SystemVerilog -- 10.2 SystemVerilog Coverpoint Bins

SystemVerilog Coverpoint Bins

Usage

coverpoint 用于在 covergroup 中指定要进行覆盖率收集统计收集的目标的变量。它记录单个变量或表达式的观测值。

• coverpoint后面跟变量名或表达式，用于指定要收集覆盖率的目标。
• 可以使用bins关键字手动定义覆盖仓（bins），记录变量在不同值域范围内被采样的次数。
• 也可以使用option.auto_bin_max自动创建指定数量的覆盖仓，将变量值域平均分配。

coverpoint mode {
  // Manually create a separate bin for each value
  bins zero = {0};
  bins one  = {1};

  // Allow SystemVerilog to automatically create separate bins for each value
  // Values from 0 to maximum possible value is split into separate bins
  bins range[] = {[0:$]};

  // Create automatic bins for both the given ranges
  bins c[] = {[2:3], [5:7]};

  // Use fixed number of automatic bins. Entire ranges is broken up into 4 bins
  bins range[4] = {[0:$]};

  // If the number of bins cannot be equally divided for the given range, then 
  // the last bin will include remaining items; Here there are 13 values to be 
  // distributed into 4 bins which yields:
  bins range[4] = {[1:10], 1, 3, 6};
  
  // A single bin to store all other values that don't belong to any other bin
  bins others = default;
}

Examples

module tb;
  bit [2:0] mode;

  // This covergroup does not get sample automatically because the sample event is missing in declaration
  covergroup cg;
    cooverpoint mode {
      bins one  = {1};
      bins five = {5};
    }
  endgroup

  // Stimulus : Simply randomize mode to have different values and manually sample each time
  initial begin
    cg cg_inst = new ();
    for (int i = 0; i < 5; i++) begin
      #10 mode = $random;
      $display ("[%0t] mode = 0x%0h", $time, mode);
      cg_inst.sample ();
    end
    $display ("Coverage = %0.2f %%", cg_inst.get_inst_coverage());
  end
endmodule

模拟日志

ncsim> run
[10] mode = 0x4
[20] mode = 0x1
[30] mode = 0x1
[40] mode = 0x3
[50] mode = 0x5
Coverage = 100.00 %
ncsim: *W,RNQUIE: Simulation is complete.

Automatic Bins

covergroup cg;
  coverpoint mode {
    // Declares a separate bin for each values -> Here there will 8 bins
    bins range[] = {[0:$]};
  }
endgroup

模拟日志

ncsim> run
[10] mode = 0x4
[20] mode = 0x1
[30] mode = 0x1
[40] mode = 0x3
[50] mode = 0x5
Coverage = 50.00 %
ncsim: *W,RNQUIE: Simulation is complete.

Fixed Number of automatic bins

covergroup cg;
  coverpoint mode {
    // Declares 4 bins for the total range of 8 values
    // So bib0->[0:1] bib1->[2:3] bib2->[4:5] bib3->[6:7]
    bins range[4] = {[0:$]};
  }
endgroup

mode从未获得 6 或 7 的值，因此 bin3 不会被命中。但是所有其它 bins 都被 hit，因此覆盖率为 75%。

模拟日志

ncsim> run
[10] mode = 0x4
[20] mode = 0x1
[30] mode = 0x1
[40] mode = 0x3
[50] mode = 0x5
Coverage = 75.00 %
ncsim: *W,RNQUIE: Simulation is complete.

Split fixed number of bins between a given range

covergroup cg;
  coverpoint mode {
    // defines 3 bins
    // Two bins for values from 1:4, and one bin for value 7 
    // bin1->[1,2] bin2->[3:4 bin3->7
    bins range[3] = {[1:4], 7};
  }
endgroup

只有 2/3 的 bin s被 hit，因此覆盖率为 66.7%。具体来说， bin1 和 bin2 被 hit 是因为对 mode 的采样分别为 1 和 [3,4]。

模拟日志

ncsim> run
[10] mode = 0x4
[20] mode = 0x1
[30] mode = 0x1
[40] mode = 0x3
[50] mode = 0x5
Coverage = 66.67 %
ncsim: *W,RNQUIE: Simulation is complete.