凿子3。功能模块 Mux4

Question

我正在按照文档学习 Chisel on Github

到目前为止，一切都完美无缺。但是我卡在了第 13 章，"Functional Module Creation"

我无法使代码工作。我在 chisel-template-project 的副本中创建了我所有的 .scala classes。这是我编写/复制的内容，用于创建具有可变位宽的 Mux4:

/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
  }
}

Tester scala class 我写道：

/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)
    }
  }
}

来自输出的重要部分

STEP 0 -> 1
Circuit: 0  Expected: 5

Mux4 class (Circuit) returns 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 class 中我写了 val sel = 3。这个的位表示是 11 因此我期望 in0 = 5.

我哪里错了？

Answer 1

没有阅读你所有的代码，但我认为 Mux2 参数在这里的顺序错误：

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

Answer 2

感谢您对 Chisel 的关注！

我运行你的例子，摸索了一会儿后我发现了问题：当你实例化一个凿子模块时，你需要确保将它包装在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 应该改为：

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
  }
}

经过此更改，代码看起来可以正常工作了！

凿子3。功能模块 Mux4

Chisel3. Functional Module Mux4

scala

module

riscv

mux

chisel