Constant declarations

A constant is a value that does not change throughout the execution of the design. The declaration should appear:

constant-declaration :
    name-list ":" subtype ":=" expression(static) ";"

The expression is an expression of the value of the constants named by the name list. The expression is static if all values in the expression are literal values or named constants. For example, the following are valid constant declarations

constant word_length : natural := 32;
constant word_size : natural := 2**word_length;
constant hello : string := "hello" & " " & "world";