OSCPU · good-circle · Sep 18, 2026 · Sep 19, 2026
diff --git a/difftest b/difftest
diff --git a/src/main/scala/nutcore/NutCoreTrap.scala b/src/main/scala/nutcore/NutCoreTrap.scala
@@ -25,6 +25,9 @@ object NutCoreTrap extends HasInstrType {
   def StateInvOpcode = 2.U
   def StateRunning   = 3.U
 
+  // custom-trap: opcode=1101011, funct3=000. Matches NEMU nemu_trap (e.g. 0x0005006b).
+  // DUT executes it as add (typically rd=x0). DiffTest uses a0 to tell control
+  // markers (0x100/0x101, keep running) from exit codes (0/1, stop the sim).
   def TRAP    = BitPat("b????????????_?????_000_?????_1101011")
   val table = Array(TRAP -> List(InstrI, FuType.alu, ALUOpType.add))
 }

diff --git a/src/main/scala/nutcore/backend/ooo/ROB.scala b/src/main/scala/nutcore/backend/ooo/ROB.scala
@@ -504,7 +504,8 @@ class ROB(implicit val p: NutCoreConfig) extends NutCoreModule with HasInstrType
       difftest_commit.valid    := (if (i == 0) retireATerm else retireMultiTerms)
       difftest_commit.pc       := SignExt(decode(ringBufferTail)(i).cf.pc, AddrBits)
       difftest_commit.instr    := decode(ringBufferTail)(i).cf.instr
-      difftest_commit.skip     := isMMIO(ringBufferTail)(i) && valid(ringBufferTail)(i)
+      // DiffTest still stops the sim on a0=0/1; otherwise skip comparison.
+      difftest_commit.skip     := (isMMIO(ringBufferTail)(i) || decode(ringBufferTail)(i).ctrl.isNutCoreTrap) && valid(ringBufferTail)(i)
       difftest_commit.isRVC    := decode(ringBufferTail)(i).cf.isRVC
       difftest_commit.rfwen    := io.wb(i).rfWen && io.wb(i).rfDest =/= 0.U // && valid(ringBufferTail)(i) && commited(ringBufferTail)(i)
       difftest_commit.fpwen    := false.B

diff --git a/src/main/scala/nutcore/backend/seq/EXU.scala b/src/main/scala/nutcore/backend/seq/EXU.scala
@@ -90,6 +90,7 @@ class EXU(implicit val p: NutCoreConfig) extends NutCoreModule {
     o.rfWen := i.rfWen && (!lsuTlbPF && !lsu.io.loadAddrMisaligned && !lsu.io.storeAddrMisaligned || !fuValids(FuType.lsu)) && !(csr.io.wenFix && fuValids(FuType.csr))
     o.rfDest := i.rfDest
     o.fuType := i.fuType
+    o.isNutCoreTrap := i.isNutCoreTrap
   }
   io.out.bits.decode.cf.pc := io.in.bits.cf.pc
   io.out.bits.decode.cf.instr := io.in.bits.cf.instr

diff --git a/src/main/scala/nutcore/backend/seq/WBU.scala b/src/main/scala/nutcore/backend/seq/WBU.scala
@@ -51,7 +51,8 @@ class WBU(implicit val p: NutCoreConfig) extends NutCoreModule{
     difftest_commit.valid  := io.in.valid
     difftest_commit.pc     := SignExt(io.in.bits.decode.cf.pc, AddrBits)
     difftest_commit.instr  := io.in.bits.decode.cf.instr
-    difftest_commit.skip   := io.in.bits.isMMIO
+    // DiffTest still stops the sim on a0=0/1; otherwise skip comparison.
+    difftest_commit.skip   := io.in.bits.isMMIO || io.in.bits.decode.ctrl.isNutCoreTrap
     difftest_commit.isRVC  := io.in.bits.decode.cf.instr(1,0)=/="b11".U
     difftest_commit.rfwen  := io.wb.rfWen && io.wb.rfDest =/= 0.U // && valid(ringBufferTail)(i) && commited(ringBufferTail)(i)
     difftest_commit.fpwen  := false.B
+73 −8		src/test/csrc/difftest/checkers/matrix.cpp
+7 −0		src/test/csrc/difftest/difftest.h
+34 −4		src/test/csrc/difftest/refproxy.h
+2 −2		verilator.mk