refactor ICache to be reusable by other frontends (#808)

* refactor ICache to be reusable by other frontends

specifically one that would like to change the fetch width and number of
bytes in an instruction

src/main/scala/rocket/Frontend.scala

@@ -45,9 +45,9 @@ class FrontendIO(implicit p: Parameters) extends CoreBundle()(p) {
   val perf = new FrontendPerfEvents().asInput
 }
 
-class Frontend(hartid: Int)(implicit p: Parameters) extends LazyModule {
+class Frontend(val icacheParams: ICacheParams, hartid: Int)(implicit p: Parameters) extends LazyModule {
   lazy val module = new FrontendModule(this)
-  val icache = LazyModule(new ICache(latency = 2, hartid))
+  val icache = LazyModule(new ICache(icacheParams, hartid))
   val masterNode = TLOutputNode()
   val slaveNode = TLInputNode()
 
@@ -70,6 +70,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
   val io = new FrontendBundle(outer)
   implicit val edge = outer.masterNode.edgesOut.head
   val icache = outer.icache.module
+  require(fetchWidth*coreInstBytes == outer.icacheParams.fetchBytes)
 
   val tlb = Module(new TLB(log2Ceil(coreInstBytes*fetchWidth), nTLBEntries))
   val fq = withReset(reset || io.cpu.req.valid) { Module(new ShiftQueue(new FrontendResp, 4, flow = true)) }
@@ -183,7 +184,7 @@ class FrontendModule(outer: Frontend) extends LazyModuleImp(outer)
 /** Mix-ins for constructing tiles that have an ICache-based pipeline frontend */
 trait HasICacheFrontend extends CanHavePTW with HasTileLinkMasterPort {
   val module: HasICacheFrontendModule
-  val frontend = LazyModule(new Frontend(hartid: Int))
+  val frontend = LazyModule(new Frontend(tileParams.icache.get, hartid: Int))
   val hartid: Int
   tileBus.node := frontend.masterNode
   nPTWPorts += 1

src/main/scala/rocket/ICache.scala

@@ -21,7 +21,9 @@ case class ICacheParams(
     tagECC: Code = new IdentityCode,
     dataECC: Code = new IdentityCode,
     itimAddr: Option[BigInt] = None,
-    blockBytes: Int = 64) extends L1CacheParams {
+    blockBytes: Int = 64,
+    latency: Int = 2,
+    fetchBytes: Int = 4) extends L1CacheParams {
   def replacement = new RandomReplacement(nWays)
 }
 
@@ -33,15 +35,13 @@ class ICacheReq(implicit p: Parameters) extends CoreBundle()(p) with HasL1ICache
   val addr = UInt(width = vaddrBits)
 }
 
-class ICache(val latency: Int, val hartid: Int)(implicit p: Parameters) extends LazyModule
+class ICache(val icacheParams: ICacheParams, val hartid: Int)(implicit p: Parameters) extends LazyModule {
-    with HasRocketCoreParameters {
   lazy val module = new ICacheModule(this)
   val masterNode = TLClientNode(TLClientParameters(name = s"Core ${hartid} ICache"))
 
-  val icacheParams = tileParams.icache.get
   val size = icacheParams.nSets * icacheParams.nWays * icacheParams.blockBytes
   val slaveNode = icacheParams.itimAddr.map { itimAddr =>
-    val wordBytes = coreInstBytes * fetchWidth
+    val wordBytes = icacheParams.fetchBytes
     TLManagerNode(Seq(TLManagerPortParameters(
       Seq(TLManagerParameters(
         address         = Seq(AddressSet(itimAddr, size-1)),
@@ -64,7 +64,7 @@ class ICacheBundle(outer: ICache) extends CoreBundle()(outer.p) {
   val s1_kill = Bool(INPUT) // delayed one cycle w.r.t. req
   val s2_kill = Bool(INPUT) // delayed two cycles; prevents I$ miss emission
 
-  val resp = Valid(UInt(width = coreInstBits * fetchWidth))
+  val resp = Valid(UInt(width = outer.icacheParams.fetchBytes*8))
   val invalidate = Bool(INPUT)
   val tl_out = outer.masterNode.bundleOut
   val tl_in = outer.slaveNode.map(_.bundleIn)
@@ -79,6 +79,8 @@ object GetPropertyByHartId {
 
 class ICacheModule(outer: ICache) extends LazyModuleImp(outer)
     with HasL1ICacheParameters {
+  override val cacheParams = outer.icacheParams // Use the local parameters
+
   val io = new ICacheBundle(outer)
   val edge_out = outer.masterNode.edgesOut.head
   val tl_out = io.tl_out.head
@@ -89,7 +91,6 @@ class ICacheModule(outer: ICache) extends LazyModuleImp(outer)
   val dECC = cacheParams.dataECC
 
   require(isPow2(nSets) && isPow2(nWays))
-  require(isPow2(coreInstBytes))
   require(!usingVM || pgIdxBits >= untagBits)
 
   val scratchpadOn = RegInit(false.B)
@@ -161,7 +162,7 @@ class ICacheModule(outer: ICache) extends LazyModuleImp(outer)
   }
 
   val s1_tag_disparity = Wire(Vec(nWays, Bool()))
-  val wordBits = coreInstBits * fetchWidth
+  val wordBits = outer.icacheParams.fetchBytes*8
   val s1_dout = Wire(Vec(nWays, UInt(width = dECC.width(wordBits))))
 
   val s0_slaveAddr = tl_in.map(_.a.bits.address).getOrElse(0.U)
@@ -204,7 +205,7 @@ class ICacheModule(outer: ICache) extends LazyModuleImp(outer)
   }
 
   // output signals
-  outer.latency match {
+  outer.icacheParams.latency match {
     case 1 =>
       require(tECC.isInstanceOf[uncore.util.IdentityCode])
       require(dECC.isInstanceOf[uncore.util.IdentityCode])