等待硬件事件

虽然通常driver会负责正常的硬件同步，但sequence运行过程中可能需要与硬件事件同步，例如边界信号的转换或复位事件的结束。 不应该去修改driver然后为sequence_item添加一个新的字段，而是建议在包含指向virtual interface的指针的配置对象中实现 wait_for_hardware_event 方法。

举个例子，可以利用一个配置类，内含虚接口，传递给sequence，然后在配置类中实现相关方法。

///// Transaction Class
class transaction extends uvm_sequence_item;
    `uvm_object_utils(transaction)

    rand logic [31:0] addr;
    rand logic [31:0] write_data;
    rand bit read;
    rand int delay;

    bit error;
    logic [31:0] read_data;

    function new (string name);
        super.new(name);
    endfunction: new

    constraint at_least_1 { delay inside {[1:20]};}

    constraint 32bit_align {addr[1:0] == 0;}

endclass: transaction

///// Bus Configuration Object
class bus_config extends uvm_object;
    `uvm_object_utils(bus_config)

    virtual bus_interface bus_if;

    function new (string name);
        super.new(name);
    endfunction: new

 /// wait_for_clock
    task wait_for_clock( int m = 1 );
        repeat ( m ) begin
            @(posedge bus_if.clk);
        end
    endtask: wait_for_clock

 /// wait_for_reset
    task wait_for_reset;
        @(posedge bus_if.reset);
    endtask: wait_for_reset

endclass: bus_config

///// Bus Sequence
class bus_seq extends uvm_sequence #(transaction);
    `uvm_object_utils(bus_seq)

    transaction txn;
    bus_config bus_cfg;

    rand int limit = 25;

    function new (string name);
        super.new(name);
    endfunction: new

    task body;
        int i = 5;
        txn = transaction::type_id::create("txn", this);
 /// Get the Configuration object
        if(!uvm_config_db #(bus_config)::get(null, get_full_name(), "config", bus_cfg)) begin
            `uvm_error(" SEQ BODY ", "bus_config is not found")
        end
    repeat (limit) begin
            start_item(txn);
            if(!txn.randomize() with {addr inside {[32'h0010_0000:32'h0010_001C]};}) begin
                `uvm_error(" SEQ BODY ", " Transaction randomization failed")
            end
            finish_item(txn);
 /// wait for interface clock
            bus_cfg.wait_for_clock(i);
            i++;
 /// The txn handle points to the object that the driver has updated with response data
            `uvm_info(" SEQ BODY ", " txn.read_data ", UVM_LOW)
        end
    endtask: body
endclass: bus_seq