1. Step 2 in behavioral modeling. Use of procedures.
Project Step 5
Step 2 in behavioral modeling. Use of procedures.
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

2. The nature of the process
Will still use P, K, and R to control the operation.
Previously have use P to compute Pi, K to compute Ki, and then R to generate the final result.
Now will use a combined P&K&R to choose the operation being performed
For op A have P,K,R of 1100,1111,1100
For op A AND B hove 1000,1111,1100
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

3. Copyright 2006 - Joanne DeGroat, ECE, OSU
continued
For A + B have 0110,0001,0110
Then we can use a case statement on a variable that concatenates P&K&R to choose which operation to perform.
opersw := P & K & R; --Note use of variable
CASE opersw IS
WHEN “ ” => Zout <= A;
Cout <= ‘0’; --op A
WHEN “ ” =>
neg(A,Ztemp,CoutTemp);
Zout <= Ztemp; Cout<= CoutTemp;
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

4. Copyright 2006 - Joanne DeGroat, ECE, OSU
Note on operations
For logical operation can do vector operations
Zout <= A AND B;
Where A and B are the input bit vectors
Both vectors must be of the same size
Arithmetic operations will need procedures
One for Add
One for 2’s complement
One for Subtract that can be an implementation of binary subtraction, or subtraction using 2’s complement addition
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

5. Copyright 2006 - Joanne DeGroat, ECE, OSU
The procedures
The procedures are to be declared in the declarative region of the process
In the declarative region of the process can only declare a procedure body. And thus no procedure declaration part is done.
Scope of procedure is limited to just this process. (We will later move these to a package.)
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

6. Copyright 2006 - Joanne DeGroat, ECE, OSU
Addition
BINADD
A procedure for binary addition using sequential statements.
Will make the arguments to the procedure unconstrained so that it will be capable of adding words of any length (constraint that both inputs are the same index range).
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

7. Unconstrained declaration
PROCEDURE binadd (l,r : IN BIT_VECTOR;
cin : IN BIT;
sum : OUT BIT_VECTOR;
cout : OUT BIT) IS
VARIABLE carry : BIT: --internal variable carry
BEGIN
carry := cin;
FOR i IN l’reverse_range LOOP
-- compute sum for position I
-- compute carry out for position I into carry variable
END LOOP;
-- assign cout from final value of carry
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

8. Copyright 2006 - Joanne DeGroat, ECE, OSU
Highlights on the code
Inputs are “unconstrained” – they can be any size
We will later use these same procedures in a package and the data size will be 16 bits.
Outputs are variables
Need to use attribute for loop parameter
If L declared (x downto 0) such that leftmost bit is the msb and highest index
THEN L’REVERSE_RANGE has the designation 0 to x
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

9. Copyright 2006 - Joanne DeGroat, ECE, OSU
Overall look of code
Same ENTITY as before
ARCHITECTURE v_3 OF adder_8 IS
BEGIN
--A single process as just described
PROCESS (sensitivity list)
PROCEDURES
Local Variables
opersw:=
CASE opersw…….
END;
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU