VMM ATOMIC GENERATOR

VMM has two types of generators. Atomic generator and Scenario generator.

Atomic generator is a simple generator which generates transactions randomly.

`vmm_atomic_gen is a macro which is used to define a class named <class_name>_atomic_gen for any user-specified class derived from vmm_data, using a process similar to the `vmm_channel macro.

 
To use <class_name>_atomic_gen class, a <class_name>_channel must exist. <class_name>_atomic_gen generates transactions and pushes it to <class_name>_channel. A <class_name>_channel object can be passed to generator while constructing.

function new ( string instance ,
            int stream_id = - 1 ,
            <class_name >_channel out_chan = null );


The generator will stop generating the transaction after generating stop_after_n_insts.  User can set the stop_after_n_insts to any unsigned int value. By default this values is 0. 

If stop_after_n_insts is 0, then generator generates infinite number of transactions.
 If stop_after_n_insts is non zero positive number, then generator generates stop_after_n_insts transactions.

We will see an example of creating a atomic generator for a packet class. Packet class is in file Packet.sv .

1) define `vmm_atomic_gen macro for packet class. This macro creates a packet_atomic_gen class creates and randomizes packet transactions.

    `vmm_atomic_gen (packet , "packet atomic generator" )

2) define `vmm_channel for the packet class. This macro creates a packet_channel which will be used by the packet_atomic_gen to store the transactions. Any other component can take the transactions from this channel.

     `vmm_channel (packet )

3) Create an object of pcakt_atomic_gen.

    packet_atomic_gen pkt_gen = new ( "Atomic Gen" , "test" );

4) Set the number of transactions to be generated to 4

    pkt_gen .stop_after_n_insts = 4 ;

5) Start the generator to generate transactions. These transactions are available to access through pkt_chan as soon as they are generated.

    pkt_gen .start_xator ();

6) Collect the packets from the pkt_chan and display the packet content to terminal.

    pkt_gen .out_chan . get (pkt );
    pkt .display ();


   Completed Example 

`vmm_channel (Packet )
`vmm_atomic_gen (Packet , "Atomic Packet Generator" )

program test_atomic_gen ();
 
  Packet_atomic_gen pkt_gen = new ( "Atomic Gen" , "test" );
  Packet pkt ;
    initial
       begin
          pkt_gen .stop_after_n_insts = 4 ;
          # 100 ; pkt_gen .start_xactor ();
       end

    initial
       # 200 forever
            begin
                pkt_gen .out_chan . get (pkt );
                pkt .display ();
            end
    
endprogram

   Download the example

vmm_atomic_gen.tar
Browse the code in vmm_atomic_gen.tar

   Commands to run the simulation
vcs -sverilog -f filelist -R -ntb_opts rvm -ntb_opts dtm

   Log file report

      packet #1952805748.0.0
      da:0xdb
      sa:0x71
      length:0x0e (data.size=1)
      data[0]:0x63
      fcs:0xe9

      packet #1952805748.0.1
      da:0xa7
      sa:0x45
      length:0xa4 (data.size=5)
      data[0]:0x00   data[1]:0x4f  ....     data[3]:0xe7   data[4]:0xd8
      fcs:0x31

      packet #1952805748.0.2
      da:0x15
      sa:0xe6
      length:0xa1 (data.size=1)
      data[0]:0x80
      fcs:0x01

      packet #1952805748.0.3
      da:0xd7
      sa:0xa9
      length:0xdc (data.size=3)
      data[0]:0xcc   data[1]:0x7c   data[1]:0x7c
      fcs:0x67