diff --git a/artiq/coredevice/core.py b/artiq/coredevice/core.py
index 7f7549115..6923b8ce9 100644
--- a/artiq/coredevice/core.py
+++ b/artiq/coredevice/core.py
@@ -121,10 +121,9 @@ class Core(AutoDB):
         self.first_run = False
 
     @kernel
-    def get_rtio_time(self):
-        return cycles_to_time(syscall("rtio_get_counter"))
+    def get_rtio_counter_mu(self):
+        return syscall("rtio_get_counter")
 
     @kernel
     def break_realtime(self):
-        t = syscall("rtio_get_counter") + 125000
-        at(cycles_to_time(t))
+        at_mu(syscall("rtio_get_counter") + 125000)
diff --git a/artiq/coredevice/dds.py b/artiq/coredevice/dds.py
index f016b4cc0..09c4cb78b 100644
--- a/artiq/coredevice/dds.py
+++ b/artiq/coredevice/dds.py
@@ -37,7 +37,7 @@ class DDSBus(AutoDB):
     def batch_enter(self):
         """Starts a DDS command batch. All DDS commands are buffered
         after this call, until ``batch_exit`` is called."""
-        syscall("dds_batch_enter", time_to_cycles(now()))
+        syscall("dds_batch_enter", now_mu())
 
     @kernel
     def batch_exit(self):
@@ -76,12 +76,24 @@ class DDS(AutoDB):
         """
         return ftw*self.sysclk/2**32
 
+    @portable
+    def turns_to_pow(self, turns):
+        """Returns the phase offset word corresponding to the given phase
+        in turns."""
+        return round(turns*2**14)
+
+    @portable
+    def pow_to_turns(self, pow):
+        """Returns the phase in turns corresponding to the given phase offset
+        word."""
+        return pow/2**14
+
     @kernel
     def init(self):
         """Resets and initializes the DDS channel.
 
         The runtime does this for all channels upon core device startup."""
-        syscall("dds_init", time_to_cycles(now()), self.channel)
+        syscall("dds_init", now_mu(), self.channel)
 
     @kernel
     def set_phase_mode(self, phase_mode):
@@ -104,9 +116,11 @@ class DDS(AutoDB):
         self.phase_mode = phase_mode
 
     @kernel
-    def set(self, frequency, phase=0, phase_mode=_PHASE_MODE_DEFAULT):
+    def set_mu(self, frequency, phase=0, phase_mode=_PHASE_MODE_DEFAULT):
         """Sets the DDS channel to the specified frequency and phase.
 
+        This uses machine units (FTW and POW).
+
         :param frequency: frequency to generate.
         :param phase: adds an offset, in turns, to the phase.
         :param phase_mode: if specified, overrides the default phase mode set
@@ -114,7 +128,11 @@ class DDS(AutoDB):
         """
         if phase_mode == _PHASE_MODE_DEFAULT:
             phase_mode = self.phase_mode
+        syscall("dds_set", now_mu(), self.channel,
+           frequency, round(phase*2**14), phase_mode)
 
-        syscall("dds_set", time_to_cycles(now()), self.channel,
-           self.frequency_to_ftw(frequency), round(phase*2**14),
-           phase_mode)
+    @kernel
+    def set(self, frequency, phase=0, phase_mode=_PHASE_MODE_DEFAULT):
+        """Like ``set_mu``, but uses Hz and turns."""
+        self.set_mu(self.frequency_to_ftw(frequency),
+                    self.turns_to_pow(phase), phase_mode)
diff --git a/artiq/coredevice/ttl.py b/artiq/coredevice/ttl.py
index 359b9b590..9a363b83d 100644
--- a/artiq/coredevice/ttl.py
+++ b/artiq/coredevice/ttl.py
@@ -2,47 +2,6 @@ from artiq.language.core import *
 from artiq.language.db import *
 
