Potential Bug at DCache WriteArb

[Jerry-Tianchen]

Type of issue: bug report

Impact: new rtl

Development Phase: proposal

Other information

  def onReset = L1Metadata(0.U, ClientMetadata.onReset)
  val meta = Seq.fill(memWidth) { Module(new L1MetadataArray(onReset _)) }
  val metaWriteArb = Module(new Arbiter(new L1MetaWriteReq, 2))
  // 0 goes to MSHR refills, 1 goes to prober
  val metaReadArb = Module(new Arbiter(new BoomL1MetaReadReq, 6))
  // 0 goes to MSHR replays, 1 goes to prober, 2 goes to wb, 3 goes to MSHR meta read,
  // 4 goes to pipeline, 5 goes to prefetcher

  metaReadArb.io.in := DontCare
  for (w <- 0 until memWidth) {
    meta(w).io.write.valid := metaWriteArb.io.out.fire
    meta(w).io.write.bits  := metaWriteArb.io.out.bits
    meta(w).io.read.valid  := metaReadArb.io.out.valid
    meta(w).io.read.bits   := metaReadArb.io.out.bits.req(w)
  }
  metaReadArb.io.out.ready  := meta.map(_.io.read.ready).reduce(_||_)
  metaWriteArb.io.out.ready := meta.map(_.io.write.ready).reduce(_||_)

  // data
  val data = Module(if (boomParams.numDCacheBanks == 1) new BoomDuplicatedDataArray else new BoomBankedDataArray)
  val dataWriteArb = Module(new Arbiter(new L1DataWriteReq, 2))
  // 0 goes to pipeline, 1 goes to MSHR refills
  val dataReadArb = Module(new Arbiter(new BoomL1DataReadReq, 3))
  // 0 goes to MSHR replays, 1 goes to wb, 2 goes to pipeline
  dataReadArb.io.in := DontCare

For the metaWriteArb.io.out.ready := meta.map(_.io.write.ready).reduce(_||_)
are you sure it is really reduce (||) instead of reduce (&&)?
When writing aren't we supposed to write both Array Blocks?

I realized this when analyzing the code.

What is the current behavior?

What is the expected behavior?

Please tell us about your environment:
Not Important

What is the use case for changing the behavior?

[jerryz123]

I think you are right, I suspect for some reason we never entered a condition where this mattered, but I think your suggestion is more correct.

[jerryz123]

Feel free to open a PR with the fix

[Jerry-Tianchen]

Oh I am working on older version right now. Once I have the time to look at the newest version I will do that~