一、为什么需要Layering Sequence

随着集成电路技术的发展，芯片的复杂度日益提升。对验证而言，为了更好地应对这种复杂性，一方面是提高各个级别的可移植性和复用性，另一方面是提高抽象级别，减小复杂度。
Layering Sequence这正是从第二个方面出发衍生的，它能够将高抽象级的uvm_sequence_item和低抽象级的uvm_sequence_item相互转换。

二、Layering Sequence机制

下面以《芯片验证漫游指南》13.5.3节为例，简单分析Layering Sequence的工作机制

1、高抽象级的layer_trans和低抽象级的bus_trans

首先定义一个低抽象级的bus_trans，并且将其打包成为packet_seq

点击查看代码

//低抽象级的bus_trans
class bus_trans extends uvm_sequence_item;
    rand phy_cmd_t cmd;
    rand int addr;
    rand int data;
    constraint cstr{
      soft addr == 'h0;
      soft data == 'h0;
    }
    ...
endclass

//打包后的packet_seq
class packet_seq extends uvm_sequence;
    rand int len;
    rand int addr;
    rand int data[];
    rand phy_cmd_t cmd;
    constraint cstr{
      soft len inside {[30:50]};
      soft addr[31:16] == 'hFF00;
      data.size() == len;
    }
    ...
    task body();
      bus_trans req;
      foreach(data[i])
        `uvm_do_with(req, {cmd == local::cmd; 
                           addr == local::addr;
                           data == local::data[i];})
    endtask
  endclass

其对应的sequencer是：

点击查看代码

 class phy_master_sequencer extends uvm_sequencer;
    layering_sequencer up_sqr;
	...
endclass

接下来定义一个高抽象级layer_trasn

点击查看代码 ```verilog class layer_trans extends uvm_sequence_item; rand layer_cmd_t layer_cmd; rand int pkt_len; rand int pkt_idle; constraint cstr { soft pkt_len inside {[10: 20]}; layer_cmd == FREQ_LOW_TRANS -> pkt_idle inside {[300:400]}; layer_cmd == FREQ_MED_TRANS -> pkt_idle inside {[100:200]}; layer_cmd == FREQ_HIGH_TRANS -> pkt_idle inside {[20:40]}; } ... endclass ```

其对应的sequencer是：

点击查看代码 ```verilog class layering_sequencer extends uvm_sequencer; ... endclass ```

可以看到高抽象级的layer_trans和低抽象级的bus_trans差别很大，也没有任何层次上的关系，因此需要有中间的转化层将两者进行转化后才能够正常发送给DUT。

2、转化层的sequece

用adapter_seq作为转化层

点击查看代码

class adapter_seq extends uvm_sequence;
    `uvm_object_utils(adapter_seq)
    `uvm_declare_p_sequencer(phy_master_sequencer)//句1
    function new(string name = "adapter_seq");
      super.new(name);
    endfunction
    task body();
      layer_trans trans;
      packet_seq pkt;
      forever begin
          p_sequencer.up_sqr.get_next_item(req);//句2-1
        void'($cast(trans, req));
        repeat(trans.pkt_len) begin
            `uvm_do(pkt)//句3
          delay(trans.pkt_idle);
        end
          p_sequencer.up_sqr.item_done();//句2-2
      end
    endtask
    virtual task delay(int delay);
    endtask
  endclass

3、layering sequence的工作机制

下面结合结构图分析一下layering sequence的工作机制

句1：通过uvm_declare_p_sequencer宏指定adapter_seq的item由phy_master_sequencer来发送，也构建了adapter_seq访问phy_master_sequencer成员变量和成员方法的桥梁（详见初识m_sequencer、p_sequencer和uvm_declare_p_sequencer宏）
句2-1：如图绿色曲线所示，通过p_sequencer访问phy_master_sequencer中的up_sqr，而up_sqr在test中通过句4将up_sqr指向layer_sqr（test代码第13行）。此时adapter_seq能够调用layer_sqr的get_next_item任务取得一个高抽象级的layer_trans。
句3：按照已取得的layer_trans中的属性（pkt_len和pkt_idle）约束低抽象级的packet_seq类型的pkt的属性，并交给phy_master_sequencer通过driver发送给DUT。
句2-2：依旧通过绿色曲线所示通路，使用item_done通知layer_sqr。

