Update rvv_idle signal to include frontend and fix mpause dispatch.

Change-Id: I98c613ccf3609cbb4d8dccca7bd2c86a4d85c85f

hdl/chisel/src/kelvin/scalar/Decode.scala

diff --git a/hdl/chisel/src/kelvin/scalar/Decode.scala b/hdl/chisel/src/kelvin/scalar/Decode.scala
index 828666c..5553453 100644
--- a/hdl/chisel/src/kelvin/scalar/Decode.scala
+++ b/hdl/chisel/src/kelvin/scalar/Decode.scala
@@ -205,6 +205,12 @@
   def isVector(): Bool = { vld || vst || viop || getvl || getmaxvl }
   def isFency(): Bool = { fencei || ebreak || wfi || mpause || flushat || flushall }
 
+  // Instructions that should dispatch out of slot 0, with no other instructions
+  // dispatched on the same cycle.
+  def forceSlot0Only(): Bool = {
+    isFency() || isCsr()
+  }
+
   // Checks if an instruction is a jump or changes context switch. Instructions
   // after these should not be executed on the same cycle.
   def isJump(): Bool = {
@@ -422,12 +428,12 @@
   val fence = decodedInsts.map(x => x.isFency() && (io.mactive || io.lsuActive))
 
   // ---------------------------------------------------------------------------
-  // Csr interlock
-  val csrInterlock = (0 until p.instructionLanes).map(i =>
+  // Slot 0 interlock
+  val slot0Interlock = (0 until p.instructionLanes).map(i =>
     if (i == 0) {
       true.B
     } else {
-      !decodedInsts(0).isCsr()
+      !decodedInsts(0).forceSlot0Only() && !decodedInsts(i).forceSlot0Only()
     }
   )
 
@@ -518,6 +524,10 @@
     !io.single_step.getOrElse(false.B) || ((i == 0).B && coreIdle))
 
   // ---------------------------------------------------------------------------
+  // MPAUSE
+  val mpauseInterlock = decodedInsts.map(x => (!x.mpause || coreIdle))
+
+  // ---------------------------------------------------------------------------
   // Combine above rules. This variable represents which instructions can be
   // dispatched before in-orderness and back-pressure are considered.
   val canDispatch = (0 until p.instructionLanes).map(i =>
@@ -531,7 +541,7 @@
       !floatWriteAfterWrite(i) && // Avoid WAW hazards
       !branchInterlock(i) && // Only branch/alu can be dispatched after a branch
       !fence(i) &&           // Don't dispatch if fence interlocked
-      csrInterlock(i) &&
+      slot0Interlock(i) &&   // Special instructions execute out of slot 0 only
       rvvConfigInterlock(i) &&     // Rvv interlock rules
       rvvReductionInterlock(i) && // Don't dispatch reduction if vstart != 0
       // rvvLsuInterlock(i) &&  // Dispatch only one Rvv LsuOp
@@ -539,7 +549,8 @@
       rvvInterlock(i) && // Ensure rvv instructions can be dispatched into queue
       !undefInterlock(i) &&     // Ensure undef is only dispatched from first slot
       io.retirement_buffer_nSpace.map(x => i.U < x).getOrElse(true.B) && // Retirement buffer needs space for our slot
-      singleStepInterlock(i)
+      singleStepInterlock(i) &&
+      mpauseInterlock(i)
   )
 
   // ---------------------------------------------------------------------------

hdl/verilog/rvv/design/RvvCore.sv

diff --git a/hdl/verilog/rvv/design/RvvCore.sv b/hdl/verilog/rvv/design/RvvCore.sv
index f7f1642..fdd885a 100644
--- a/hdl/verilog/rvv/design/RvvCore.sv
+++ b/hdl/verilog/rvv/design/RvvCore.sv
@@ -192,6 +192,8 @@
   assign rd_rob2rt_o = rd_rob2rt;
 
   logic   [`ISSUE_LANE-1:0] insts_ready_cq2rvs;
+  logic rvv_backend_idle;
+  assign rvv_idle = rvv_backend_idle && (frontend_cmd_valid == 0);
   rvv_backend backend(
       .clk(clk),
       .rst_n(rstn),
@@ -219,7 +221,7 @@
       .vcsr_valid(vcsr_valid),
       .vector_csr(vector_csr),
       .vcsr_ready(vcsr_ready),
-      .rvv_idle(rvv_idle),
+      .rvv_idle(rvv_backend_idle),
       .rd_rob2rt_o(rd_rob2rt)
   );