【芯片验证】异步电路碎碎念（十一）在静态对象内构建可控随机·方案二

在上一篇文章中，我们讨论并得出了一种构建可控随机的方案：

【芯片验证】异步电路碎碎念（十）在静态对象内构建可控随机·方案一

这篇文章呢我们讨论另外一种方案，为啥有方案了还要尝试其他的方案呢？我自己对$random这个函数相当的不信任，这个函数不受seed控制到低随机时候从哪找的种子我也不太清楚，万一跟地域、时间、服务器、工具等特性有关系，环境一迁移导致随机无法复现怎么办呢。所以我希望有一种原理明明白白的可控随机方案，当然这里并不是说$random+$urandom不能用哈，实际上我知道的很多地方就是直接用这个的。

原理明明白白的可控随机方案怎么来呢？既然不信任$random那必然是从$urandom入手看了，还记得$random的问题是啥来着吧？不能感知静态模块的不同例化路径差异。那么让他感知一下例化路径差异不就好了嘛，怎么感知这个事，相信大家对这个字符都很熟悉：%m，对就是在打印里用的那个字符。这个字符的作用是打印当前模块（或独立命名域）的例化路径，打印里的前半部分就是靠这个打印出来的：

$display("%m new_rand_value = 'h%0h", new_rand_value);
----->
testbench.u_rand_test1 new_rand_value = 'hd7

string   path_str;
initial  begin
  path_str = $psprintf(path_str, "%m");
  $display("inst path is %s", path_str);
end

inst path is testbench.u_rand_test0
inst path is testbench.u_rand_test1

string   path_str;
int      path_int;
initial  begin
  path_str = $psprintf(path_str, "%m");
  path_int = path_str;
  $display("inst path is %s, path_int = 'h%0h", path_str, path_int);
end
----->
inst path is testbench.u_rand_test0, path_int = 'h65737430
inst path is testbench.u_rand_test1, path_int = 'h65737431

string   path_str;
int      path_int;
initial  begin
  path_str = $psprintf(path_str, "%m");
  path_int = $urandom();
  for(int i=path_str.len; i>=0; i=i-1)begin
    path_int = path_int ^ path_str.getc(i);
    path_int = $urandom(path_int);
  end
  path_int = $abs(path_int);
  $display("inst path is %s, path_int = 'h%0h", path_str, path_int);
end

经过这些操作后，咱们来看下进行随机后的结果：

inst path is testbench.u_rand_test0, path_int = 'h66b884a6
inst path is testbench.u_rand_test1, path_int = 'h49aee46

inst path is testbench.u_rand_test0, path_int = 'h21669974
inst path is testbench.u_rand_test1, path_int = 'h19e00dfa
tc seed = 62302096

inst path is testbench.u_rand_test0, path_int = 'h19bc271c
inst path is testbench.u_rand_test1, path_int = 'h7eef9304
tc seed = 81054216

inst path is testbench.u_rand_test0, path_int = 'h268220ce
inst path is testbench.u_rand_test1, path_int = 'h44c8d731
tc seed = 53991314

inst path is testbench.u_rand_test0, path_int = 'h21669974
inst path is testbench.u_rand_test1, path_int = 'h19e00dfa
tc seed = 62302096

string   path_str;
int      path_int;
initial  begin
  path_str = $psprintf(path_str, "%m");
  path_int = path_str;
  path_int = $urandom($urandom($urandom($urandom(path_int))));
  $display("inst path is %s, path_int = 'h%0h", path_str, path_int);
end
----->
inst path is testbench.u_rand_test0, path_int = 'h6a6ed13
inst path is testbench.u_rand_test1, path_int = 'h86b6f7a1
tc seed = 0

inst path is testbench.u_rand_test0, path_int = 'h6a6ed13
inst path is testbench.u_rand_test1, path_int = 'h86b6f7a1
tc seed = 38445033

