Using Packages in Behavioral Modeling of an 8-bit ALU: A Step-by-Step Guide, Slides of Computer Aided Design (CAD)

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Project Step 6

Step 3 in behavioral modeling. Use

of packages.

So far

• Modeled the ALU structurally with dataflow

models of the leaf units.

• Modeled the structure exactly in the first

behavioral architecture. Code=Structure

• 2 nd^ Behavioral model used a combined P&K&R

to choose the operation

• For op A have P,K,R of 1100,1111,
• For op A AND B have 1000,1111,

The new ENTITY

• ENTITY alu_8bit_v4 IS
• PORT ( alu_op : IN operations;
• a,b : IN BIT_VECTOR(7 downto 0);
• Cin : IN BIT;
• Zout : OUT BIT_VECTOR(7 downto 0);
• Cout : OUT BIT);
• END alu_8bit_v4;
• Note that this ENTITY uses type operations

Type Operations

• Type OPERATIONS was declared in the declarative region of the ARCHITECTURE of the testbench.
• The scope of TYPE operations is limited to the ARCHITECTURE in which it is declared.
• So how can this ENTITY declaration use it?
• Move the declaration to a PACKAGE
  • that both the testbench ARCHITECTURE and this ENTITY use.
• So declare a package declarative part and package body. TYPE operations is moved to the declarative part.

The package and use.

• As the declaration is now in the package the

testbench architecture must now have a USE clause prior to it so that it can see the declaration.

• USE work.step6_package.all;
• ARCHITECTURE test OF p6 IS …

• BE SURE TO COMMENT OUT THE DECLARATION IN

THE TESTBENCH ARCHITECTURE

Type Operations

• The declaration for type operations in the

testbench and the package would be identical

so why not just have both of them.

• They are different declarations and therefore a

different type.

The Procedures

• Also move the procedures declared in the

process declarative region out to the package

body.

• Add declarations for them in the package

declarative part. (but the code from before

goes in the package body)

• The declaration can be cut and pasted.

A final modification

• Modify the case statement to switch on

opu_op instead of the concatenated PKR value

which is no longer even available.

• And once again
  • Move the declaration for TYPE operations to the package and comment it out in the testbench architecture