1/8/2007 - L10 AttributesCopyright 2006 - Joanne DeGroat, ECE, OSU1 Language Attributes and Package Standard A very useful aspect of the language

1/8/2007 - L10 Attributes Copyright 2006 - Joanne DeGroat, ECE, OSU 1

Language Attributes and Package StandardA very useful aspect of the language.


Attributes What are attributes? VHDL Attributes

Types Signal Variables Examples Signal Specific Other

Package Standard


What are attributes? John is just plain nasty!!!!

Being nasty is an attribute of John.

Language attributes Lovely, pretty and handsome are adjectives which

describe and a attribute of the language element they apply to. Lovely Rita ….. (Do you remember the Beatles!)


What are attributes? VHDL attributes provide additional

information on the language element to which they are associated.

For example They can tell you the size of an array and whether

the index is X to Y or Y downto X. They can tell you a signal’s last value Etc.


Attributes that relate to TYPES ATTRIBUTE: T’BASE

Kind: Type Prefix: Any Type or Subtype T Result Type: The base type of T Result: Same – a type Restrictions: This attribute is allowed only as a prefix of

the name of another attribute; T’BASE’LEFT Example: BIT’BASE’LEFT is ‘0’

Base Type: The base type of a type is the type itself


Attributes that relate to TYPES ATTRIBUTE: T’LEFT

Kind: Value Prefix: Any scalar type or subtype T Result Type: Same type a T Result: The left bound of T Example: BIT’LEFT has value ‘0’

Scalar type consist of enumeration, integer, physical, and floating point types.


Attributes that relate to TYPES ATTRIBUTE: T’RIGHT

Kind: Value Prefix: Any scalar type or subtype T Result Type: Same type a T Result: The right bound of T Example: BIT’RIGHT has value ‘1’


Attributes that relate to TYPES ATTRIBUTE: T’HIGH

Kind: Value Prefix: Any scalar type or subtype T Result Type: Same type a T Result: The upper bound of T Example: BIT’ HIGH has value ‘1’


Attributes that relate to TYPES ATTRIBUTE: T’LOW

Kind: Value Prefix: Any scalar type or subtype T Result Type: Same type a T Result: The lower bound of T Example: BIT’LOW has value ‘0’


Attributes that relate to TYPES ATTRIBUTE: T’POS(X)

Kind: Function Prefix: Any discrete or physical type or subtype T

A discrete type is an enumeration or intger type. Parameter: Any expression whose type is the base type of T Result Type: Universal Integer

Universal integer is an integer of an anonymous predefined integer type. An integer.

Result: The position number of the value of the parameter. Example:

type operations is (OPADD, OPSUB, OPAND, OPOR); signal oper : operations; Then operations’POS(OPSUB) has value 2 operations’POS(OPOR) has value 4


Attributes that relate to TYPES ATTRIBUTE: T’VAL(X)

Kind: Function Prefix: Any discrete or physical type or subtype T Parameter: Any expression of any integer type Result Type: The base type of T Result: The value from the type whose position number is

the universal integer value corresponding to X Example:

type operations is (OPADD, OPSUB, OPAND, OPOR); signal oper : operations; Then operations’VAL(2) has value OPSUB operations’VAL(4) has value OPOR


Attributes that relate to TYPES ATTRIBUTE: T’SUCC(X)

Kind: Function Prefix: Any discrete or physical type or subtype T Parameter: Any expression whose type is the base type of T Result Type: The base type of T Result: The value whose position number is one greater than that of

the parameter. Restricitons: An error occurs if X equals T’BASE’HIGH Example:

type operations is (OPADD, OPSUB, OPAND, OPOR); signal oper : operations; Then operations’SUCC(OPSUB) has value OPAND operations’SUCC(OPAND) has value OPOR


Attributes that relate to TYPES ATTRIBUTE: T’PRED(X)

