I’m studying RAL and I experienced this situation wherein the uvm_config_db get method is failing when I use null handle for the sequencer in the seq.start() method.
The uvm_config_db get method is in the body() task of my base_sequence class:
// From base_sequence class
virtual task body();
if(!uvm_config_db#(testbench_env_config)::get(null, get_full_name(), "cfg", cfg)) begin
`uvm_fatal("CFG_GET_FAILED", "Failed to get cfg from configuration database")
end
this.tb_reg_block = cfg.tb_reg_block;
endtask : body
In my test class, when I used env.agt.sqr for the seq.start() method, I’m not having any issues and the simulation is working fine. But when I used null, the uvm_config_db get method on the base sequence class is failing:
// In test class
virtual task run_phase(uvm_phase phase);
super.run_phase(phase);
phase.raise_objection(this);
reg_type_b_seq = register_type_b_1_sequence::type_id::create("reg_type_b_seq");
//reg_type_b_seq.start(env.mst_agt.sqr); // If this is used, there is no issue
reg_type_b_seq.start(null); // If null is used, uvm_config_db get method is failing
phase.drop_objection(this);
endtask : run_phase
This is the code of my sequence extended from base_sequence:
// In sequence class extended from base_sequence
virtual task body();
super.body(); // This is will call uvm_config_db get method from the base_sequence class
// The methods below use RAL methods like reg.write(), reg.peek(), etc.
this.init_regs(); // Initialize the registers with a random value
this.do_backdoor_read(); // Do backdoor read access to check initial random values
this.do_frontdoor_wr_backdoor_rd(); // Do frontdoor write then backdoor read
endtask : body
What is the reason why the uvm_config_db get method is failing when I use null instead of env.agt.sqr?
I would like to use null because I’m using the register model to pass transaction to the agent. Take note that I don’t have start_item() and finish_item() in my sequence body() task, that’s why I think it’s okay to pass null for the seq.start() method.
From my understanding, the visibility of “cfg” is “test_h.*”, which means it is visible everywhere. (Correct me if I’m wrong).
Another thing is, if the problem is in the visibility, then even if I use env.agt.sqr instead of null, uvm_fatal should have flagged too… But it didn’t. Therefore, my guess is there might be some connection with the use of a null sequencer and it somehow alters the set visibility… I’m guessing this could be a bug in the UVM itself. I don’t know.
makes configuration visible from test to downward hierarchy. But, the sequence is part of uvm_top/uvm_root where config visibility is not there. e.g. uvm_top.sequence_h
Sequences and uvm_object’s are not part of any hierarchy by default like component. When we pass sequencer to sequence it uses sequencer hierarchy. If you want to pass null as sequencer, you can pass an extra argument while instantiating sequence to put it under desired hierarchy. for ex :