Chapter 5 Copyright 2012 G. Tumbush, C. Spear v1.2

Transcription

1 Chapter 5, Basic OOP topics Why OOP OOP terminology Classes Objects Custom constructors Static variables/methods Classes within classes Handles Copying objects 1

2 5.1 Introduction Why OOP? Gains in productivity/maintainability/thoroughness Strongly couples data with code that manipulates it. Allows the testbench to be reused Facilitates testing at the transaction level SystemVerilog allows inheritance and polymorphism 2

3 5.2 Think of Nouns, not Verbs Create Transactions Transmit Transactions Scenario Generator Environment Functional Agent Scoreboard Checker Receive Transactions Command Driver Assertions Monitor Check Transactions Signal DUT Report 3

4 5.5 OOP Terminology Blueprint for a house A complete house House Address 123 Elm Street Class Object Handle Turn on/off switches Light switches Methods Properties Dr. Meeta Yadiv, ASIC Verification, North Carolina State University Fall

5 5.5 OOP Terminology (cont.) Blueprint for a house A complete house Address of a house Light switches Turn on/off switches Class Programming element containing related groups of features and functionality Provides a template for building objects Can be used as a data structure Object An object is an instance of a class Handle Type-safe pointer to an object can not be corrupted Properties Variables contained in the instance of the class Methods Tasks/functions (algorithms) that operate on the properties in this instance of the class Dr. Meeta Yadiv, ASIC Verification, North Carolina State University Fall

6 5.5 OOP Terminology (cont.) HDL OOP Verilog Block definition module class Block instance instance object Block name instance name handle SystemVerilog Data Types registers & wires Properties: Variables Executable Code behavioral blocks Methods: tasks (always, initial), and functions tasks, functions Communication between blocks Ports or crossmodule task calls Dr. Meeta Yadiv, ASIC Verification, North Carolina State University Fall 2007 task/function calls, mailboxes, semaphores, etc. 6

7 5.3 Your First Class class Transaction; bit [31:0] addr, crc, data[8]; function void display; $display( Transaction: %h, addr); : display properties (variables) class method function void calc_crc; crc = addr ^ data.xor; : calc_crc class method xor method : Transaction 7

8 5.4 Where to define (and use) a Class A class can be defined in: 1. program 2. module 3. package A class can be used in: 1. module 2. program 3. package 4. Can be constructed and extended Locations for defining classes: Each class in a separate file Related classes in a package 8

9 5.6 Creating new objects Call new() to allocate space for the object Transaction tr; tr = new(); Object Handle of class Transaction: does not create object itself, uninitialized value is null Class Transaction creates an object of class Transaction tr now points to the object OR Transaction tr = new(); () not required No control over initialization order and if automatic omitted, constructor called at start of simulation 9

10 5.6 Creating new objects Call new() to allocate space for the object Transaction tr; tr = new(); Calling new() procedurally: module test; Transaction tr; initial tr = new(); endmodule tr null tr transaction object 10

11 Class in a package package abc; class Transaction; // Class body endpackage program automatic test; import abc::*; Transaction tr; // Test code endprogram 11

12 Class Exercise Create a class called MemTrans that contains the following members: An 8-bit data_in of logic type A 4-bit address of logic type A void function that prints out the value of data_in and address Construct a MemTrans object in an initial block 12

13 Class Exercise (cont.) Create a class called MemTrans that contains the following members: An 8-bit data_in of logic type A 4-bit address of logic type A void function that prints out the value of data_in and address class MemTrans; logic [7:0] data_in; logic [3:0] address; function void print; $display( Data_in = %h, address = %h, data_in, address); Construct a MemTrans object in an initial block initial begin MemTrans MyMemTrans; MyMemTrans = new(); end // or initial begin MemTrans MyMemTrans = new(); end 13

14 5.6.2 Custom Constructor For every class SystemVerilog creates a default new() Memory space is allocated All variables initialized to their default value The custom constructor does more than allocate memory it also initializes the values. Overloads new() class Transaction; logic [31:0] addr, crc, data[8]; function new(); addr = 3; data = '{default:5}; 14

15 Custom Constructor Exercise Using your MemTrans class create a custom constructor so that data_in and address are both initialized to 0. 15

