Chisel bootcamp 3.2 Muxes 结果错误？

Question

这是 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)}")
} }

我得到的结果是这样的：

[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) 结果是 30？ PS: 30是随机数，不是10+20的结果

Answer 1

Mux1H 的行为在其多个选择为高时未定义。如果您查看实现，它正在使用 or 来创建行为。 30 是 10 | 的结果20. 但是，同样，因为它是未定义的，所以当多重选择很高时，你不能依赖这个结果。

Chisel bootcamp 3.2 Muxes 结果错误？

Chisel bootcamp 3.2 Muxes result wrong?

scala

chisel

riscv