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UVM-SC Sequence getting stuck at wait_for_grant()

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Hi Guys,

I have a simple framework for an IP level testbench, written using UVM-SC libraries. The intent is to be able to pump basic AHB write/read request to the DUT(in System C) using this BFM. I have created all basic components, snippet for which are pasted below. 

I have an ahb_sequencer, which is just an extension oh uvm_sequencer with specific ahb_transaction type.

In ahb_driver run_phase is as under:

void run_phase(uvm::uvm_phase phase) 
            REQ req, rsp;

               UVM_INFO(this->get_name(), "run_phase Entered", UVM_LOW);




In ahb_env, driver and seqr are connected and sequences are started.

class ahb_basic_env : public uvm::uvm_env
        ahb_driver<ahb_transaction>* ahb_driver_inst;
        ahb_sequencer<ahb_transaction>* ahb_sequencer_inst;
        ahb_basic_write_sequence* ahb_wr_seq[NUM_SEQS];

        ahb_basic_env( uvm::uvm_component_name name) : uvm::uvm_env(name)
         std::cout << sc_core::sc_time_stamp() << ": constructor " << name << std::endl;

        void build_phase(uvm::uvm_phase& phase)
          std::cout << sc_core::sc_time_stamp() << ": build_phase " << name() << std::endl;

                UVM_INFO(this->get_name(), " is ACTIVE", UVM_LOW);

                ahb_sequencer_inst = ahb_sequencer<ahb_transaction>::type_id::create("ahb_sequencer_inst",this);

                ahb_driver_inst = ahb_driver<ahb_transaction>::type_id::create("ahb_driver_inst",this);

          for (int i = 0; i < NUM_SEQS; i++)
              std::ostringstream str;
              str << "ahb_basic_write_sequence" << i;
              ahb_wr_seq = new ahb_basic_write_sequence(str.str());

        void connect_phase(uvm::uvm_phase& phase)
          std::cout << sc_core::sc_time_stamp() << ": connect_phase " << name() << std::endl;

        void run_phase(uvm::uvm_phase& phase) 
          std::cout << sc_core::sc_time_stamp() << ": run_phase Entered " << name() << std::endl;
              sc_core::sc_spawn(sc_bind(&ahb_basic_env::start_sequence, this, 0)),
              sc_core::sc_spawn(sc_bind(&ahb_basic_env::start_sequence, this, 1)),
          std::cout << sc_core::sc_time_stamp() << ": run_phase Exited " << name() << std::endl;
        void start_sequence(int n)
          ahb_wr_seq[n]->start(ahb_sequencer_inst, NULL);



The sequence uses wait_for_grant() and start_item() calls to initiate the transaction:

class ahb_basic_write_sequence : public uvm::uvm_sequence<ahb_transaction,ahb_transaction>
        ahb_basic_write_sequence( const std::string& name = "ahb_basic_write_sequence") : uvm::uvm_sequence< ahb_transaction,ahb_transaction > ( name )
            std::cout << sc_core::sc_time_stamp() << ": constructor " << name << std::endl;
        void pre_body()
          // raise objection if started as a root sequence
          if(this->starting_phase != NULL)

        void body() 

            ahb_transaction* req_pkt;
            ahb_transaction* rsp;
            unsigned transaction_numb;

            UVM_INFO(this->get_name(), "Starting sequence ahb_basic_write_sequence", uvm::UVM_INFO);
            transaction_numb = 10;

            for(unsigned int i = 0; i < transaction_numb; i++) {
                req_pkt = new ahb_transaction();
                rsp     = new ahb_transaction();

                UVM_INFO(this->get_name(), "Sending transaction from sequence ahb_basic_write_sequence", uvm::UVM_INFO);
                req_pkt->haddr  = 0x100000 + 4*i;
                req_pkt->hwrite = 1;
                //req_pkt->hwrite = ahbConfig::WRITE_XACT;
                req_pkt->htrans = 2;
                //req_pkt->htrans = ahbConfig::HTRANS_NONSEQ;
                req_pkt->hwdata = (sc_uint<32>)(0xAAAABBBB + 4*i);
                req_pkt->hsize  = ahbConfig::HSIZE_WORD;
                UVM_INFO(this->get_name(), "Calling send_request from sequence ahb_basic_write_sequence", uvm::UVM_INFO);
                UVM_INFO(this->get_name(), "Getting response from sequence ahb_basic_write_sequence", uvm::UVM_INFO);
            UVM_INFO(this->get_name(), "Finishing sequence", uvm::UVM_INFO);
        void post_body()
          // drop objection if started as a root sequence
          if(this->starting_phase != NULL)


But when i run the code, it gets stuck at wait_for_grant() call and also I don't see the run_phase prints from the driver class.