16 Custom Constructor Exercise Using your MemTrans class create a custom constructor so that data_in and address are both initialized to 0. class MemTrans; logic [7:0] data_in; logic [3:0] address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new; data_in = 8 h0; address = 4 h0; 16

17 5.6.2 Custom Constructor with arguments Make the custom constructor more flexible by passing in values Defaults are used if argument(s) are not passed class Transaction; logic [31:0] addr, crc, data[8]; function new(logic [31:0] a=3, d=5); addr = a; data = '{default:d}; tr1 = new(10); tr2 = new(, 6); tr3 = new(10, 6); tr4 = new(.a(10),.d(6)); 17

18 Custom Constructor with args Exercise Using your MemTrans class create a custom constructor so that data_in and address are both initialized to 0 but can also be initialized through arguments passed into the constructor 1. Create 2 new MemTrans objects 2. Initialize address to 2 in the 1 st object, passing arguments by name 3. Initialize data_in to 3 and address to 4 in the 2 nd object, passing arguments by name. 18

19 Custom Constructor with args Exercise Using your MemTrans class create a custom constructor so that data_in and address are both initialized to 0 but can also be initialized through arguments passed into the constructor 1. Create 2 new MemTrans objects class MemTrans; logic [7:0] data_in; logic [3:0] address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new(logic [7:0] data_init = 0, logic [3:0] address_init = 0); data_in = data_init; address = address_init; 2. Initialize address to 2 in the 1 st object, passing arguments by name 3. Initialize data_in to 3 and address to 4 in the 2 nd object, passing arguments by name. initial begin MemTrans mt1, mt2; mt1 = new(.address_init(2)); mt2 = new(.data_init(3),.address_init(4)); end 19

20 5.7 Object Deallocation Garbage collection, i.e. reclaiming unused memory, is automatic An object is deallocated if no handles point to it. Transaction t1, t2; t1 = new(); t2 = t1; t1 = null, t2=null t2=null, t1 t2 Object A t1 = new(); t2 t1 t1 = null; Object A t2 Object A Object B t1 = null Object B 20

21 5.8 Using Objects Similar to Verilog, use the. delimiter to access properties (variables) and methods (tasks and functions) of a class. Recall: class Transaction; bit [31:0] addr, crc, data[8]; function void display; $display( Transaction: %h, addr); Endfunction function void calc_crc; crc = addr ^ data.xor; Endfunction properties (variables) methods (tasks or functions) Usage: Transaction t; t = new(); t.addr = 32 h42; t.display(); () not required 21

22 Using Objects Exercise Using the previous MemTrans exercise assign the address of the first object to 4 hf after construction Use the print function to print out the values of data_in and address for the 2 objects. Explicitly deallocate the 2 nd object. 22

23 Using Objects Exercise Assign the address of the first object to 4 hf after construction Use the print function to print out the values of data_in and address for the 2 objects. Explicitly deallocate the 2 nd object. class MemTrans; logic [7:0] data_in; logic [3:0] address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new(logic [7:0] data_init = 0, logic [3:0] address_init = 0); data_in = data_init; address = address_init; initial begin MemTrans mt1, mt2; mt1 = new(,.address_init(2)); mt2 = new(3, 4); mt1.address = 4 hf; mt1.print; $display(" "); mt2.print; mt2 = null; end # Data_in = 00, address = f # # Data_in = 00, address = 0 23

24 5.10 Defining Methods Outside of the Class Done to keep the class definition readable Define a prototype of the method in the class Use the extern keyword to indicate the full definition is external class PCI_Tran; bit [31:0] addr, data; extern function void display(); Specify the class that the function is defined for function void PCI_Tran::display(); $display( %0t: PCI: addr = %h, data = %h, $time, addr, data); 24

25 5.11 Static Variables vs. Global Variables Global variable has no limits on manipulation Static variable: Can only be modified by objects of one class Shared among all objects Associated with the class, not the object class Transaction; static int count = 0; int id; function new(); id = count++; Only one copy of static variable count exists which is shared amongst all instances of the class Non-static variable id and thus one copy per object and specific to each object 25

