systemverilog之OOP

what is oop

terminology

an example class

default methods for classes

static attibute

assigment and copying

inheritance

polymorphism

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why oop?

1.    helps in creating and maintaining large testbench:

You can creat complex data types and tie them together with

the routines that work with them

2.increases productivity:

You can creat testbenches and system-level models at a more

abstract level by calling a routine to perform an action rather than toggling bits

You can work with transactions rather than signals transitions

3.Allows the Testbench to be reused

OOP decouples the testbench from design details make it more rebust and easier

to maintain and reuse

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How should the data and code be brought tegother?

transactions

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OOP Basics:Terminology

Blueprint for a house ===> Class

A compelet house     ====> Object

House Address          ====> Handle

Turn on/off swithes     =====> Methods

Light swithes             ======> Properties

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verilog                 VS     OOP

Block definition     module                            class

Block  instance      instance                         object

Block  name          instance name                handle

Data Type             reg & wire                      properties & variables

Executable Code    behavioral blocks              Methods:functions

(always / initial)               and tasks

tasks / functions

communication         ports or cross-module    mailboxes/semaphores/calls

between blocks      task calls                       ……..

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OOP:Your First Class

略。。。

BusTran b; <—Declare a handle that points to an object of the type BusTran .When a handle is declared it is initialized to null

b= new();<- call the new function to construct the BusTran object.

when you call new you are allocating a new block of

memory to store variable for that object

1.new allocates space for ButTran

2.Initialize the variable to their default value( 0 for 2state

and x for 4-state variables)

3.Return the address where the object is stored

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how gettint a handle on objects?

how deallocating a handle on objects?

BusTran b1,b2; <-----declare a handle

b1 = new();      <-----allocate bustran object

b2 = b1;           <------

b1 = new();       <------allocate another buttran object

b2 = null;          <-------deallocate the second bustran object

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How do I create a variable shared by all objects of a class,but not make it global?

static variable

1.The static variable is associted with the class definition , not the instantiated object

2.It is often used to store meta-data,such as number of  instances construncted

3.It is shared by all objects of that class

Using  the id field can help keep track of transactions as flow through test

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class routines : tasks and functions

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Using one class inside another class

mainly use a handle to an object

using hierarchical syntax

done for reuse and controll complexity

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copy:object copy

1.shallow copy  ===> b2 = new()b1  copy的只是句柄，但b1 & b2 指向同一个空间

2.deep copy      ====b2  = copy(b1) copy之后，b1 & b2有独立的空间

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Inheritance

1.易于debug

2.在以前的基础进行代码扩展，而不是修改以前的代码.

super.parent_method/property

Inheritance chain

1.base class can hold extended class handle

2.extended class cannot hold base handle,this fails because the base object is missing properties(variable)

that only exist in the extended class,such as bad_src in the following example

$cast(badtr,tr) ===>必须badtr tr的类型一致

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Abstract Classes and Virtual Methods

1.virtual class

2.polymorphism

the oop term for multiple routines sharing a common name is “polymorphism”

polymorphism is realized by virtual method

always declare routines inside a class as virtual so that they can be redefine

in an extended class.This applies to all tasks and functions ,except the new

function.which is called when the object is constructed, and there is no way to extend it

virtual fucntion在run时实现，compile并不关注 (有绑定的意思)

new在compile时实现

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parameterized classes

It is often useful to define a generic class whose objects can be

instantiated to have different array sizes or data types

1.The normal verilog parameter machanism is used to parameterize the calss

class vector #(int size = 1)

bit [size-1:0] a;

endclass

2.Instance of this class can then be instantiated like modules or interfaces

vecor #(.size(2)) vtwo;

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Initializing class properties (new)

How does systemverilog know which new function to call?

it does that by looking at the type of handle(有的概念根据句柄所指向的对象类型比如通过句柄调用method)