Verification Engineer's Blog: Automatic raise/drop objection with UVM-1.2

Variable uvm_sequence_base::starting_phase is deprecated and replaced by two new methods set_starting_phase and get_starting_phase, which prevent starting_phase from being modified in the middle of a phase. This change is not backward-compatible with UVM 1.1, though variable starting_phase, although deprecated, has not yet been removed from the base class library.

New method uvm_sequence_base::set_automatic_phase_objection causes raise_objection and drop_objection to be called automatically around a sequence, avoiding the need to call raise/drop_objection manually in one common situation.

Lets understand it trough below mentioned example.

------------------------------------------------

	import uvm_pkg :: *;

	class my_seq_item extends uvm_sequence_item;
	rand logic [7:0] addr;
	rand logic [7:0] data;

	constraint addr_range_cn {
	addr inside {[10:20]};
	}
	constraint data_range_cn {
	data inside {[100:200]};
	}
	`uvm_object_utils_begin(my_seq_item)
	`uvm_field_int(addr, UVM_ALL_ON\| UVM_DEC)
	`uvm_field_int(data, UVM_ALL_ON\| UVM_DEC)
	`uvm_object_utils_end

	function new(string name="my_seq_item");
	super.new(name);
	endfunction : new

	virtual function string convert2string();
	convert2string = $sformatf("addr=%0d, data=%0d", addr, data);
	endfunction : convert2string
	endclass : my_seq_item

	class my_sequencer extends uvm_sequencer #(my_seq_item);
	`uvm_component_utils (my_sequencer)

	function new (string name="my_sequencer", uvm_component parent=null);
	super.new(name, parent);
	endfunction : new
	endclass : my_sequencer

	class my_driver extends uvm_driver #(my_seq_item);
	`uvm_component_utils (my_driver)

	function new (string name="my_driver", uvm_component parent=null);
	super.new(name, parent);
	endfunction : new

	function void build_phase (uvm_phase phase);
	super.build_phase(phase);
	endfunction : build_phase

	task run_phase(uvm_phase phase);
	forever begin
	seq_item_port.get_next_item(req);
	`uvm_info(get_name(),
	$sformatf("in driver after get_next_item my_seq_item= %s", req.convert2string()), UVM_LOW);
	#50;
	`uvm_info(get_name(), $sformatf("item_done called"), UVM_LOW);
	seq_item_port.item_done();
	end
	endtask : run_phase
	endclass : my_driver

	class my_agent extends uvm_agent;
	`uvm_component_utils (my_agent)
	my_sequencer sqr;
	my_driver drv;

	function new (string name="my_agent", uvm_component parent=null);
	super.new(name, parent);
	endfunction : new

	function void build_phase (uvm_phase phase);
	super.build_phase(phase);
	sqr = my_sequencer :: type_id :: create("sqr", this);
	drv = my_driver :: type_id :: create("drv", this);
	endfunction : build_phase

	function void connect_phase (uvm_phase phase);
	super.connect_phase(phase);
	drv.seq_item_port.connect(sqr.seq_item_export);
	endfunction : connect_phase
	endclass : my_agent

	class my_seq extends uvm_sequence #(my_seq_item);
	`uvm_object_utils (my_seq)
	function new(string name="my_seq");
	super.new(name);

	// The most common interaction with the starting phase
	// within a sequence is to simply ~raise~ the phase's objection
	// prior to executing the sequence, and ~drop~ the objection
	// after ending the sequence (either naturally, or
	// via a call to <kill>). In order to
	// simplify this interaction for the user, the UVM
	// provides the ability to perform this functionality
	// automatically.

	// From a timeline point of view, the automatic phase objection
	// looks like:
	//\| start() is executed
	//\| --! Objection is raised !--
	//\| pre_start() is executed
	//\| pre_body() is optionally executed
	//\| body() is executed
	//\| post_body() is optionally executed
	//\| post_start() is executed
	//\| --! Objection is dropped !--
	//\| start() unblocks

	// NEVER set the automatic phase objection bit to 1 if your sequence
	// runs with a forever loop inside of the body, as the objection will
	// never get dropped!
	set_automatic_phase_objection(1);
	endfunction : new

	task body ();
	`uvm_create(req)
	if(!req.randomize()) begin
	`uvm_fatal(get_name(), $sformatf("Randomization failed"))
	end
	`uvm_info (get_name(),
	$sformatf("After randomizating in my_seq my_seq_item= %s",
	req.convert2string()), UVM_LOW)
	`uvm_send(req)
	endtask : body
	endclass : my_seq

	class my_test extends uvm_test;
	`uvm_component_utils (my_test)
	my_agent agent;

	function new (string name="my_test", uvm_component parent=null);
	super.new(name, parent);
	endfunction : new

	function void build_phase (uvm_phase phase);
	super.build_phase(phase);
	agent = my_agent::type_id::create("agent", this);
	endfunction : build_phase

	task run_phase(uvm_phase phase);
	my_seq seq;
	uvm_phase starting_phase;
	bit automatic_phase_objection_status;
	seq = my_seq::type_id::create ("seq");
	// Function: set_starting_phase
	// Sets the 'starting phase'.
	seq.set_starting_phase(phase);