The output looks something like this:

Starting SC tests ...                                                                                                  
Running AHB tests                                                                                                      
0 sIn dut
UVM_INFO @ 0 s: reporter [RNTST] Running test ...
0 s: build_phase tb
UVM_INFO ahb_basic_env.h(65) @ 0 s: tb [tb]  is ACTIVE
0 s: constructor ahb_sequencer_inst
0 s: constructor ahb_driver_inst
0 s: constructor ahb_basic_write_sequence0
0 s: constructor ahb_basic_write_sequence1
UVM_INFO ahb_driver.h(53) @ 0 s: reporter [ahb_driver_inst] build_phase Entered
0 s: connect_phase tb

Info: (I804) /IEEE_Std_1666/deprecated: all waits except wait() and wait(N)
             are deprecated for SC_CTHREAD, use an SC_THREAD instead
0 s: run_phase Entered tb
UVM_INFO ahb_basic_write_sequence.h(66) @ 0 s: reporter [ahb_basic_write_sequence0] Starting sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(76) @ 0 s: reporter [ahb_basic_write_sequence0] Sending transaction from sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(66) @ 0 s: reporter [ahb_basic_write_sequence1] Starting sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(76) @ 0 s: reporter [ahb_basic_write_sequence1] Sending transaction from sequence ahb_basic_write_sequence



Any idea why is this happening? wait_for_grant() should unblock when driver takes the request right? Not sure why isnt the driver getting the request.

Appreciate your help here!


PS: Attached the files for reference.






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Hi Guys,


Not sure if someone else has faced similar issue. After little more debug the issue seems to be with the simulator not entering into driver's run_phase at all. Ideally all run phases should be executed in parallel. Currently it gets stuck after the sequence raises objection and times out.

Please let me know if I can try some alternatives.



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Hi All,

I found one basic issue with the run phase method in driver. There was a typo. I used run_phase(uvm_phase phase), instead of run_phase(uvm_phase& phase).

So the phase was not passed by reference, hence I think the phases in driver class were not in sync with other classes. 

Sorry about that, i too spent a lot of time in figuring this out :(.

Now I can see that the simulation enters all run_phases (i.e. of test and driver) and exits after the sequence is over. But even though all phases are exited, the simulation is getting stuck. 

I believe in UVM-SC also we look for objections and exit if there is none after the run phase? Is there a way to query for raised objections? Tried using get_obejctions method, but faced some error.



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Hello All,

Another update from my side here:

I could query the objections in final_phase of my test and saw that there were no pending ones. I had to explicitly call sc_stop() and only then end_of_simulation method was called by the simulator. is it the expected behavior?

Pasted the updated methods in my test:

virtual void final_phase(uvm::uvm_phase& phase)
          std::cout << sc_core::sc_time_stamp() << ": Final phase of test entered " << name() << std::endl;
          uvm_objection* uvm_obj;
          uvm_obj = new uvm_objection("obj_cnt");
          std::cout << sc_core::sc_time_stamp() << ": Final phase of test happened " << name() << std::endl;
        virtual void end_of_simulation()
          std::cout << sc_core::sc_time_stamp() << ": end_of_simulation phase of test happened " << name() << std::endl;

The output message from simulator looks like as under:. Just wanted to know if this is the recommended way of exiting from simulation.

