SystemVerilog Mailbox

前言：mailboxe是一种通信机制，允许进程之间交换消息。希望与另一个进程通信的进程将消息发送到mailboxe，mailboxe将消息临时存储在系统定义的内存对象中，以便将消息传递给所需的进程。根据大小，mailboxe被分类为：

bounded mailbox
unbounded mailbox

A bounded mailbox is with the size defined. mailbox becomes full when on storing a bounded number of messages. A process that attempts to place a message into a full mailbox shall be suspended until enough space becomes available in the mailbox queue.
Unbounded mailboxes are with unlimited size.

一、Mailbox types

There are two types of mailboxes,

Generic Mailbox
Parameterized mailbox

1.1 Generic Mailbox (type-less mailbox)

The default mailbox is type-less. that is, a single mailbox can send and receive data of any type.

mailbox mailbox_name;

Parameterized mailbox (mailbox with particular type)
Parameterized mailbox is used to transfer a data of particular type.

mailbox#(type) mailbox_name;

1.2 Mailbox Methods

SystemVerilog Mailbox is a built-in class that provides the following methods. these are applicable for both Generic and Parameterized mailboxes

No.	Method	Description
1	new()	Creat a mailbox
2	put()	Place a message in a mailbox
3	try_put()	Try to place a message in a mailbox without blocking
4	get() / peek()	Retrieve a message from a mailbox
5	num()	Returns the number of messages in the mailbox
6	try_get() / try_peek()	Try to retrieve a message from a mailbox without blocking

new( );

Mailboxes are created with the new() method.

mailbox_name = new();        // Creates unbounded mailbox and returns mailbox handlemailbox_name = new(m_size);  //Creates bounded mailbox with size m_size and returns mailbox
//handle ,where m_size is integer  variable

1.3 SystemVerilog Mailbox example

In the example below,Mailbox is used for communication between generator and driver.

Process-1(Generator class) will generate (created and randomize) the packet and put into the mailbox mb_box
Process-2(Driver class) gets the generated packet from the mailbox and display the fields

//-------------------------------------------------------------------------
// Packet
//-------------------------------------------------------------------------
class packet;rand bit [7:0] addr;rand bit [7:0] data;//Displaying randomized valuesfunction void post_randomize();$display("Packet::Packet Generated");$display("Packet::Addr=%0d,Data=%0d",addr,data);endfunction
endclass//-------------------------------------------------------------------------
//Generator - Generates the transaction packet and send to driver
//-------------------------------------------------------------------------
class generator;packet pkt;mailbox m_box;//constructor, getting mailbox handlefunction new(mailbox m_box);this.m_box = m_box;endfunctiontask run;repeat(2) beginpkt = new();pkt.randomize(); //generating packetm_box.put(pkt);  //putting packet into mailbox$display("Generator::Packet Put into Mailbox");#5;endendtask
endclass//-------------------------------------------------------------------------
// Driver - Gets the packet from generator and display's the packet items
//-------------------------------------------------------------------------
class driver;packet pkt;mailbox m_box;//constructor, getting mailbox handlefunction new(mailbox m_box);this.m_box = m_box;endfunctiontask run;repeat(2) beginm_box.get(pkt); //getting packet from mailbox$display("Driver::Packet Recived");$display("Driver::Addr=%0d,Data=%0d\n",pkt.addr,pkt.data);endendtask
endclass//-------------------------------------------------------------------------
//     tbench_top
//-------------------------------------------------------------------------
module mailbox_ex;generator gen;driver    dri;mailbox m_box; //declaring mailbox m_boxinitial begin//Creating the mailbox, Passing the same handle to generator and driver, //because same mailbox should be shared in-order to communicate.m_box = new(); //creating mailboxgen = new(m_box); //creating generator and passing mailbox handledri = new(m_box); //creating driver and passing mailbox handle$display("------------------------------------------");forkgen.run(); //Process-1dri.run(); //Process-2join$display("------------------------------------------");end
endmodule

Simulator Output

------------------------------------------
Packet::Packet Generated
Packet::Addr=3,Data=38
Generator::Packet Put into Mailbox
Driver::Packet Recived
Driver::Addr=3,Data=38Packet::Packet Generated
Packet::Addr=118,Data=92
Generator::Packet Put into Mailbox
Driver::Packet Recived
Driver::Addr=118,Data=92------------------------------------------

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