Bus Slave Factory Implementation

Introduction

This page will document the implementation of the BusSlaveFactory tool and one of those variant. You can get more information about the functionality of that tool there.

Specification

The class diagram is the following :

The BusSlaveFactory abstract class define minimum requirements that each implementation of it should provide :

Name	Description
busDataWidth	Return the data width of the bus
read(that,address,bitOffset)	When the bus read the `address`, fill the response with `that` at `bitOffset`
write(that,address,bitOffset)	When the bus write the `address`, assign `that` with bus’s data from `bitOffset`
onWrite(address)(doThat)	Call `doThat` when a write transaction occur on `address`
onRead(address)(doThat)	Call `doThat` when a read transaction occur on `address`
nonStopWrite(that,bitOffset)	Permanently assign `that` by the bus write data from `bitOffset`

By using them the BusSlaveFactory should also be able to provide many utilities :

Name	Return	Description
readAndWrite(that,address,bitOffset)		Make `that` readable and writable at `address` and placed at `bitOffset` in the word
readMultiWord(that,address)		Create the memory mapping to read `that` from ‘address’. : If `that` is bigger than one word it extends the register on followings addresses
writeMultiWord(that,address)		Create the memory mapping to write `that` at ‘address’. : If `that` is bigger than one word it extends the register on followings addresses
createWriteOnly(dataType,address,bitOffset)	T	Create a write only register of type `dataType` at `address` and placed at `bitOffset` in the word
createReadWrite(dataType,address,bitOffset)	T	Create a read write register of type `dataType` at `address` and placed at `bitOffset` in the word
createAndDriveFlow(dataType,address,bitOffset)	Flow[T]	Create a writable Flow register of type `dataType` at `address` and placed at `bitOffset` in the word
drive(that,address,bitOffset)		Drive `that` with a register writable at `address` placed at `bitOffset` in the word
driveAndRead(that,address,bitOffset)		Drive `that` with a register writable and readable at `address` placed at `bitOffset` in the word
driveFlow(that,address,bitOffset)		Emit on `that` a transaction when a write happen at `address` by using data placed at `bitOffset` in the word
readStreamNonBlocking(that,address, validBitOffset,payloadBitOffset)		Read `that` and consume the transaction when a read happen at `address`. valid <= validBitOffset bit payload <= payloadBitOffset+widthOf(payload) downto `payloadBitOffset`
doBitsAccumulationAndClearOnRead (that,address,bitOffset)		Instanciate an internal register which at each cycle do : reg := reg \| that Then when a read occur, the register is cleared. This register is readable at `address` and placed at `bitOffset` in the word

About BusSlaveFactoryDelayed, it’s still an abstract class, but it capture each primitives (BusSlaveFactoryElement) calls into a data-model. This datamodel is one list that contain all primitives, but also a HashMap that link each address used to a list of primitives that are using it. Then when they all are collected (at the end of the current component), it do a callback that should be implemented by classes that extends it. The implementation of this callback should implement the hardware corresponding to all primitives collected.

Implementation

BusSlaveFactory

Let’s describe primitives abstract function :

trait BusSlaveFactory  extends Area{

  def busDataWidth : Int

  def read(that : Data,
           address : BigInt,
           bitOffset : Int = 0) : Unit

  def write(that : Data,
            address : BigInt,
            bitOffset : Int = 0) : Unit

  def onWrite(address : BigInt)(doThat : => Unit) : Unit
  def onRead (address : BigInt)(doThat : => Unit) : Unit

  def nonStopWrite( that : Data,
                    bitOffset : Int = 0) : Unit

  //...
}

Then let’s operate the magic to implement all utile based on them :

trait BusSlaveFactory  extends Area{
  //...
  def readAndWrite(that : Data,
                   address: BigInt,
                   bitOffset : Int = 0): Unit = {
    write(that,address,bitOffset)
    read(that,address,bitOffset)
  }

  def drive(that : Data,
            address : BigInt,
            bitOffset : Int = 0) : Unit = {
    val reg = Reg(that)
    write(reg,address,bitOffset)
    that := reg
  }

  def driveAndRead(that : Data,
                   address : BigInt,
                   bitOffset : Int = 0) : Unit = {
    val reg = Reg(that)
    write(reg,address,bitOffset)
    read(reg,address,bitOffset)
    that := reg
  }