26 5.11 Static Variables vs. Global Variables Global variable has no limits on manipulation Static variable: Can only be modified by objects of one class Shared among all objects Associated with the class, not the object class Transaction; static int count = 0; int id; function new(); id = count++; transaction t1, t2, t3; initial begin t1 = new(); t2 = new(); t3 = new(); end object of class Transaction id =0 object of class Transaction id =1 object of class Transaction id =2 class Transaction count =3 26

27 5.11 Static/Global Variables (cont) initial begin Transaction t1, t2, t3; t1 = new(); $display("first id = %0d, count = %0d", t1.id, t1.count); t2 = new(); $display("first id = %0d, count = %0d", t1.id, t1.count); $display("second id = %0d, count = %0d", t2.id, t2.count); t3 = new(); $display("first id = %0d, count = %0d", t1.id, t1.count); $display("second id = %0d, count = %0d", t2.id, t2.count); $display( Third id = %0d, count = %0d", t3.id, t3.count); end # First id = 0, count = 1 # First id = 0, count = 2 # Second id = 1, count = 2 # First id = 0, count = 3 # Second id = 1, count = 3 # Third id = 2, count = 3 If count was not declared as static: # First id = 0, count = 1 # Second id = 0, count = 1 27

28 Class Scope Resolution Operator :: Object member reference operator. Refers to the member of the class Applies to all static elements of a class: static properties static methods typdefs enumerations unions nested class declarations Object member reference operator. Refers to a member of a class instance Chapter 5 Copyright 2012 G. Tumbush, C. Spear v1.2 28

29 Accessing Static Variables... Only one copy of a static variable exists. Static variables can be accessed through the class or handle class Transaction; static int count = 0; int id; function new(); id = count++; // new initial begin Transaction t1, t2; Print count value before object created # 1) Transaction::count = 0 # First id = 0d0, count = 0d1 # Second id = 0d1, count = 0d2 # 2) Transaction::count = 0d2 class scope resolution operator $display("1) Transaction::count = %0d", Transaction::count); t1 = new(); $display("first id = 0d%0d, count = 0d%0d", t1.id, t1.count); t2 = new(); $display("second id = 0d%0d, count = 0d%0d", t2.id, t2.count); $display("2) Transaction::count = 0d%0d", Transaction::count); end 29

30 Static Variables Exercise Using the previous MemTrans exercise create a static variable last_address that holds the initial value of the address variable from the most recently created object, as set in the constructor. After allocating objects of class MemTrans (done in last exercise) print out the current value of last_address. class MemTrans; logic [7:0] data_in; logic [3:0] address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new(logic [7:0] data_init = 0, logic [3:0] address_init = 0); data_in = data_init; address = address_init; initial begin MemTrans mt1, mt2; mt1 = new(,.address_init(2)); mt2 = new(3, 4); mt1.address = 4 hf; mt1.print; $display(" "); mt2.print; mt2 = null; end 30

31 Static Variables Exercise Using the previous MemTrans exercise create a static variable last_address that holds the initial value of the address variable from the most recently created object, as set in the constructor. class MemTrans; logic [7:0] data_in; logic [3:0] address; static logic [3:0] last_address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new(logic [7:0] data_init = 0, logic [3:0] address_init = 0); data_in = data_init; address = address_init; last_address = address; 31

32 Static Variables Exercise After allocating objects of class MemTrans (done in last exercise) print out the current value of last_address. initial begin # Data_in = 00, address = f MemTrans mt1, mt2; # Data_in = 03, address = 4 mt1 = new(,.address_init(2)); # last_address is 4 mt2 = new(3, 4); # last_address is 4 mt1.print; mt2.print; $display("last_address is %h", MemTrans::last_address); // or $display("last_address is %h", mt2.last_address); mt2 = null; end 32

33 Initializing static variables Useful when every instance of a class needs info from an object of another class class Transaction; static Config cfg; A handle with static storage initial begin Transaction::cfg = new(.num_trans(42)); end Create a new config object and assign handle of new Config object to static handle cfg in class Transaction 33