	// If set_automatic_phase_objection is not called in new (constructor)
	// of sequence then can be calleb from test-case
	// seq.set_automatic_phase_objection(1);

	fork
	begin
	#30;
	// Function: get_starting_phase
	// Returns the 'starting phase'.
	// If non-null, the starting phase specifies the phase in which this
	// sequence was started.
	starting_phase = seq.get_starting_phase();
	`uvm_info(get_name(),
	$sformatf("starting_phase:%s", starting_phase.get_full_name()), UVM_LOW)

	// Function: get_automatic_phase_objection
	// Returns (and locks) the value of the 'automatically object to
	// starting phase' bit.
	//
	// If 1, then the sequence will automatically raise an objection
	// to the starting phase (if the starting phase is not ~null~) immediately
	// prior to <pre_start> being called. The objection will be dropped
	// after <post_start> has executed, or <kill> has been called.
	automatic_phase_objection_status = seq.get_automatic_phase_objection();
	`uvm_info(get_name(),
	$sformatf("during seq is running, get_automatic_phase_objection returns :%b", automatic_phase_objection_status), UVM_LOW)
	end
	join_none
	seq.start(agent.sqr);
	automatic_phase_objection_status = seq.get_automatic_phase_objection();
	`uvm_info(get_name(),
	$sformatf("After seq finished, get_automatic_phase_objection returns :%b", automatic_phase_objection_status), UVM_LOW)
	endtask : run_phase
	endclass : my_test

	module top();
	initial begin
	run_test("my_test");
	end
	endmodule : top

	//Output:
	// UVM_INFO @ 0: reporter [RNTST] Running test my_test...
	// UVM_INFO @ 0: run [OBJTN_TRC] Object uvm_test_top.agent.sqr.seq raised 1 objection(s) (automatic phase objection): count=1 total=1
	// UVM_INFO @ 0: run [OBJTN_TRC] Object uvm_test_top.agent.sqr added 1 objection(s) to its total (raised from source object , automatic phase objection): count=0 total=1
	// UVM_INFO @ 0: run [OBJTN_TRC] Object uvm_test_top.agent added 1 objection(s) to its total (raised from source object , automatic phase objection): count=0 total=1
	// UVM_INFO @ 0: run [OBJTN_TRC] Object uvm_test_top added 1 objection(s) to its total (raised from source object uvm_test_top.agent.sqr.seq, automatic phase objection): count=0 total=1
	// UVM_INFO @ 0: run [OBJTN_TRC] Object uvm_top added 1 objection(s) to its total (raised from source object uvm_test_top.agent.sqr.seq, automatic phase objection): count=0 total=1
	// UVM_INFO testbench.sv(118) @ 0: uvm_test_top.agent.sqr@@seq [seq] After randomizating in my_seq my_seq_item= addr=19, data=140
	// UVM_INFO testbench.sv(50) @ 0: uvm_test_top.agent.drv [drv] in driver after get_next_item my_seq_item= addr=19, data=140
	// UVM_INFO testbench.sv(158) @ 30: uvm_test_top [uvm_test_top] starting_phase:common.run
	// UVM_INFO testbench.sv(170) @ 30: uvm_test_top [uvm_test_top] during seq is running, get_automatic_phase_objection returns :1
	// UVM_INFO testbench.sv(52) @ 50: uvm_test_top.agent.drv [drv] item_done called
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top.agent.sqr.seq dropped 1 objection(s) (automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top.agent.sqr.seq all_dropped 1 objection(s) (automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top.agent.sqr subtracted 1 objection(s) from its total (dropped from source object , automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top.agent.sqr subtracted 1 objection(s) from its total (all_dropped from source object , automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top.agent subtracted 1 objection(s) from its total (dropped from source object , automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top.agent subtracted 1 objection(s) from its total (all_dropped from source object , automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top subtracted 1 objection(s) from its total (dropped from source object uvm_test_top.agent.sqr.seq, automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_test_top subtracted 1 objection(s) from its total (all_dropped from source object uvm_test_top.agent.sqr.seq, automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_top subtracted 1 objection(s) from its total (dropped from source object uvm_test_top.agent.sqr.seq, automatic phase objection): count=0 total=0
	// UVM_INFO @ 50: run [OBJTN_TRC] Object uvm_top subtracted 1 objection(s) from its total (all_dropped from source object uvm_test_top.agent.sqr.seq, automatic phase objection): count=0 total=0
	// UVM_INFO uvm-1.2/src/base/uvm_objection.svh(1271) @ 50: reporter [TEST_DONE] 'run' phase is ready to proceed to the 'extract' phase
	// UVM_INFO testbench.sv(176) @ 50: uvm_test_top [uvm_test_top] After seq finished, get_automatic_phase_objection returns :1
	// UVM_INFO uvm-1.2/src/base/uvm_report_server.svh(847) @ 50: reporter [UVM/REPORT/SERVER]