diff --git a/extra_script.py b/extra_script.py
index 6650b29..95ccbb2 100644
--- a/extra_script.py
+++ b/extra_script.py
@@ -17,6 +17,7 @@ CFG_INCLUDE='GwConfigDefinitions.h'
 CFG_INCLUDE_IMPL='GwConfigDefImpl.h'
 XDR_INCLUDE='GwXdrTypeMappings.h'
 TASK_INCLUDE='GwUserTasks.h'
+TASK_INCLUDE_IF='GwUserTasksIf.h'
 EMBEDDED_INCLUDE="GwEmbeddedFiles.h"
 
 def getEmbeddedFiles(env):
@@ -219,23 +220,28 @@ def getUserTaskDirs():
     for task in taskdirs:
         rt.append(task)
     return rt
-def genereateUserTasks(outfile):
+
+def checkAndAdd(file,names,ilist):
+    if not file.endswith('.h'):
+        return
+    match=False
+    for cmp in names:
+        #print("##check %s<->%s"%(f.lower(),cmp))
+        if file.lower() == cmp:
+            match=True
+    if not match:
+        return
+    ilist.append(file) 
+def genereateUserTasks(outfile,forIf=False):
     includes=[]
     for task in userTaskDirs:
         #print("##taskdir=%s"%task)
         base=os.path.basename(task)
         includeNames=[base.lower()+".h",'gw'+base.lower()+'.h']
+        if forIf:
+            includeNames=["i"+base.lower()+".h",'gwi'+base.lower()+'.h']
         for f in os.listdir(task):
-            if not f.endswith('.h'):
-                continue
-            match=False
-            for cmp in includeNames:
-                #print("##check %s<->%s"%(f.lower(),cmp))
-                if f.lower() == cmp:
-                    match=True
-            if not match:
-                continue
-            includes.append(f)
+            checkAndAdd(f,includeNames,includes)
     includeData=""
     for i in includes:
         print("#task include %s"%i)
@@ -291,6 +297,7 @@ def prebuild(env):
             print("#WARNING: infile %s for %s not found"%(inFile,ef))
     generateEmbedded(filedefs,os.path.join(outPath(),EMBEDDED_INCLUDE))
     genereateUserTasks(os.path.join(outPath(), TASK_INCLUDE))
+    genereateUserTasks(os.path.join(outPath(), TASK_INCLUDE_IF),forIf=True)
     generateFile(os.path.join(basePath(),XDR_FILE),os.path.join(outPath(),XDR_INCLUDE),generateXdrMappings)
     version="dev"+datetime.now().strftime("%Y%m%d")
     env.Append(CPPDEFINES=[('GWDEVVERSION',version)])
diff --git a/lib/api/GwApi.h b/lib/api/GwApi.h
index 7fdf8cd..6fbad61 100644
--- a/lib/api/GwApi.h
+++ b/lib/api/GwApi.h
@@ -5,6 +5,7 @@
 #include "NMEA0183Msg.h"
 #include "GWConfig.h"
 #include "GwBoatData.h"
+#include <map>
 //API to be used for additional tasks
 class GwApi{
     public:
@@ -33,29 +34,31 @@ class GwApi{
                 }
         };
         /**
-         * a simple value container
-         * to exchange data between tasks
-        */
-        class Value{
-            long lvalue=0;
-            String svalue;
-            bool isString=false;
-            bool isValid=false;
+         * an interface for the data exchange between tasks
+         * the core part will not handle this data at all but
+         * this interface ensures that there is a correct locking of the
+         * data to correctly handle multi threading
+         * The user code should not use this intterface directly
+         * but instead it should use the static functions
+         * apiGetXXX(GwApi *,...)
+         * apiSetXXX(GwApi *,...)
+         * that will be created by the macro DECLARE_TASK_INTERFACE
+         */
+        class TaskInterfaces
+        {
+        public:
+            class Base
+            {
             public:
-            Value(const String &v){isString=true;svalue=v;isValid=true;}
-            Value(long l){lvalue=l;isValid=true;}
-            Value(){}
-            long getLValue() const{
-                if(!isString) return lvalue;
-                return atol(svalue.c_str());
-            }
-            String getSValue() const{
-                if(isString) return svalue;
-                return String(lvalue);
-            }
-            bool valid() const{return isValid;}
+                virtual ~Base()
+                {
+                }
+            };
+            using Ptr = std::shared_ptr<Base>;
+        public:
+            virtual bool iset(const String &file, const String &name, Ptr v) = 0;
+            virtual Ptr iget(const String &name, int &result) = 0;
         };
-
         class Status{
             public:
                 typedef enum{
@@ -156,14 +159,7 @@ class GwApi{
         virtual void increment(int idx,const String &name,bool failed=false){}
         virtual void reset(int idx){}
         virtual void remove(int idx){}
-
-        /**
-         * exchange data between different user tasks
-         * each task can set arbitrary items
-         * that can be accessed by other tasks
-        */
-        virtual void setTaskValue(const String &name,const Value &v){}
-        virtual Value getTaskValue(const String &taskName,const String &name){return Value();}
+        virtual TaskInterfaces * taskInterfaces()=0;
 
