Merge pull request #975 from freechipsproject/async_reg
Cleanup some register primitives
This commit is contained in:
commit
929a924779
@ -6,6 +6,7 @@ import Chisel._
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import chisel3.internal.sourceinfo.SourceInfo
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import freechips.rocketchip.config.Parameters
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import freechips.rocketchip.diplomacy._
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import freechips.rocketchip.util.SynchronizerShiftReg
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import scala.collection.mutable.ListBuffer
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import scala.math.max
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@ -139,7 +140,7 @@ class IntXing(sync: Int = 3)(implicit p: Parameters) extends LazyModule
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}
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(io.in zip io.out) foreach { case (in, out) =>
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out := (0 to sync).foldLeft(in) { case (a, _) => RegNext(a) }
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out := SynchronizerShiftReg(in, sync)
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}
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}
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}
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@ -13,27 +13,12 @@ object GrayCounter {
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}
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}
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object UIntSyncChain {
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def apply(in: UInt, sync: Int, name: String = "gray"): UInt = {
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val syncv = List.tabulate(sync) { i =>
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Module (new AsyncResetRegVec(w = in.getWidth, 0)).suggestName(s"${name}_sync_${i}")
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}
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syncv.last.io.d := in
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syncv.last.io.en := Bool(true)
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(syncv.init zip syncv.tail).foreach { case (sink, source) =>
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sink.io.d := source.io.q
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sink.io.en := Bool(true)
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}
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syncv.head.io.q
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}
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}
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class AsyncValidSync(sync: Int, desc: String) extends Module {
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val io = new Bundle {
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val in = Bool(INPUT)
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val out = Bool(OUTPUT)
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}
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io.out := UIntSyncChain(io.in.asUInt, sync, desc)(0)
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io.out := AsyncResetSynchronizerShiftReg(io.in, sync, Some(desc))
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}
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class AsyncQueueSource[T <: Data](gen: T, depth: Int, sync: Int, safe: Boolean = true, narrowData: Boolean = false) extends Module {
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@ -55,7 +40,7 @@ class AsyncQueueSource[T <: Data](gen: T, depth: Int, sync: Int, safe: Boolean =
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val sink_ready = Wire(init = Bool(true))
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val mem = Reg(Vec(depth, gen)) // This does NOT need to be reset at all.
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val widx = GrayCounter(bits+1, io.enq.fire(), !sink_ready, "widx_bin")
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val ridx = UIntSyncChain(io.ridx, sync, "ridx_gray")
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val ridx = AsyncResetSynchronizerShiftReg(io.ridx, sync, Some("ridx_gray"))
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val ready = sink_ready && widx =/= (ridx ^ UInt(depth | depth >> 1))
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val index = if (depth == 1) UInt(0) else io.widx(bits-1, 0) ^ (io.widx(bits, bits) << (bits-1))
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@ -112,7 +97,7 @@ class AsyncQueueSink[T <: Data](gen: T, depth: Int, sync: Int, safe: Boolean = t
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val source_ready = Wire(init = Bool(true))
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val ridx = GrayCounter(bits+1, io.deq.fire(), !source_ready, "ridx_bin")
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val widx = UIntSyncChain(io.widx, sync, "widx_gray")
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val widx = AsyncResetSynchronizerShiftReg(io.widx, sync, Some("widx_gray"))
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val valid = source_ready && ridx =/= widx
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// The mux is safe because timing analysis ensures ridx has reached the register
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@ -125,7 +110,8 @@ class AsyncQueueSink[T <: Data](gen: T, depth: Int, sync: Int, safe: Boolean = t
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// be considered unless the asynchronously reset deq valid register is set.