  def driveFlow[T <: Data](that : Flow[T],
                           address: BigInt,
                           bitOffset : Int = 0) : Unit = {
    that.valid := False
    onWrite(address){
      that.valid := True
    }
    nonStopWrite(that.payload,bitOffset)
  }

  def createReadWrite[T <: Data](dataType: T,
                                 address: BigInt,
                                 bitOffset : Int = 0): T = {
    val reg = Reg(dataType)
    write(reg,address,bitOffset)
    read(reg,address,bitOffset)
    reg
  }

  def createAndDriveFlow[T <: Data](dataType : T,
                                 address: BigInt,
                                 bitOffset : Int = 0) : Flow[T] = {
    val flow = Flow(dataType)
    driveFlow(flow,address,bitOffset)
    flow
  }

  def doBitsAccumulationAndClearOnRead(   that : Bits,
                                          address : BigInt,
                                          bitOffset : Int = 0): Unit = {
    assert(that.getWidth <= busDataWidth)
    val reg = Reg(that)
    reg := reg | that
    read(reg,address,bitOffset)
    onRead(address){
      reg := that
    }
  }

  def readStreamNonBlocking[T <: Data] (that : Stream[T],
                                        address: BigInt,
                                        validBitOffset : Int,
                                        payloadBitOffset : Int) : Unit = {
    that.ready := False
    onRead(address){
      that.ready := True
    }
    read(that.valid  ,address,validBitOffset)
    read(that.payload,address,payloadBitOffset)
  }

  def readMultiWord(that : Data,
                address : BigInt) : Unit  = {
    val wordCount = (widthOf(that) - 1) / busDataWidth + 1
    val valueBits = that.asBits.resize(wordCount*busDataWidth)
    val words = (0 until wordCount).map(id => valueBits(id * busDataWidth , busDataWidth bits))
    for (wordId <- (0 until wordCount)) {
      read(words(wordId), address + wordId*busDataWidth/8)
    }
  }

  def writeMultiWord(that : Data,
                 address : BigInt) : Unit  = {
    val wordCount = (widthOf(that) - 1) / busDataWidth + 1
    for (wordId <- (0 until wordCount)) {
      write(
        that = new DataWrapper{
          override def getBitsWidth: Int =
            Math.min(busDataWidth, widthOf(that) - wordId * busDataWidth)

          override def assignFromBits(value : Bits): Unit = {
            that.assignFromBits(
              bits     = value.resized,
              offset   = wordId * busDataWidth,
              bitCount = getBitsWidth bits)
          }
        },address = address + wordId * busDataWidth / 8,0
      )
    }
  }
}

BusSlaveFactoryDelayed

Let’s implement classes that will be used to store primitives :

trait BusSlaveFactoryElement

// Ask to make `that` readable when a access is done on `address`.
// bitOffset specify where `that` is placed on the answer
case class BusSlaveFactoryRead(that : Data,
                               address : BigInt,
                               bitOffset : Int) extends BusSlaveFactoryElement

// Ask to make `that` writable when a access is done on `address`.
// bitOffset specify where `that` get bits from the request
case class BusSlaveFactoryWrite(that : Data,
                                address : BigInt,
                                bitOffset : Int) extends BusSlaveFactoryElement

// Ask to execute `doThat` when a write access is done on `address`
case class BusSlaveFactoryOnWrite(address : BigInt,
                                  doThat : () => Unit) extends BusSlaveFactoryElement

// Ask to execute `doThat` when a read access is done on `address`
case class BusSlaveFactoryOnRead( address : BigInt,
                                  doThat : () => Unit) extends BusSlaveFactoryElement

// Ask to constantly drive `that` with the data bus
// bitOffset specify where `that` get bits from the request
case class BusSlaveFactoryNonStopWrite(that : Data,
                                       bitOffset : Int) extends BusSlaveFactoryElement

Then let’s implement the BusSlaveFactoryDelayed itself :

trait BusSlaveFactoryDelayed extends BusSlaveFactory{
  // elements is an array of all BusSlaveFactoryElement requested
  val elements = ArrayBuffer[BusSlaveFactoryElement]()