 
-class LLTTLOut(AutoDB):
-    """Low-level RTIO TTL output driver.
-
-    Allows setting RTIO TTL outputs at arbitrary times, without time
-    unit conversion.
-
-    This is meant to be used mostly in drivers; consider using
-    ``TTLOut`` instead.
-
-    This should be used with output-only channels.
-    """
-    class DBKeys:
-        core = Device()
-        channel = Argument()
-
-    @kernel
-    def set_o(self, t, value):
-        """Sets the output value of the RTIO channel.
-
-        :param t: timestamp in RTIO cycles (64-bit integer).
-        :param value: value to set at the output.
-        """
-        syscall("ttl_set_o", t, self.channel, value)
-
-    @kernel
-    def on(self, t):
-        """Turns the RTIO channel on.
-
-        :param t: timestamp in RTIO cycles (64-bit integer).
-        """
-        self.set_o(t, True)
-
-    @kernel
-    def off(self, t):
-        """Turns the RTIO channel off.
-
-        :param t: timestamp in RTIO cycles (64-bit integer).
-        """
-        self.set_o(t, False)
-
-
 class TTLOut(AutoDB):
     """RTIO TTL output driver.
 
@@ -61,9 +20,9 @@ class TTLOut(AutoDB):
         self.o_previous_timestamp = int64(0)
 
     @kernel
-    def _set_o(self, o):
-        syscall("ttl_set_o", time_to_cycles(now()), self.channel, o)
-        self.o_previous_timestamp = time_to_cycles(now())
+    def set_o(self, o):
+        syscall("ttl_set_o", now_mu(), self.channel, o)
+        self.o_previous_timestamp = now_mu()
 
     @kernel
     def sync(self):
@@ -74,16 +33,25 @@ class TTLOut(AutoDB):
     @kernel
     def on(self):
         """Sets the output to a logic high state."""
-        self._set_o(True)
+        self.set_o(True)
 
     @kernel
     def off(self):
         """Sets the output to a logic low state."""
-        self._set_o(False)
+        self.set_o(False)
+
+    @kernel
+    def pulse_mu(self, duration):
+        """Pulses the output high for the specified duration
+        (in machine units)."""
+        self.on()
+        delay_mu(duration)
+        self.off()
 
     @kernel
     def pulse(self, duration):
-        """Pulses the output high for the specified duration."""
+        """Pulses the output high for the specified duration
+        (in seconds)."""
         self.on()
         delay(duration)
         self.off()
@@ -117,21 +85,21 @@ class TTLInOut(AutoDB):
         self.i_previous_timestamp = int64(0)
 
     @kernel
-    def _set_oe(self, oe):
-        syscall("ttl_set_oe", time_to_cycles(now()), self.channel, oe)
+    def set_oe(self, oe):
+        syscall("ttl_set_oe", now_mu(), self.channel, oe)
 
     @kernel
     def output(self):
-        self._set_oe(True)
+        self.set_oe(True)
 
     @kernel
     def input(self):
-        self._set_oe(False)
+        self.set_oe(False)
 
     @kernel
-    def _set_o(self, o):
-        syscall("ttl_set_o", time_to_cycles(now()), self.channel, o)
-        self.o_previous_timestamp = time_to_cycles(now())
+    def set_o(self, o):
+        syscall("ttl_set_o", now_mu(), self.channel, o)
+        self.o_previous_timestamp = now_mu()
 
     @kernel
     def sync(self):
@@ -142,43 +110,78 @@ class TTLInOut(AutoDB):
     @kernel
     def on(self):
         """Sets the output to a logic high state."""
-        self._set_o(True)
+        self.set_o(True)
 
     @kernel
     def off(self):
         """Sets the output to a logic low state."""
-        self._set_o(False)
+        self.set_o(False)
+
+    @kernel
+    def pulse_mu(self, duration):
+        """Pulses the output high for the specified duration
+        (in machine units)."""
+        self.on()
+        delay_mu(duration)
+        self.off()
 
