path: root/src/main/scala/chisel3/util/Decoupled.scala

// See LICENSE for license details.

/** Wrappers for ready-valid (Decoupled) interfaces and associated circuit generators using them.
  */

package chisel3.util

import chisel3._
import chisel3.experimental.{DataMirror, Direction, requireIsChiselType}
import chisel3.internal.naming._  // can't use chisel3_ version because of compile order

/** An I/O Bundle containing 'valid' and 'ready' signals that handshake
  * the transfer of data stored in the 'bits' subfield.
  * The base protocol implied by the directionality is that
  * the producer uses the interface as-is (outputs bits)
  * while the consumer uses the flipped interface (inputs bits).
  * The actual semantics of ready/valid are enforced via the use of concrete subclasses.
  * @param gen the type of data to be wrapped in Ready/Valid
  */
abstract class ReadyValidIO[+T <: Data](gen: T) extends Bundle
{
  // Compatibility hack for rocket-chip
  private val genType = (DataMirror.internal.isSynthesizable(gen), chisel3.internal.Builder.currentModule) match {
    case (true, Some(module: chisel3.core.MultiIOModule))
        if !module.compileOptions.declaredTypeMustBeUnbound => chiselTypeOf(gen)
    case _ => gen
  }

  val ready = Input(Bool())
  val valid = Output(Bool())
  val bits  = Output(genType)
}

object ReadyValidIO {

  implicit class AddMethodsToReadyValid[T<:Data](target: ReadyValidIO[T]) {
    def fire(): Bool = target.ready && target.valid

    /** Push dat onto the output bits of this interface to let the consumer know it has happened.
      * @param dat the values to assign to bits.
      * @return    dat.
      */
    def enq(dat: T): T = {
      target.valid := true.B
      target.bits := dat
      dat
    }

    /** Indicate no enqueue occurs. Valid is set to false, and bits are
      * connected to an uninitialized wire.
      */
    def noenq(): Unit = {
      target.valid := false.B
      target.bits := DontCare
    }

    /** Assert ready on this port and return the associated data bits.
      * This is typically used when valid has been asserted by the producer side.
      * @return The data bits.
      */
    def deq(): T = {
      target.ready := true.B
      target.bits
    }

    /** Indicate no dequeue occurs. Ready is set to false.
      */
    def nodeq(): Unit = {
      target.ready := false.B
    }
  }
}

/** A concrete subclass of ReadyValidIO signaling that the user expects a
  * "decoupled" interface: 'valid' indicates that the producer has
  * put valid data in 'bits', and 'ready' indicates that the consumer is ready
  * to accept the data this cycle. No requirements are placed on the signaling
  * of ready or valid.
  * @param gen the type of data to be wrapped in DecoupledIO
  */
class DecoupledIO[+T <: Data](gen: T) extends ReadyValidIO[T](gen)
{
  override def cloneType: this.type = new DecoupledIO(gen).asInstanceOf[this.type]
}

/** This factory adds a decoupled handshaking protocol to a data bundle. */
object Decoupled
{
  /** Wraps some Data with a DecoupledIO interface. */
  def apply[T <: Data](gen: T): DecoupledIO[T] = new DecoupledIO(gen)

  /** Downconverts an IrrevocableIO output to a DecoupledIO, dropping guarantees of irrevocability.
    *
    * @note unsafe (and will error) on the producer (input) side of an IrrevocableIO
    */
  @chiselName
  def apply[T <: Data](irr: IrrevocableIO[T]): DecoupledIO[T] = {
    require(DataMirror.directionOf(irr.bits) == Direction.Output, "Only safe to cast produced Irrevocable bits to Decoupled.") // scalastyle:ignore line.size.limit
    val d = Wire(new DecoupledIO(irr.bits))
    d.bits := irr.bits
    d.valid := irr.valid
    irr.ready := d.ready
    d
  }
}

