Uvm dcon2013
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John Aynsley provides an in-depth overview of advanced UVM concepts including sequences and sequencers, virtual sequences, layered sequencers for request-response transactions, and strategies for synchronizing multiple sequencer stacks. The document discusses techniques for modeling pipelined interfaces, out-of-order responses, and idle cycles in a driver. It also examines the arbitration queue, user-defined arbitration algorithms, locking versus grabbing sequences, and using events to synchronize different components.
![User-Defined Arbitration Algorithm
12
class my_sequencer extends uvm_sequencer #(my_tx);
...
function integer user_priority_arbitration(
integer avail_sequences[$]);
foreach (avail_sequences[i])
begin
integer index = avail_sequences[i];
uvm_sequence_request req = arb_sequence_q[index];
int pri = req.item_priority;
uvm_sequence_base seq = req.sequence_ptr;
if (pri > max_pri)
...
end
return max_index;
endfunction
endclass
Could access properties of the sequence objectCould access properties of the sequence object](https://image.slidesharecdn.com/uvmdcon2013-130607034447-phpapp01/85/Uvm-dcon2013-12-320.jpg)
Uvm dcon2013
- 1. John Aynsley, Doulos The Finer Points of UVM: Tasting Tips for the Connoisseur
- 2. The Finer Points of UVM • Sequences and sequencers • The arbitration queue • Virtual sequences • Request and response • Multiple sequencer stacks
- 4. Sequences and Sequencers 4 TLM exportTLM export TLM portTLM port start_item(req); finish_item(req); seq_item_port.get(req);
- 5. A Simple Sequence 5 class my_seq extends uvm_sequence #(my_tx); `uvm_object_utils(my_seq) function new(string name = ""); super.new(name); endfunction: new task body; repeat(4) begin req = my_tx::type_id::create("req"); start_item(req); if (!req.randomize()) `uvm_error("", "failed to randomize") finish_item(req); end endtask endclass
- 6. Nested Sequences 6 class top_seq extends uvm_sequence #(my_tx); ... `uvm_declare_p_sequencer(my_seqr) ... task body; repeat(3) begin my_seq seq; seq = my_seq::type_id::create("seq"); if (!seq.randomize()) `uvm_error("", "failed to randomize") seq.start(p_sequencer, this); end endtask ... Parent sequenceParent sequenceSequencerSequencer Variable that points to sequencerVariable that points to sequencer
- 7. Concurrent Sequences 7 task body; fork begin seq1 = my_seq::type_id::create("seq1"); if (!seq1.randomize()) `uvm_error("", "failed to randomize") seq1.start(p_sequencer, this); end begin seq2 = my_seq::type_id::create("seq2"); if (!seq2.randomize()) ... seq2.start(p_sequencer, this); end begin ... seq3.start(p_sequencer, this); end join endtask Transactions will be strictly interleavedTransactions will be strictly interleaved
- 8. The Finer Points of UVM • Sequences and sequencers • The arbitration queue • Virtual sequences • Request and response • Multiple sequencer stacks
- 9. The Arbitration Queue 9 priority sequence priority sequence priority sequence priority sequence priority sequence priority sequence Arbitration queueArbitration queue First inFirst in start body start_item seq_item_port.get(req); Arbitration start body start_item fork start body start_item seq_item_port.get(req); seq_item_port.get(req); begin finish_item finish_item finish_item FIFOFIFO join end
- 10. Setting the Arbritration Algorithm 10 task body; p_sequencer.set_arbitration( SEQ_ARB_STRICT_RANDOM); fork begin seq1 = my_seq::type_id::create("seq1"); if (!seq1.randomize()) `uvm_error("", "failed to randomize") seq1.start(p_sequencer, this, 1); end begin ... seq2.start(p_sequencer, this, 2); end begin ... seq3.start(p_sequencer, this, 3); end join endtask Priority (default 100)Priority (default 100)
- 11. Arbitration Algorithms 11 Arbitration mode Order in which requests granted SEQ_ARB_FIFO FIFO order (default) SEQ_ARB_RANDOM Random order SEQ_ARB_STRICT_FIFO Highest priority first, then FIFO order SEQ_ARB_STRICT_RANDOM Highest priority first, then random order SEQ_ARB_WEIGHTED Weighted by priority SEQ_ARB_USER User-defined
