Revamp VendingMachine.scala as cookbook example

* Move to cookbook
* Change FSM implementation to use switch & is
* Add non-FSM implementation
* Add execution-driven test

7 files changed, 337 insertions, 70 deletions

diff --git a/src/test/resources/VerilogVendingMachine.v b/src/test/resources/VerilogVendingMachine.v
new file mode 100644
index 00000000..c01259bd
--- /dev/null
+++ b/src/test/resources/VerilogVendingMachine.v
@@ -0,0 +1,44 @@
+// See LICENSE for license details.
+
+// A simple Verilog FSM vending machine implementation
+module VerilogVendingMachine(
+  input clock,
+  input reset,
+  input nickel,
+  input dime,
+  output dispense
+);
+  parameter sIdle = 3'd0, s5 = 3'd1, s10 = 3'd2, s15 = 3'd3, sOk = 3'd4;
+  reg [2:0] state;
+  wire [2:0] next_state;
+
+  assign dispense = (state == sOk) ? 1'd1 : 1'd0;
+
+  always @(*) begin
+    case (state)
+      sIdle: if (nickel) next_state <= s5;
+             else if (dime) next_state <= s10;
+             else next_state <= state;
+      s5: if (nickel) next_state <= s10;
+             else if (dime) next_state <= s15;
+             else next_state <= state;
+      s10: if (nickel) next_state <= s15;
+             else if (dime) next_state <= sOk;
+             else next_state <= state;
+      s15: if (nickel) next_state <= sOk;
+             else if (dime) next_state <= sOk;
+             else next_state <= state;
+      sOk: next_state <= sIdle;
+    endcase
+  end
+
+  // Go to next state
+  always @(posedge clock) begin
+    if (reset) begin
+      state <= sIdle;
+    end else begin
+      state <= next_state;
+    end
+  end
+endmodule
+
diff --git a/src/test/scala/chiselTests/VendingMachine.scala b/src/test/scala/chiselTests/VendingMachine.scala
deleted file mode 100644
index 712b5b7a..00000000
--- a/src/test/scala/chiselTests/VendingMachine.scala
+++ /dev/null
@@ -1,69 +0,0 @@
-// See LICENSE for license details.
-
-package chiselTests
-
-import chisel3._
-import chisel3.util._
-
-class VendingMachine extends Module {
-  val io = IO(new Bundle {
-    val nickel = Input(Bool())
-    val dime   = Input(Bool())
-    val valid  = Output(Bool())
-  })
-  val c = 5.U(3.W)
-  val sIdle :: s5 :: s10 :: s15 :: sOk :: Nil = Enum(5)
-  val state = Reg(init = sIdle)
-  when (state === sIdle) {
-    when (io.nickel) { state := s5 }
-    when (io.dime)   { state := s10 }
-  }
-  when (state === s5) {
-    when (io.nickel) { state := s10 }
-    when (io.dime)   { state := s15 }
-  }
-  when (state === s10) {
-    when (io.nickel) { state := s15 }
-    when (io.dime)   { state := sOk }
-  }
-  when (state === s15) {
-    when (io.nickel) { state := sOk }
-    when (io.dime)   { state := sOk }
-  }
-  when (state === sOk) {
-    state := sIdle
-  }
-  io.valid := (state === sOk)
-}
-
-/*
-class VendingMachineTester(c: VendingMachine) extends Tester(c) {
-  var money = 0
-  var isValid = false
-  for (t <- 0 until 20) {
-    val coin     = rnd.nextInt(3)*5
-    val isNickel = coin == 5
-    val isDime   = coin == 10
-
-    // Advance circuit
-    poke(c.io.nickel, int(isNickel))
-    poke(c.io.dime,   int(isDime))
-    step(1)
-
-    // Advance model
-    money = if (isValid) 0 else (money + coin)
-    isValid = money >= 20
-
-    // Compare
-    expect(c.io.valid, int(isValid))
-  }
-}
-*/
-
-class VendingMachineSpec extends ChiselPropSpec {
-  property("VendingMachine should elaborate") {
-    elaborate { new VendingMachine }
-  }
-
-  ignore("VendingMachineTester should return the correct result") { }
-}
diff --git a/src/test/scala/cookbook/FSM.scala b/src/test/scala/cookbook/FSM.scala
index 58f6a9a2..45359c9e 100644
--- a/src/test/scala/cookbook/FSM.scala
+++ b/src/test/scala/cookbook/FSM.scala
@@ -6,7 +6,7 @@ import chisel3._
 import chisel3.util._
 
 /* ### How do I create a finite state machine?
