diff --git a/src/cpu/o3/cpu.cc b/src/cpu/o3/cpu.cc
index 562a332..613ffd1 100644
--- a/src/cpu/o3/cpu.cc
+++ b/src/cpu/o3/cpu.cc
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2012, 2014, 2016, 2017, 2019 ARM Limited
+ * Copyright (c) 2011-2012, 2014, 2016, 2017, 2019-2020 ARM Limited
  * Copyright (c) 2013 Advanced Micro Devices, Inc.
  * All rights reserved
  *
@@ -1827,5 +1827,13 @@
     }
 }
 
+template <class Impl>
+void
+FullO3CPU<Impl>::htmSendAbortSignal(ThreadID tid, uint64_t htmUid,
+     HtmFailureFaultCause cause)
+{
+    panic("not yet supported!");
+}
+
 // Forward declaration of FullO3CPU.
 template class FullO3CPU<O3CPUImpl>;
diff --git a/src/cpu/o3/cpu.hh b/src/cpu/o3/cpu.hh
index cc0e2cd..137fbc8 100644
--- a/src/cpu/o3/cpu.hh
+++ b/src/cpu/o3/cpu.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011-2013, 2016-2019 ARM Limited
+ * Copyright (c) 2011-2013, 2016-2020 ARM Limited
  * Copyright (c) 2013 Advanced Micro Devices, Inc.
  * All rights reserved
  *
@@ -788,6 +788,11 @@
     //number of misc
     Stats::Scalar miscRegfileReads;
     Stats::Scalar miscRegfileWrites;
+
+  public:
+    // hardware transactional memory
+    void htmSendAbortSignal(ThreadID tid, uint64_t htm_uid,
+                            HtmFailureFaultCause cause);
 };
 
 #endif // __CPU_O3_CPU_HH__
diff --git a/src/cpu/simple/atomic.hh b/src/cpu/simple/atomic.hh
index 7333e1f..2d0a465 100644
--- a/src/cpu/simple/atomic.hh
+++ b/src/cpu/simple/atomic.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012-2013, 2015, 2018 ARM Limited
+ * Copyright (c) 2012-2013, 2015, 2018, 2020 ARM Limited
  * All rights reserved.
  *
  * The license below extends only to copyright in the software and shall
@@ -219,6 +219,18 @@
                   const std::vector<bool>& byte_enable = std::vector<bool>())
         override;
 
+    Fault initiateHtmCmd(Request::Flags flags) override
+    {
+        panic("initiateHtmCmd() is for timing accesses, and should "
+              "never be called on AtomicSimpleCPU.\n");
+    }
+
+    void htmSendAbortSignal(HtmFailureFaultCause cause) override
+    {
+        panic("htmSendAbortSignal() is for timing accesses, and should "
+              "never be called on AtomicSimpleCPU.\n");
+    }
+
     Fault writeMem(uint8_t *data, unsigned size,
                    Addr addr, Request::Flags flags, uint64_t *res,
                    const std::vector<bool>& byte_enable = std::vector<bool>())
diff --git a/src/cpu/simple/base.hh b/src/cpu/simple/base.hh
index 9f5bf66..82f52d9 100644
--- a/src/cpu/simple/base.hh
+++ b/src/cpu/simple/base.hh
@@ -176,6 +176,21 @@
     void serializeThread(CheckpointOut &cp, ThreadID tid) const override;
     void unserializeThread(CheckpointIn &cp, ThreadID tid) override;
 
+    /** Hardware transactional memory commands (HtmCmds), e.g. start a
+     * transaction and commit a transaction, are memory operations but are
+     * neither really (true) loads nor stores. For this reason the interface
+     * is extended and initiateHtmCmd() is used to instigate the command. */
+    virtual Fault initiateHtmCmd(Request::Flags flags) = 0;
+
+    /** This function is used to instruct the memory subsystem that a
+     * transaction should be aborted and the speculative state should be
+     * thrown away.  This is called in the transaction's very last breath in
+     * the core.  Afterwards, the core throws away its speculative state and
+     * resumes execution at the point the transaction started, i.e. reverses
+     * time.  When instruction execution resumes, the core expects the
+     * memory subsystem to be in a stable, i.e. pre-speculative, state as
+     * well. */
+    virtual void htmSendAbortSignal(HtmFailureFaultCause cause) = 0;
 };
 
 #endif // __CPU_SIMPLE_BASE_HH__
diff --git a/src/cpu/simple/timing.cc b/src/cpu/simple/timing.cc
index 84d7d0e..d3adbcc 100644
--- a/src/cpu/simple/timing.cc
+++ b/src/cpu/simple/timing.cc
@@ -1055,6 +1055,19 @@
     dcachePort.printAddr(a);
 }
 
+Fault
+TimingSimpleCPU::initiateHtmCmd(Request::Flags flags)
+{
+    panic("not yet supported!");
+    return NoFault;
+}
+
+void
+TimingSimpleCPU::htmSendAbortSignal(HtmFailureFaultCause cause)
+{
+    panic("not yet supported!");
+}
+
 
 ////////////////////////////////////////////////////////////////////////
 //
diff --git a/src/cpu/simple/timing.hh b/src/cpu/simple/timing.hh
index 2bb0fe6..c055896 100644
--- a/src/cpu/simple/timing.hh
+++ b/src/cpu/simple/timing.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012-2013,2015,2018 ARM Limited
+ * Copyright (c) 2012-2013,2015,2018,2020 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -320,6 +320,11 @@
      */
     void finishTranslation(WholeTranslationState *state);
 
+    /** hardware transactional memory **/
+    Fault initiateHtmCmd(Request::Flags flags) override;
+
+    void htmSendAbortSignal(HtmFailureFaultCause) override;
+
   private:
 
     EventFunctionWrapper fetchEvent;