答案也很简单，封装成一个函数不就好了嘛：

string  path_str;
initial path_str = $psprintf(path_str, "%m");
function integer urandom;
  integer seed, i;
  begin
    seed = $urandom();
    for(i=path_str.len; i>=0; i=i-1)begin
      seed = seed ^ path_str.getc(i);
      seed = $urandom(seed);
    end
    urandom = $abs(seed);
  end
endfunction

initial  begin
  int rand_test;
  rand_test = urandom();
  $display("%m, rand_test = %0d", rand_test);
end

testbench.u_rand_test0.unnamed$$_0, rand_test = 1641770003
testbench.u_rand_test1.unnamed$$_0, rand_test = 621788312
tc name = sanity
tc seed = 59908161

testbench.u_rand_test0.unnamed$$_0, rand_test = 1271321994
testbench.u_rand_test1.unnamed$$_0, rand_test = 588367474
tc name = sanity
tc seed = 73017818

testbench.u_rand_test0.unnamed$$_0, rand_test = 97687901
testbench.u_rand_test1.unnamed$$_0, rand_test = 704389240
tc name = sanity
tc seed = 75798405

在宏定义文件中做宏：

`define module_urandom_define \
string   path_str; \
initial  path_str = $psprintf(path_str, "%m"); \
\
function integer urandom; \
  integer seed, i; \
  begin \
    seed = $urandom(); \
    for(i=path_str.len; i>=0; i=i-1)begin \
      seed = seed ^ path_str.getc(i); \
      seed = $urandom(seed); \
    end \
    urandom = $abs(seed); \
  end \
endfunction

`module_urandom_define

initial  begin
  int rand_test;
  rand_test = urandom();
  $display("%m test1, rand_test = %0d", rand_test);
  rand_test = urandom();
  $display("%m test2, rand_test = %0d", rand_test);
end

testbench.u_rand_test0.unnamed$$_0 test1, rand_test = 1970541737
testbench.u_rand_test0.unnamed$$_0 test2, rand_test = 128592474
testbench.u_rand_test1.unnamed$$_0 test1, rand_test = 849448805
testbench.u_rand_test1.unnamed$$_0 test2, rand_test = 1978420876
tc name = sanity
tc seed = 17411917

testbench.u_rand_test0.unnamed$$_0 test1, rand_test = 887806234
testbench.u_rand_test0.unnamed$$_0 test2, rand_test = 216253277
testbench.u_rand_test1.unnamed$$_0 test1, rand_test = 1150158848
testbench.u_rand_test1.unnamed$$_0 test2, rand_test = 1381425996
tc name = sanity
tc seed = 50449658

testbench.u_rand_test0.unnamed$$_0 test1, rand_test = 439486355
testbench.u_rand_test0.unnamed$$_0 test2, rand_test = 1519906787
testbench.u_rand_test1.unnamed$$_0 test1, rand_test = 219267827
testbench.u_rand_test1.unnamed$$_0 test2, rand_test = 133804852
tc name = sanity
tc seed = 64935128

function integer urandom_range(); \
    input integer min, max; \
    integer seed, i; \
    begin \
      seed = $urandom(); \
      for(i=path_str.len; i>=0; i=i-1)begin \
        seed = seed ^ path_str.getc(i); \
        seed = $urandom(seed); \
      end \
      urandom_range = min + $abs(seed % (max - min)); \
    end \
  endfunction

initial  begin
  int rand_test;
  rand_test = urandom_range(0,100);
  $display("%m test1, rand_test = %0d", rand_test);
  rand_test = urandom_range(100,1000);
  $display("%m test2, rand_test = %0d", rand_test);
end

testbench.u_rand_test0.unnamed$$_0 test1, rand_test = 75
testbench.u_rand_test0.unnamed$$_0 test2, rand_test = 892
testbench.u_rand_test1.unnamed$$_0 test1, rand_test = 71
testbench.u_rand_test1.unnamed$$_0 test2, rand_test = 461
tc name = sanity
tc seed = 16870716

testbench.u_rand_test0.unnamed$$_0 test1, rand_test = 63
testbench.u_rand_test0.unnamed$$_0 test2, rand_test = 944
testbench.u_rand_test1.unnamed$$_0 test1, rand_test = 54
testbench.u_rand_test1.unnamed$$_0 test2, rand_test = 172
tc name = sanity
tc seed = 47491380

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