Hi.
I came to know that start_item() is a method of an already running sequence - the sequencer was set when you started it. start_item/finish_item is used to send transactions to a driver, and thus must be connected to a sequencer. and start() is a method of a sequence object you just created, and in turn calls its body() method.
To understand the behavior of start_item() I commented out the task body() and implement as the below ,
class core_A_seq extends uvm_sequence #(seq_item);
seq_item req;
`uvm_object_utils(core_A_seq)
function new (string name = "core_A_seq");
super.new(name);
endfunction
task body();
`uvm_info(get_type_name(), "core_A_seq: Inside Body", UVM_LOW);
req = seq_item::type_id::create("req");
req.core = CORE_A;
wait_for_grant();
assert(req.randomize());
send_request(req);
wait_for_item_done();
endtask
endclass
class core_B_seq extends uvm_sequence #(seq_item);
seq_item req;
`uvm_object_utils(core_B_seq)
function new (string name = "core_B_seq");
super.new(name);
endfunction
task body();
`uvm_info(get_type_name(), "core_B_seq: Inside Body", UVM_LOW);
req = seq_item::type_id::create("req");
req.core = CORE_B;
wait_for_grant();
assert(req.randomize());
send_request(req);
wait_for_item_done();
endtask
endclass
// create a virtual sequence which holds core_A_seq and core_B_seq
class virtual_seq extends uvm_sequence #(seq_item);
core_A_seq Aseq;
core_B_seq Bseq;
core_A_sequencer seqr_A;
core_B_sequencer seqr_B;
`uvm_object_utils(virtual_seq)
`uvm_declare_p_sequencer(virtual_sequencer)
function new (string name = "virtual_seq");
super.new(name);
endfunction
/*
task body();
`uvm_info(get_type_name(), "virtual_seq: Inside Body", UVM_LOW);
Aseq = core_A_seq::type_id::create("Aseq");
Bseq = core_B_seq::type_id::create("Bseq");
Aseq.start(p_sequencer.seqr_A);
Bseq.start(p_sequencer.seqr_B);
endtask
*/
task my_task();
`uvm_info(get_type_name(), "virtual_seq: Inside Body", UVM_LOW);
Aseq = core_A_seq::type_id::create("Aseq");
Bseq = core_B_seq::type_id::create("Bseq");
Aseq.start(p_sequencer.seqr_A);
Bseq.start(p_sequencer.seqr_B);
endtask
endclassWhen I execute the sequence with start_item() I get the error
UVM_INFO @ 0: reporter [RNTST] Running test base_test...
UVM_INFO sequence.sv(65) @ 0: reporter@@v_seq [virtual_seq] virtual_seq: Inside Body
xmsim: *E,TRNULLID: NULL pointer dereference.
File: ./sequence.sv, line = 69, pos = 25
Scope: worklib.$unit_0x4ccdf83b::virtual_seq@4292_23.my_task
Time: 0 FS + 44
But I can't understand why I can't get the p_sequencer ?
