当前bit的实际值和补码值

当前bit的实际值和补码值取决于该bit所在的位置和所表示的数值。在正数的补码表示中，最高位为0，其余位表示该数的二进制数值；在负数的补码表示中，最高位为1，其余位表示该数的绝对值的二进制补码（即反码+1）。例如，在8位补码表示中，01100101的实际值为101（即二进制数值69），而11100101的实际值为-27（即-（10001011）的补码表示）。

相关问题

写一个uvm环境，在monitor中检测当前bit和改bit的补码值，然后在scoreboard中进行比对

以下是一个基本的UVM环境，包含一个monitor和一个scoreboard，用于检测当前bit和改bit的补码值：

`include "uvm_macros.svh"

class my_env extends uvm_env;

  my_agent m_agent;
  my_scoreboard m_scoreboard;

  function new(string name = "my_env", uvm_component parent);
    super.new(name, parent);
  endfunction : new

  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    m_agent = my_agent::type_id::create("m_agent", this);
    m_scoreboard = my_scoreboard::type_id::create("m_scoreboard", this);
  endfunction : build_phase

  function void connect_phase(uvm_phase phase);
    super.connect_phase(phase);
    m_agent.monitor_ap.connect(m_scoreboard.analysis_export);
  endfunction : connect_phase

endclass : my_env

class my_monitor extends uvm_monitor;

  uvm_analysis_port#(my_analysis_item) analysis_port;
  my_analysis_item analysis_item;

  function new(string name = "my_monitor", uvm_component parent);
    super.new(name, parent);
  endfunction : new

  virtual function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    analysis_port = new("analysis_port", this);
  endfunction : build_phase

  virtual task run_phase(uvm_phase phase);
    super.run_phase(phase);
    while(1) begin
      // Read current bit and its two's complement
      bit curr_bit = my_interface.read_bit();
      logic signed [31:0] curr_twos_comp = $signed(curr_bit) ? -1 - curr_bit : curr_bit;

      // Wait for change in bit value
      @(my_interface.posedge);

      // Read changed bit and its two's complement
      bit changed_bit = my_interface.read_bit();
      logic signed [31:0] changed_twos_comp = $signed(changed_bit) ? -1 - changed_bit : changed_bit;

      // Create analysis item and send to scoreboard
      analysis_item = new("analysis_item");
      analysis_item.curr_bit = curr_bit;
      analysis_item.curr_twos_comp = curr_twos_comp;
      analysis_item.changed_bit = changed_bit;
      analysis_item.changed_twos_comp = changed_twos_comp;
      analysis_port.write(analysis_item);

      // Wait for next posedge
      @(my_interface.posedge);
    end
  endtask : run_phase

endclass : my_monitor

class my_scoreboard extends uvm_scoreboard;

  uvm_analysis_export#(my_analysis_item) analysis_export;
  my_analysis_item analysis_item;

  function new(string name = "my_scoreboard", uvm_component parent);
    super.new(name, parent);
  endfunction : new

  virtual function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    analysis_export = new("analysis_export", this);
  endfunction : build_phase

  virtual function void run_phase(uvm_phase phase);
    super.run_phase(phase);
    while(1) begin
      // Wait for analysis item from monitor
      analysis_export.get_next_item(analysis_item);

      // Compare current bit and its two's complement with changed bit and its two's complement
      if (analysis_item.curr_bit != analysis_item.changed_bit) begin
        if (analysis_item.curr_twos_comp != analysis_item.changed_twos_comp) begin
          `uvm_error("BIT_ERROR", $sformatf("Bit value changed from %0d to %0d, but two's complement changed from %0d to %0d", analysis_item.curr_bit, analysis_item.changed_bit, analysis_item.curr_twos_comp, analysis_item.changed_twos_comp))
        end
      end
    end
  endfunction : run_phase

endclass : my_scoreboard

class my_agent extends uvm_agent;

  my_monitor monitor_ap;

  function new(string name = "my_agent", uvm_component parent);
    super.new(name, parent);
  endfunction : new

  virtual function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    monitor_ap = my_monitor::type_id::create("monitor_ap", this);
  endfunction : build_phase

endclass : my_agent

class my_analysis_item extends uvm_sequence_item;

  bit curr_bit;
  logic signed [31:0] curr_twos_comp;
  bit changed_bit;
  logic signed [31:0] changed_twos_comp;

  `uvm_object_utils(my_analysis_item)

  function new(string name = "my_analysis_item");
    super.new(name);
  endfunction : new

endclass : my_analysis_item

在这个环境中，`my_monitor`任务读取当前的bit和它的补码值，然后等待bit值的改变。一旦有改变，它读取新的bit和它的补码值，并创建一个`my_analysis_item`对象，其中包含了当前bit和改变的bit以及它们的补码值。然后，它使用`analysis_port`将该对象发送到`my_scoreboard`。

`my_scoreboard`在接收到`my_analysis_item`对象后，比较当前bit和它的补码值与改变的bit和它的补码值。如果bit值不同，那么它会检查补码值是否也不同。如果补码值也不同，那么它将在控制台上输出一条错误消息。

在`my_env`中，`my_agent`和`my_scoreboard`被创建，并通过`monitor_ap`和`analysis_export`连接起来。然后，整个环境可以被实例化并运行。

补码与真实值的计算公式

补码与真实值的计算公式根据不同的运算有所不同。在进行加法运算时，可以使用补码的加法公式 [X+Y]补 = [X]补 + [Y]补 ，其中 [X]补 和 [Y]补 分别表示 X 和 Y 的补码形式。需要注意的是，在进行补码加法时，符号位和数值部分一起参与运算，进位的符号位需要丢掉。而在进行减法运算时，可以使用补码的减法公式 [X-Y]补 = [X]补 - [Y]补 ，其中 [X]补 和 [Y]补 分别表示 X 和 Y 的补码形式。对于负数的补码，需要先求负补，即对补码的每一位（包括符号位）求反，然后末位加1。在进行补码与真实值的转换时，如果补码是正数（符号位为0），则补码与真实值相同；如果补码是负数（符号位为1），则需要再次取补码即可得到真实值。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
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