4、在test中的连接关系

test代码：

点击查看代码

class test extends uvm_test;
    layering_sequencer layer_sqr;
    phy_master_agent phy_agt;
    `uvm_component_utils(test1)
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
    function void build_phase(uvm_phase phase);
      layer_sqr = layering_sequencer::type_id::create("layer_sqr", this);
      phy_agt = phy_master_agent::type_id::create("phy_agt", this);
    endfunction
    function void connect_phase(uvm_phase phase);
      phy_agt.sqr.up_sqr = layer_sqr;//句4
    endfunction
    task run_phase(uvm_phase phase);
      top_seq seq;
      adapter_seq adapter;
      phase.raise_objection(phase);
      seq = new();
      adapter = new();
      fork
          adapter.start(phy_agt.sqr);//句5
      join_none
        seq.start(layer_sqr);//句6
      phase.drop_objection(phase);
    endtask
  endclass

句4：将phy_master_sequencer中的up_sqr指向layer_sqr，构建与layer_sqr的通路，使得adapter能够取得layer_trans。
句5：将adapter_seq挂载到phy_master_sequencer。
句6：将top_seq挂载到layer_sqr。

一些其他问题：

为什么使用fork-join_none：在adapter_seq的body()中使用的forever语句，使得adapter_seq永不停歇的取得高抽象级item，转化成低抽象级的item去执行。因此使用fork-join_none使adapter_seq不阻挡其他功能正常运行。
为什么采用句4和get_next_item()而不是TLM的方式：这是为了最大程度的提高复用性和减小复杂度。

《芯片验证漫游指南——从系统理论到UVM的验证全视界》刘斌著
Universal Verification Methodology (UVM) 1.2 User’s Guide

完整代码如下：

点击查看代码

module layer_seq;
  import uvm_pkg::*;
  `include "uvm_macros.svh"

  typedef class phy_master_sequencer;
  typedef enum {CLKON, CLKOFF, RESET, WRREG, RDREG} phy_cmd_t;
  typedef enum {FREQ_LOW_TRANS, FREQ_MED_TRANS, FREQ_HIGH_TRANS} layer_cmd_t;

  class bus_trans extends uvm_sequence_item;
    rand phy_cmd_t cmd;
    rand int addr;
    rand int data;
    constraint cstr{
      soft addr == 'h0;
      soft data == 'h0;
    }
    `uvm_object_utils_begin(bus_trans)
      `uvm_field_enum(phy_cmd_t, cmd, UVM_ALL_ON)
      `uvm_field_int(addr, UVM_ALL_ON)
      `uvm_field_int(data, UVM_ALL_ON)
    `uvm_object_utils_end
    function new(string name = "bus_trans");
      super.new(name);
    endfunction
  endclass

  class packet_seq extends uvm_sequence;
    rand int len;
    rand int addr;
    rand int data[];
    rand phy_cmd_t cmd;
    constraint cstr{
      soft len inside {[30:50]};
      soft addr[31:16] == 'hFF00;
      data.size() == len;
    }
    `uvm_object_utils(packet_seq)
    function new(string name = "reg_test_seq");
      super.new(name);
    endfunction
    task body();
      bus_trans req;
      foreach(data[i])
        `uvm_do_with(req, {cmd == local::cmd; 
                           addr == local::addr;
                           data == local::data[i];})
    endtask
  endclass

