目录

1. The software and hardware is world

2. 什么是package

3. import pkg::*是将pkgAll are imported？

4. import vs include

1. The software and hardware is world

        ClassOn behalf of the software world,ModuleOn behalf of the hardware of the world,InterfaceIs the bridge connecting the software and hardware of the world,But some more partial hardware.

        PackageIs software world,相当于是SV中用于定义namescope的东西.Interface和Module（Because contain hardware world）不能包含在（Software belongs to the world）Package中.

        类中的成员(数据、函数、任务)By default areautomatic类型.如果需要staticType members,需要用static显式地指定.Module中的所有变量、函数、Tasks are the default asstatic.如果需要automaticType members,需要用automatic显式地指定.

        ModuleAre instantiated static.ClassObject creation is a dynamic.Here refers to the so-called static compiled already generated.And dynamic is refers to the simulation of actual after the start of executionnew()创建.

        ModuleOnce instantiated,All the module instance has always been.而SVFor object lifetime management is used in automatic recovery mechanism,If an object has no ahandle指向它,它就被自动回收了.

        由于Module和InterfaceThe hardware of the world,They are instantiated static,So in the compiled them has already been created.But it is dynamic object creation,Must be at the beginning of the simulation and real will be created after.以QuestaSimThe simulation for example,Even in the performvsim命令后,Object actually has not been created,直到执行了“run 0ns”以后（Those should be created in the beginning）Object really is created.

2. 什么是package

        Ref: SystemVerilog Package (chipverify.com)

        SystemVerilog中的packageProvides a save and share data、Parameters and the method of mechanism,可以在多个module、class、program和interface中重用.

        packageThe content of the statement in the belong to thispackage作用域（scope）.

        如果要想使用package中的东西,就需要先import这个package,然后通过package引用.SV中的import与python中的import是相同的功能.

package my_pkg;
  typedefenumbit [1:0] { RED,YELLOW, GREEN, RSVD } e_signal;
  typedefstruct { bit [3:0]signal_id;
                  bit       active;
                  bit [1:0] timeout;
                } e_sig_param;
 
  function my_func();
    $display ("mypkg::my_func is called...");
  endfunction
endpackage

        importWhen can one by oneimportWant to use something,Or the ones will bepackageAll the thingsimport进来,如以下例子所示：

//import my_pkg::* ;    // Import all things defined in my_pkg
import my_pkg::my_func ;// Import my_func only from my_pkg

module tb_top;

initial begin
    my_func();
end

        如果在packageThe definition of a variable or function names and other external definition of a variable or function name conflict,需要用pkg_name::varIn the form of a reference to distinguish.

import my_pkg::* ;    // Import all things defined in my_pkg
typedef enum bit [1:0] { RED,YELLOW,GREEN} e_pixel;

module tb_top;
  initial begin
    e_signal signal = RED;
    e_pixel  pixel  = RED;
    my_func();
  end
endmodule

        以上例子中,用到了两个RED,会发生冲突.This is to addpackageA prefix is used to distinguish between,如下所示

...
    e_signal  signal  = my_pkg::RED;
...

3. import pkg::*是将pkgAll are imported？

        A common misconception is the use of“import pkg::*”会将一个packageAll the things together, imported.So someone will worry about it will not make to compile the library become unduly large and simulation memory nervous？

        其实不会.

        “import pkg::*”The effect of this statement is to tell the emulator,当在当前namescopeIs not found in a class、变量或者函数、Tasks such as stating can go to thepkg中去找.And simulators are looking for a类、变量、函数、任务等Is to follow the so-called“就近原则”.

        当有多个packgeContains a to search{ 类、变量、函数、任务}名,And they all with“import pkg::*”The form of import,此时会发生name collision,The most sensible thing to do is as above mentioned in section as topkg::nameThe explicit form for reference.

4. import vs include

        如上所述,import是用于package的导入.

        `includeInsert the file all the text in the same file contains.这是一个预处理语句,`include在import之前执行.

        importDon't copy the text content.但是import可packageContent in the introduction ofimportStatements in the scope of the.

        To put it simply, include is equivalent to copy/paste or insertion of whatever is present in that file to wherever you include;  import is used to make all/select variables from a package visible.