/** A concrete subclass of ReadyValidIO that promises to not change
  * the value of 'bits' after a cycle where 'valid' is high and 'ready' is low.
  * Additionally, once 'valid' is raised it will never be lowered until after
  * 'ready' has also been raised.
  * @param gen the type of data to be wrapped in IrrevocableIO
  */
class IrrevocableIO[+T <: Data](gen: T) extends ReadyValidIO[T](gen)
{
  override def cloneType: this.type = new IrrevocableIO(gen).asInstanceOf[this.type]
}

/** Factory adds an irrevocable handshaking protocol to a data bundle. */
object Irrevocable
{
  def apply[T <: Data](gen: T): IrrevocableIO[T] = new IrrevocableIO(gen)

  /** Upconverts a DecoupledIO input to an IrrevocableIO, allowing an IrrevocableIO to be used
    * where a DecoupledIO is expected.
    *
    * @note unsafe (and will error) on the consumer (output) side of an DecoupledIO
    */
  def apply[T <: Data](dec: DecoupledIO[T]): IrrevocableIO[T] = {
    require(DataMirror.directionOf(dec.bits) == Direction.Input, "Only safe to cast consumed Decoupled bits to Irrevocable.") // scalastyle:ignore line.size.limit
    val i = Wire(new IrrevocableIO(dec.bits))
    dec.bits := i.bits
    dec.valid := i.valid
    i.ready := dec.ready
    i
  }
}

/** Producer - drives (outputs) valid and bits, inputs ready.
  * @param gen The type of data to enqueue
  */
object EnqIO {
  def apply[T<:Data](gen: T): DecoupledIO[T] = Decoupled(gen)
}
/** Consumer - drives (outputs) ready, inputs valid and bits.
  * @param gen The type of data to dequeue
  */
object DeqIO {
  def apply[T<:Data](gen: T): DecoupledIO[T] = Flipped(Decoupled(gen))
}

/** An I/O Bundle for Queues
  * @param gen The type of data to queue
  * @param entries The max number of entries in the queue.
  */
class QueueIO[T <: Data](private val gen: T, val entries: Int) extends Bundle
{ // See github.com/freechipsproject/chisel3/issues/765 for why gen is a private val and proposed replacement APIs.

  /* These may look inverted, because the names (enq/deq) are from the perspective of the client,
   *  but internally, the queue implementation itself sits on the other side
   *  of the interface so uses the flipped instance.
   */
  /** I/O to enqueue data (client is producer, and Queue object is consumer), is [[Chisel.DecoupledIO]] flipped. */
  val enq = Flipped(EnqIO(gen))
  /** I/O to dequeue data (client is consumer and Queue object is producer), is [[Chisel.DecoupledIO]]*/
  val deq = Flipped(DeqIO(gen))
  /** The current amount of data in the queue */
  val count = Output(UInt(log2Ceil(entries + 1).W))
}

/** A hardware module implementing a Queue
  * @param gen The type of data to queue
  * @param entries The max number of entries in the queue
  * @param pipe True if a single entry queue can run at full throughput (like a pipeline). The ''ready'' signals are
  * combinationally coupled.
  * @param flow True if the inputs can be consumed on the same cycle (the inputs "flow" through the queue immediately).
  * The ''valid'' signals are coupled.
  *
  * @example {{{
  * val q = Module(new Queue(UInt(), 16))
  * q.io.enq <> producer.io.out
  * consumer.io.in <> q.io.deq
  * }}}
  */
@chiselName
class Queue[T <: Data](gen: T,
                       val entries: Int,
                       pipe: Boolean = false,
                       flow: Boolean = false)
                      (implicit compileOptions: chisel3.core.CompileOptions)
    extends Module() {
  @deprecated("Module constructor with override _reset deprecated, use withReset", "chisel3")
  def this(gen: T, entries: Int, pipe: Boolean, flow: Boolean, override_reset: Option[Bool]) = {
    this(gen, entries, pipe, flow)
    this.override_reset = override_reset
  }
  @deprecated("Module constructor with override _reset deprecated, use withReset", "chisel3")
  def this(gen: T, entries: Int, pipe: Boolean, flow: Boolean, _reset: Bool) = {
    this(gen, entries, pipe, flow)
    this.override_reset = Some(_reset)
  }