Kind: Function Prefix: Any discrete or physical type or subtype T Parameter: Any expression whose type is the base type of T Result Type: The base type of T Result: The value whose position number is one less than that of the

parameter. Restricitons: An error occurs if X equals T’BASE’LOW Example:

type operations is (OPADD, OPSUB, OPAND, OPOR); signal oper : operations; Then operations’PRED(OPSUB) has value OPADD operations’PRED(OPAND) has value OPSUB


Attributes that relate to TYPES ATTRIBUTE: T’LEFTOF(X)

Kind: Function Prefix: Any discrete or physical type or subtype T Parameter: Any expression whose type is the base type of T Result Type: The base type of T Result: The value which is to the left of the parameter in the range of

T. Restricitons: An error occurs if X equals T’BASE’LEFT Example:

type operations is (OPADD, OPSUB, OPAND, OPOR); signal oper : operations; Then operations’LEFTOF(OPSUB) has value OPADD


Attributes that relate to TYPES ATTRIBUTE: T’RIGHTOF(X)

Kind: Function Prefix: Any discrete or physical type or subtype T Parameter: Any expression whose type is the base type of T Result Type: The base type of T Result: The value which is to the right of the parameter in the range

of T. Restricitons: An error occurs if X equals T’BASE’RIGHT Example:

type operations is (OPADD, OPSUB, OPAND, OPOR); signal oper : operations; Then operations’RIGHTOF(OPSUB) has value OPAND


Attributes that relate to ARRAYS ATTRIBUTE: A’LEFT[(N)]

Kind: Function Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer. Defaults to 1. Result Type: Type of the Nth index range of A Result: Left bound of the Nth index range of A.

ATTRIBUTE: A’RIGHT[(N)] Kind: Function Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer. Defaults to 1. Result Type: Type of the Nth index range of A Result: Right bound of the Nth index range of A.


Attributes that relate to ARRAYS ATTRIBUTE: A’HIGH[(N)]

Kind: Function Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer. Defaults to 1. Result Type: Type of the Nth index range of A Result: Upper bound of the Nth index range of A.

ATTRIBUTE: A’LOW[(N)] Kind: Function Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer. Defaults to 1. Result Type: Type of the Nth index range of A Result: Lower bound of the Nth index range of A.


Attributes that relate to ARRAYS ATTRIBUTE: A’RANGE[(N)]

Kind: Range Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer. Defaults to 1. Result Type: Type of the Nth index range of A Result: The range A’LEFT(N) to A’RIGHT(N) or

A’LEFT(N) downto A’RIGHT(N) ATTRIBUTE: A’REVERSE_RANGE[(N)]

Kind: Range Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer. Defaults to 1. Result Type: Type of the Nth index range of A Result:. The range A’ RIGHT(N) to A’ LEFT(N) or A’

RIGHT(N) downto A’ LEFT(N)


Attributes that relate to ARRAYS ATTRIBUTE: A’LENGHT[(N)]

Kind: Range Prefix: Any prefix A that is an array object Parameter: Locally static expression of type integer.

Defaults to 1. Result Type: Universal Integer Result: Number of values in the Nth index range, i.e.,

A’HIGH(N) – A’LOW(N) +1


Attributes that relate to ARRAYS EXAMPLE:

signal mydt : bit_vector (31 downto 0); signal myto : bit_vector ( 0 to 15);

Then the mydt myto ‘LEFT | | | ‘RIGHT | | | ‘HIGH | | | ‘LOW | | | ‘RANGE | | | ‘REVERSE_RANGE | | | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | | | ‘HIGH | | | ‘LOW | | | ‘RANGE | | | ‘REVERSE_RANGE | | | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | 0 | 15 | ‘HIGH | | | ‘LOW | | | ‘RANGE | | | ‘REVERSE_RANGE | | | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | 0 | 15 | ‘HIGH | 31 | 15 | ‘LOW | | | ‘RANGE | | | ‘REVERSE_RANGE | | | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | 0 | 15 | ‘HIGH | 31 | 15 | ‘LOW | 0 | 0 | ‘RANGE | | | ‘REVERSE_RANGE | | | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | 0 | 15 | ‘HIGH | 31 | 15 | ‘LOW | 0 | 0 | ‘RANGE | 31 downto 0 | 0 to 15 | ‘REVERSE_RANGE | | | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | 0 | 15 | ‘HIGH | 31 | 15 | ‘LOW | 0 | 0 | ‘RANGE | 31 downto 0 | 0 to 15 | ‘REVERSE_RANGE | 0 to 31 | 15 downto 0 | ‘LENGTH | | |




