fpga: sim: Add PkgComplex, PkgMath, and PkgRandom

PkgComplex adds functions for doing complex arithmetic in SystemVerilog
simulation.

PkgMath provides mathematical operations and constants that aren't
built into SystemVerilog, such as a constant for pi and the function
round().

PkgRandom adds randomization functions beyond what standard Verilog
supports but that don't require any special licenses or simulators.

1 files changed, 146 insertions, 0 deletions

diff --git a/fpga/usrp3/sim/packages/PkgRandom.sv b/fpga/usrp3/sim/packages/PkgRandom.sv
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+++ b/fpga/usrp3/sim/packages/PkgRandom.sv
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+//
+// Copyright 2021 Ettus Research, A National Instruments Brand
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+//
+// Package: PkgRandom
+//
+// Description:
+//
+//   SystemVerilog has great randomization support, but some features require a
+//   more expensive license or aren't supported by all tools. This package
+//   tries to fill that gap by providing some useful randomization functions
+//   beyond what's supported by standard Verilog.
+//
+
+package PkgRandom;
+
+  import PkgMath::*;
+
+  //---------------------------------------------------------------------------
+  // Functions
+  //---------------------------------------------------------------------------
+
+  // Return a real value in the range [0,max), where max is 1.0 by default.
+  function automatic real frand(real max = 1.0);
+    bit [63:0] real_bits;
+    real num;
+
+    // Build a double-precision floating point value per IEEE-754 standard,
+    // which SystemVerilog follows.
+
+    // Positive, with exponent 0
+    real_bits[63:52] = 12'h3FF;
+
+    // Mantissa in the range [1.0, 2.0). The leading 1 in the mantissa is
+    // implied by the floating point format.
+    real_bits[31: 0] = $urandom();
+    real_bits[51:32] = $urandom();
+
+    // Compensate for the implied leading 1 in the mantissa by subtracting 1.
+    num = $bitstoreal(real_bits) - 1.0;
+
+    // Scale the result to return a value in the desired range.
+    return num * max;
+  endfunction : frand
+
+
+  // Return a real value in the range [a,b), [b,a), or [0,a) depending on
+  // whether a or b is larger and whether b is provided. This matches the
+  // behavior of $urandom_range().
+  //
+  //   frand_range(1.0, 2.0) -> Random value in the range [1,2)
+  //   frand_range(2.0, 1.0) -> Random value in the range [1,2)
+  //   frand_range(1.0)      -> Random value in the range [0,1)
+  //
+  function automatic real frand_range(real a = 1.0, real b = 0.0);
+    if (a > b) return b + frand(a - b);
+    if (b > a) return a + frand(b - a);
+    return a;
+  endfunction : frand_range
+
+
+  // Return a real value with a normal distribution, having the mean value mu
+  // and standard deviation sigma.
+  function automatic real frandn(real sigma = 1.0, real mu = 0.0);
+    // Use the Box-Muller transform to convert uniform random variables to a
+    // Gaussian one.
+    return sigma*$sqrt(-2.0*$ln(frand())) * $cos(TAU*frand()) + mu;
+  endfunction : frandn
+
+
+  //---------------------------------------------------------------------------
+  // Template Functions
+  //---------------------------------------------------------------------------
+
+  class Rand #(WIDTH = 64);
+
+    // These are static class functions. They can be called directly, as in:
+    //
+    //   Rand#(N)::rand_bit()
+    //
+    // Or, you can declare an object reference, as in:
+    //
+    //   Rand #(N) rand;
+    //   rand.rand_bit();
+
+    typedef bit        [WIDTH-1:0] unsigned_t;
+    typedef bit signed [WIDTH-1:0] signed_t;
+
+
+    // Returns a WIDTH-bit random bit packed array.
+    static function unsigned_t rand_bit();
+      unsigned_t result;
+      int num_rand32 = (WIDTH + 31) / 32;
+      for (int i = 0; i < num_rand32; i++) begin
+        result = {result, $urandom()};
+      end
+      return result;
+    endfunction : rand_bit
+
+
+    // Returns a WIDTH-bit random number in the UNSIGNED range [a,b], [b,a], or
+    // [0,a] depending on whether a or b is greater and if b is provided. This
+    // is equivalent to $urandom_range() but works with any length.
+    static function bit [WIDTH-1:0] rand_bit_range(
+      unsigned_t a = {WIDTH{1'b1}},
+      unsigned_t b = 0
+    );
+      unsigned_t num;
+      int num_bits;
+      if (a > b) begin
+        // Swap a and b
+        unsigned_t temp;
+        temp = a;
+        a = b;
+        b = temp;
+      end
+      num_bits = $clog2(b - a + unsigned_t'{1});
+      do begin
+        num = a + (rand_bit() & ((unsigned_t'{1} << num_bits) - 1));
+      end while (num > b);
+      return num;
+    endfunction : rand_bit_range
+
+
+    // Returns a random number in the given SIGNED range. Behavior is the same
+    // as rand_bit_range(), bunsigned_t treats the range values as SIGNED numbers.
+    static function signed_t rand_sbit_range(
+      signed_t a = {1'b0, {WIDTH{1'b1}}},
+      signed_t b = 0
+    );
+      if (a > b) return b + $signed(rand_bit_range(0, a-b));
+      if (b > a) return a + $signed(rand_bit_range(0, b-a));
+      return a;
+    endfunction : rand_sbit_range
+
+
+    // Rand#(WIDTH)::rand_logic() returns a WIDTH-bit random logic packed
+    // array. Each bit will be 0 or 1 with equal probability (not X or Z).
+    static function logic [WIDTH-1:0] rand_logic();
+      return rand_bit();
+    endfunction : rand_logic
+
+  endclass : Rand
+
+endpackage : PkgRandom