UVM Subscriber

The uvm_subscriber class provides an analysis export that connects with the analysis port. As the name suggests, it subscribes to the broadcaster i.e. analysis port to receive broadcasted transactions.

The uvm_subscriber is derived from uvm_component and adds up the analysis_export port in the class.
The user-defined subscriber is derived from uvm_subscriber that must define the write method (A write method is a pure virtual method that is declared in the uvm_subscriber class). The analysis_export provides access to the write method by outside components.
Since uvm_subscriber has built-in analysis_export, it is generally used to implement a functional coverage monitor.

uvm_subscriber class definitation:

virtual class uvm_subscriber #(type T=int) extends uvm_component;

  typedef uvm_subscriber #(T) this_type;
  uvm_analysis_imp #(T, this_type) analysis_export;
  
  function new (string name, uvm_component parent);
    super.new(name, parent);
    analysis_export = new("analysis_imp", this);
  endfunction
  
  pure virtual function void write(T t);
endclass

uvm_subscriber class hierarchy

UVM subscriber example

In the below example, a functional coverage monitor is created by extending the uvm_subscriber class.

class func_cov extends uvm_subscriber #(seq_item);
  covergroup cg;
  ...
  endgroup

  function void write (seq_item req);
    ...
    cg.sample();
  endfunction
endclass

// Env class connects broadcaster and subscriber class using analysis port connection.
class env extends uvm_env;
  `uvm_component_utils(env)
  agent agt;
  func_cov fc;
 
  function new(string name = "env", uvm_component parent = null);
    super.new(name, parent);
  endfunction
  
  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    agt = agent::type_id::create("agt", this);
    fc = func_cov::type_id::create("fc", this);
  endfunction
  
  function void connect_phase(uvm_phase phase);
    agt.mon.item_collect_port.connect(fc.analysis_export); // Here, Monitor behaves as a broadcaster.
  endfunction
endclass

UVM Tutorials