SystemVerilog enum data type
Table of Contents
An enumerated type defines a set of named values. The simplest enumerated type declaration contains a list of constant names and one or more variables.
In the following example, colors are defined to be variable of the unnamed enumerated int type that includes the members red, green, blue, yellow, white, black.
enum { red, green, blue, yellow, white, black } Colors;
The actual values are defaulted to integers starting at 0 and then increase. in the above example by default variable will get the default value of 0,1,2,3,4,5 respectively from red. The values can be set for the names and also values can be set for some of the names and not set for other names. A name without a value is automatically assigned an increment of the value of the previous name.
In the following example value is set for red = 0, blue = 4, white = 10.
enum { red=0, green, blue=4, yellow, white=10, black } Colors;
green, yellow, black automatically assigned to the increment-value of 1,5,11 respectively.
If an automatically incremented value is assigned elsewhere in the same enumeration, this shall be a syntax error.
In the below example yellow will get the increment-value of 5, the value of white is set with 5. this will cause the syntax error.
enum { red=0, green=0, blue=4, yellow, white=5, black=6 } Colors
Defining new data types as enumerated types
A type name can be given so that the same type can be used in many places.
typedef enum {GOOD, BAD} pkt_type;
pkt_type pkt_a; // named type
enum methods
| Method | Description |
|---|---|
| first() | returns the value of the first member of the enumeration |
| last() | returns the value of the last member of the enumeration |
| next() | returns the value of next member of the enumeration |
| next(N) | returns the value of next Nth member of the enumeration |
| prev() | returns the value of previous member of the enumeration |
| prev(N) | returns the value of previous Nth member of the enumeration |
| num() | returns the number of elements in the given enumeration |
| name() | returns the string representation of the given enumeration value |
enum examples
Example-1 : Enumeration Type [DataTypes] This example shows how to declare enum.
module enum_datatype;
//declaration
enum { red, green, blue, yellow, white, black } Colors;
//display members of Colors
initial begin
Colors = Colors.first;
for(int i=0;i<6;i++) begin
$display("Colors :: Value of %0s \t is = %0d",Colors.name,Colors);
Colors = Colors.next;
end
end
endmodule
Simulator Output
Colors :: Value of red is = 0
Colors :: Value of green is = 1
Colors :: Value of blue is = 2
Colors :: Value of yellow is = 3
Colors :: Value of white is = 4
Colors :: Value of black is = 5
Example-2 : Enumeration Type [DataTypes]
This example shows how to set other than default values to an enum.
module enum_datatype;
//declaration
enum { red=0, green, blue=4, yellow, white=10, black } Colors;
//display members of Colors
initial begin
Colors = Colors.first;
for(int i=0;i<6;i++) begin
$display("Colors :: Value of %0s \t is = %0d",Colors.name,Colors);
Colors = Colors.next;
end
end
endmodule
Simulator Output
Colors :: Value of red is = 0
Colors :: Value of green is = 1
Colors :: Value of blue is = 4
Colors :: Value of yellow is = 5
Colors :: Value of white is = 10
Colors :: Value of black is = 11