diff --git a/nac3embedded/demo.py b/nac3embedded/demo.py
index 4160f325e..532c623de 100644
--- a/nac3embedded/demo.py
+++ b/nac3embedded/demo.py
@@ -1,11 +1,37 @@
 from language import *
+from numpy import int32, int64
+
+
+@syscall
+def rtio_init():
+    raise NotImplementedError("syscall not simulated")
+
+
+@syscall
+def rtio_get_counter() -> int64:
+    raise NotImplementedError("syscall not simulated")
+
+
+@syscall
+def rtio_output(target: int32, data: int32):
+    raise NotImplementedError("syscall not simulated")
+
+
+@syscall
+def rtio_input_timestamp(timeout_mu: int64, channel: int32) -> int64:
+    raise NotImplementedError("syscall not simulated")
+
+
+@syscall
+def rtio_input_data(channel: int32) -> int32:
+    raise NotImplementedError("syscall not simulated")
 
 
 @kernel
 class Demo:
     @kernel
     def run(self):
-        pass
+        rtio_init()
 
 
 if __name__ == "__main__":
diff --git a/nac3embedded/language.py b/nac3embedded/language.py
index a9ed614dc..3a767a212 100644
--- a/nac3embedded/language.py
+++ b/nac3embedded/language.py
@@ -4,26 +4,32 @@ from functools import wraps
 import nac3embedded
 
 
-__all__ = ["kernel"]
+__all__ = ["syscall", "kernel"]
 
 
 nac3 = nac3embedded.NAC3()
-allow_class_registration = True
+allow_object_registration = True
+
+
+def syscall(function):
+    assert allow_object_registration
+    nac3.register_object(function)
+    return function
 
 
 def kernel(function_or_class):
-    global allow_class_registration
+    global allow_object_registration
 
     if isclass(function_or_class):
-        assert allow_class_registration
-        nac3.register_class(function_or_class)
+        assert allow_object_registration
+        nac3.register_object(function_or_class)
         return function_or_class
     else:
         @wraps(function_or_class)
         def run_on_core(self, *args, **kwargs):
-            global allow_class_registration
-            if allow_class_registration:
+            global allow_object_registration
+            if allow_object_registration:
                 nac3.analyze()
-                allow_class_registration = False
+                allow_object_registration = False
             nac3.compile_method(self.__class__.__name__, function_or_class.__name__)
         return run_on_core
diff --git a/nac3embedded/src/lib.rs b/nac3embedded/src/lib.rs
index 94ce172ed..a7b31074f 100644
--- a/nac3embedded/src/lib.rs
+++ b/nac3embedded/src/lib.rs
@@ -67,7 +67,7 @@ impl Nac3 {
         }
     }
 
-    fn register_class(&mut self, obj: PyObject) -> PyResult<()> {
+    fn register_object(&mut self, obj: PyObject) -> PyResult<()> {
         Python::with_gil(|py| -> PyResult<()> {
             let obj: &PyAny = obj.extract(py)?;
 
diff --git a/shell.nix b/shell.nix
index 070196c7e..7a073d6ee 100644
--- a/shell.nix
+++ b/shell.nix
@@ -12,5 +12,6 @@ in
       libffi
       libxml2
       clippy
+      python3.withPackages(ps: [ps.numpy])
     ];
   }