diff --git a/compiler/obc/c/cgen.ml b/compiler/obc/c/cgen.ml
index 0ab7b67..84286fd 100644
--- a/compiler/obc/c/cgen.ml
+++ b/compiler/obc/c/cgen.ml
@@ -473,7 +473,7 @@ let out_var_name_of_objn o =
 (** Creates the list of arguments to call a node. [targeting] is the targeting
     of the called node, [mem] represents the node context and [args] the
     argument list.*)
-let step_fun_call vr var_env sig_info objn out args =
+let step_fun_call vr var_env sig_info objn out args async =
   let rec add_targeting l ads = match l, ads with
     | [], [] -> []
     | e::l, ad::ads ->
@@ -496,9 +496,13 @@ let step_fun_call vr var_env sig_info objn out args =
              in
              mk_idx l
       ) in
-      args@[Caddrof out; Caddrof mem]
+      match async with
+        | Some async -> args @ [Caddrof out; Caddrof async]
+        | None -> args @ [Caddrof out; Caddrof mem]
   ) else
-    args@[Caddrof out]
+    match async with
+      | Some async -> args @ [Caddrof out; Caddrof async]
+      | None -> args @ [Caddrof out]
 
 (** Generate the statement to call [objn].
     [outvl] is a list of lhs where to put the results.
@@ -516,18 +520,21 @@ let generate_function_call vr var_env obj_env outvl objn args =
     if is_op classln then
       cop_of_op_aux classln args
     else
+      let async = match od.o_ack with
+        | Some _ -> Some (Cvar "GlobalValueToChange")
+        | None -> None
+      in
       (* The step function takes scalar arguments and its own internal
          memory holding structure. *)
       let args =
-        step_fun_call vr var_env sig_info objn out args
+        step_fun_call vr var_env sig_info objn out args async
       in
       (* Our C expression for the function call. *)
-      Cfun_call (classn ^ "_step", args)
-      (* TODO(Arduino):
-         1. pack arguments in local variable
-         2. "send" arguments to global variable
-         3. "retrieve" outputs from global variable
-       *)
+      let suffix = match od.o_ack with
+        | Some _ -> "_step_async_stub"
+        | None -> "_step"
+      in
+      Cfun_call (classn ^ suffix, args)
   in
 
   (* Act according to the length of our list. Step functions with
@@ -671,8 +678,6 @@ let rec cstm_of_act vr var_env obj_env act =
        local structure to hold the results, before allocating to our
        variables. *)
     | Acall (outvl, objn, Mstep, el) ->
-        (* 1. Atomic copy of the inputs *)
-        (* 2. Atomic copy of the outputs *)
         let args = cexprs_of_exps vr var_env el in
         let outvl = clhs_list_of_pattern_list vr var_env outvl in
         generate_function_call vr var_env obj_env outvl objn args