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// It is possible that bits latches when the source domain is reset / has power cut
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// This is safe, because isolation gates brought mem low before the zeroed widx reached us
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io.deq.bits := RegEnable(io.mem(if(narrowData) UInt(0) else index), valid)
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val deq_bits_nxt = Mux(valid, io.mem(if(narrowData) UInt(0) else index), io.deq.bits)
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io.deq.bits := SynchronizerShiftReg(deq_bits_nxt, sync = 1, name = Some("deq_bits_reg"))
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val valid_reg = AsyncResetReg(valid.asUInt, "valid_reg")(0)
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io.deq.valid := valid_reg && source_ready
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@ -63,6 +63,9 @@ class AsyncResetRegVec(val w: Int, val init: BigInt) extends Module {
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}
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io.q := q.asUInt
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override def desiredName = s"AsyncResetRegVec_w${w}_i${init}"
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}
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object AsyncResetReg {
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@ -103,3 +106,4 @@ object AsyncResetReg {
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def apply(updateData: UInt): UInt = apply(updateData, resetData=BigInt(0), enable=Bool(true))
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def apply(updateData: UInt, name:String): UInt = apply(updateData, resetData=BigInt(0), enable=Bool(true), Some(name))
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}
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@ -99,7 +99,7 @@ object LevelSyncCrossing {
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val out = Bool(OUTPUT)
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}
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io.out := ShiftRegister(io.in, sync)
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io.out := SynchronizerShiftReg(io.in, sync)
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}
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class SynchronizerFrontend(_clock: Clock) extends Module(Some(_clock)) {
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@ -15,12 +15,7 @@ class ResetCatchAndSync (sync: Int = 3) extends Module {
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val sync_reset = Bool(OUTPUT)
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}
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val reset_n_catch_reg = Module (new AsyncResetRegVec(sync, 0))
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reset_n_catch_reg.io.en := Bool(true)
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reset_n_catch_reg.io.d := Cat(Bool(true), reset_n_catch_reg.io.q >> 1)
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io.sync_reset := ~reset_n_catch_reg.io.q(0)
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io.sync_reset := ~AsyncResetSynchronizerShiftReg(Bool(true), sync)
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}
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144
src/main/scala/util/ShiftReg.scala
Normal file
144
src/main/scala/util/ShiftReg.scala
Normal file
@ -0,0 +1,144 @@
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// See LICENSE.SiFive for license details.
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package freechips.rocketchip.util
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import Chisel._
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// Similar to the Chisel ShiftRegister but allows the user to suggest a
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// name to the registers that get instantiated, and
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// to provide a reset value.
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object ShiftRegInit {
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def apply[T <: Data](in: T, n: Int, init: T, name: Option[String] = None): T =
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(0 until n).foldRight(in) {
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case (i, next) => {
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val r = Reg(next, next = next, init = init)
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name.foreach { na => r.suggestName(s"${na}_${i}") }
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r
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}
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}
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}
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/** These wrap behavioral
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* shift registers into specific modules to allow for
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* backend flows to replace or constrain
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* them properly when used for CDC synchronization,
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* rather than buffering.
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*
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* The different types vary in their reset behavior:
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* AsyncResetShiftReg -- This is identical to the AsyncResetSynchronizerShiftReg,
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* it is just named differently to distinguish its use case.
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* This is an async ShiftRegister meant for timing,
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* not for synchronization.
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* AsyncResetSynchronizerShiftReg -- asynchronously reset to specific value.
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* SyncResetSynchronizerShiftReg -- reset to specific value.
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* SynchronizerShiftReg -- no reset, pipeline only.
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*/
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abstract class AbstractPipelineReg(w: Int = 1) extends Module {
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val io = new Bundle {
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val d = UInt(INPUT, width = w)
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val q = UInt(OUTPUT, width = w)
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}
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}
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object AbstractPipelineReg {
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def apply [T <: Chisel.Data](gen: => AbstractPipelineReg, in: T, name: Option[String] = None): T = {
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val chain = Module(gen)
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name.foreach{ chain.suggestName(_) }
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chain.io.d := in.asUInt
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chain.io.q.asTypeOf(in)
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}
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}
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class AsyncResetShiftReg(w: Int = 1, depth: Int = 1, init: Int = 0, name: String = "pipe") extends AbstractPipelineReg(w) {
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require(depth > 0, "Depth must be greater than 0.")
