Chisel CRV

Chisel CRV is a project that aims to mimic the functionality of SystemVerilog constraint programming and integrates them into chisel-tester2. Chisel CRV combines a Constraint Satisfactory Problem Solver, with some helper classes to create and use random objects inside your tests.

Comparison

System Verilog

class frame_t;
rand pkt_type ptype;
rand integer len;
randc bit [1:0] no_repeat;
rand bit  [7:0] payload [];
// Constraint the members
constraint legal {
  len >= 2;
  len <= 5;
  payload.size() == len;
}

Chisel CRV

class Frame extends sv.Random(33) {
  var pkType: RandInt = rand(pkType, pktType.domainValues())
  var len: RandInt = rand(len, 0 to 10 toList)
  var noRepeat: RandCInt = randc(noRepeat, 0 to 1 toList)
  var payload: RandInt = rand(payload, 0 to 7 toList)

  val myBlock: ConstraintBlock = constraintBlock (
    unary ( len => len >= 2),
    unary (len =>  len <= 5),
    binary ((len, payload) => len == payload)
  )
}

CSP Solver

Based on the ideas of the book Artificial Intelligence A Modern Approach, Is a combination of BacktrackSearching and Constraint Propagation. The pseudocode for the algorithm used can be found here. The CSP solver and the relative components are stored in the csp package.

Random Class

The random class is the base class that each Random object should extend in order to implement constrained programming.

Declaration

Create a class that inherits from the base class sv.Random

class Frame extends sv.Random

The class can also be seeded like

class Frame extends sv.Random(33)

You can add random field by declaring a var field as type RandInt and assigin it a domain with the rand macro. A domain is a list of values. For now only integer values are supported.

  var len: RandInt = rand(len, 0 to 10 toList)

You can also add a continuous Random Integer by adding a var field to your class and declaring it RandIntC

  var noRepeat: RandCInt = randc(noRepeat, 0 to 1 toList)

Finally you can constraint the newly added fields by creating a constraint block

  val myBlock: ConstraintBlock = constraintBlock (
    unary ( len => len >= 2),
    unary (len =>  len <= 5),
  )

Usage

To randomize the newly create random object, just call the randomize method

val frame = new Frame
while (frame.randomize) {
  println(frame.debug())
  assert(frame.len >= 2)
  assert(frame.len <= 5)
}

output

pkType = 1; len = 5; noRepeat = 0; payload = 5;
pkType = 0; len = 5; noRepeat = 1; payload = 5;
pkType = 11; len = 5; noRepeat = 0; payload = 5;
pkType = 1; len = 3; noRepeat = 1; payload = 3;
[...]

Online Resources

• Constraint Solvingwithout Surprises in Object-ConstraintProgramming Languages
• Exact Cover Series of 3 articles about constraint programming
• CLP(FD) Prolog library about constraints

Todo list

• Refactoring the csp package
• Add random arrays
• Add soft constraint