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 Pctl to compute Pint, Kctl to compute Ki, and then Rctl 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 have 1000,1111,1100
For op A + B have 0110,0001,0110
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

3. Copyright 2006 - Joanne DeGroat, ECE, OSU
continued
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;
-- Ztemp and CoutTemp are variables
WHEN …
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
And the vectors must be of the same size for a bit-wise vector operation
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 and write the procedure declaration.)
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

6. Copyright 2006 - Joanne DeGroat, ECE, OSU
Addition
Procedure 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). (right now size is 8 bits, later will use the procedure for 16 bit arguments).
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, sum := …
-- compute carry out for position I into carry variable, carry := …
END LOOP;
-- assign cout from final value of carry
- - I provide a lot but you must finish this
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 of the procedure are variables. These need to be assigned to the appropriate signal.
Need to use attribute for loop parameter as shown
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. Now use the procedure in the case
Within the main process
BEGIN …
CASE opersw IS
WHEN “ ” => Zout <= A;
Cout <= ‘0’; --op A
WHEN “0110xxxxxxxx” => --and add
binaddd(a,b,cin,sum,vcout);
zout <= sum;
cout<= vcout;
WHEN “xxxxxxxxxxxx” => …
1/8/ L11 Project Step 5
Copyright Joanne DeGroat, ECE, OSU

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