diff --git a/artiq/runtime.rs/src/clock.rs b/artiq/runtime.rs/src/clock.rs
index b9a0584b3..3c203a196 100644
--- a/artiq/runtime.rs/src/clock.rs
+++ b/artiq/runtime.rs/src/clock.rs
@@ -58,7 +58,6 @@ impl WatchdogSet {
             }
         }
 
-        warn!("cannot add watchdog; all {} watchdogs used", MAX_WATCHDOGS);
         Err(())
     }
 
diff --git a/artiq/runtime.rs/src/session.rs b/artiq/runtime.rs/src/session.rs
index 65c250279..c9ef4383f 100644
--- a/artiq/runtime.rs/src/session.rs
+++ b/artiq/runtime.rs/src/session.rs
@@ -17,6 +17,10 @@ macro_rules! unexpected {
     };
 }
 
+fn io_error(msg: &str) -> io::Error {
+    io::Error::new(io::ErrorKind::Other, msg)
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum KernelState {
     Absent,
@@ -49,6 +53,12 @@ impl Session {
     }
 }
 
+impl Drop for Session {
+    fn drop(&mut self) {
+        kernel::stop()
+    }
+}
+
 fn check_magic(stream: &mut TcpStream) -> io::Result<()> {
     const MAGIC: &'static [u8] = b"ARTIQ coredev\n";
 
@@ -226,6 +236,17 @@ fn kern_handle(waiter: Waiter,
                 kern_acknowledge()
             }
 
+            kern::WatchdogSetRequest { ms } => {
+                let id = try!(session.watchdog_set.set_ms(ms)
+                                .map_err(|()| io_error("out of watchdogs")));
+                kern_send(waiter, kern::WatchdogSetReply { id: id })
+            }
+
+            kern::WatchdogClear { id } => {
+                session.watchdog_set.clear(id);
+                kern_acknowledge()
+            }
+
             request => unexpected!("unexpected request {:?} from kernel CPU", request)
         }
     })
@@ -249,12 +270,12 @@ fn handle(waiter: Waiter,
         if session.kernel_state == KernelState::Running {
             if session.watchdog_set.expired() {
                 try!(host_write(stream, host::Reply::WatchdogExpired));
-                return Err(io::Error::new(io::ErrorKind::Other, "watchdog expired"))
+                return Err(io_error("watchdog expired"))
             }
 
             if !rtio_crg::check() {
                 try!(host_write(stream, host::Reply::ClockFailure));
-                return Err(io::Error::new(io::ErrorKind::Other, "RTIO clock failure"))
+                return Err(io_error("RTIO clock failure"))
             }
         }