  class layer_trans extends uvm_sequence_item;
    rand layer_cmd_t layer_cmd;
    rand int pkt_len;
    rand int pkt_idle;
    constraint cstr {
      soft pkt_len inside {[10: 20]};
      layer_cmd == FREQ_LOW_TRANS -> pkt_idle inside {[300:400]};
      layer_cmd == FREQ_MED_TRANS -> pkt_idle inside {[100:200]};
      layer_cmd == FREQ_HIGH_TRANS -> pkt_idle inside {[20:40]};
    }
    `uvm_object_utils(layer_trans)
    function new(string name = "layer_trans");
      super.new(name);
    endfunction
  endclass

  class adapter_seq extends uvm_sequence;
    `uvm_object_utils(adapter_seq)
    `uvm_declare_p_sequencer(phy_master_sequencer)
    function new(string name = "adapter_seq");
      super.new(name);
    endfunction
    task body();
      layer_trans trans;
      packet_seq pkt;
      forever begin
        p_sequencer.up_sqr.get_next_item(req);
        void'($cast(trans, req));
        repeat(trans.pkt_len) begin
          `uvm_do(pkt)
          delay(trans.pkt_idle);
        end
        p_sequencer.up_sqr.item_done();
      end
    endtask
    virtual task delay(int delay);
    endtask
  endclass

  class top_seq extends uvm_sequence;
    `uvm_object_utils(top_seq)
    function new(string name = "top_seq");
      super.new(name);
    endfunction
    task body();
      layer_trans trans;
      `uvm_do_with(trans, {layer_cmd == FREQ_LOW_TRANS;})
      `uvm_do_with(trans, {layer_cmd == FREQ_HIGH_TRANS;})
    endtask
  endclass

  class layering_sequencer extends uvm_sequencer;
    `uvm_component_utils(layering_sequencer)
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
  endclass

  class phy_master_sequencer extends uvm_sequencer;
    layering_sequencer up_sqr;
    `uvm_component_utils(phy_master_sequencer)
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
  endclass

  class phy_master_driver extends uvm_driver;
    `uvm_component_utils(phy_master_driver)
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
    task run_phase(uvm_phase phase);
      REQ tmp;
      bus_trans req;
      forever begin
        seq_item_port.get_next_item(tmp);
        void'($cast(req, tmp));
        `uvm_info("DRV", $sformatf("got a item \n %s", req.sprint()), UVM_LOW)
        seq_item_port.item_done();
      end
    endtask
  endclass

  class phy_master_agent extends uvm_agent;
    phy_master_sequencer sqr;
    phy_master_driver drv;
    `uvm_component_utils(phy_master_agent)
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
    function void build_phase(uvm_phase phase);
      sqr = phy_master_sequencer::type_id::create("sqr", this);
      drv = phy_master_driver::type_id::create("drv", this);
    endfunction
    function void connect_phase(uvm_phase phase);
      drv.seq_item_port.connect(sqr.seq_item_export);
    endfunction
  endclass

  class test extends uvm_test;
    layering_sequencer layer_sqr;
    phy_master_agent phy_agt;
    `uvm_component_utils(test1)
    function new(string name, uvm_component parent);
      super.new(name, parent);
    endfunction
    function void build_phase(uvm_phase phase);
      layer_sqr = layering_sequencer::type_id::create("layer_sqr", this);
      phy_agt = phy_master_agent::type_id::create("phy_agt", this);
    endfunction
    function void connect_phase(uvm_phase phase);
      phy_agt.sqr.up_sqr = layer_sqr;
    endfunction
    task run_phase(uvm_phase phase);
      top_seq seq;
      adapter_seq adapter;
      phase.raise_objection(phase);
      seq = new();
      adapter = new();
      fork
        adapter.start(phy_agt.sqr);
      join_none
      seq.start(layer_sqr);
      phase.drop_objection(phase);
    endtask
  endclass

  initial begin
    run_test("test");
  end
endmodule

初识Layering Sequence - 程默白

一、为什么需要Layering Sequence

二、Layering Sequence机制

1、高抽象级的layer_trans和低抽象级的bus_trans

2、转化层的sequece

3、layering sequence的工作机制

4、在test中的连接关系

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