rocket-chip/src/main/scala/uncore/tilelink2/SRAM.scala

// See LICENSE.SiFive for license details.

package uncore.tilelink2

import Chisel._
import diplomacy._

class TLRAM(address: AddressSet, executable: Boolean = true, beatBytes: Int = 4) extends LazyModule
{
  val node = TLManagerNode(TLManagerPortParameters(
    Seq(TLManagerParameters(
      address            = List(address),
      regionType         = RegionType.UNCACHED,
      executable         = executable,
      supportsGet        = TransferSizes(1, beatBytes),
      supportsPutPartial = TransferSizes(1, beatBytes),
      supportsPutFull    = TransferSizes(1, beatBytes),
      fifoId             = Some(0))), // requests are handled in order
    beatBytes  = beatBytes,
    minLatency = 1)) // no bypass needed for this device

  // We require the address range to include an entire beat (for the write mask)
  require ((address.mask & (beatBytes-1)) == beatBytes-1)

  lazy val module = new LazyModuleImp(this) {
    val io = new Bundle {
      val in = node.bundleIn
    }

    def bigBits(x: BigInt, tail: List[Boolean] = List.empty[Boolean]): List[Boolean] =
      if (x == 0) tail.reverse else bigBits(x >> 1, ((x & 1) == 1) :: tail)
    val mask = bigBits(address.mask >> log2Ceil(beatBytes))

    val in = io.in(0)
    val edge = node.edgesIn(0)

    val addrBits = (mask zip edge.addr_hi(in.a.bits).toBools).filter(_._1).map(_._2)
    val memAddress = Cat(addrBits.reverse)
    val mem = SeqMem(1 << addrBits.size, Vec(beatBytes, Bits(width = 8)))

    val d_full = RegInit(Bool(false))
    val d_read = Reg(Bool())
    val d_size = Reg(UInt())
    val d_source = Reg(UInt())
    val d_addr = Reg(UInt())
    val d_data = Wire(UInt())

    // Flow control
    when (in.d.fire()) { d_full := Bool(false) }
    when (in.a.fire()) { d_full := Bool(true)  }
    in.d.valid := d_full
    in.a.ready := in.d.ready || !d_full

    in.d.bits := edge.AccessAck(d_addr, UInt(0), d_source, d_size)
    // avoid data-bus Mux
    in.d.bits.data := d_data
    in.d.bits.opcode := Mux(d_read, TLMessages.AccessAckData, TLMessages.AccessAck)

    val read = in.a.bits.opcode === TLMessages.Get
    val rdata = Wire(Vec(beatBytes, Bits(width = 8)))
    val wdata = Vec.tabulate(beatBytes) { i => in.a.bits.data(8*(i+1)-1, 8*i) }
    d_data := Cat(rdata.reverse)
    when (in.a.fire()) {
      d_read   := read
      d_size   := in.a.bits.size
      d_source := in.a.bits.source
      d_addr   := edge.addr_lo(in.a.bits)
    }

    // exactly this pattern is required to get a RWM memory
    when (in.a.fire() && !read) {
      mem.write(memAddress, wdata, in.a.bits.mask.toBools)
    }
    val ren = in.a.fire() && read
    rdata := holdUnless(mem.read(memAddress, ren), RegNext(ren))

    // Tie off unused channels
    in.b.valid := Bool(false)
    in.c.ready := Bool(true)
    in.e.ready := Bool(true)
  }
}

/** Synthesizeable unit testing */
import unittest._

class TLRAMSimple(ramBeatBytes: Int) extends LazyModule {
  val fuzz = LazyModule(new TLFuzzer(5000))
  val model = LazyModule(new TLRAMModel)
  val ram  = LazyModule(new TLRAM(AddressSet(0x0, 0x3ff), beatBytes = ramBeatBytes))

  model.node := fuzz.node
  ram.node := model.node

  lazy val module = new LazyModuleImp(this) with HasUnitTestIO {
    io.finished := fuzz.module.io.finished
  }
}

class TLRAMSimpleTest(ramBeatBytes: Int) extends UnitTest(timeout = 500000) {
  io.finished := Module(LazyModule(new TLRAMSimple(ramBeatBytes)).module).io.finished
}