A sequencer generates data transactions as class objects and sends it to the Driver for execution. It is recommended to extend uvm_sequencer base class since it contains all of the functionality required to allow a sequence to communicate with a driver. The base class is parameterized by the request and response item types that can be handled by the sequencer.

Sequencer的工作是產生data object 傳送給Driver執行。通常Sequencer會繼承自 uvm_sequencer，就會繼承 uvm_sequencer所有可以與Driver通訊的相關功能。

Usage

預設情況下，request type和response type相同，如果request和reponse不同的話可以在產生instance的時候指定第二個參數。除非有其他額外的port要include進來，不然應該直接將其實例化作為uvm_sequencer所需要的參數帶入。

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// class uvm_sequencer #(type REQ=uvm_sequence_item, RSP=REQ)
//                                   extends uvm_sequencer_param_base #(REQ, RSP);

uvm_sequencer #(my_data)           seqr0; // without RSP
uvm_sequencer #(my_data, data_rsp) seqr0; // with    RSP

Sequencer生成的object在靈活性(flexibility)和可重用性(re-usability)方面有很大的限制。因此要使用UVM_sequence來克服這個限制。

Custom Sequencer

其實並不需要客製化sequencer來執行每個sequence或agent。但是我們一樣可以建立具有額外自己客製化功能的 UVM sequencer，並在整個testbench中建立它的instance。

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class my_sequencer extends uvm_sequencer;
  `uvm_component_utils (my_sequencer)
  function new (string name="m_sequencer", uvm_component parent);
    super.new (name, parent);
  endfunction
endclass

Class Hierarchy