Then the mydt myto ‘LEFT | 31 | 0 | ‘RIGHT | 0 | 15 | ‘HIGH | 31 | 15 | ‘LOW | 0 | 0 | ‘RANGE | 31 downto 0 | 0 to 15 | ‘REVERSE_RANGE | 0 to 31 | 15 downto 0 | ‘LENGTH | 32 | 16 |


Attributes that relate to SIGNALS ATTRIBUTE: S’DELAYED[(T)]

Kind: Signal Prefix: Any signal Parameter: Any static expression of type TIME

that evaluates to a non-negative value. Result Type: Base type of S Result: A signal equivalent to S delayed T units

of time. The value of S’DELAYED(t) is always equal to the value of S t units of time previous.


Attributes that relate to SIGNALS ATTRIBUTE: S’STABLE[(T)]

Kind: Signal Prefix: Any signal Parameter: Any static expression of type TIME that

evaluates to a non-negative value. Defaults to 0 if omitted.

Result Type: Boolean Result: A signal that has value TRUE when an event has

not occurred on signal S for T units of time, and the value FALSE otherwise.


Attributes that relate to SIGNALS ATTRIBUTE: S’QUIET[(T)]

Kind: Signal Prefix: Any signal Parameter: Any static expression of type TIME that

evaluates to a non-negative value. Defaults to 0 if omitted.

Result Type: Boolean Result: A signal that has value TRUE when the signal has

been quiet (not had a change in value) for T units of time.


Attributes that relate to SIGNALS ATTRIBUTE: S’TRANSACTION

Kind: Signal Prefix: Any signal Result Type: Type BIT Result: A signal that toggles to the inverse of its previous value in

each simulation cycle in which the signal S becomes active. ATTRIBUTE: S’EVENT

Kind: Signal Prefix: Any signal Result Type: Type BOOLEAN Result: A value that indicates whether an event has just occurred on

signal S.


Attributes that relate to SIGNALS ATTRIBUTE: S’ACTIVE

Kind: Function Prefix: Any signal Result Type: Type BOOLEAN Result: A value that indicated whether S is active, i.e., has a new

value generated for it this simulation cycle. ATTRIBUTE: S’LAST_EVENT

Kind: Function Prefix: Any signal Result Type: Type TIME Result: The amount of time that has elapsed since the last event on

signal S.


Attributes that relate to SIGNALS ATTRIBUTE: S’LAST_ACTIVE

Kind: Function Prefix: Any signal Result Type: Type TIME Result: The amount of time that has elapsed since the last

time the signal S was active. ATTRIBUTE: S’LAST_VALUE

Kind: Function Prefix: Any signal Result Type: Base type of S Result: The previous value of S.


Attributes that relate to Design Units ATTRIBUTE: B’BEHAVIOR

Kind: Value Prefix: Any block denoted by a label or entity denoted by

its architecture name. Result Type: BOOLEAN Result: The value if TRUE if the block defined by the

block statement or entity does not contain a component instantiation statement.

ATTRIBUTE: B’STRUCTURE The same except that TRUE when the block/entity

contains only component instantiations


Package STANDARD


Package Standard (cont.)


Package Standard (completed)

Documents

1/8/2007 - L10 AttributesCopyright 2006 - Joanne DeGroat, ECE, OSU1 Language Attributes and Package Standard A very useful aspect of the language