diff --git a/cmake/Platform/aarch64-rtems6.cmake b/cmake/Platform/aarch64-rtems6.cmake
new file mode 100644
index 000000000..1d6b84007
--- /dev/null
+++ b/cmake/Platform/aarch64-rtems6.cmake
@@ -0,0 +1,3 @@
+add_compile_options("-mcpu=cortex-a72" "-I/opt/rtems/6/aarch64-rtems6/a72_lp64_qemu/lib/include" "-I/home/mohr/data/git/fsfw/unittests/testcfg/rtems/include")
+
+add_link_options("-B/opt/rtems/6/aarch64-rtems6/a72_lp64_qemu/lib" "-qrtems")
diff --git a/src/fsfw/osal/rtems/CpuUsage.cpp b/src/fsfw/osal/rtems/CpuUsage.cpp
index 4ffc22717..776d3586b 100644
--- a/src/fsfw/osal/rtems/CpuUsage.cpp
+++ b/src/fsfw/osal/rtems/CpuUsage.cpp
@@ -93,8 +93,8 @@ ReturnValue_t CpuUsage::serialize(uint8_t** buffer, size_t* size, size_t maxSize
                                                        streamEndianness);
 }
 
-uint32_t CpuUsage::getSerializedSize() const {
-  uint32_t size = 0;
+size_t CpuUsage::getSerializedSize() const {
+  size_t size = 0;
 
   size += sizeof(timeSinceLastReset);
   size += SerialArrayListAdapter<ThreadData>::getSerializedSize(&threadData);
@@ -136,8 +136,8 @@ ReturnValue_t CpuUsage::ThreadData::serialize(uint8_t** buffer, size_t* size, si
   return returnvalue::OK;
 }
 
-uint32_t CpuUsage::ThreadData::getSerializedSize() const {
-  uint32_t size = 0;
+size_t CpuUsage::ThreadData::getSerializedSize() const {
+  size_t size = 0;
 
   size += sizeof(id);
   size += MAX_LENGTH_OF_THREAD_NAME;
diff --git a/src/fsfw/osal/rtems/InternalErrorCodes.cpp b/src/fsfw/osal/rtems/InternalErrorCodes.cpp
index 9e0c1ae77..659840f9c 100644
--- a/src/fsfw/osal/rtems/InternalErrorCodes.cpp
+++ b/src/fsfw/osal/rtems/InternalErrorCodes.cpp
@@ -35,10 +35,9 @@ ReturnValue_t InternalErrorCodes::translate(uint8_t code) {
       return OUT_OF_PROXIES;
     case INTERNAL_ERROR_INVALID_GLOBAL_ID:
       return INVALID_GLOBAL_ID;
-#ifndef STM32H743ZI_NUCLEO
-    case INTERNAL_ERROR_BAD_STACK_HOOK:
-      return BAD_STACK_HOOK;
-#endif
+    //TODO this one is not there anymore in rtems-6 (5 as well?)
+    //case INTERNAL_ERROR_BAD_STACK_HOOK:
+    //  return BAD_STACK_HOOK;
       //	case INTERNAL_ERROR_BAD_ATTRIBUTES:
       //		return BAD_ATTRIBUTES;
       //	case INTERNAL_ERROR_IMPLEMENTATION_KEY_CREATE_INCONSISTENCY:
diff --git a/src/fsfw/timemanager/TimeReaderIF.h b/src/fsfw/timemanager/TimeReaderIF.h
index aa64b7548..b66f470fb 100644
--- a/src/fsfw/timemanager/TimeReaderIF.h
+++ b/src/fsfw/timemanager/TimeReaderIF.h
@@ -3,6 +3,8 @@
 
 #include <cstdio>
 #include <cstdlib>
+#include <sys/time.h>
+
 
 #include "fsfw/platform.h"
 
diff --git a/unittests/CatchRunner.cpp b/unittests/CatchRunner.cpp
index a25d523d6..b6017b430 100644
--- a/unittests/CatchRunner.cpp
+++ b/unittests/CatchRunner.cpp
@@ -43,6 +43,44 @@ void unittestTaskFunction(void* pvParameters) {
 }
 #endif
 
+#ifdef FSFW_OSAL_RTEMS
+#include <signal.h>
+
+int sigaltstack(const stack_t * ss, stack_t * old_ss){
+  return 0;
+}
+extern "C" {
+
+#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
+#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
+
+#define CONFIGURE_UNLIMITED_OBJECTS
+#define CONFIGURE_UNIFIED_WORK_AREAS
+
+#define CONFIGURE_RTEMS_INIT_TASKS_TABLE
+
+#define CONFIGURE_INIT
+
+#include <rtems/confdefs.h>
+
+
+#include <rtems.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+rtems_task Init(
+  rtems_task_argument ignored
+)
+{
+  printf( "\nHello World\n" );
+  char* argv[] = {"fsfw-test"};
+  int result = Catch::Session().run(1, argv);
+  exit( result );
+}
+
+}
+#endif
+
 int main(int argc, char* argv[]) {
   customSetup();
 
diff --git a/unittests/testcfg/rtems/cmake/rtems-qemu-toolchain.cmake b/unittests/testcfg/rtems/cmake/rtems-qemu-toolchain.cmake
new file mode 100644
index 000000000..b75ca5d0d
--- /dev/null
+++ b/unittests/testcfg/rtems/cmake/rtems-qemu-toolchain.cmake
@@ -0,0 +1,23 @@
+# the name of the target operating system
+set(CMAKE_SYSTEM_NAME aarch64-rtems6)
+
+set(CMAKE_SYSTEM_PROCESSOR a72)
+
+# which compilers to use for C and C++
+set(CMAKE_C_COMPILER   aarch64-rtems6-gcc)
+set(CMAKE_CXX_COMPILER aarch64-rtems6-g++)
+
+set(CMAKE_C_COMPILER_WORKS 1)
+set(CMAKE_CXX_COMPILER_WORKS 1)
+
+# where is the target environment located
+#set(CMAKE_FIND_ROOT_PATH  /usr/i586-mingw32msvc
+#    /home/alex/mingw-install)
+
+# adjust the default behavior of the FIND_XXX() commands:
+# search programs in the host environment
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+
+# search headers and libraries in the target environment
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
diff --git a/unittests/testcfg/rtems/include/cmath b/unittests/testcfg/rtems/include/cmath
new file mode 100644
index 000000000..a62ea66ba
--- /dev/null
+++ b/unittests/testcfg/rtems/include/cmath
@@ -0,0 +1,39 @@
+#pragma once
+
+#include_next <cmath>
+
+extern "C++"
+{
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+
+#undef lround
+#undef erfc
+#undef round
+
+
+using ::lround;
+
+long
+  lround(float __x);
+
+  constexpr long
+  lround(long double __x);
+
+using ::erfc;
+  
+constexpr float
+  erfc(float __x);
+
+  constexpr long double
+  erfc(long double __x);
+  
+  constexpr float
+  round(float __x);
+
+  using ::round;
+  
+  constexpr long double
+  round(long double __x);
+}
+}