VMM DATA

VMM DATA


vmm_data class is to be used to model all transactions in the infrastructure . It provides a standard set of methods expected to be found in all transactions. All transactions in the verification environment inherit this object and override its main generic virtual tasks such as copy(), byte_pack(), byte_unpack(), compare() and psdisplay().

vmm_data has 3 unique identifiers for identifying transaction instance.

int stream_id;  // Stream identifier
int scenario_id;// Sequence identifier within stream
int data_id;    // instance identifier within sequence

This class is used to generate random, constraint random and directed transactions.

We will see the implementation of some methods.

Let us implement a simple packet using vmm_data.

Packet Specification
-------------------------------
Packet has DA,SA,Len and ..... few more feilds.
All the feilds are 8 bit.

1) Define a packet class by extending vmm_data

   class Packet extends vmm_data;

2) Define all the packet fields as rand variables

    rand bit [7:0] da;
    rand bit [7:0] sa;
    rand bit [7:0] length;
    ....
    ....

3) Constraint the rand variables based on the specification.

    constraint address_c { da inside {`P0,`P1,`P2,`P3}; }
    ....
    .....

4) Define psdisplay() method.
  
psdisplay() method displays the current value of the transaction or data described by this instance in a human-readable format on the standard output.

    virtual function string psdisplay(string prefix= "");
         int i;

         $write(psdisplay,"   %s%s   da:0x%h\n", psdisplay, prefix,this.da);
         $write(psdisplay,"   %s%s   sa:0x%h\n", psdisplay, prefix,this.sa);
         $write(psdisplay,"   %s%s   length:0x%h (data.size=%0d)\n", psdisplay, prefix,this.length,this.data.size());
         .........
         
    endfunction

5) Define copy() method.

copy() method copies the current value of the object instance to the specified object instance.


     virtual function vmm_data copy(vmm_data to= null);
         Packet cpy;
         cpy = new;
        
         super.copy_data(cpy);
        
         cpy.da =this.da;
         cpy.sa =this.sa;
         cpy.length = this.length;
         ...........
注：copy函数的返回值类型为vmm_data类，而不是扩展类类型，这是因为扩展类的虚函数必须跟其基类的函数相匹配，包括所有的参数和返回类型。

6) Define compare() method.

Compare method compares the current value of the object instance with the current value of the specified object instance.

    virtual function bitcompare(input vmm_data   to,outputstring diff,inputint   kind = -1);
        Packet cmp;
    
        compare =1; // Assume success by default.
        diff    = "No differences found";
       
        // data types are the same, do comparison:
        if (this.da!= cmp.da)
        begin
           diff = $psprintf("Different DA values: %b != %b",this.da, cmp.da);
           compare = 0;
        end
         
        if (this.sa!= cmp.sa)
        begin
           diff = $psprintf("Different SA values: %b != %b",this.sa, cmp.sa);
           compare = 0;
        end
        ........
        ........

7) Define byte_pack() method.

   byte_pack() method Packs the content of the transaction or data into the specified dynamic array of bytes.

   virtual function intunsigned byte_pack(
                     ref logic [7:0] bytes[],
                     input int unsigned offset=0 ,
                     input int   kind = -1);
      byte_pack = 0;
      bytes = new[this.data.size()+ 4];
      bytes[0]= this.da;
      bytes[1]= this.sa;
      bytes[2]= this.length;
      ........
      ........

8) Define byte_unpack() method.

   byte_unpack() method unpacket the array in to different data feilds.

    virtual function intunsigned byte_unpack(
                     const ref logic[7:0] bytes[],
                     input int unsigned offset= 0,
                     input int len = -1,
                     input int kind = -1);
      this.da= bytes[0];
      this.sa= bytes[1];
      this.length= bytes[2];
      .........
      .........


  Complete Packet Class 


class Packet extends vmm_data;

static vmm_log log = new("Packet","Class");

rand bit [7:0] length;
rand bit [7:0] da;
rand bit [7:0] sa;
rand bit [7:0]data[];//Payload using Dynamic array,size is generated on the fly
rand byte fcs;


constraint payload_size_c { data.sizeinside { [1: 6]};}

function new();
     super.new(this.log);
endfunction:new

virtual function vmm_data allocate();
     Packet pkt;
     pkt = new();
     return pkt;
endfunction:allocate

virtual function string psdisplay(string prefix= "");
    int i;

