diff --git a/artiq/coredevice/comm_generic.py b/artiq/coredevice/comm_generic.py
index 30804d541..8afa8c096 100644
--- a/artiq/coredevice/comm_generic.py
+++ b/artiq/coredevice/comm_generic.py
@@ -413,23 +413,27 @@ class CommGeneric:
     def _serve_rpc(self, embedding_map):
         async        = self._read_bool()
         service_id   = self._read_int32()
-        service      = embedding_map.retrieve_object(service_id)
         args, kwargs = self._receive_rpc_args(embedding_map)
         return_tags  = self._read_bytes()
+
+        if service_id is 0:
+            service  = lambda obj, attr, value: setattr(obj, attr, value)
+        else:
+            service  = embedding_map.retrieve_object(service_id)
         logger.debug("rpc service: [%d]%r%s %r %r -> %s", service_id, service,
                      (" (async)" if async else ""), args, kwargs, return_tags)
 
+        if async:
+            service(*args, **kwargs)
+            return
+
         try:
             result = service(*args, **kwargs)
-            if async:
-                return
-            else:
-                self._write_header(_H2DMsgType.RPC_REPLY)
-                self._write_bytes(return_tags)
-                self._send_rpc_value(bytearray(return_tags), result, result, service)
-
             logger.debug("rpc service: %d %r %r = %r", service_id, args, kwargs, result)
 
+            self._write_header(_H2DMsgType.RPC_REPLY)
+            self._write_bytes(return_tags)
+            self._send_rpc_value(bytearray(return_tags), result, result, service)
         except Exception as exn:
             logger.debug("rpc service: %d %r %r ! %r", service_id, args, kwargs, exn)
 
diff --git a/artiq/runtime.rs/Cargo.toml b/artiq/runtime.rs/Cargo.toml
index 146ff9089..5a459d204 100644
--- a/artiq/runtime.rs/Cargo.toml
+++ b/artiq/runtime.rs/Cargo.toml
@@ -16,7 +16,7 @@ path = "src/lib.rs"
 std_artiq = { path = "libstd_artiq", features = ["alloc"] }
 lwip = { path = "liblwip", default-features = false }
 fringe = { version = "= 1.1.0", default-features = false, features = ["alloc"] }
-log = { version = "0.3", default-features = false, features = [] }
+log = { version = "0.3", default-features = false, features = ["max_level_debug"] }
 log_buffer = { version = "1.0" }
 byteorder = { version = "0.5", default-features = false }
 
diff --git a/artiq/runtime.rs/libksupport/lib.rs b/artiq/runtime.rs/libksupport/lib.rs
index 73b35c4bc..dc1c853e4 100644
--- a/artiq/runtime.rs/libksupport/lib.rs
+++ b/artiq/runtime.rs/libksupport/lib.rs
@@ -12,8 +12,6 @@ extern crate byteorder;
 mod board;
 #[path = "../src/mailbox.rs"]
 mod mailbox;
-#[path = "../src/rpc_queue.rs"]
-mod rpc_queue;
 
 #[path = "../src/proto.rs"]
 mod proto;
@@ -72,7 +70,7 @@ macro_rules! recv {
 }
 
 macro_rules! print {
-    ($($arg:tt)*) => ($crate::send(&Log(format_args!($($arg)*))));
+    ($($arg:tt)*) => ($crate::send(&$crate::kernel_proto::Log(format_args!($($arg)*))));
 }
 
 macro_rules! println {
@@ -80,6 +78,9 @@ macro_rules! println {
     ($fmt:expr, $($arg:tt)*) => (print!(concat!($fmt, "\n"), $($arg)*));
 }
 
+#[path = "../src/rpc_queue.rs"]
+mod rpc_queue;
+
 #[lang = "panic_fmt"]
 extern fn panic_fmt(args: core::fmt::Arguments, file: &'static str, line: u32) -> ! {
     println!("panic at {}:{}: {}", file, line, args);
diff --git a/artiq/runtime.rs/src/session.rs b/artiq/runtime.rs/src/session.rs
index 5a7bb76c2..8ad957a61 100644
--- a/artiq/runtime.rs/src/session.rs
+++ b/artiq/runtime.rs/src/session.rs
@@ -471,6 +471,7 @@ fn process_kern_queued_rpc(stream: &mut TcpStream,
         trace!("comm<-kern (async RPC)");
         let length = NetworkEndian::read_u32(slice) as usize;
         try!(host_write(stream, host::Reply::RpcRequest { async: true }));
+        trace!("{:?}" ,&slice[4..][..length]);
         try!(stream.write(&slice[4..][..length]));
         Ok(())
     })
@@ -482,7 +483,7 @@ fn host_kernel_worker(waiter: Waiter,
     let mut session = Session::new(congress);
 
     loop {
-        if !rpc_queue::empty() {
+        while !rpc_queue::empty() {
             try!(process_kern_queued_rpc(stream, &mut session))
         }
 
diff --git a/artiq/runtime/ksupport_glue.c b/artiq/runtime/ksupport_glue.c
index 2fa056f5e..515635c94 100644
--- a/artiq/runtime/ksupport_glue.c
+++ b/artiq/runtime/ksupport_glue.c
@@ -8,7 +8,7 @@
 
 void send_to_log(const char *ptr, size_t length);
 
-#define KERNELCPU_EXEC_ADDRESS    0x40800080
+#define KERNELCPU_EXEC_ADDRESS    0x40800000
 #define KERNELCPU_PAYLOAD_ADDRESS 0x40840000
 #define KERNELCPU_LAST_ADDRESS    0x4fffffff
 #define KSUPPORT_HEADER_SIZE      0x80
diff --git a/artiq/test/coredevice/test_embedding.py b/artiq/test/coredevice/test_embedding.py
index 683468b1d..8ad7cef63 100644
--- a/artiq/test/coredevice/test_embedding.py
+++ b/artiq/test/coredevice/test_embedding.py
@@ -217,6 +217,27 @@ class AnnotationTest(ExperimentCase):
         exp = self.create(_Annotation)
         self.assertEqual(exp.overflow(1), True)
 
+class _Async(EnvExperiment):
+    def build(self):
+        self.setattr_device("core")
+
+    @rpc(flags={"async"})
+    def recv_async(self, data):
+        pass
+
+    @kernel
+    def run(self):
+        # fast async path
+        self.recv_async([0]*128)
+        # slow async path
+        self.recv_async([0]*4096)
+
+
+class AsyncTest(ExperimentCase):
+    def test_args(self):
+        exp = self.create(_RPCTypes)
+        exp.run()
+
 
 class _Payload1MB(EnvExperiment):
     def build(self):