Introduction

What is PyVSC?

PyVSC is a Python library that implements random verification-stimulus generation and coverage collection. PyVSC provides this capability in two forms: an object-oriented Model API, and a Python-embedded domain-specific language built on top of the Model API. This allows coverage and randomization features to be programmatically built, defined with user-friendly constructs, or defined using a mix of the two.

Blog Posts

One great way to get an overview of PyVSC is to read a series of blog posts about PyVSC. Links are below:

• The fundamentals of modeling stimulus and functional coverage in Python.

• Modeling verification data types in Python.

• Modeling and capturing functional coverage in Python.

• Making use of captured coverage data.

• Python Verification Stimulus and Coverage: Constraints.

Papers

• PyVSC: SystemVerilog-Style Constraints and Coverage in Python.

Currently, the Python-embedded domain-specific language supports similar features to those supported by SystemVerilog. Not all SystemVerilog features are supported, but in some cases features not supported by SystemVerilog are also supported. Please see the following section PyVSC Features for a comparison of the user-level coverage and randomization features supported by PyVSC compared to SystemVerilog.

Here is a quick example showing capturing random data fields, constraints, coverage, and inline randomization.

@vsc.randobj
class my_item_c(object):
    def __init__(self):
        self.a = vsc.rand_bit_t(8)
        self.b = vsc.rand_bit_t(8)

     @vsc.constraint
     def ab_c(self):
         self.a != 0
         self.a <= self.b
         self.b in vsc.rangelist(1,2,4,8)

  @vsc.covergroup
  class my_cg(object):

      def __init__(self):
          # Define the parameters accepted by the sample function
          self.with_sample(dict(
              it=my_item_c()
           ))

           self.a_cp = vsc.coverpoint( self.it.a, bins=dict(
              # Create 4 bins across the space 0..255
              a_bins = bin_array([4], [0,255])
           )
           self.b_cp = vsc.coverpoint(self.it.b, bins=dict(
              # Create one bin for each value (1,2,4,8)
              b_bins = bin_array([], 1, 2, 4, 8)
           )
           self.ab_cross = vsc.cross([self.a_cp, self.b_cp])

  # Create an instance of the covergroup
  my_cg_i = my_cg()

  # Create an instance of the item class
  my_item_i = my_item_c()

  # Randomize and sample coverage
  for i in range(16):
      my_item_i.randomize()
      my_cg_i.sample(my_item_i)

  # Now, randomize keeping b in the range [1,2]
  for i in range(16):
      with my_item_i.randomize_with() as it:
          it.b in vsc.rangelist(1,2)
      my_cg_i.sample(my_item_i)

  print("Coverage: %f \%" % (my_cg_i.get_coverage()))

Contributors