UVM_INFO ahb_driver.h(65) @ 0 s: tb.top_env_inst.agent.ahb_driver_inst [ahb_driver_inst] CHICKY:run_phase Entered
UVM_INFO ahb_driver.h(70) @ 0 s: tb.top_env_inst.agent.ahb_driver_inst [ahb_driver_inst] AKHILA:run_phase FOR Entered
0 s: run_phase Entered tb.top_env_inst                                                                               
0 s: UVM test started tb
UVM_INFO ahb_basic_write_sequence.h(62) @ 0 s: reporter [ahb_wr_seq] Starting sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(68) @ 0 s: reporter [ahb_wr_seq] Starting sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(76) @ 0 s: reporter [ahb_wr_seq] Sending transaction from sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(87) @ 0 s: reporter [ahb_wr_seq] Calling start_item from sequence ahb_basic_write_sequence
UVM_INFO ahb_driver.h(72) @ 0 s: tb.top_env_inst.agent.ahb_driver_inst [ahb_driver_inst] AKHILA:run_phase after get_next_item Entered
UVM_INFO ahb_driver.h(78) @ 0 s: tb.top_env_inst.agent.ahb_driver_inst [ahb_driver_inst] AKHILA:write trans Entered
UVM_INFO ahb_basic_write_sequence.h(89) @ 10 ns: reporter [ahb_wr_seq] Getting response from sequence ahb_basic_write_sequence
UVM_INFO ahb_basic_write_sequence.h(93) @ 10 ns: reporter [ahb_wr_seq] Finishing sequence
UVM_INFO ahb_driver.h(93) @ 10 ns: tb.top_env_inst.agent.ahb_driver_inst [ahb_driver_inst] AKHILA:run_phase finished
20 ns: run_phase Exited tb.top_env_inst
20 ns: Final phase of test entered tb

The total objection count is 0
20 ns: Final phase of test happened tb
UVM_INFO @ 20 ns: reporter [FINISH] UVM-SystemC phasing completed; simulation finished
20 ns: end_of_simulation phase of test happened tb

Warning: (W545) sc_stop has already been called
In file: ../../../../src/sysc/kernel/sc_simcontext.cpp:1045
||              All tests passed OK                ||

Info: (I804) /IEEE_Std_1666/deprecated: You can turn off warnings about
             IEEE 1666 deprecated features by placing this method call
             as the first statement in your sc_main() function:

  sc_core::sc_report_handler::set_actions( "/IEEE_Std_1666/deprecated",
                                           sc_core::SC_DO_NOTHING );




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UVM-SystemC simulation will automatically finish if all UVM phases have been executed (without any pending objections). You can look in the examples/simple/objections/basic example how to get the objection count. I expect somewhere you raise an objection, but you do not drop it.

The SystemC sc_stop will trigger end_of_simulation. So this is expected behaviour. However, in UVM-SystemC you should not call sc_stop yourself (in a similar way, as a user you do not start the simulation with sc_start)


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Thanks Martin. I looked at the example you mentioned. I will add call to get_objection() in my test's run_phase and check. But if i call display_objections() in final_phase and find the count to be 0, wouldn't this imply there are no pending objections? Also, will the simulation enter into subsequent phases (viz. final, report), if there is a pending objection in previous phase( viz. run_phase) ?



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Hi Martin,

I tried adding callback dropped to my top level test. I can that objection->get_objection_total(this) is returning 0 whereas objection->get_objection_total(uvm_root::get()) is returning 1. So this tells that there is some objection pending.

Now when I added all_dropped callback to the test, its also executing. This implies that there is no pending objection for this class and its children correct? 

And the pending one is from uvm_top as shown by display_objections() method(pasted the output below). Any idea from where is this getting generated? 

0 s: UVM test started ahb_basic_test
UVM_INFO ahb_basic_write_sequence.h(62) @ 0 s: reporter [ahb_wr_seq] Starting sequence ahb_basic_write_sequence
[SEQCHECK]: start_item called at 0 s
UVM_INFO ahb_basic_write_sequence.h(94) @ 0 s: reporter [ahb_wr_seq] Finishing sequence
UVM_INFO @ 0 s: ahb_basic_test [dropped] 1 objection(s) dropped from ahb_basic_test, total count is now 0 top: 1

--> This is the result of display_obejctions()

The total objection count is 1
 Source  Total
 Count   Count   Object
      0      0   ahb_basic_test
      0      1   uvm_top
0 s: Stopping simulation as objection count is 0
0 s: UVM test finished ahb_basic_test
UVM_INFO @ 0 s: ahb_basic_test [all_dropped] ALL OBEJCTIONS DROPPED

--- UVM Report Summary ---

** Report counts by severity
UVM_INFO      :   9
UVM_ERROR     :   0
UVM_FATAL     :   0
** Report counts by id
[RNTST]                 1
[agent]                 1
[ahb_driver_inst]       3
[ahb_wr_seq]            2
[all_dropped]           1
[dropped]               1

------------------SIM HANGS HERE-------------

I have only one test which is then called in sc_main(which looks something like this)

 * SC main function
int sc_main(int, char*[])
    cout << "=====================================================" << endl;
    cout << "||              All tests passed OK                ||" << endl;
    cout << "=====================================================" << endl;

    return 0;

Appreciate any suggestions here.




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