CODEWITHSUNDEEP
scalachisel
tonysamaritano
tonysamaritano

Reputation: 41

ChiselTest: Cast a signed int to unsigned int for an expected value

I'm having trouble identifying the correct method for converting a signed int to unsigned int for unit testing using the new ChiselTest framework.

Here is the method I have been using to unit test an ALU (example is 16-bit), the problem is that it is not scalable:

    test(new ALU) { c =>
    ...
        /* Sub */
        c.io.ctl.poke(Control.ALU_SUB)
        c.io.src0.poke(4321.U)
        c.io.src1.poke(1234.U)
        c.io.out.expect(3087.U)
        c.io.src0.poke(1234.U)
        c.io.src1.poke(4321.U)
        c.io.out.expect("b_1111_0011_1111_0001".U) /* 2's compliment */
    }

The problem with this method is that when I generate a 32-bit ALU (which outputs an unsigned int), the unit test will fail because the string will zero extend to 32-bits using the hacky string method above...

I'd like to rewrite the test like this:

test(new ALU) { c =>
    /* Sub */
    c.io.ctl.poke(Control.ALU_SUB)
    c.io.src0.poke(4321.U)
    c.io.src1.poke(1234.U)
    c.io.out.expect(3087.U)
    c.io.src0.poke(1234.U)
    c.io.src1.poke(4321.U)
    c.io.out.expect(-3087.S.asUInt)
}

But, although the design does elaborate, I get the following error:

[error] (run-main-9) chisel3.internal.ChiselException: Error: Not in a UserModule. Likely cause: Missed Module() wrap, bare chisel API call, or attempting to construct hardware inside a BlackBox.
[error] chisel3.internal.ChiselException: Error: Not in a UserModule. Likely cause: Missed Module() wrap, bare chisel API call, or attempting to construct hardware inside a BlackBox.
[error]         at chisel3.internal.throwException$.apply(Error.scala:85)
[error]         at chisel3.internal.Builder$.forcedUserModule(Builder.scala:298)
[error]         at chisel3.internal.Builder$.pushOp(Builder.scala:336)
[error]         at chisel3.SInt.do_asUInt(Bits.scala:925)
[error]         at cpu.alu$.$anonfun$new$2(Main.scala:26)
[error]         at cpu.alu$.$anonfun$new$2$adapted(Main.scala:18)
[error]         at chiseltest.backends.treadle.TreadleBackend.$anonfun$run$1(TreadleBackend.scala:144)
[error]         at chiseltest.internal.ThreadedBackend$TesterThread$$anon$1.$anonfun$run$1(ThreadedBackend.scala:453)
[error]         at chiseltest.backends.treadle.TreadleBackend.doTimescope(TreadleBackend.scala:103)
[error]         at chiseltest.internal.ThreadedBackend$TesterThread$$anon$1.run(ThreadedBackend.scala:453)
[error]         at java.lang.Thread.run(Thread.java:748)
[error] stack trace is suppressed; run last Test / bgRunMain for the full output
[error] Nonzero exit code: 1
[error] (Test / runMain) Nonzero exit code: 1

I can't figure out the right way of addressing this. Any help would be much appreciated.

For reference, the ALU is pretty simple, here is the ALU class:

class ALU extends Module {
  val io = IO(new Bundle {
    val ctl   = Input(UInt(Control.ALU_BITWIDTH))
    val src0  = Input(UInt(Instructions.WORD_SIZE.W))
    val src1  = Input(UInt(Instructions.WORD_SIZE.W))
    val out   = Output(UInt(Instructions.WORD_SIZE.W))
  })

  val shift = io.src1(3,0).asUInt

  /* Lookup the operation to execute */
  io.out := MuxLookup(io.ctl, 0.U, Seq(
    Control.ALU_ADD -> (io.src0 + io.src1),
    Control.ALU_SUB -> (io.src0 - io.src1),
    Control.ALU_AND -> (io.src0 & io.src1),
    Control.ALU_OR  -> (io.src0 | io.src1),
    Control.ALU_XOR -> (io.src0 ^ io.src1),
    Control.ALU_NOT -> (~io.src0),
    Control.ALU_SLL -> (io.src0 << shift),
    Control.ALU_SRL -> (io.src0 >> shift),
  ))
}

Upvotes: 3

Views: 574

Answers (2)

Reset
Reset

Reputation: 11

Made some improvements based on @tonysamaritano's solution. Write an independent Scala function to make it look better.

ToSInt(x: Int): Int = scala.math.pow(2, bitwidth).toInt - x

Upvotes: 0

tonysamaritano
tonysamaritano

Reputation: 41

This feels a little gross, but at least it's scalable (maybe a possible solution?)... I'm still interested in the best way of casting a SInt to UInt in the test framework.

    /* Sub */
    c.io.ctl.poke(Control.ALU_SUB)
    c.io.src0.poke(4321.U)
    c.io.src1.poke(1234.U)
    c.io.out.expect(3087.U)
    c.io.src0.poke(1234.U)
    c.io.src1.poke(4321.U)
    def bitwidth = 16 // for example
    def max = scala.math.pow(2,bitwidth).toInt
    c.io.out.expect((max-3087).U)

Upvotes: 1

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