    $write(psdisplay,"   %s   packet #%0d.%0d.%0d\n", prefix,this.stream_id,this.scenario_id,this.data_id);
    $write(psdisplay,"   %s%s   da:0x%h\n", psdisplay, prefix,this.da);
    $write(psdisplay,"   %s%s   sa:0x%h\n", psdisplay, prefix,this.sa);
    $write(psdisplay,"   %s%s   length:0x%h (data.size=%0d)\n", psdisplay, prefix,this.length,this.data.size());
    $write(psdisplay,"   %s%s   data[%0d]:0x%h", psdisplay, prefix,0,data[0]);
    if(data.size()> 1)
        $write(psdisplay,"   data[%0d]:0x%h",1,data[1]);
    if(data.size()> 4)
        $write(psdisplay,"  ....  ");
    if(data.size()> 2)
        $write(psdisplay,"   data[%0d]:0x%h",data.size()-2,data[data.size()-2]);
    if(data.size()> 3)
        $write(psdisplay,"   data[%0d]:0x%h",data.size()-1,data[data.size()-1]);
    $write(psdisplay,"\n   %s%s   fcs:0x%h \n", psdisplay, prefix,this.fcs);
   
endfunction


virtual function vmm_data copy(vmm_data to= null);
    Packet cpy;

    // Copying to a new instance?
    if (to == null)
       cpy = new;
     else

    // Copying to an existing instance. Correct type?
    if (!$cast(cpy, to))   
       begin
       `vmm_fatal(this.log,"Attempting to copy to a non packet instance");
       copy = null;
       return copy;
       end
   

    super.copy_data(cpy);
   
    cpy.da =this.da;
    cpy.sa =this.sa;
    cpy.length =this.length;
    cpy.data= new[this.data.size()];
    foreach(data[i])
        begin
       cpy.data[i]= this.data[i];
        end                   
    cpy.fcs =this.fcs;
    copy = cpy;
endfunction:copy



virtual function bitcompare(input vmm_data   to,outputstring diff,inputint   kind = -1);
    Packet cmp;

    compare =1; // Assume success by default.
    diff    = "No differences found";
   
    if (!$cast(cmp, to))
    begin
       `vmm_fatal(this.log,"Attempting to compare to a non packet instance");
       compare =0;
       diff = "Cannot compare non packets";
       return compare;
     end

    // data types are the same, do comparison:
    if (this.da!= cmp.da)
    begin
       diff = $psprintf("Different DA values: %b != %b",this.da, cmp.da);
       compare =0;
       return compare;
    end
     
    if (this.sa!= cmp.sa)
    begin
       diff = $psprintf("Different SA values: %b != %b",this.sa, cmp.sa);
       compare =0;
       return compare;
    end
    if (this.length!= cmp.length)
    begin
       diff = $psprintf("Different LEN values: %b != %b",this.length, cmp.length);
       compare =0;
       return compare;
    end

    foreach(data[i])
       if (this.data[i]!= cmp.data[i])
       begin
          diff = $psprintf("Different data[%0d] values: 0x%h != 0x%h",i,this.data[i], cmp.data[i]);
          compare = 0;
          return compare;
       end
    if (this.fcs!= cmp.fcs)
    begin
       diff = $psprintf("Different FCS values: %b != %b",this.fcs, cmp.fcs);
       compare =0;
       return compare;
    end
endfunction:compare

virtual function intunsigned byte_pack(
                     ref logic [7:0] bytes[],
                     input int unsigned offset=0 ,
                     input int   kind = -1);
      byte_pack = 0;
      bytes = new[this.data.size()+ 4];
      bytes[0]= this.da;
      bytes[1]= this.sa;
      bytes[2]= this.length;

      foreach(data[i])
          bytes[3+i]= data[i];

      bytes[this.data.size()+ 3 ] = fcs;
      byte_pack = this.data.size()+ 4;
endfunction:byte_pack    

virtual function intunsigned byte_unpack(
                     const ref logic[7:0] bytes[],
                     input int unsigned offset= 0,
                     input int len = -1,
                     input int kind = -1);
      this.da= bytes[0];
      this.sa= bytes[1];
      this.length= bytes[2];
      this.fcs= bytes[bytes.size()-1];
      this.data= new[bytes.size()- 4];
      foreach(data[i])
      this.data[i]= bytes[i+3];
      return bytes.size();
endfunction:byte_unpack

endclass


   Vmm_data Methods 

      virtual function string psdisplay( string prefix= "" );
      virtual function bit is_valid( bit silent= 1,int kind = -1);
      virtual function vmm_data allocate ();
      virtual function vmm_data copy ( vmm_data to= null);
      virtual function bitcompare (
      input vmm_data to,output string diff, input int kind= -1);
      function void display(string prefix= "");
      virtual protected functionvoid copy_data ( vmm_data to );
      virtual function intunsigned byte_pack (
      ref logic [7:0] bytes[ ], int unsigned offset= 0,int kind = -1);
      virtual function intunsigned byte_unpack (
      const ref logic[7:0] bytes[ ], input intunsigned offset = 0,
      input int len = -1,input int kind = -1 );
      virtual function intunsigned byte_size ( int kind = -1);
      virtual function intunsigned max_byte_size ( int kind = -1);
      virtual function void save( int file);
      virtual function bit load( int file);