sv_enum_datatypes_sample.pdf

8/14/2019 sv_enum_datatypes_sample.pdf

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The SystemVerilogReference Guide


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enum

Declares a user-defined enumerated type having a setof explicitly named values.

Syntax

Where dat a_t ype is optional and defaults to i nt . var is a variable name.

Rules and Examples

Declares a variable mst at e which can only take valuesi dl e , s t a r t , pause or done . By default, mst at e is oftype i nt , and the first item in the enumerated list,i dl e , is represented as 0, s ta r t as 1, pause as 2 anddone as 3.

An enum type declaration is only visible in the scope in

which it is declared, and the enumeration values mustbe unique in that scope.

A range notation, using integer constants, can be usedfor name sequences in the enumerated list.

Control of EncodingExplicit values can be defined in the enumerated list toallow one-hot, gray encoding etc.:-

Explicit and default encoding can be mixed. Nameswithout an explicit encoding increment from theprevious name:-

Here S1 has the encoding 3, S2 = 4, S4 = 9. It is anerror if explicit and default encodings overlap, forexample if S3 = 3 , S2 and S3 would have the sameencoding, and this would be a compilation error.

enum data_type { item1 , item2 . . . } var

enum {i dl e, st ar t , pause, done} mst at e;

enum {S[ 2] } seq; / / = S0, S1, S2

enum {RST, P[ 4: 5] } r ng; / / = RST, P4, P5

enum {i dl e = 1, st ar t = 2,pause = 4, done = 8} mst at e;

enum {S0 = 2, S1, S2, S3 = 8, S4} st at es;


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enum

Explicit Data Types

An explicit data type can also be defined. Here enumvariable st bi t is a bi t vector of length 3:-

With explicit data types, any explicit encodings must match the length of the data type:-

Typing in AssignmentSystemVerilog enumerated types are strongly typed.

An enum variable can only be directly assigned:-

A value from the its enumerated list

A variable of the same enumerated type

Type casting must be used to assign other types to theenumerated variable.

A t ypedef declaration can be used to associate a name

with the enumerated type. The type name can then beused for type casting:-

Typing in ExpressionWhen used in an expression, an enumerated variablebecomes an object of its data type.

enum bi t [ 2: 0] {S[ 2] } s t bi t ;

enum bi t [ 2: 0] {S0 = 3 b001,S1 = 3 b010, S2 = 3 b100} st bi t ;

mst at e = i dl e;

mst at e = next _mst at e;mst at e = 2; / / er r or

t ypedef enum {i dl e, s t ar t ,pause, done} st at e_t ;

st at e_t mst at e, next _mst at e;mst at e = st at e_t ( 2) ; / / t ype cast

i nt ai nt ;/ / mst at e i s i nt i n expr essi onai nt = mst at e + 1;


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enum

Enum Methods

Enumerte values can be accessed via methods:-

Methods can be cascaded.

This example produces the following output:-

done = 2st ar t = 1i dl e = 0

next and pr ev methods wrap around the enumeratetype declaration order.

Warning : use of f i r s t , l ast , pr ev and next methods creates code which is dependent on thedeclaration order of the enumerated type values.

See Also

i nt , t ypedef

Method Description

f i r s t ( ) Returns first value of enumeration

l ast ( ) Returns last value of enumeration

next ( N) Returns Nth next value, wrapping to

begining if need be. N defaults to 1.pr ev( N) Returns Nth previous value, wrapping

to end if need be. N defaults to 1.

num( ) Returns number of values in theenumeration

name( ) Returns string representation of givenenumeration value

t ypedef enum {i dl e, st ar t , done} st at e_t ;st at e_ t st = st . l ast ( ) ;

i ni t i al f or ever begi n $di spl ay ( " %s = %d" , st . name( ) , st ) ; i f ( st == st . f i r s t ( ) )

br eak st = s t . pr ev( ) ; end

t ypedef enum {i dl e, st ar t , done} st at e_t ;s t at e_t s t = s t ar t ;i ni t i al s t = s t . next ( 2) ; / / s t ar t + 2 = i dl e

sv_enum_datatypes_sample.pdf

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