VHDL是一种广泛用于系统级和硬件描述设计的高级硬件描述语言，它允许工程师以抽象的方式描述数字系统的功能和行为，包括组合逻辑、时序逻辑、并行处理和流水线设计。IEEE Std 1076-2008定义了VHDL的语法、语义、数据类型、结构化设计元素（如实体、架构、配置、包和程序块）、以及接口描述和模块化设计的原则。此标准文档涵盖了以下几个关键部分： 1. **语言特性**：详细描述了VHDL的构造规则，包括基本的声明、赋值语句、过程和函数、并发与顺序执行等。它还定义了异常处理机制，如assertions（断言）和coverage分析，以确保设计的正确性和可测试性。 2. **类型系统**：VHDL支持多种数据类型，包括整型、布尔型、浮点型、数组、记录和枚举类型，以及它们之间的转换规则。 3. **设计流程**：阐述了如何组织和模块化设计，包括使用实体（Entity）来定义接口和架构（Architecture）来实现功能。标准还强调了设计复用的重要性，通过包（Package）和库（Library）来管理模块和实体。 4. **仿真与验证**：规定了VHDL设计的模拟、综合（Synthesis）和验证方法，包括模型和测试bench的设计，以及与仿真器的交互。 5. **兼容性与移植**：IEEE Std 1076-2008确保了与其他VHDL版本的兼容性，并提供了指导，使设计者能够在不同的工具链和硬件平台上进行无缝迁移。 6. **版权与版权声明**：所有内容受IEEE的版权保护，任何使用必须遵守相关规定，包括PDF格式的ISBN号码。通过学习和遵循IEEE Std 1076-2008，硬件开发者能够创建更高质量、可重用且可验证的硬件设计，同时在整个电子设计自动化（EDA）行业中保持一致性。这个标准对于硬件工程师、系统集成者和半导体制造商来说，都是必不可少的技术参考文献。

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.

IEEE

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.

IEEE

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/).

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