-
+ *
  * Use Chisel Enum to construct the states and switch & is to construct the FSM
  * control logic
  */
diff --git a/src/test/scala/examples/ImplicitStateVendingMachine.scala b/src/test/scala/examples/ImplicitStateVendingMachine.scala
new file mode 100644
index 00000000..ae1e28dd
--- /dev/null
+++ b/src/test/scala/examples/ImplicitStateVendingMachine.scala
@@ -0,0 +1,31 @@
+// See LICENSE for license details.
+
+package examples
+
+import chiselTests.ChiselFlatSpec
+import chisel3._
+
+// Vending machine implemented with an implicit state machine
+class ImplicitStateVendingMachine extends SimpleVendingMachine {
+  // We let the value of nickel be 1 and dime be 2 for efficiency reasons
+  val value = Reg(init = 0.asUInt(3.W))
+  val incValue = Wire(init = 0.asUInt(3.W))
+  val doDispense = value >= 4.U // 4 * nickel as 1 == $0.20
+
+  when (doDispense) {
+    value := 0.U // No change given
+  } .otherwise {
+    value := value + incValue
+  }
+
+  when (io.nickel) { incValue := 1.U }
+  when (io.dime) { incValue := 2.U }
+
+  io.dispense := doDispense
+}
+
+class ImplicitStateVendingMachineSpec extends ChiselFlatSpec {
+  "An vending machine implemented with implicit state" should "work" in {
+    assertTesterPasses { new SimpleVendingMachineTester(new ImplicitStateVendingMachine) }
+  }
+}
diff --git a/src/test/scala/examples/SimpleVendingMachine.scala b/src/test/scala/examples/SimpleVendingMachine.scala
new file mode 100644
index 00000000..d935b611
--- /dev/null
+++ b/src/test/scala/examples/SimpleVendingMachine.scala
@@ -0,0 +1,95 @@
+// See LICENSE for license details.
+
+package examples
+
+import chiselTests.ChiselFlatSpec
+import chisel3.testers.BasicTester
+import chisel3._
+import chisel3.util._
+
+class SimpleVendingMachineIO extends Bundle {
+  val nickel = Input(Bool())
+  val dime   = Input(Bool())
+  val dispense  = Output(Bool())
+}
+
+// Superclass for vending machines with very simple IO
+abstract class SimpleVendingMachine extends Module {
+  val io = IO(new SimpleVendingMachineIO)
+  assert(!(io.nickel && io.dime), "Only one of nickel or dime can be input at a time!")
+}
+
+// Vending machine implemented with a Finite State Machine
+class FSMVendingMachine extends SimpleVendingMachine {
+  val sIdle :: s5 :: s10 :: s15 :: sOk :: Nil = Enum(5)
+  val state = Reg(init = sIdle)
+
+  switch (state) {
+    is (sIdle) {
+      when (io.nickel) { state := s5 }
+      when (io.dime)   { state := s10 }
+    }
+    is (s5) {
+      when (io.nickel) { state := s10 }
+      when (io.dime)   { state := s15 }
+    }
+    is (s10) {
+      when (io.nickel) { state := s15 }
+      when (io.dime)   { state := sOk }
+    }
+    is (s15) {
+      when (io.nickel) { state := sOk }
+      when (io.dime)   { state := sOk }
+    }
+    is (sOk) {
+      state := sIdle
+    }
+  }
+  io.dispense := (state === sOk)
+}
+
+class VerilogVendingMachine extends BlackBox {
+  // Because this is a blackbox, we must explicity add clock and reset
+  val io = IO(new SimpleVendingMachineIO {
+    val clock = Input(Clock())
+    val reset = Input(Bool())
+  })
+}
+
+// Shim because Blackbox io is slightly different than normal Chisel Modules
+class VerilogVendingMachineWrapper extends SimpleVendingMachine {
+  val impl = Module(new VerilogVendingMachine)
+  impl.io.clock := clock
+  impl.io.reset := reset
+  impl.io.nickel := io.nickel
+  impl.io.dime := io.dime
+  io.dispense := impl.io.dispense
+}
+
+// Accept a reference to a SimpleVendingMachine so it can be constructed inside
+// the tester (in a call to Module.apply as required by Chisel
+class SimpleVendingMachineTester(mod: => SimpleVendingMachine) extends BasicTester {
+
+  val dut = Module(mod)
+
+  val (cycle, done) = Counter(true.B, 10)