         /**
          * not thread safe methods
@@ -188,4 +184,58 @@ class GwApi{
 #ifndef DECLARE_STRING_CAPABILITY
 #define DECLARE_STRING_CAPABILITY(name,value)
 #endif
+/**
+ * macro to declare an interface that a task provides to other tasks
+ * this macro must be used in an File I<taskname>.h or GwI<taskname>.h
+ * the first parameter must be the name of the task that should be able
+ * to write this data (the same name as being used in DECLARE_TASK).
+ * The second parameter must be a type (class) that inherits from 
+ * GwApi::TaskInterfaces::Base.
+ * This class must provide copy constructors and empty constructors.
+ * The attributes should only be simple values or structs but no pointers.
+ * example:
+ * class TestTaskApi: public GwApi::TaskInterfaces::Base{
+ *      public:
+ *          int ival1=0;
+ *          int ival2=99;
+ *          String sval="unset";
+ * };
+ * DECLARE_TASKIF(testTask,TestTaskApi);
+ * The macro will generate 2 static funtions:
+ * 
+ * bool apiSetTestTaskApi(GwApi *api, const TestTaskApi &v);
+ * TestTaskApi apiGetTestTaskApi(GwApi *api, int &result);
+ * 
+ * The setter will return true on success.
+ * It is intended to be used by the task that did declare the api.
+ * The getter will set the result to -1 if no data is available, otherwise
+ * it will return the update count (so you can check if there was a change 
+ * compared to the last call).
+ * It is intended to be used by any task.
+ * Be aware that all the apis share a common namespace - so be sure to somehow
+ * make your API names unique.
+ * 
+ * 
+*/
+#define DECLARE_TASKIF_IMPL(task,type) \
+    static bool apiSet##type(GwApi *a,const type &v){ \
+        if (! a || ! a->taskInterfaces()) return false; \
+        return a->taskInterfaces()->iset(__FILE__,#type,GwApi::TaskInterfaces::Ptr(new type(v)));\
+    }\
+    static const type apiGet##type(GwApi *a, int &result) {\
+        if (! a || ! a->taskInterfaces()) {\
+            result=-1; \
+            return type(); \
+            }\
+        auto ptr=a->taskInterfaces()->iget(#type,result); \
+        if (!ptr) {\
+            result=-1; \
+            return type(); \
+        }\
+        type *tp=(type*)ptr.get(); \
+        return type(*tp); \
+    }
+#ifndef DECLARE_TASKIF
+    #define DECLARE_TASKIF(task,type) DECLARE_TASKIF_IMPL(task,type)
+#endif
 #endif
diff --git a/lib/exampletask/GwIExampleTask.h b/lib/exampletask/GwIExampleTask.h
new file mode 100644
index 0000000..b09a2f4
--- /dev/null
+++ b/lib/exampletask/GwIExampleTask.h
@@ -0,0 +1,14 @@
+#ifndef GWIEXAMPLETASK_H
+#define GWIEXAMPLETASK_H
+#include "GwApi.h"
+/**
+ * an interface for the example task
+*/
+class ExampleIf : public GwApi::TaskInterfaces::Base{
+    public:
+    long count=0;
+    String someValue;
+};
+DECLARE_TASKIF(exampleTask,ExampleIf);
+
+#endif
\ No newline at end of file
diff --git a/lib/usercode/GwUserCode.cpp b/lib/usercode/GwUserCode.cpp
index f5e9f97..4f12b03 100644
--- a/lib/usercode/GwUserCode.cpp
+++ b/lib/usercode/GwUserCode.cpp
@@ -17,7 +17,46 @@
 std::vector<GwUserTask> userTasks;
 std::vector<GwUserTask> initTasks;
 GwUserCode::Capabilities userCapabilities;
+class RegEntry{
+    public:
+    String file;
+    String task;
+    RegEntry(const String &t, const String &f):file(f),task(t){}
+    RegEntry(){}
+};
+using RegMap=std::map<String,RegEntry>;
+static RegMap &registrations(){
+    static RegMap *regMap=new RegMap();
+    return *regMap;
+} 
 
