csr: allow for superscalar decode (#1069)

* CSR provides a decode port to check for an illegal instruction.
   * This commit now allows for multiple instructions in decode to get this
      illegal instruction information.
   * This commit leverages the existing decodeWidth parameter. This will
      potentially over-provision the number of decode ports needed for
      RVC-enabled cores.

Closes #1068

src/main/scala/rocket/CSR.scala

@@ -160,6 +160,16 @@ class TracedInstruction(implicit p: Parameters) extends CoreBundle {
   val tval = UInt(width = coreMaxAddrBits max iLen)
 }
 
+class CSRDecodeIO extends Bundle {
+  val csr = UInt(INPUT, CSR.ADDRSZ)
+  val fp_illegal = Bool(OUTPUT)
+  val rocc_illegal = Bool(OUTPUT)
+  val read_illegal = Bool(OUTPUT)
+  val write_illegal = Bool(OUTPUT)
+  val write_flush = Bool(OUTPUT)
+  val system_illegal = Bool(OUTPUT)
+}
+
 class CSRFileIO(implicit p: Parameters) extends CoreBundle
     with HasCoreParameters {
   val interrupts = new TileInterrupts().asInput
@@ -171,15 +181,7 @@ class CSRFileIO(implicit p: Parameters) extends CoreBundle
     val wdata = Bits(INPUT, xLen)
   }
 
-  val decode = new Bundle {
+  val decode = Vec(decodeWidth, new CSRDecodeIO)
-    val csr = UInt(INPUT, CSR.ADDRSZ)
-    val fp_illegal = Bool(OUTPUT)
-    val rocc_illegal = Bool(OUTPUT)
-    val read_illegal = Bool(OUTPUT)
-    val write_illegal = Bool(OUTPUT)
-    val write_flush = Bool(OUTPUT)
-    val system_illegal = Bool(OUTPUT)
-  }
 
   val csr_stall = Bool(OUTPUT)
   val eret = Bool(OUTPUT)
@@ -453,24 +455,26 @@ class CSRFile(perfEventSets: EventSets = new EventSets(Seq()))(implicit p: Param
   val insn_ret = system_insn && opcode(2)
   val insn_wfi = system_insn && opcode(5)
 
-  private def decodeAny(m: LinkedHashMap[Int,Bits]): Bool = m.map { case(k: Int, _: Bits) => io.decode.csr === k }.reduce(_||_)
+  for (io_dec <- io.decode) {
+    def decodeAny(m: LinkedHashMap[Int,Bits]): Bool = m.map { case(k: Int, _: Bits) => io_dec.csr === k }.reduce(_||_)
     val allow_wfi = Bool(!usingVM) || reg_mstatus.prv > PRV.S || !reg_mstatus.tw
     val allow_sfence_vma = Bool(!usingVM) || reg_mstatus.prv > PRV.S || !reg_mstatus.tvm
     val allow_sret = Bool(!usingVM) || reg_mstatus.prv > PRV.S || !reg_mstatus.tsr
-  io.decode.fp_illegal := io.status.fs === 0 || !reg_misa('f'-'a')
+    io_dec.fp_illegal := io.status.fs === 0 || !reg_misa('f'-'a')
-  io.decode.rocc_illegal := io.status.xs === 0 || !reg_misa('x'-'a')
+    io_dec.rocc_illegal := io.status.xs === 0 || !reg_misa('x'-'a')
-  io.decode.read_illegal := reg_mstatus.prv < io.decode.csr(9,8) ||
+    io_dec.read_illegal := reg_mstatus.prv < io_dec.csr(9,8) ||
       !decodeAny(read_mapping) ||
-    io.decode.csr === CSRs.sptbr && !allow_sfence_vma ||
+      io_dec.csr === CSRs.sptbr && !allow_sfence_vma ||
-    (io.decode.csr.inRange(CSR.firstCtr, CSR.firstCtr + CSR.nCtr) || io.decode.csr.inRange(CSR.firstCtrH, CSR.firstCtrH + CSR.nCtr)) && reg_mstatus.prv <= PRV.S && hpm_mask(io.decode.csr(log2Ceil(CSR.firstCtr)-1,0)) ||
+      (io_dec.csr.inRange(CSR.firstCtr, CSR.firstCtr + CSR.nCtr) || io_dec.csr.inRange(CSR.firstCtrH, CSR.firstCtrH + CSR.nCtr)) && reg_mstatus.prv <= PRV.S && hpm_mask(io_dec.csr(log2Ceil(CSR.firstCtr)-1,0)) ||
       Bool(usingDebug) && decodeAny(debug_csrs) && !reg_debug ||
-    Bool(usingFPU) && decodeAny(fp_csrs) && io.decode.fp_illegal
+      Bool(usingFPU) && decodeAny(fp_csrs) && io_dec.fp_illegal
-  io.decode.write_illegal := io.decode.csr(11,10).andR
+    io_dec.write_illegal := io_dec.csr(11,10).andR
-  io.decode.write_flush := !(io.decode.csr >= CSRs.mscratch && io.decode.csr <= CSRs.mbadaddr || io.decode.csr >= CSRs.sscratch && io.decode.csr <= CSRs.sbadaddr)
+    io_dec.write_flush := !(io_dec.csr >= CSRs.mscratch && io_dec.csr <= CSRs.mbadaddr || io_dec.csr >= CSRs.sscratch && io_dec.csr <= CSRs.sbadaddr)
-  io.decode.system_illegal := reg_mstatus.prv < io.decode.csr(9,8) ||
+    io_dec.system_illegal := reg_mstatus.prv < io_dec.csr(9,8) ||
-    !io.decode.csr(5) && io.decode.csr(2) && !allow_wfi ||
+      !io_dec.csr(5) && io_dec.csr(2) && !allow_wfi ||
-    !io.decode.csr(5) && io.decode.csr(1) && !allow_sret ||
+      !io_dec.csr(5) && io_dec.csr(1) && !allow_sret ||
-    io.decode.csr(5) && !allow_sfence_vma
+      io_dec.csr(5) && !allow_sfence_vma
+  }
 
