凿子3.功能模块Mux4

我正在按照文档学习 Chisel在 Github 上 https://github.com/ucb-bar/chisel3/wiki/Short%20Users%20Guide%20to%20Chisel

到目前为止，一切都完美无缺。但我还是卡在了第13章《功能模块创建》 https://github.com/ucb-bar/chisel3/wiki/Functional%20Module%20Creation

I 无法让代码工作。我在 chisel-template-project 的副本中创建了所有 .scala 类。这是我写/复制来创建的具有可变位宽的 Mux4:

/凿子模板/src/main/scala/Mux4.scala

import Chisel._

class Mux4(w: Int) extends Module {
  val io = IO(new Bundle {
        val sel = UInt(INPUT, 2)
        val in0 = UInt(INPUT, w)
        val in1 = UInt(INPUT, w)
        val in2 = UInt(INPUT, w)
        val in3 = UInt(INPUT, w)
        val out = UInt(OUTPUT, w)
  })

  io.out := Mux2(io.sel(1), 
                    Mux2(io.sel(0), io.in0, io.in1),
                    Mux2(io.sel(0), io.in2, io.in3))
}


class Mux2(w: Int) extends Module {
  val io = IO(new Bundle {
        val sel = Bool(INPUT)
        val in0 = UInt(INPUT, w)
        val in1 = UInt(INPUT, w)
        val out = UInt(OUTPUT, w)
  })

  when(io.sel) {
    io.out := io.in0
  }.otherwise {
    io.out := io.in1
  }
}


object Mux2 {
  def apply(sel: UInt, in0: UInt, in1: UInt): UInt = {
    val m = new Mux2(in0.getWidth) 
    m.io.sel := sel.toBool()
    m.io.in0 := in0
    m.io.in1 := in1
    m.io.out
  }
}

我写的 Tester scala 类：

/凿子模板/src/test/scala/Mux4Test.scala

import Chisel.iotesters.{ChiselFlatSpec, Driver, PeekPokeTester}

class Mux4Test(c: Mux4) extends PeekPokeTester(c) {

      val sel = 3
      val (in0, in1, in2, in3) = (5, 7, 11, 15)

      poke(c.io.sel, sel)
      poke(c.io.in0, in0)
      poke(c.io.in1, in1)
      poke(c.io.in2, in2)
      poke(c.io.in3, in3)
      step(1)
      System.out.println("Circuit: "+peek(c.io.out)
          +"  Expected: "+TestMux4.result(sel, in0, in1, in2, in3))
}

object TestMux4{
  def result(sel: Int, in0: Int, in1: Int, in2: Int, in3: Int): Int = {
    val out = sel match{
      case 0 => in3
      case 1 => in2
      case 2 => in1
      case 3 => in0
    }
    out
  }
}

class Mux4Tester extends ChiselFlatSpec {
  behavior of "Mux4"
  backends foreach {backend =>
    it should s"do Mux4 $backend" in {
      Driver(() => new Mux4(4), backend)(c => new Mux4Test(c)) should be (true)
    }
  }
}

重要的部分来自output

STEP 0 -> 1
Circuit: 0  Expected: 5

Mux4 类（Circuit）返回 0 作为输出，而它应该是 5，因为选择过程如下：

00 -> io.out = in3 = 15

01 -> io.out = 输入2 = 11

10 -> io.out = 输入1 = 7

11 -> io.out = in0 = 5

在我写的 Mux4Test.scala 类中值选择 = 3。它的位表示是11因此我期望in0 = 5.

我哪里错了？

感谢您对凿子的兴趣！

我运行了你的示例，在挠头一段时间后我发现了问题：当你实例化 Chisel 模块时，你需要确保将其包装在Module(...)（编辑：维基上的代码省略了这个包装器。这已被修复）。因此，对象 Mux2 应该是：

object Mux2 {
  def apply(sel: UInt, in0: UInt, in1: UInt): UInt = {
    val m = Module(new Mux2(in0.getWidth)) // <- See Here
    m.io.sel := sel.toBool()
    m.io.in0 := in0
    m.io.in1 := in1
    m.io.out
  }
}

通过此更改，代码看起来可以工作了！