Flow

Specification

The Flow interface is a simple valid/payload protocol which means the slave can’t halt the bus. It could be used to represent data coming from an UART controller, requests to write an on-chip memory, etc.

Signal	Type	Driver	Description	Don’t care when
valid	Bool	Master	When high => payload present on the interface
payload	T	Master	Content of the transaction	valid is low

Functions

Syntax	Description	Return	Latency
Flow(type : Data)	Create a Flow of a given type	Flow[T]
master/slave Flow(type : Data)	Create a Flow of a given type Initialized with corresponding in/out setup	Flow[T]
x.m2sPipe()	Return a Flow driven by x through a register stage that cut valid/payload paths	Flow[T]	1
x.stage()	Equivalent to x.m2sPipe()	Flow[T]	1
x << y y >> x	Connect y to x		0
x <-< y y >-> x	Connect y to x through a m2sPipe		1
x.throwWhen(cond : Bool)	Return a Flow connected to x When cond is high, transaction are dropped	Flow[T]	0
x.toReg()	Return a register which is loaded with `payload` when valid is high	T
x.setIdle()	Set the Flow in an Idle state: `valid` is `False` and don’t care about `payload`.
x.push(newPayload: T)	Assign a new valid payload to the Flow. `valid` is set to `True`.

Code examplecase class FlowExample() extends Component {
  val io = new Bundle {
    val request = slave(Flow(Bits(8 bit)))
    val answer = master(Flow(Bits(8 bit)))
  }
  val storage = Reg(Bits(8 bit))

  val fsm = new StateMachine {
    io.answer.setIdle()

    val idle: State = new State with EntryPoint {
      whenIsActive {
        when(io.request.valid) {
          storage := io.request.payload
          goto(sendEcho)
        }
      }
    }

    val sendEcho: State = new State {
      whenIsActive {
        io.answer.push(storage)
        goto(idle)
      }
    }
  }

  // This StateMachine behaves equivalently to
  // io.answer <-< io.request
}

Simulation Support

Class	Usage
FlowMonitor	Used for both master and slave sides, calls function with payload if Flow transmits data.
FlowDriver	Testbench master side, drives values by calling function to apply value (if available). Function must return if value was available. Supports random delays.
ScoreboardInOrder	Often used to compare reference/dut data

package spinaldoc.libraries.flow

import spinal.core._
import spinal.core.sim._
import spinal.lib._
import spinal.lib.sim.{FlowDriver, FlowMonitor, ScoreboardInOrder}

import scala.language.postfixOps

case class SomeDUT() extends Component {
  val io = new Bundle {
    val input = slave(Flow(UInt(8 bit)))
    val output = master(Flow(UInt(8 bit)))
  }
  io.output <-< io.input
}

object Example extends App {
  val dut = SimConfig.withWave.compile(SomeDUT())

  dut.doSim("simple test") { dut =>
    SimTimeout(10000)

    val scoreboard = ScoreboardInOrder[Int]()

    // drive random data at random intervals, and add inputted data to scoreboard
    FlowDriver(dut.io.input, dut.clockDomain) { payload =>
      payload.randomize()
      true
    }
    FlowMonitor(dut.io.input, dut.clockDomain) { payload =>
      scoreboard.pushRef(payload.toInt)
    }

    // add all data coming out of DUT to scoreboard
    FlowMonitor(dut.io.output, dut.clockDomain) { payload =>
      scoreboard.pushDut(payload.toInt)
    }

    dut.clockDomain.forkStimulus(10)
    dut.clockDomain.waitActiveEdgeWhere(scoreboard.matches == 100)
  }
}