+  when (done) { stop(); stop() } // Stop twice because of Verilator
+
+  val nickelInputs = Vec(true.B, true.B, true.B, true.B, true.B, false.B, false.B, false.B, true.B, false.B)
+  val dimeInputs   = Vec(false.B, false.B, false.B, false.B, false.B, true.B, true.B, false.B, false.B, true.B)
+  val expected     = Vec(false.B, false.B, false.B, false.B, true.B , false.B, false.B, true.B, false.B, false.B)
+
+  dut.io.nickel := nickelInputs(cycle)
+  dut.io.dime := dimeInputs(cycle)
+  assert(dut.io.dispense === expected(cycle))
+}
+
+class SimpleVendingMachineSpec extends ChiselFlatSpec {
+  "An FSM implementation of a vending machine" should "work" in {
+    assertTesterPasses { new SimpleVendingMachineTester(new FSMVendingMachine) }
+  }
+  "An Verilog implementation of a vending machine" should "work" in {
+    assertTesterPasses(new SimpleVendingMachineTester(new VerilogVendingMachineWrapper),
+                       List("/VerilogVendingMachine.v"))
+  }
+}
diff --git a/src/test/scala/examples/VendingMachineGenerator.scala b/src/test/scala/examples/VendingMachineGenerator.scala
new file mode 100644
index 00000000..fc44a47e
--- /dev/null
+++ b/src/test/scala/examples/VendingMachineGenerator.scala
@@ -0,0 +1,127 @@
+// See LICENSE for license details.
+
+package examples
+
+import chiselTests.ChiselFlatSpec
+import chisel3.testers.BasicTester
+import chisel3._
+import chisel3.util._
+
+import VendingMachineUtils._
+
+class VendingMachineIO(legalCoins: Seq[Coin]) extends Bundle {
+  require(legalCoins.size >= 1, "The vending machine must accept at least 1 coin!")
+  // Order of coins by value
+  val coins: Seq[Coin] = legalCoins sortBy (_.value)
+  // Map of coin names to their relative position in value (ie. index in inputs)
+  val indexMap: Map[String, Int] = coins.map(_.name).zipWithIndex.toMap
+
+  require(coins map (_.value % coins.head.value == 0) reduce (_ && _),
+          "All coins must be a multiple of the lowest value coin!")
+
+  val inputs = Input(Vec(legalCoins.size, Bool()))
+  val dispense = Output(Bool())
+
+  def apply(coin: String): Unit = {
+    val idx = indexMap(coin)
+    inputs(idx) := true.B
+  }
+}
+
+// Superclass for parameterized vending machines
+abstract class ParameterizedVendingMachine(legalCoins: Seq[Coin], val sodaCost: Int) extends Module {
+  val io = IO(new VendingMachineIO(legalCoins))
+  // Enforce one hot
+  if (io.inputs.size > 1) {
+    for (input <- io.inputs) {
+      when (input) {
+        assert(io.inputs.filterNot(_ == input).map(!_).reduce(_ && _),
+               "Only 1 coin can be input in a given cycle!")
+      }
+    }
+  }
+}
+
+class VendingMachineGenerator(
+    legalCoins: Seq[Coin],
+    sodaCost: Int) extends ParameterizedVendingMachine(legalCoins, sodaCost) {
+  require(sodaCost > 0, "Sodas must actually cost something!")
+
+  // All coin values are normalized to a multiple of the minimum coin value
+  val minCoin = io.coins.head.value
+  val maxCoin = io.coins.last.value
+  val maxValue = (sodaCost + maxCoin - minCoin) / minCoin // normalize to minimum value
+
+  val width = log2Up(maxValue + 1).W
+  val value = Reg(init = 0.asUInt(width))
+  val incValue = Wire(init = 0.asUInt(width))
+  val doDispense = value >= (sodaCost / minCoin).U
+
+  when (doDispense) {
+    value := 0.U // No change given
+  } .otherwise {
+    value := value + incValue
+  }
+
+  for ((coin, index) <- io.coins.zipWithIndex) {
+    when (io.inputs(index)) { incValue := (coin.value / minCoin).U }
+  }
+  io.dispense := doDispense
+}
+
+class ParameterizedVendingMachineTester(
+    mod: => ParameterizedVendingMachine,
+    testLength: Int) extends BasicTester {
+  require(testLength > 0, "Test length must be positive!")