34 class Transaction; static int count = 2; int id; function new(); id = count++; static function void dec_count(); --count; Static Methods Manipulating static variables with a method accessed with the class name requires a static method Static methods can only access static class properties or methods of their own class. Static methods can be called anywhere within a SystemVerilog program, even without any class instantiation (as shown below). method dec_count must be declared as static # 3) Transaction.count = 1 # 3) Transaction.count = 1 initial begin $display("3) Transaction.count = %0d", Transaction::count); Transaction::dec_count(); $display("3) Transaction.count = %0d", Transaction::count); end 34

35 Static Methods Exercise Using the previous MemTrans exercise create a static method called print_last_address that prints out the value of static variable last_address After allocating objects of class MemTrans, call the method print_last_address to print out the value of last_address class MemTrans; logic [7:0] data_in; logic [3:0] address; static logic [3:0] last_address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new(logic [7:0] data_init = 0, logic [3:0] address_init = 0); data_in = data_init; address = address_init; last_address = address; MemTrans::last_address = address; 35

36 Static Methods Exercise Using the previous MemTrans exercise create a static method called print_last_address that prints out the value of static variable last_address class MemTrans; logic [7:0] data_in; logic [3:0] address; static logic [3:0] last_address; function void print; $display( Data_in = %h, address = %h, data_in, address); function new(logic [7:0] data_init = 0, logic [3:0] address_init = 0); data_in = data_init; address = address_init; MemTrans::last_address = address; static function void print_last_address; $display("last_address is %h", last_address); 36

37 Static Methods Exercise After allocating objects of class MemTrans, call the method print_last_address to print out the value of last_address initial begin MemTrans mt1, mt2; mt1 = new(,.address_init(2)); mt2 = new(3, 4); m1.address = 4 hf; mt1.print; mt2.print; MemTrans::print_last_address; or mt2.print_last_address; <- don t recommend this. mt2 = null; end 37

38 5.12 Scoping Rules int limit = 3; program automatic p; int limit; class Foo; int limit = 5, array[]; function void print (int limit); for (int i=0; i<limit; i++) $display( %m: array[%0d]=%0d, i, array[i]); initial begin int limit = $root.top.limit; Foo bar; // Declare bar = new(); // Construct bar.print(limit); bar.print(bar.limit); end endprogram # top.p.foo.print: array[0]=0 # top.p.foo.print: array[1]=0 # top.p.foo.print: array[2]=0 # # top.p.foo.print: array[0]=0 # top.p.foo.print: array[1]=0 # top.p.foo.print: array[2]=0 # top.p.foo.print: array[3]=0 # top.p.foo.print: array[4]=0 38

39 5.12 Scoping Rules (cont.) SystemVerilog searches up the scopes for variables program automatic test; int i; class Bad; logic [31:0] data[] = {1,2,3,4,5}; function void display; for (i=0;i<data.size(); i++) $display( data[%0d]d=%x, i, data[i]); initial begin Bad stuff; stuff = new(); stuff.display; $display("int i = %0d",i); end endprogram # data[0]= # data[1]= # data[2]= # data[3]= # data[4]= # int i = 5 Declare classes in a package. 39

40 5.12 Scoping Rules (cont.) SystemVerilog searches up the scopes for variables program automatic test; int i; class Bad; logic [31:0] data[] = {1,2,3,4,5}; function void display; for (int i=0;i<data.size(); i++) $display( data[%0d]d=%x, i, data[i]); initial begin Bad stuff; stuff = new(); stuff.display; $display("int i = %0d",i); end endprogram # data[0]= # data[1]= # data[2]= # data[3]= # data[4]= # int i = 0 Declare classes in a package. 40

41 What is this? Keyword this allows unambiguous reference to class variables/methods, etc. Commonly used in custom constructors where argument to constructor matches a class variable. Lazy programming??? class Scoping; string oname; function new(string oname); this.oname = oname; class Scoping; string oname; function new(string new_oname); oname = new_oname; initial begin Scoping mine; mine = new("test"); $display("%s",mine.oname); end # test 41

42 Another example: What is this? (cont.) module sample5p21(); class ASICwithAnkit ; int a, b; function new (int default_a = 333, int default_b = 444); this.a = default_a; b = default_b; Custom Constructor initial begin ASICwithAnkit AwA = new (123); ASICwithAnkit AwB = new (,456); $display ("AwA.a = %d", AwA.a); $display ("AwA.b = %d", AwA.b); end # AwA.a = 123 # AwA.b = 444 endmodule 42