  val genType = if (compileOptions.declaredTypeMustBeUnbound) {
    requireIsChiselType(gen)
    gen
  } else {
    if (DataMirror.internal.isSynthesizable(gen)) {
      chiselTypeOf(gen)
    } else {
      gen
    }
  }

  val io = IO(new QueueIO(genType, entries))

  private val ram = Mem(entries, genType)
  private val enq_ptr = Counter(entries)
  private val deq_ptr = Counter(entries)
  private val maybe_full = RegInit(false.B)

  private val ptr_match = enq_ptr.value === deq_ptr.value
  private val empty = ptr_match && !maybe_full
  private val full = ptr_match && maybe_full
  private val do_enq = WireDefault(io.enq.fire())
  private val do_deq = WireDefault(io.deq.fire())

  when (do_enq) {
    ram(enq_ptr.value) := io.enq.bits
    enq_ptr.inc()
  }
  when (do_deq) {
    deq_ptr.inc()
  }
  when (do_enq =/= do_deq) {
    maybe_full := do_enq
  }

  io.deq.valid := !empty
  io.enq.ready := !full
  io.deq.bits := ram(deq_ptr.value)

  if (flow) {
    when (io.enq.valid) { io.deq.valid := true.B }
    when (empty) {
      io.deq.bits := io.enq.bits
      do_deq := false.B
      when (io.deq.ready) { do_enq := false.B }
    }
  }

  if (pipe) {
    when (io.deq.ready) { io.enq.ready := true.B }
  }

  private val ptr_diff = enq_ptr.value - deq_ptr.value
  if (isPow2(entries)) {
    io.count := Mux(maybe_full && ptr_match, entries.U, 0.U) | ptr_diff
  } else {
    io.count := Mux(ptr_match,
                    Mux(maybe_full,
                      entries.asUInt, 0.U),
                    Mux(deq_ptr.value > enq_ptr.value,
                      entries.asUInt + ptr_diff, ptr_diff))
  }
}

/** Factory for a generic hardware queue.
  *
  * @param enq input (enqueue) interface to the queue, also determines width of queue elements
  * @param entries depth (number of elements) of the queue
  *
  * @return output (dequeue) interface from the queue
  *
  * @example {{{
  * consumer.io.in <> Queue(producer.io.out, 16)
  * }}}
  */
object Queue
{
  /** Create a queue and supply a DecoupledIO containing the product. */
  @chiselName
  def apply[T <: Data](
      enq: ReadyValidIO[T],
      entries: Int = 2,
      pipe: Boolean = false,
      flow: Boolean = false): DecoupledIO[T] = {
    if (entries == 0) {
      val deq = Wire(new DecoupledIO(enq.bits))
      deq.valid := enq.valid
      deq.bits := enq.bits
      enq.ready := deq.ready
      deq
    } else {
      require(entries > 0)
      val q = Module(new Queue(chiselTypeOf(enq.bits), entries, pipe, flow))
      q.io.enq.valid := enq.valid // not using <> so that override is allowed
      q.io.enq.bits := enq.bits
      enq.ready := q.io.enq.ready
      TransitName(q.io.deq, q)
    }
  }

  /** Create a queue and supply a IrrevocableIO containing the product.
    * Casting from Decoupled is safe here because we know the Queue has
    * Irrevocable semantics; we didn't want to change the return type of
    * apply() for backwards compatibility reasons.
    */
  @chiselName
  def irrevocable[T <: Data](
      enq: ReadyValidIO[T],
      entries: Int = 2,
      pipe: Boolean = false,
      flow: Boolean = false): IrrevocableIO[T] = {
    require(entries > 0) // Zero-entry queues don't guarantee Irrevocability
    val deq = apply(enq, entries, pipe, flow)
    val irr = Wire(new IrrevocableIO(deq.bits))
    irr.bits := deq.bits
    irr.valid := deq.valid
    deq.ready := irr.ready
    irr
  }
}