  // elementsPerAddress is more structured than elements, it group all BusSlaveFactoryElement per requested addresses
  val elementsPerAddress = collection.mutable.HashMap[BigInt,ArrayBuffer[BusSlaveFactoryElement]]()

  private def addAddressableElement(e : BusSlaveFactoryElement,address : BigInt) = {
    elements += e
    elementsPerAddress.getOrElseUpdate(address, ArrayBuffer[BusSlaveFactoryElement]()) += e
  }

  override def read(that : Data,
           address : BigInt,
           bitOffset : Int = 0) : Unit  = {
    assert(bitOffset + that.getBitsWidth <= busDataWidth)
    addAddressableElement(BusSlaveFactoryRead(that,address,bitOffset),address)
  }

  override def write(that : Data,
            address : BigInt,
            bitOffset : Int = 0) : Unit  = {
    assert(bitOffset + that.getBitsWidth <= busDataWidth)
    addAddressableElement(BusSlaveFactoryWrite(that,address,bitOffset),address)
  }

  def onWrite(address : BigInt)(doThat : => Unit) : Unit = {
    addAddressableElement(BusSlaveFactoryOnWrite(address,() => doThat),address)
  }
  def onRead (address : BigInt)(doThat : => Unit) : Unit = {
    addAddressableElement(BusSlaveFactoryOnRead(address,() => doThat),address)
  }

  def nonStopWrite( that : Data,
                    bitOffset : Int = 0) : Unit = {
    assert(bitOffset + that.getBitsWidth <= busDataWidth)
    elements += BusSlaveFactoryNonStopWrite(that,bitOffset)
  }

  //This is the only thing that should be implement by class that extends BusSlaveFactoryDelayed
  def build() : Unit

  component.addPrePopTask(() => build())
}

AvalonMMSlaveFactory

First let’s implement the companion object that provide the compatible AvalonMM configuration object that correspond to the following table :

Pin name	Type	Description
read	Bool	High one cycle to produce a read request
write	Bool	High one cycle to produce a write request
address	UInt(addressWidth bits)	Byte granularity but word aligned
writeData	Bits(dataWidth bits)
readDataValid	Bool	High to respond a read command
readData	Bool(dataWidth bits)	Valid when readDataValid is high

object AvalonMMSlaveFactory{
  def getAvalonConfig( addressWidth : Int,
                       dataWidth : Int) = {
    AvalonMMConfig.pipelined(   //Create a simple pipelined configuration of the Avalon Bus
      addressWidth = addressWidth,
      dataWidth = dataWidth
    ).copy(                    //Change some parameters of the configuration
      useByteEnable = false,
      useWaitRequestn = false
    )
  }

  def apply(bus : AvalonMM) = new AvalonMMSlaveFactory(bus)
}

Then, let’s implement the AvalonMMSlaveFactory itself.

class AvalonMMSlaveFactory(bus : AvalonMM) extends BusSlaveFactoryDelayed{
  assert(bus.c == AvalonMMSlaveFactory.getAvalonConfig(bus.c.addressWidth,bus.c.dataWidth))

  val readAtCmd = Flow(Bits(bus.c.dataWidth bits))
  val readAtRsp = readAtCmd.stage()

  bus.readDataValid := readAtRsp.valid
  bus.readData := readAtRsp.payload

  readAtCmd.valid := bus.read
  readAtCmd.payload := 0

  override def build(): Unit = {
    for(element <- elements) element match {
      case element : BusSlaveFactoryNonStopWrite =>
        element.that.assignFromBits(bus.writeData(element.bitOffset, element.that.getBitsWidth bits))
      case _ =>
    }

    for((address,jobs) <- elementsPerAddress){
      when(bus.address === address){
        when(bus.write){
          for(element <- jobs) element match{
            case element : BusSlaveFactoryWrite => {
              element.that.assignFromBits(bus.writeData(element.bitOffset, element.that.getBitsWidth bits))
            }
            case element : BusSlaveFactoryOnWrite => element.doThat()
            case _ =>
          }
        }
        when(bus.read){
          for(element <- jobs) element match{
            case element : BusSlaveFactoryRead => {
              readAtCmd.payload(element.bitOffset, element.that.getBitsWidth bits) := element.that.asBits
            }
            case element : BusSlaveFactoryOnRead => element.doThat()
            case _ =>
          }
        }
      }
    }
  }

  override def busDataWidth: Int = bus.c.dataWidth
}

Conclusion

That’s all, you can check one example that use this Apb3SlaveFactory to create an Apb3UartCtrl there.

If you want to add the support of a new memory bus, it’s very simple you just need to implement another variation of the BusSlaveFactoryDelayed trait. The Apb3SlaveFactory is probably a good starting point :D