Callbacks in general are used to executed a user defined method of predefined name when certain event happens in BFM or any class of interest.

Some of the applications of callbacks are

• Before sending CRC field, so callback, in callback user can decide to inject CRC in frame
• Once a frame is received, do callback, in callback user can decide if he wants to send flow control frame
• Once a frame is received, do callback, in callback decide if frame needs to be dropped

For any kind of callback implementation, one needs base class of callback. In vmm this class name is vmm_xactor_callback.

To use this class following steps needs to be followed

• Extend vmm_xactor_callback class and create my_callback class (You can have any name)
• Define standard virtual methods (Example my_cb) which will be executed by your bfm class
• User need to extend my_callback class (example my_abc_callback) and create body of standard virtual methods (my_cb)
• Create instance of this new clas (my_abc_callback)
• Add this new class instance to vmm_xactor class with method append_callback

   1 `include "vmm.sv"
   2 
   3 class my_data extends vmm_data;
   4   vmm_log log;
   5   int corrupt_crc;
   6   int crc;
   7   int addr;
   8   int data;
   9   int drop;
  10   function new(vmm_log log);
  11     super.new(log);
  12     this.log         = log;
  13     this.corrupt_crc = 0;
  14     this.crc         = 0;
  15     this.addr        = 0;
  16     this.data        = 0;
  17     this.drop        = 0;
  18   endfunction
  19 endclass
  20 
  21 // Need to extend from base class vmm_xactor_callback
  22 virtual class my_callback extends vmm_xactor_callbacks;
  23   vmm_log log;
  24   
  25   function new(vmm_log log);
  26     super.new();
  27     this.log = log;
  28   endfunction
  29 
  30   virtual function my_cb(ref my_data my_d);
  31     `vmm_warning(this.log,"Nothing is implemented here");
  32   endfunction
  33 
  34 endclass
  35 
  36 // Need to extend from base class my_callback
  37 class my_abc_callback extends my_callback;
  38   int cnt; 
  39   function new(vmm_log log);
  40     super.new(log);
  41     cnt = 0;
  42   endfunction
  43 
  44   virtual function my_cb(ref my_data my_d);
  45     cnt ++;
  46     if (cnt %2 == 0) begin
  47       `vmm_warning(this.log,"Corrupting CRC");
  48       my_d.corrupt_crc = 1;
  49     end
  50   endfunction
  51 endclass
  52 
  53 // Need to extend from base class my_callback
  54 class my_xyz_callback extends my_callback;
  55   int cnt; 
  56   function new(vmm_log log);
  57     super.new(log);
  58     cnt = 0;
  59   endfunction
  60 
  61   virtual function my_cb(ref my_data my_d);
  62     cnt ++;
  63     if (cnt %2 == 1) begin
  64       `vmm_warning(this.log,"Doing nothing");
  65     end
  66   endfunction
  67 endclass
  68 
  69 // Need to extend from base class vmm_xactor
  70 class eth_tx extends vmm_xactor;
  71   vmm_log log;
  72   
  73   function new(vmm_log log,string name);
  74     super.new(name, "parent");
  75     this.log = log;
  76   endfunction
  77 
  78   virtual task main();
  79     super.main();
  80     fork
  81       begin
  82         this.bfm();
  83       end
  84     join_none
  85   endtask
  86 
  87   task bfm();
  88    my_data mdata;
  89     while(1) begin
  90        #10 ; // This can be clock event
  91       wait_if_stopped();
  92       mdata = new(log);
  93       `vmm_note(log,"Ethernet transmit bfm is running");
  94        #10 ; // Lets execute callback
  95       `vmm_callback(my_callback,my_cb(mdata));
  96       if (mdata.corrupt_crc) begin
  97         `vmm_warning(this.log,"Corrupting CRC on user request");
  98       end
  99     end
 100   endtask
 101 endclass
 102 
 103 program test();
 104   vmm_log log = new("test","test");
 105   eth_tx  tx    = new(log,"PROGRAM");
 106   my_xyz_callback xyz = new(log);
 107   my_abc_callback abc = new(log);
 108 
 109   initial begin
 110      tx.append_callback(abc);
 111      tx.append_callback(xyz);
 112      tx.start_xactor();
 113       #40 ;
 114   end
 115 endprogram

 Trace[INTERNAL] on PROGRAM(parent) at                    0:
     Started
 Normal[NOTE] on test(test) at                   10:
     Ethernet transmit bfm is running
 WARNING[FAILURE] on test(test) at                   20:
     Doing nothing
 Normal[NOTE] on test(test) at                   30:
     Ethernet transmit bfm is running
 WARNING[FAILURE] on test(test) at                   40:
     Corrupting CRC
 WARNING[FAILURE] on test(test) at                   40:
     Corrupting CRC on user request

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Deepak Kumar Tala - All rights reserved

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