Missing sequence when using response handler

OVM
1

in my sequence i send the request in the run task, and i want to check the reaponse in the response handler task:
function void response_handler(ovm_sequence_item response) ;
cmi_src_cmd req;
assert($cast(req, response)) else
ovm_report_error(get_full_name()," received completion with unmatched type");
// verify data
if(req.CompareCompletion)
for (int i = 0 ; i < 16 ; i++)
if (req.ExpectedData[i] != req.WData[i])
ovm_report_error(get_full_name(), …));
else
$display(“cmp: %d == %d”,req.ExpectedData[i],req.WData[i]);
endfunction

i am sending the reuest from driver using :
seq_item_port.put_response(my_rsp);

but i keep getting error messages of the type :
sequencer [Sequencer] Dropping response for sequence 4, sequence not found. Probable cause: sequence exited or has been killed

can you please help me to solve it?

i must use response handler becouse i don’t want to block the reguest driver while waiting to completions, which can be out-of-order

2

In reply to zgluzer:

Are you setting the sequence_id for the response correctly? You need to make sure that you copy the sequence_id from the request you are responding to.

my_rsp.set_id_info(req); // Set the rsp id = req id
3

In reply to cgales:

yes . i’m saving that id for the response.
i thought maybe the initial sequence ( initiated by ovm_do) , was terminated after the driver get the request.
this is why the xact_id returned by rsp - does not match the latest response handler.

4

In reply to zgluzer:

just to make it clear, my flow is as following:
driver get the requst.
rsp get the req_act_id.
driver generate response with the same xact_id.
the sequence response handler only print the above warning and does not enter the handler. i realized it after adding a display for the handler first line.

so my problem is that the sequence is probebly exited before its handler is being called.

any suggestion?

5

In reply to zgluzer:

The sequence still needs to be active to receive its response. The sequence will call get_response() soon after finish_item() to receive the response(s).

You will need to post more code from your sequence to show how you are trying to handle the responses for a better answer.

6

In reply to cgales:

i try to keep the sequence alive , but now i can’t get requests back to back. the next request is received only after the former request got its response.
i need a way to get back to back requests from the sequence.

the sequence is :
…
// send xaction

    finish_item(this_transfer);
    if (this_transfer.NeedRsp)
    begin
        expected_responses++;
        $display("start wait for expected_responses at %t",$time());
        wait(expected_responses == 0);
        $display("finish wait for expected_responses at %t",$time());
    end
   endtask // body

   function void    response_handler(ovm_sequence_item response) ;
       cmi_src_cmd req;
       assert($cast(req, response)) else
            ovm_report_error(get_full_name()," received completion with unmatched type");
       $display("in sequence: got xact_id of response = %d",req.xact_id);
       // verify data
       if(req.CompareCompletion)
            for (int i = 0 ; i < 16 ; i++) 
                if (req.ExpectedData[i] != req.WData[i])
                    ovm_report_error(get_full_name(), $psprintf("data mismatch! index = %1d : expected = %h actual = %h @ TID = %h, SRC = %h , DST = %h . CHID = %d, Adress = %h",i,
                    req.ExpectedData[i] ,req.WData[i],req.TID,req.SrcID,req.DstID,req.ChId,req.Addr));
                else
                    $display("cmp: %d == %d",req.ExpectedData[i],req.WData[i]);
       expected_responses--;
   endfunction
7

In reply to zgluzer:

A sequence will terminate when it completes the body() phase. In order to receive a response, you must make the get_response() call part of your body, like such:


task body();

req = my_seq_item::type_id::create("req");
start_item(req);
req.randomize();
finish_item(req);

if (req.NeedRsp)
  get_response(rsp);

endtask

If you want to have multiple transactions in parallel, then you will need to fork off each sequence. This will allow each sequence to generate its sequence_item when dictated and still be ‘alive’ to receive the required response. Note that you can have 0 to as many responses for each sequence_item. You only need to make sure that you match the sequence_items and responses, otherwise you will have hung sequences or your response queue will overflow.

8

In reply to cgales:

thanks .
it worked and with fork…join in my sequence i can get parallel requests.
in order to keep 1st request to be first served i added a logic for that in my driver.