凿子3。功能模块 Mux4

Question

我正在按照文档 on Github 学习 Chisel

到目前为止，一切都完美无缺。但我被困在第 13 章，"Functional Module Creation"

我无法让代码工作。我在 chisel-template-project 的副本中创建了所有 .scala 类。以下是我为创建具有可变位宽的Mux4而编写/复制的内容：

/chisel-template/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：

/chisel-template/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)
    }
  }
}

输出

的重要部分

STEP 0 -> 1
Circuit: 0  Expected: 5

Mux4类（Circuit）返回0作为输出，而应该是5，因为选择过程如下：

00 -> io.out = in3 = 15

01 -> io.out = in2 = 11

10 -> io.out = in1 = 7

11 -> io.out = in0 = 5

在 Mux4Test.scala 类中我写了 val sel = 3。它的位表示是 11，因此我希望 in0 = 5。

我哪里错了？

Answer 1

感谢您对 Chisel 的关注！

我运行了您的示例，在摸索了一会儿后，我发现了问题：当您实例化 Chisel 模块时，您需要确保将其包装在 Module(...) 中（编辑：wiki 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，代码看起来可以正常工作！

Answer 2

没有阅读您的所有代码，但我认为 Mux2 参数的顺序错误：

Mux2(io.sel(0), io.in0, io.in1)