attribute-name : prefix "'" simple-name ["(" expression ")"]

The following is a description of the predefined attributes:

base

The base attribute designates the base type of its prefix. The prefix must be a type or subtype name. This attribute is only allowed as the prefix of another attribute. For example, natural'base'low.

left

The left attribute designates the left-most bound of its prefix. The prefix may be any scalar type or subtype.

right

The right attribute designates the right-most bound of its prefix. The prefix may be any scalar type or subtype.

low

The low attribute designates the lower bound of its prefix. The prefix may be any scalar type or subtype.

high

The high attribute designates the upper bound of its prefix. The prefix may be any scalar type or subtype.

pos(X)

This attribute returns the position number of its parameter X. Its prefix must be a discrete or physical type or subtype.

val(X)

This attribute returns the value at the position, in the type, given by its parameter X. Its prefix must be a discrete or physical type or subtype.

succ(X)

This returns the value whose position number is one more than its parameter X. Its prefix must be a discrete or physical type or subtype.

pred(X)

This returns the value whose position number is one less than its parameter X. Its prefix must be a discrete or physical type or subtype.

leftof(X)

This returns the value that is left of its parameter X in the type given by the prefix. Its prefix must be a discrete or physical type or subtype.

rightof(X)

This returns the value that is right of its parameter X in the type given by the prefix. Its prefix must be a discrete or physical type or subtype.

left [(X)]

The left attribute returns the left bound of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

right [(X)]

The right attribute returns the right bound of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

low [(X)]

The low attribute returns the lower bound of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

high [(X)]

The high attribute returns the upper bound of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

range [(X)]

This attribute designates the range of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

reverse_range [(X)]

This attribute designates the reverse of the range of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

length [(X)]

This attribute returns the length of the Nth dimension of its prefix. If the option argument is given, then N is X; otherwise, N is 1. The prefix must be an array object or constrained array type.

delayed [(T)]

The delayed attribute creates a signal whose value is the value of its prefix delayed by T time units. The prefix must be a signal. If the optional value for T does not appear, then T is 0 fs.

stable [(T)]

The stable attribute creates a signal whose value is true when an event has not occurred on the prefix signal in T units of time. The prefix must be a signal. If the optional value for T does not appear, then T is 0 fs.

quiet [(T)]

The quiet attribute creates a signal whose value is true when the signal prefix has been quiet for T units of time. The prefix must be a signal. If the optional value for T does not appear, then T is 0 fs.

transaction

This attribute creates a boolean signal whose value toggles every time there is a transaction on its signal prefix. The prefix must be a signal.

event

The event attribute returns true if an event has occurred on its signal prefix during the current simulation cycle. The prefix must denote a signal.

active

The event attribute returns true if a transaction has occurred on its signal prefix during the current simulation cycle. The prefix must denote a signal.

last_event

This attribute returns the time that has elapsed since the last event occurred on its signal prefix. The prefix must denote a signal.

last_active

This attribute returns the time that has elapsed since the last transaction occured on its signal prefix. The prefix must denote a signal.

last_value

This attribute returns the value its signal prefix had prior to the last event. The prefix must denote a signal.

behavior

Designates true if the prefix does not contain a component instantiation statement. The prefix must be an architecture or block name.

structure

Designates true if the prefix contains only component instantiation statements. The prefix must be an architecture or block name.

The users may also declare attributes with the attribute declaration and specification. They follow the rules:

attribute-declaration : ATTRIBUTE simple-name ":" type ";"
entity-class : ENTITY | ARCHITECTURE | PROCEDURE | FUNCTION | 
    PACKAGE | TYPE | SUBTYPE | CONSTANT | SIGNAL | VARIABLE |
    COMPONENT | LABEL
entity-list : name-list | OTHERS | ALL
entity-specification : entity-list ":" entity-class
attribute-specification :
    ATTRIBUTE simple-name OF entity-specification IS expression ";"

The attribute declaration creates the attribute with the specified name. Attribute specifications indicate the values that the attribute has for various prefixes. Each specification indicates the value of that attribute for the prefixes listed in the entity specification. The value is given by the expression part. If the entity specification contains a name list, then the named entities will have the specified attribute with the specified value. The list of names must denote objects of the entity class specified. If the entity specification contains the reserved word OTHERS, then all the entities of the specified class that do not appear in another attribute specification will have the specified attribute with the specified value. If the entity specification contains the reserved word ALL, then all the entities of the specified class will have the specified attribute with the specified value.