43 5.13 Using one Class Inside Another Objects of a class can be created inside another class Enables reuse and is similar to composition class Statistics; time startt; static int ntrans = 0; static time total_elapsed_time = 0; extern function void start(); extern function void stop(); // Statistics function void Statistics::start(); startt = $time; $display("startt = %0t", startt); // start total_elapsed_time = total_elapsed_time + how_long function void Statistics::stop(); time how_long = $time - startt; $display("how_long = %0t", how_long); ntrans++; $display("ntrans = %0d", ntrans); total_elapsed_time += how_long; $display("total_elapsed_tim = %0t", total_elapsed_time); 43

44 Using Statistics inside another Class (cont.) class Transactions; bit [31:0] addr, csm, data[8]; Statistics stats; function new(); stats = new(); task transmit_me(); stats.start(); #100; stats.stop(); endtask // Transactions Transactions t1; // Declare handle initial begin t1 = new(); // Allocate a Transactions object t1.transmit_me; end # startt = 0 # how_long = 100 # ntrans = 1 # total_elapsed_tim =

45 Compilation Order Issue Compilation order of classes is not as lenient as modules Example: two classes each need a handle to the other. class Transaction; Statistics stats; class Statistics; Invalid type 'Statistics'. typedef class Statistics; class Transaction; Statistics stats; class Statistics; 45

46 Classes within Classes Exercise Complete function print_all in class MemTrans to print out data_in and address using base class PrintUtilities. Demonstrate its usage. class PrintUtilities; function void print_4(input string name, input [3:0] val_4bits); $display("%t: %s = %h", $time, name, val_4bits); function void print_8(input string name, input [7:0] val_8bits); $display("%t: %s = %h", $time, name, val_8bits); class MemTrans; bit [7:0] data_in; bit [3:0] address; PrintUtilities print; function new(); print = new(); function void print_all;... 46

47 class MemTrans; bit [7:0] data_in; bit [3:0] address; PrintUtilities print; function new(); print = new(); // new Classes within Classes Exercise function void print_all; print.print_8("data_in", data_in); print.print_4("address", address); // print_data_address program automatic test; // import my_package::*; initial begin MemTrans mt1, mt2; mt1 = new(); mt1.print_all; mt1.print.print_8("data_in", mt1.data_in); end endprogram # 0: data_in = 00 # 0: address = 0 # 0: data_in = 00 47

48 Passing objects/handles to methods What happens when an object (instance of a class) is passed to a method? The handle to the object is passed, not the object. A copy of the handle is made task generator; Transaction gen; gen = new; transmit(gen); endtask task transmit(input Transaction trans);... endtask gen handle object of class Transaction trans handle 48

49 Modifying a handle in a task Specify ref on method arguments you want to modify function automatic void create(ref Transaction tr); function void create(transaction tr); tr = new(); tr.addr = 42;... original tr cannot be modified as copied Transaction t; initial begin create(t); $display(t.addr); end What does t point to? # 42 49

50 task generator_bad(int n); Transaction t; t = new(); repeat (n) begin t.addr = $random(); $display( Sending addr = %h, t.addr); transmit(t); end endtask Modifying Objects in Flight Be sure to create a new object for each transaction Otherwise every object could be the same initial begin generator_bad(5); end 1 object shared by n transmit calls class Transaction; logic[3:0] addr; static int count = 0; int id; function new(); id = count++; // new $display("transaction::count = %0d", Transaction::count); $display("t.addr = %h", generator_bad.t.addr); # Sending addr = 4 # Sending addr = 1 # Sending addr = 9 # Sending addr = 3 # Sending addr = d # Transaction::count = 1 # t.addr = d 50

51 task generator_bad(int n); Transaction t; repeat (n) begin t = new(); t.addr = $random(); $display( Sending addr = %h, t.addr); transmit(t); end endtask Modifying Objects in Flight Be sure to create a new object for each transaction Otherwise every object could be the same initial begin generator_bad(5); end class Transaction; logic[3:0] addr; static int count = 0; int id; function new(); id = count++; // new $display("transaction::count = %0d", Transaction::count); $display("t.addr = %h", generator_bad.t.addr); # Sending addr = 4 # Sending addr = 1 # Sending addr = 9 # Sending addr = 3 # Sending addr = d # Transaction::count = 5 # t.addr = d 51

