diff --git a/artiq/sim/devices.py b/artiq/sim/devices.py
index 18b997b69..fc258ed48 100644
--- a/artiq/sim/devices.py
+++ b/artiq/sim/devices.py
@@ -1,18 +1,18 @@
 from random import Random
-import numpy
 
-from artiq.language.core import kernel
+from artiq.language.core import kernel, sequential, delay_mu
 from artiq.sim import time
 
 
 class Core:
     def __init__(self, dmgr):
-        self.ref_period = 1
+        self.ref_period = 1e-6
         self._level = 0
 
     def run(self, k_function, k_args, k_kwargs):
         self._level += 1
-        r = k_function.artiq_embedded.function(*k_args, **k_kwargs)
+        with sequential:
+            r = getattr(k_function.__self__, k_function.__name__).__wrapped__(k_function.__self__, *k_args, **k_kwargs)
         self._level -= 1
         if self._level == 0:
             print(time.manager.format_timeline())
@@ -20,33 +20,35 @@ class Core:
         return r
 
     def seconds_to_mu(self, seconds):
-        return numpy.int64(seconds//self.ref_period)
+        return round(seconds/self.ref_period)
 
     def mu_to_seconds(self, mu):
         return mu*self.ref_period
 
+    def delay(self, seconds):
+        delay_mu(self.seconds_to_mu(seconds))
+
 
 class Input:
     def __init__(self, dmgr, name):
         self.core = dmgr.get("core")
         self.name = name
-
         self.prng = Random()
 
     @kernel
     def gate_rising(self, duration):
         time.manager.event(("gate_rising", self.name, duration))
-        delay(duration)
+        self.core.delay(duration)
 
     @kernel
     def gate_falling(self, duration):
         time.manager.event(("gate_falling", self.name, duration))
-        delay(duration)
+        self.core.delay(duration)
 
     @kernel
     def gate_both(self, duration):
         time.manager.event(("gate_both", self.name, duration))
-        delay(duration)
+        self.core.delay(duration)
 
     @kernel
     def count(self, up_to_timestamp_mu):
@@ -75,7 +77,7 @@ class Output:
     @kernel
     def pulse(self, duration):
         time.manager.event(("pulse", self.name, duration))
-        delay(duration)
+        self.core.delay(duration)
 
     @kernel
     def on(self):
@@ -94,7 +96,7 @@ class WaveOutput:
     @kernel
     def pulse(self, frequency, duration):
         time.manager.event(("pulse", self.name, frequency, self.core.seconds_to_mu(duration)))
-        delay(duration)
+        self.core.delay(duration)
 
 
 class VoltageOutput: