diff --git a/lib/Target/MSP430/MSP430ISelLowering.cpp b/lib/Target/MSP430/MSP430ISelLowering.cpp
index 5c4ccc8..801129a 100644
--- a/lib/Target/MSP430/MSP430ISelLowering.cpp
+++ b/lib/Target/MSP430/MSP430ISelLowering.cpp
@@ -254,6 +254,13 @@
   case CallingConv::C:
   case CallingConv::Fast:
     return LowerCCCArguments(Chain, CallConv, isVarArg, Ins, dl, DAG, InVals);
+  case CallingConv::MSP430_INTR:
+   if (Ins.empty())
+     return Chain;
+   else {
+    llvm_report_error("ISRs cannot have arguments");
+    return SDValue();
+   }
   }
 }
 
@@ -273,6 +280,9 @@
   case CallingConv::C:
     return LowerCCCCallTo(Chain, Callee, CallConv, isVarArg, isTailCall,
                           Outs, Ins, dl, DAG, InVals);
+  case CallingConv::MSP430_INTR:
+    llvm_report_error("ISRs cannot be called directly");
+    return SDValue();
   }
 }
 
@@ -369,6 +379,12 @@
   // CCValAssign - represent the assignment of the return value to a location
   SmallVector<CCValAssign, 16> RVLocs;
 
+  // ISRs cannot return any value.
+  if (CallConv == CallingConv::MSP430_INTR && !Outs.empty()) {
+    llvm_report_error("ISRs cannot return any value");
+    return SDValue();
+  }
+
   // CCState - Info about the registers and stack slot.
   CCState CCInfo(CallConv, isVarArg, getTargetMachine(),
                  RVLocs, *DAG.getContext());
@@ -399,11 +415,14 @@
     Flag = Chain.getValue(1);
   }
 
+  unsigned Opc = (CallConv == CallingConv::MSP430_INTR ?
+                  MSP430ISD::RETI_FLAG : MSP430ISD::RET_FLAG);
+
   if (Flag.getNode())
-    return DAG.getNode(MSP430ISD::RET_FLAG, dl, MVT::Other, Chain, Flag);
+    return DAG.getNode(Opc, dl, MVT::Other, Chain, Flag);
 
   // Return Void
-  return DAG.getNode(MSP430ISD::RET_FLAG, dl, MVT::Other, Chain);
+  return DAG.getNode(Opc, dl, MVT::Other, Chain);
 }
 
 /// LowerCCCCallTo - functions arguments are copied from virtual regs to
diff --git a/lib/Target/MSP430/MSP430ISelLowering.h b/lib/Target/MSP430/MSP430ISelLowering.h
index d413ccb..6a1a73e 100644
--- a/lib/Target/MSP430/MSP430ISelLowering.h
+++ b/lib/Target/MSP430/MSP430ISelLowering.h
@@ -27,6 +27,9 @@
       /// Return with a flag operand. Operand 0 is the chain operand.
       RET_FLAG,
 
+      /// Same as RET_FLAG, but used for returning from ISRs.
+      RETI_FLAG,
+
       /// Y = R{R,L}A X, rotate right (left) arithmetically
       RRA, RLA,
 
diff --git a/lib/Target/MSP430/MSP430InstrInfo.td b/lib/Target/MSP430/MSP430InstrInfo.td
index 7a26f6c..3ce0a66 100644
--- a/lib/Target/MSP430/MSP430InstrInfo.td
+++ b/lib/Target/MSP430/MSP430InstrInfo.td
@@ -35,8 +35,10 @@
 //===----------------------------------------------------------------------===//
 // MSP430 Specific Node Definitions.
 //===----------------------------------------------------------------------===//
-def MSP430retflag : SDNode<"MSP430ISD::RET_FLAG", SDTNone,
-                     [SDNPHasChain, SDNPOptInFlag]>;
+def MSP430retflag  : SDNode<"MSP430ISD::RET_FLAG", SDTNone,
+                       [SDNPHasChain, SDNPOptInFlag]>;
+def MSP430retiflag : SDNode<"MSP430ISD::RETI_FLAG", SDTNone,
+                       [SDNPHasChain, SDNPOptInFlag]>;
 
 def MSP430rra     : SDNode<"MSP430ISD::RRA", SDTIntUnaryOp, []>;
 def MSP430rla     : SDNode<"MSP430ISD::RLA", SDTIntUnaryOp, []>;
@@ -128,7 +130,8 @@
 
 // FIXME: Provide proper encoding!
 let isReturn = 1, isTerminator = 1, isBarrier = 1 in {
-  def RET : Pseudo<(outs), (ins), "ret", [(MSP430retflag)]>;
+  def RET  : Pseudo<(outs), (ins), "ret",  [(MSP430retflag)]>;
+  def RETI : Pseudo<(outs), (ins), "reti", [(MSP430retiflag)]>;
 }
 
 let isBranch = 1, isTerminator = 1 in {
diff --git a/lib/Target/MSP430/MSP430RegisterInfo.cpp b/lib/Target/MSP430/MSP430RegisterInfo.cpp
index 7178440..e85c7a2 100644
--- a/lib/Target/MSP430/MSP430RegisterInfo.cpp
+++ b/lib/Target/MSP430/MSP430RegisterInfo.cpp
@@ -17,6 +17,7 @@
 #include "MSP430MachineFunctionInfo.h"
 #include "MSP430RegisterInfo.h"
 #include "MSP430TargetMachine.h"
+#include "llvm/Function.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
@@ -37,17 +38,26 @@
 
 const unsigned*
 MSP430RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
+  const Function* F = MF->getFunction();
   static const unsigned CalleeSavedRegs[] = {
     MSP430::FPW, MSP430::R5W, MSP430::R6W, MSP430::R7W,
     MSP430::R8W, MSP430::R9W, MSP430::R10W, MSP430::R11W,
     0
   };
+  static const unsigned CalleeSavedRegsIntr[] = {
+    MSP430::FPW,  MSP430::R5W,  MSP430::R6W,  MSP430::R7W,
+    MSP430::R8W,  MSP430::R9W,  MSP430::R10W, MSP430::R11W,
+    MSP430::R12W, MSP430::R13W, MSP430::R14W, MSP430::R15W,
+    0
+  };
 
-  return CalleeSavedRegs;
+  return (F->getCallingConv() == CallingConv::MSP430_INTR ?
+          CalleeSavedRegsIntr : CalleeSavedRegs);
 }
 
 const TargetRegisterClass *const *
 MSP430RegisterInfo::getCalleeSavedRegClasses(const MachineFunction *MF) const {
+  const Function* F = MF->getFunction();
   static const TargetRegisterClass * const CalleeSavedRegClasses[] = {
     &MSP430::GR16RegClass, &MSP430::GR16RegClass,
     &MSP430::GR16RegClass, &MSP430::GR16RegClass,
@@ -55,8 +65,18 @@
     &MSP430::GR16RegClass, &MSP430::GR16RegClass,
     0
   };
+  static const TargetRegisterClass * const CalleeSavedRegClassesIntr[] = {
+    &MSP430::GR16RegClass, &MSP430::GR16RegClass,
+    &MSP430::GR16RegClass, &MSP430::GR16RegClass,
+    &MSP430::GR16RegClass, &MSP430::GR16RegClass,
+    &MSP430::GR16RegClass, &MSP430::GR16RegClass,
+    &MSP430::GR16RegClass, &MSP430::GR16RegClass,
+    &MSP430::GR16RegClass, &MSP430::GR16RegClass,
+    0
+  };
 
-  return CalleeSavedRegClasses;
+  return (F->getCallingConv() == CallingConv::MSP430_INTR ?
+          CalleeSavedRegClassesIntr : CalleeSavedRegClasses);
 }
 
 BitVector MSP430RegisterInfo::getReservedRegs(const MachineFunction &MF) const {
@@ -292,7 +312,8 @@
   DebugLoc DL = MBBI->getDebugLoc();
 
   switch (RetOpcode) {
-  case MSP430::RET: break;  // These are ok
+  case MSP430::RET:
+  case MSP430::RETI: break;  // These are ok
   default:
     llvm_unreachable("Can only insert epilog into returning blocks");
   }