A procedure defines a group of sequential statements executed when the procedure is called. A procedure can return any number of values (or no values) via its parameter list. A procedure call invokes the execution of the procedure body.

PROCEDURE procedure_name [(formal_parameters)] IS

…declarations

BEGIN

…sequential statements

END [PROCEDURE] [procedure_name];

…

procedure_name[actual_parameters] -- procedure call

formal_parameters

Specifies a list of parameters (constants, signals, or variables with the mode in, out, or inout).

declarations

Declarations include data types, constants, signals, files, variables, attributes, and subprograms.

sequential statements

Statements that are executed in the order in which they appear, that define algorithms for the execution of a subprogram or process.

-- declaration with formal parameters int and bin

PROCEDURE int2bin (VARIABLE int: IN INTEGER; VARIABLE bin: OUT BIT_VECTOR) IS

VARIABLE temp: INTEGER;

BEGIN -- start of sequential procedure statements

temp := int;

FOR i IN 0 TO (bin'LENGTH -1) LOOP

IF (temp mod 2 = 1) THEN

bin(i) := '1';

ELSE

bin(i) := '0';

END IF;

temp := temp/2;

END LOOP;

END int2bin; -- end of sequential procedure statements

…

PROCESS -- continued model description

VARIABLE in_var: INTEGER:=10;

VARIABLE out_vec: BIT_VECTOR (1 to 8);

BEGIN

-- procedure call with actual parameters int_var and out_vec

int2bin (in_var, out_vec);

WAIT;

END PROCESS;