- 12. User-Defined Arbitration Algorithm 12 class my_sequencer extends uvm_sequencer #(my_tx); ... function integer user_priority_arbitration( integer avail_sequences[$]); foreach (avail_sequences[i]) begin integer index = avail_sequences[i]; uvm_sequence_request req = arb_sequence_q[index]; int pri = req.item_priority; uvm_sequence_base seq = req.sequence_ptr; if (pri > max_pri) ... end return max_index; endfunction endclass Could access properties of the sequence objectCould access properties of the sequence object
- 13. The Finer Points of UVM • Sequences and sequencers • The arbitration queue • Virtual sequences • Request and response • Multiple sequencer stacks
- 14. Virtual Sequences 14 priority seq1 priority seq1 vseq.start(seqr0, null, priority) body fork seq1.start(seqr1, this) body start_item ... seq2.start(seqr2, this, 50) body start_item ... seqr1 seqr2 seqr3 Blocks Inherits priority Blocks Inherits priority seqr0 Can be nullCan be null No transactions
- 15. Sequencer Lock 15 seqr1 seqr0 No transactions vseq.start(seqr0, null) body begin this.lock(seqr1); seq1.start(seqr1, this); body start_item finish_item this.unlock(seqr1); ... priority seqx priority seqx priority seqy priority seqy priority seq1 priority seq1 Important!Important!
- 16. Lock versus Grab 16 priority seqx priority seqx priority seqy priority seqy vseq1.start body begin lock seq1.start unlock vseq2.start body begin lock seq2.start unlock vseq3.start body begin grab seq3.start ungrab lock req vseq2 lock req vseq2 grab req vseq3 grab req vseq3 priority seq3 priority seq3 Locks inserted here Locks inserted here Grabs inserted here Grabs inserted here Head Tail priority seq1 priority seq1 priority seq2 priority seq2
- 17. The Finer Points of UVM • Sequences and sequencers • The arbitration queue • Virtual sequences • Request and response • Multiple sequencer stacks
- 18. Request and Response 18 TLM exportTLM export TLM portTLM port start_item(req); finish_item(req); get_response(rsp); seq_item_port.get(req); seq_item_port.put(rsp); req rsp The paper describes in detail how to code pipelined req/rsp and out-of-order responses The paper describes in detail how to code pipelined req/rsp and out-of-order responses
- 19. Layered Sequencers 19 seq_item_port.get(req); seq_item_port.put(rsp); seqr_upper.get(req_up); start_item(req_lo); finish_item(req_lo); get_response(rsp_lo); seqr_upper.put(rsp_up); start_item(req); finish_item(req); get_response(rsp); req rsp req rsp Ptr to upper sequencer Ptr to upper sequencer Could be one:one or one:many or many:one or many:many Could be one:one or one:many or many:one or many:many The paper shows more detailThe paper shows more detail req:rsp = 1:1req:rsp = 1:1
- 20. The Finer Points of UVM • Sequences and sequencers • The arbitration queue • Virtual sequences • Request and response • Multiple sequencer stacks
- 21. Multiple Agents / Sequencer Stacks 21 Communicate or synchronize? Communicate or synchronize? get(req) Must not block! Must not block!Driven by the DUT interface timingDriven by the DUT interface timing Analysis ports Callbacks Events Barriers Analysis ports Callbacks Events Barriers
- 22. Driver calls try_next_item 22 seq_item_port.try_next_item(req); if (req == null) begin dut_vi.idle <= 1; ... @(posedge dut_vi.clock); end else begin seq_item_port.item_done(); dut_vi.idle <= 0; ... @(posedge dut_vi.clock); ... seq_item_port.put(rsp); Wiggle pins for idle cycleWiggle pins for idle cycle Must be called in same time stepMust be called in same time step Response can be pipelinedResponse can be pipelined
- 23. The Finer Points of UVM • The UVM sequence library • Pipelined requests and responses • The response handler • UVM events and event pools • The configuration database Also in the paperAlso in the paper