+
+  // Construct the module
+  val dut = Module(mod)
+  val coins = dut.io.coins
+
+  // Inputs and expected results
+  // Do random testing
+  private val _rand = scala.util.Random
+  val inputs: Seq[Option[Coin]] = Seq.fill(testLength)(coins.lift(_rand.nextInt(coins.size + 1)))
+  val expected: Seq[Boolean] = getExpectedResults(inputs, dut.sodaCost)
+
+  val inputVec: Vec[UInt] = Vec(inputs map {
+    case Some(coin) => (1 << dut.io.indexMap(coin.name)).asUInt(coins.size.W)
+    case None => 0.asUInt(coins.size.W)
+  })
+  val expectedVec: Vec[Bool] = Vec(expected map (_.B))
+
+  val (idx, done) = Counter(true.B, testLength + 1)
+  when (done) { stop(); stop() } // Two stops for Verilator
+
+  dut.io.inputs := inputVec(idx).toBools
+  assert(dut.io.dispense === expectedVec(idx))
+}
+
+class VendingMachineGeneratorSpec extends ChiselFlatSpec {
+  behavior of "The vending machine generator"
+
+  it should "generate a vending machine that accepts only nickels and dimes and costs $0.20" in {
+    val coins = Seq(Nickel, Dime)
+    assertTesterPasses {
+      new ParameterizedVendingMachineTester(new VendingMachineGenerator(coins, 20), 100)
+    }
+  }
+  it should "generate a vending machine that only accepts one kind of coin" in {
+    val coins = Seq(Nickel)
+    assertTesterPasses {
+      new ParameterizedVendingMachineTester(new VendingMachineGenerator(coins, 30), 100)
+    }
+  }
+  it should "generate a more realistic vending machine that costs $1.50" in {
+    val coins = Seq(Penny, Nickel, Dime, Quarter)
+    assertTesterPasses {
+      new ParameterizedVendingMachineTester(new VendingMachineGenerator(coins, 150), 100)
+    }
+  }
+  it should "generate a Harry Potter themed vending machine" in {
+    val coins = Seq(Knut, Sickle) // Galleons are worth too much
+    assertTesterPasses {
+      new ParameterizedVendingMachineTester(new VendingMachineGenerator(coins, Galleon.value), 100)
+    }
+  }
+}
diff --git a/src/test/scala/examples/VendingMachineUtils.scala b/src/test/scala/examples/VendingMachineUtils.scala
new file mode 100644
index 00000000..e229dab5
--- /dev/null
+++ b/src/test/scala/examples/VendingMachineUtils.scala
@@ -0,0 +1,39 @@
+// See LICENSE for license details.
+
+package examples
+
+import scala.collection.mutable
+
+/* Useful utilities for testing vending machines */
+object VendingMachineUtils {
+  abstract class Coin(val name: String, val value: Int)
+  // US Coins
+  case object Penny extends Coin("penny", 1)
+  case object Nickel extends Coin("nickel", 5)
+  case object Dime extends Coin("dime", 10)
+  case object Quarter extends Coin("quarter", 25)
+
+  // Harry Potter Coins
+  case object Knut extends Coin("knut", Penny.value * 2) // Assuming 1 Knut is worth $0.02
+  case object Sickle extends Coin("sickle", Knut.value * 29)
+  case object Galleon extends Coin("galleon", Sickle.value * 17)
+
+  def getExpectedResults(inputs: Seq[Option[Coin]], sodaCost: Int): Seq[Boolean] = {
+    var value = 0
+    val outputs = mutable.ArrayBuffer.empty[Boolean]
+    for (input <- inputs) {
+      val incValue = input match {
+        case Some(coin) => coin.value
+        case None => 0
+      }
+      if (value >= sodaCost) {
+        outputs.append(true)
+        value = 0
+      } else {
+        outputs.append(false)
+        value += incValue
+      }
+    }
+    outputs
+  }
+}