+static void registerInterface(const String &task,const String &file, const String &name){
+    auto it=registrations().find(name);
+    if (it != registrations().end()){
+        if (it->second.file != file){
+            ESP_LOGE("Assert","type %s redefined in %s original in %s",name,file,it->second.file);
+            std::abort(); 
+        };
+        if (it->second.task != task){
+            ESP_LOGE("Assert","type %s registered for multiple tasks %s and %s",name,task,it->second.task);
+            std::abort(); 
+        };
+    }   
+    else{
+        registrations()[name]=RegEntry(task,file);
+    }
+}
+
+class GwIreg{
+    public:
+        GwIreg(const String &task,const String &file, const String &name){
+            registerInterface(task,file,name);
+        }
+    };
+
+#define DECLARE_TASKIF(task,type) \
+    DECLARE_TASKIF_IMPL(task,type) \
+    GwIreg __register##type(#task,__FILE__,#type)
 
 
 class GwUserTaskDef{
@@ -46,44 +85,79 @@ class GwUserCapability{
         }
 };
 #include "GwUserTasks.h"
-class TaskData{
-    SemaphoreHandle_t lock;
-    std::map<String,GwApi::Value> data;
-    GwLog *logger;
-    String computeKey(const String &taskName,const String &name) const{
-        return taskName+":#:"+name;
-    }
-    public:
-    TaskData(GwLog *l){
-        lock=xSemaphoreCreateMutex();
-        logger=l;
-    }
-    ~TaskData(){
-        vSemaphoreDelete(lock);
-    }
-    void setTaskValue(const String &taskName,const String &name,const GwApi::Value &v){
-        String key=computeKey(taskName,name);
-        LOG_DEBUG(GwLog::DEBUG,"set task data %s=%s",key.c_str(),v.getSValue().c_str());
-        GWSYNCHRONIZED(&lock);
-        data[key]=v;
-    }
-    GwApi::Value getTaskValue(const String &taskName,const String &name){
-        GwApi::Value rt;
-        String key=computeKey(taskName,name);
-        {
-            GWSYNCHRONIZED(&lock);
-            auto it=data.find(key);
-            if (it != data.end()) rt=it->second;
-        }
-        LOG_DEBUG(GwLog::DEBUG,"get task data %s:%s (valid=%d)",key.c_str(),rt.getSValue().c_str(),(int)rt.valid());
-        return rt;
-    }
+#include "GwUserTasksIf.h"
 
