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rocket-chip/src/main/scala/junctions/crossing.scala

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Scala
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package junctions
import Chisel._
class Crossing[T <: Data](gen: T, enq_sync: Boolean, deq_sync: Boolean) extends Bundle {
val enq = Decoupled(gen).flip()
val deq = Decoupled(gen)
val enq_clock = if (enq_sync) Some(Clock(INPUT)) else None
val deq_clock = if (deq_sync) Some(Clock(INPUT)) else None
val enq_reset = if (enq_sync) Some(Bool(INPUT)) else None
val deq_reset = if (deq_sync) Some(Bool(INPUT)) else None
}
// Output is 1 for one cycle after any edge of 'in'
object AsyncHandshakePulse {
def apply(in: Bool, sync: Int): Bool = {
val syncv = RegInit(Vec.fill(sync+1){Bool(false)})
syncv.last := in
(syncv.init zip syncv.tail).foreach { case (sink, source) => sink := source }
syncv(0) =/= syncv(1)
}
}
class AsyncHandshakeSource[T <: Data](gen: T, sync: Int, clock: Clock, reset: Bool)
extends Module(_clock = clock, _reset = reset) {
val io = new Bundle {
// These come from the source clock domain
val enq = Decoupled(gen).flip()
// These cross to the sink clock domain
val bits = gen.cloneType.asOutput
val push = Bool(OUTPUT)
val pop = Bool(INPUT)
}
val ready = RegInit(Bool(true))
val bits = Reg(gen)
val push = RegInit(Bool(false))
io.enq.ready := ready
io.bits := bits
io.push := push
val pop = AsyncHandshakePulse(io.pop, sync)
assert (!pop || !ready)
when (pop) {
ready := Bool(true)
}
when (io.enq.fire()) {
ready := Bool(false)
bits := io.enq.bits
push := !push
}
}
class AsyncHandshakeSink[T <: Data](gen: T, sync: Int, clock: Clock, reset: Bool)
extends Module(_clock = clock, _reset = reset) {
val io = new Bundle {
// These cross to the source clock domain
val bits = gen.cloneType.asInput
val push = Bool(INPUT)
val pop = Bool(OUTPUT)
// These go to the sink clock domain
val deq = Decoupled(gen)
}
val valid = RegInit(Bool(false))
val bits = Reg(gen)
val pop = RegInit(Bool(false))
io.deq.valid := valid
io.deq.bits := bits
io.pop := pop
val push = AsyncHandshakePulse(io.push, sync)
assert (!push || !valid)
when (push) {
valid := Bool(true)
bits := io.bits
}
when (io.deq.fire()) {
valid := Bool(false)
pop := !pop
}
}
class AsyncHandshake[T <: Data](gen: T, sync: Int = 2) extends Module {
val io = new Crossing(gen, true, true)
require (sync >= 2)
val source = Module(new AsyncHandshakeSource(gen, sync, io.enq_clock.get, io.enq_reset.get))
val sink = Module(new AsyncHandshakeSink (gen, sync, io.deq_clock.get, io.deq_reset.get))
source.io.enq <> io.enq
io.deq <> sink.io.deq
sink.io.bits := source.io.bits
sink.io.push := source.io.push
source.io.pop := sink.io.pop
}
class AsyncDecoupledTo[T <: Data](gen: T, depth: Int = 0, sync: Int = 2) extends Module {
val io = new Crossing(gen, false, true)
// !!! if depth == 0 { use Handshake } else { use AsyncFIFO }
val crossing = Module(new AsyncHandshake(gen, sync)).io
crossing.enq_clock.get := clock
crossing.enq_reset.get := reset
crossing.enq <> io.enq
crossing.deq_clock.get := io.deq_clock.get
crossing.deq_reset.get := io.deq_reset.get
io.deq <> crossing.deq
}
object AsyncDecoupledTo {
// source is in our clock domain, output is in the 'to' clock domain
def apply[T <: Data](to_clock: Clock, to_reset: Bool, source: DecoupledIO[T], depth: Int = 0, sync: Int = 2): DecoupledIO[T] = {
val to = Module(new AsyncDecoupledTo(source.bits, depth, sync))
to.io.deq_clock.get := to_clock
to.io.deq_reset.get := to_reset
to.io.enq <> source
to.io.deq
}
}
class AsyncDecoupledFrom[T <: Data](gen: T, depth: Int = 0, sync: Int = 2) extends Module {
val io = new Crossing(gen, true, false)
// !!! if depth == 0 { use Handshake } else { use AsyncFIFO }
val crossing = Module(new AsyncHandshake(gen, sync)).io
crossing.enq_clock.get := io.enq_clock.get
crossing.enq_reset.get := io.enq_reset.get
crossing.enq <> io.enq
crossing.deq_clock.get := clock
crossing.deq_reset.get := reset
io.deq <> crossing.deq
}
object AsyncDecoupledFrom {
// source is in the 'from' clock domain, output is in our clock domain
def apply[T <: Data](from_clock: Clock, from_reset: Bool, source: DecoupledIO[T], depth: Int = 0, sync: Int = 2): DecoupledIO[T] = {
val from = Module(new AsyncDecoupledFrom(source.bits, depth, sync))
from.io.enq_clock.get := from_clock
from.io.enq_reset.get := from_reset
from.io.enq <> source
from.io.deq
}
}