52 Array of Handles Your testbench might need to store and reference many objects An array of handles is convenient for this. tarray is made of handles, not objects. task generator(); Transaction tarray[10]; foreach (tarray[i]) begin tarray[i] = new(); transmit(tarray[i]); end endtask 52

53 Objects and Handles Exercise program automatic test; import my_package::*; initial begin end task generator endtask Declare an array of 5 Transaction handles Call a generator task to create the objects Complete the generator task header Create objects for every handle in the array and transmit the object. task transmit(transaction tr);... endtask // transmit endprogram 53

54 Objects and Handles Exercise program automatic test; import my_package::*; initial begin Transaction tarray[5]; generator(tarray); end Declare an array of 5 Transaction handles Call a generator task to create the objects task generator(ref Transaction gen_array[5]); foreach (gen_array[i]) begin Complete the generator task header gen_array[i] = new(); Create objects for every handle in the transmit(gen_array[i]); array and transmit the object. end endtask task transmit(transaction tr); endtask // transmit endprogram 54

55 5.15 Copying Objects Pass a copy of an object to a method to keep it from being modified Any custom constructor is not called class Transaction; bit [31:0] addr; static int count = 0; int id; Statistics stats; function new(); stats = new(); id = count++; # src: id = 0, startt = 0 # src: id = 0, startt = 42 # src: id = 0, startt = 42 # dst: id = 0, startt = 42 # src: id = 0, startt = 96 # dst: id = 0, startt = 96 src Transaction src, dst; initial begin src = new(); src.stats.startt=42; dst src id=0 stats dst = new src; id=0 stats id=0 stats startt=42 startt=42 dst.stats.startt = 96; 96 55

56 Writing a Deep Copy Function Suggested for all but the most trivial classes class Transaction; bit [31:0] addr; static int count = 0; int id; Statistics stats; function new(); stats = new(); id = count++; function Transaction copy(); copy = new(); copy.addr = addr; copy.stats = stats.copy(); class Statistics; time startt; function Statistics copy(); copy = new(); copy.startt = startt; UVM data macros do this for you automatically! 56

57 Using the Deep Copy Function Transaction src, dst; initial begin src = new(); src.stats.startt=42; src id=0 stats startt=42 dst = src.copy(); src dst id=0 stats id=1 stats startt=42 startt=42 end dst.stats.startt = 96; src dst id=0 stats id=1 stats startt=42 startt=96 57

58 Copy Exercise For the following class create a copy function and demonstrate its usage. Assume the Statistics class has its own copy function. package automatic my_package; class MemTrans; bit [7:0] data_in; bit [3:0] address; Statistics stats; function new(); data_in = 3; address = 5; stats = new(); ; endpackage 58

59 5.17 Public vs Local C++/Java All variables in a class are local by default Classes provide accessor functions to allow access and modify data Long term software stability is paramount. SystemVerilog All variables in a class are public by default Allows greatest control over DUT Variables can be labeled local or protected. local - Member is available only to the method of the same class. Moreover, a local member will not be available even to the subclasses. Protected - similar to a local declaration, but a member will be visible inside subclasses Tradeoff between software stability and flexibility. 59

60 local example: class baseclass; local int i; 5.17 Public vs Local program top; initial begin localvar lvar = new(); lvar.i = 123; Same error if declared protected end endprogram ** Error: localexample.sv(18): Access to local member 'i' from outside a class context is illegal. 60

61 local subclass example: class parentclass; local int i; 5.17 Public vs Local Class subclass extends parentclass; function new(); i = 10; // new Compiles sucessfully if protected ** Error: localexample.sv(9): Illegal use of local name baseclass::i' ** Error: localexample.sv(9): Undefined variable: i. 61

62 5.18 Building a Testbench Test Scenario Generator Environment Functional Command Agent Driver Scoreboard Assertions Checker Monitor Functional Coverage Signal DUT 62