凿训练营3.2 Muxes的结果是错误的？

Question

以下是Chisel Bootcamp中的代码：

Driver(() => new Module {
    // Example circuit using Mux1H
    val io = IO(new Bundle {
      val in_sels = Input(Vec(2, Bool()))
      val in_bits = Input(Vec(2, UInt(8.W)))
      val out = Output(UInt(8.W))
    })
    io.out := Mux1H(io.in_sels, io.in_bits)
  }) { c => new PeekPokeTester(c) {
    poke(c.io.in_bits(0), 10)
    poke(c.io.in_bits(1), 20)

    // Select index 1
    poke(c.io.in_sels(0), 0)
    poke(c.io.in_sels(1), 1)
    println(s"in_sels=${peek(c.io.in_sels)}, out=${peek(c.io.out)}")

    // Select index 0
    poke(c.io.in_sels(0), 1)
    poke(c.io.in_sels(1), 0)
    println(s"in_sels=${peek(c.io.in_sels)}, out=${peek(c.io.out)}")

    // Select none (invalid)
    poke(c.io.in_sels(0), 0)
    poke(c.io.in_sels(1), 0)
    println(s"in_sels=${peek(c.io.in_sels)}, out=${peek(c.io.out)}")

    // Select both (invalid)
    poke(c.io.in_sels(0), 1)
    poke(c.io.in_sels(1), 1)
    println(s"in_sels=${peek(c.io.in_sels)}, out=${peek(c.io.out)}")
} }

我得到了这样的结果：

[info] [0.001] in_sels=Vector(0, 1), out=20
[info] [0.001] in_sels=Vector(1, 0), out=10
[info] [0.002] in_sels=Vector(0, 0), out=0
[info] [0.002] in_sels=Vector(1, 1), out=30

为什么select = (1，1)时结果是30？PS: 30是一个随机数，而不是结果10 + 20

Answer 1

当多个selects为高时，Mux1H的行为是未定义的。如果你查看实现，它使用or创建行为。30是10 | 20的结果。但是，同样，因为它是未定义的，所以当多个selects为高时，您不能依赖此结果。