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override def desiredName = s"AsyncResetShiftReg_w${w}_d${depth}_i${init}"
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val chain = List.tabulate(depth) { i =>
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Module (new AsyncResetRegVec(w, init)).suggestName(s"${name}_${i}")
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}
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chain.last.io.d := io.d
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chain.last.io.en := Bool(true)
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(chain.init zip chain.tail).foreach { case (sink, source) =>
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sink.io.d := source.io.q
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sink.io.en := Bool(true)
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}
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io.q := chain.head.io.q
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}
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object AsyncResetShiftReg {
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def apply [T <: Chisel.Data](in: T, depth: Int, init: Int = 0, name: Option[String] = None): T =
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AbstractPipelineReg(new AsyncResetShiftReg(in.getWidth, depth, init), in, name)
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def apply [T <: Chisel.Data](in: T, depth: Int, name: Option[String]): T =
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apply(in, depth, 0, name)
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def apply [T <: Chisel.Data](in: T, depth: Int, init: T, name: Option[String]): T =
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apply(in, depth, init.litValue.toInt, name)
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def apply [T <: Chisel.Data](in: T, depth: Int, init: T): T =
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apply (in, depth, init.litValue.toInt, None)
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}
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// Note that it is important to ovveride "name" in order to ensure that the Chisel dedup does
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// not try to merge instances of this with instances of the superclass.
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class AsyncResetSynchronizerShiftReg(w: Int = 1, sync: Int = 3, init: Int = 0) extends AsyncResetShiftReg(w, depth = sync, init, name = "sync") {
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require(sync > 0, "Sync must be greater than 0.")
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override def desiredName = s"AsyncResetSynchronizerShiftReg_w${w}_d${sync}_i${init}"
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}
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object AsyncResetSynchronizerShiftReg {
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def apply [T <: Chisel.Data](in: T, depth: Int, init: Int = 0, name: Option[String] = None): T =
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AbstractPipelineReg(new AsyncResetSynchronizerShiftReg(in.getWidth, depth, init), in, name)
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def apply [T <: Chisel.Data](in: T, depth: Int, name: Option[String]): T =
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apply(in, depth, 0, name)
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def apply [T <: Chisel.Data](in: T, depth: Int, init: T, name: Option[String]): T =
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apply(in, depth, init.litValue.toInt, name)
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def apply [T <: Chisel.Data](in: T, depth: Int, init: T): T =
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apply (in, depth, init.litValue.toInt, None)
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}
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class SynchronizerShiftReg(w: Int = 1, sync: Int = 3) extends AbstractPipelineReg(w) {
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require(sync > 0, "Sync must be greater than 0.")
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override def desiredName = s"SynchronizerShiftReg_w${w}_d${sync}"
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val syncv = List.tabulate(sync) { i =>
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val r = Reg(UInt(width = w))
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r.suggestName(s"sync_${i}")
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}
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syncv.last := io.d
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(syncv.init zip syncv.tail).foreach { case (sink, source) =>
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sink := source
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}
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io.q := syncv.head
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}
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object SynchronizerShiftReg {
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def apply [T <: Chisel.Data](in: T, sync: Int = 3, name: Option[String] = None): T =
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AbstractPipelineReg(new SynchronizerShiftReg(in.getWidth, sync), in, name)
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}
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class SyncResetSynchronizerShiftReg(w: Int = 1, sync: Int = 3, init: Int = 0) extends AbstractPipelineReg(w) {
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require (sync >= 0, "Sync must be greater than or equal to 0")
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override def desiredName = s"SyncResetSynchronizerShiftReg_w${w}_d${sync}_i${init}"
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io.q := ShiftRegInit(io.d, n = sync, init = init.U, name = Some("sync"))
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}
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object SyncResetSynchronizerShiftReg {
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def apply [T <: Chisel.Data](in: T, sync: Int = 3, init: T, name: Option[String] = None): T =
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AbstractPipelineReg(new SyncResetSynchronizerShiftReg(in.getWidth, sync, init.litValue.toInt), in, name)
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}
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