   val cause =
     Mux(insn_call, reg_mstatus.prv + Causes.user_ecall,

src/main/scala/rocket/RocketCore.scala

@@ -200,17 +200,17 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p)
   val id_csr_ren = id_ctrl.csr.isOneOf(CSR.S, CSR.C) && id_raddr1 === UInt(0)
   val id_csr = Mux(id_csr_ren, CSR.R, id_ctrl.csr)
   val id_sfence = id_ctrl.mem && id_ctrl.mem_cmd === M_SFENCE
-  val id_csr_flush = id_sfence || id_system_insn || (id_csr_en && !id_csr_ren && csr.io.decode.write_flush)
+  val id_csr_flush = id_sfence || id_system_insn || (id_csr_en && !id_csr_ren && csr.io.decode(0).write_flush)
 
   val id_illegal_insn = !id_ctrl.legal ||
     id_ctrl.div && !csr.io.status.isa('m'-'a') ||
     id_ctrl.amo && !csr.io.status.isa('a'-'a') ||
-    id_ctrl.fp && (csr.io.decode.fp_illegal || io.fpu.illegal_rm) ||
+    id_ctrl.fp && (csr.io.decode(0).fp_illegal || io.fpu.illegal_rm) ||
     id_ctrl.dp && !csr.io.status.isa('d'-'a') ||
     ibuf.io.inst(0).bits.rvc && !csr.io.status.isa('c'-'a') ||
-    id_ctrl.rocc && csr.io.decode.rocc_illegal ||
+    id_ctrl.rocc && csr.io.decode(0).rocc_illegal ||
-    id_csr_en && (csr.io.decode.read_illegal || !id_csr_ren && csr.io.decode.write_illegal) ||
+    id_csr_en && (csr.io.decode(0).read_illegal || !id_csr_ren && csr.io.decode(0).write_illegal) ||
-    !ibuf.io.inst(0).bits.rvc && ((id_sfence || id_system_insn) && csr.io.decode.system_illegal)
+    !ibuf.io.inst(0).bits.rvc && ((id_sfence || id_system_insn) && csr.io.decode(0).system_illegal)
   // stall decode for fences (now, for AMO.aq; later, for AMO.rl and FENCE)
   val id_amo_aq = id_inst(0)(26)
   val id_amo_rl = id_inst(0)(25)
@@ -508,7 +508,7 @@ class Rocket(implicit p: Parameters) extends CoreModule()(p)
   when (rf_wen) { rf.write(rf_waddr, rf_wdata) }
 
   // hook up control/status regfile
-  csr.io.decode.csr := id_raw_inst(0)(31,20)
+  csr.io.decode(0).csr := id_raw_inst(0)(31,20)
   csr.io.exception := wb_xcpt
   csr.io.cause := wb_cause
   csr.io.retire := wb_valid