+class TaskDataEntry{
+        public:
+        GwApi::TaskInterfaces::Ptr ptr;
+        int updates=0;
+        TaskDataEntry(GwApi::TaskInterfaces::Ptr p):ptr(p){}
+        TaskDataEntry(){}
+    };
+class TaskInterfacesStorage{
+   GwLog *logger;
+    SemaphoreHandle_t lock;
+    std::map<String,TaskDataEntry> values;
+    public:
+        TaskInterfacesStorage(GwLog* l):
+            logger(l){
+                lock=xSemaphoreCreateMutex();
+            }
+        bool set(const String &file, const String &name, const String &task,GwApi::TaskInterfaces::Ptr v){
+            GWSYNCHRONIZED(&lock);
+            auto it=registrations().find(name);
+            if (it == registrations().end()){
+                LOG_DEBUG(GwLog::ERROR,"invalid set %s not known",name.c_str());
+                return false;
+            }
+            if (it->second.file != file){
+                LOG_DEBUG(GwLog::ERROR,"invalid set %s wrong file, expected %s , got %s",name.c_str(),it->second.file.c_str(),file.c_str());
+                return false;
+            }
+            if (it->second.task != task){
+                LOG_DEBUG(GwLog::ERROR,"invalid set %s wrong task, expected %s , got %s",name.c_str(),it->second.task.c_str(),task.c_str());
+                return false;
+            }
+            auto vit=values.find(name);
+            if (vit != values.end()){
+                vit->second.updates++;
+                vit->second.ptr=v;
+            }
+            else{
+                values[name]=TaskDataEntry(v);
+            }
+            return true;
+        }
+        GwApi::TaskInterfaces::Ptr get(const String &name, int &result){
+            GWSYNCHRONIZED(&lock);
+            auto it = values.find(name);
+            if (it == values.end())
+            {
+                result = -1;
+                return GwApi::TaskInterfaces::Ptr();
+            }
+            result = it->second.updates;
+            return it->second.ptr;
+        } 
+};    
+class TaskInterfacesImpl : public GwApi::TaskInterfaces{
+    String task;
+    TaskInterfacesStorage *storage;
+    public:
+        TaskInterfacesImpl(const String &n,TaskInterfacesStorage *s):
+            task(n),storage(s){}
+        virtual bool iset(const String &file, const String &name, Ptr v){
+            return storage->set(file,name,task,v);
+        }
+        virtual Ptr iget(const String &name, int &result){
+            return storage->get(name,result);
+        }
 };
+
+
 class TaskApi : public GwApiInternal
 {
     GwApiInternal *api=nullptr;
-    TaskData *taskData=nullptr;
     int sourceId;
     SemaphoreHandle_t *mainLock;
     SemaphoreHandle_t localLock;
@@ -91,20 +165,20 @@ class TaskApi : public GwApiInternal
     String name;
     bool counterUsed=false;
     int counterIdx=0;
-
+    TaskInterfacesImpl *interfaces;
 public:
     TaskApi(GwApiInternal *api, 
         int sourceId, 
         SemaphoreHandle_t *mainLock, 
         const String &name,
-        TaskData *d)
+        TaskInterfacesStorage *s)
     {
         this->sourceId = sourceId;
         this->api = api;
         this->mainLock=mainLock;
         this->name=name;
         localLock=xSemaphoreCreateMutex();
-        taskData=d;
+        interfaces=new TaskInterfacesImpl(name,s);
     }
     virtual GwRequestQueue *getQueue()
     {
@@ -153,6 +227,7 @@ public:
         api->getStatus(status);
     }
     virtual ~TaskApi(){
+        delete interfaces;
         vSemaphoreDelete(localLock);
     };
     virtual void fillStatus(GwJsonDocument &status){
@@ -202,11 +277,8 @@ public:
         else it->second=GwCounter<String>("count"+name);
         return counterIdx;
     }
-    virtual void setTaskValue(const String &name,const Value &v){
-        taskData->setTaskValue(this->name,name,v);
-    }
-    virtual Value getTaskValue(const String &taskName,const String &name){
-        return taskData->getTaskValue(taskName,name);
+    virtual TaskInterfaces * taskInterfaces(){
+        return interfaces;
     }
 
 };
@@ -215,7 +287,10 @@ GwUserCode::GwUserCode(GwApiInternal *api,SemaphoreHandle_t *mainLock){
     this->logger=api->getLogger();
     this->api=api;
     this->mainLock=mainLock;
-    this->taskData=new TaskData(this->logger);
+    this->taskData=new TaskInterfacesStorage(this->logger);
+}
+GwUserCode::~GwUserCode(){
+    delete taskData;
 }
 void userTaskStart(void *p){
     GwUserTask *task=(GwUserTask*)p;
diff --git a/lib/usercode/GwUserCode.h b/lib/usercode/GwUserCode.h
index a0d1019..548d0d1 100644
--- a/lib/usercode/GwUserCode.h
+++ b/lib/usercode/GwUserCode.h
@@ -34,14 +34,15 @@ class GwUserTask{
         }
 };
 
-class TaskData;
+class TaskInterfacesStorage;
 class GwUserCode{
     GwLog *logger;
     GwApiInternal *api;
     SemaphoreHandle_t *mainLock;
-    TaskData *taskData;
+    TaskInterfacesStorage *taskData;
     void startAddOnTask(GwApiInternal *api,GwUserTask *task,int sourceId,String name);
     public:
+        ~GwUserCode();
         typedef std::map<String,String> Capabilities;
         GwUserCode(GwApiInternal *api, SemaphoreHandle_t *mainLock);
         void startUserTasks(int baseId);
diff --git a/src/main.cpp b/src/main.cpp
index aeea06c..94825ac 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -320,6 +320,7 @@ public:
     return config.getString(config.talkerId,String("GP")).c_str();
   }
   virtual ~ApiImpl(){}
+  virtual TaskInterfaces *taskInterfaces(){ return nullptr;}
 };
 
 bool delayedRestart(){