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I have a couple of issues with a basic UVM based TB I'm trying out to understand sequences and their working.

  1. bvalid is being always picked as 0 in the driver when being updated in the response item
  2. Couple of error messages for last 2 transactions (# UVM_ERROR @ 18: uvm_test_top.axi_agent1.axi_base_seqr1@@axi_base_seq1 [uvm_test_top.axi_agent1.axi_base_seqr1.axi_base_seq1] Response queue overflow, response was dropped)

Here is the link to the compiling code on EDA Playground http://www.edaplayground.com/x/3x9

Any suggestions on what I'm missing??

Thanks

venkstart

venkstart
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1 Answers1

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Having a look at the specification for $urandom_range it shows the signature as: function int unsigned $urandom_range( int unsigned maxval, int unsigned minval = 0 ). Change your call to $urandom_range(1, 0) and it should work.

The second error comes from the fact that you are sending responses from the driver and not picking them up in your sequence. This is the line that does it: seq_item_port.item_done(axi_item_driv_src);. Either just do seq_item_port.item_done(); (don't send responses) or put a call to get_response() inside your sequence after finish_item(). What I usually do is update the fields of the original request and just call item_done(). For example, if I start a read transaction, in my driver I would drive the control signals and wait for the DUT to respond, update the data field of the request with the data I got from the DUT and call item_done() in my driver to mark the request as done. This way if I need this data in my sequence (to constrain some future item, for example) I have it.

Tudor Timi
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  • Thanks for the explanation Tudor. One more question about why the error starts coming only after about 8 txns?? If the sequence is not picking up responses I should have seen this from the start? – venkstart Apr 14 '14 at 16:56
  • @venkstart Because the sequencer can't know when `get_response()` will be called it stores outstanding responses in a queue. When the queue gets too big it starts triggering errors. This means it will only start giving errors when the queue becomes full (8-ish might be set per default in UVM, but I think you can also change this number). – Tudor Timi Apr 14 '14 at 17:02
  • @TudorTimi have you tried `get_response()` in a `fork-join_none` in a non-blocking sequence? I tried such a scenario, but `get_response()` remains blocking throughout. Is there something inherently wrong with this approach? My question [here](https://stackoverflow.com/questions/64709875/uvm-sequence-get-response-with-fork-join-none) .Thanks. – thorondor1990 Nov 08 '20 at 08:02