https://prbs23.com/blog/tags/constrained-random-verification/ Recent content in Constrained Random Verification on PRBS23 Hugo en-us Thu, 25 May 2023 23:32:04 -0600 https://prbs23.com/blog/posts/combining-dist-constraints-in-system-verilog/ Thu, 25 May 2023 23:32:04 -0600 https://prbs23.com/blog/posts/combining-dist-constraints-in-system-verilog/ <h2 id="basic-distribution-constraints">Basic Distribution Constraints</h2> <p>In SystemVerilog, almost all constraints are some form of boolean expression. The constraint solver&rsquo;s job is to satisfy all these boolean expression when choosing random values. The two exceptions to this are <code>solve before</code> constraints, which control the order of value resolution, and <code>dist</code> constraints, witch control the distribution of values chosen. This latter type of constraint is what we are looking at in this post.</p> <p>At a high level the distribution constraint provides a syntax for defining the <a href="https://en.wikipedia.org/wiki/Probability_mass_function">probability mass function</a> for a random variable over a given range of discrete values. Below are two examples of <code>dist</code> constraints and the resulting distribution of values over 100k randomizations. The first specifies linearly increasing probability over four values, while the second shows exponentially increasing probability for the same values.</p>