     @kernel
     def pulse(self, duration):
-        """Pulses the output high for the specified duration."""
+        """Pulses the output high for the specified duration
+        (in seconds)."""
         self.on()
         delay(duration)
         self.off()
 
     @kernel
     def _set_sensitivity(self, value):
-        syscall("ttl_set_sensitivity", time_to_cycles(now()), self.channel, value)
-        self.i_previous_timestamp = time_to_cycles(now())
+        syscall("ttl_set_sensitivity", now_mu(), self.channel, value)
+        self.i_previous_timestamp = now_mu()
+
+    @kernel
+    def gate_rising_mu(self, duration):
+        """Register rising edge events for the specified duration
+        (in machine units)."""
+        self._set_sensitivity(1)
+        delay_mu(duration)
+        self._set_sensitivity(0)
+
+    @kernel
+    def gate_falling_mu(self, duration):
+        """Register falling edge events for the specified duration
+        (in machine units)."""
+        self._set_sensitivity(2)
+        delay_mu(duration)
+        self._set_sensitivity(0)
+
+    @kernel
+    def gate_both_mu(self, duration):
+        """Register both rising and falling edge events for the specified
+        duration (in machine units)."""
+        self._set_sensitivity(3)
+        delay_mu(duration)
+        self._set_sensitivity(0)
 
     @kernel
     def gate_rising(self, duration):
-        """Register rising edge events for the specified duration."""
+        """Register rising edge events for the specified duration
+        (in seconds)."""
         self._set_sensitivity(1)
         delay(duration)
         self._set_sensitivity(0)
 
     @kernel
     def gate_falling(self, duration):
-        """Register falling edge events for the specified duration."""
+        """Register falling edge events for the specified duration
+        (in seconds)."""
         self._set_sensitivity(2)
         delay(duration)
         self._set_sensitivity(0)
 
     @kernel
-    def gate_both(self, duration):
+    def gate_both_mu(self, duration):
         """Register both rising and falling edge events for the specified
-        duration."""
+        duration (in seconds)."""
         self._set_sensitivity(3)
         delay(duration)
         self._set_sensitivity(0)
@@ -200,5 +203,4 @@ class TTLInOut(AutoDB):
 
         If the gate is permanently closed, returns a negative value.
         """
-        return cycles_to_time(syscall("ttl_get", self.channel,
-                                      self.i_previous_timestamp))
+        return syscall("ttl_get", self.channel, self.i_previous_timestamp)
diff --git a/artiq/devices/pdq2/mediator.py b/artiq/devices/pdq2/mediator.py
index 63d3d7b72..f3c536219 100644
--- a/artiq/devices/pdq2/mediator.py
+++ b/artiq/devices/pdq2/mediator.py
@@ -99,7 +99,7 @@ class _Frame:
 
     def _arm(self):
         self.segment_delays = [
-            time_to_cycles(s.get_duration()*delay_margin_factor, self.core)
+            seconds_to_mu(s.get_duration()*delay_margin_factor, self.core)
             for s in self.segments]
 
     def _invalidate(self):
@@ -125,7 +125,8 @@ class _Frame:
         if not self.pdq.armed:
             raise ArmError
 
-        t = time_to_cycles(now()) - time_to_cycles(trigger_duration/2)
+        call_t = now_mu()
+        trigger_start_t = call_t - seconds_to_mu(trigger_duration/2)
 
         if self.pdq.current_frame >= 0:
             # PDQ is in the middle of a frame. Check it is us.
@@ -136,15 +137,16 @@ class _Frame:
             # to play our first segment.
             self.pdq.current_frame = self.frame_number
             self.pdq.next_segment = 0
-            t2 = t - time_to_cycles(frame_setup)
-            self.pdq.frame0.set_value(t2, self.frame_number & 1)
-            self.pdq.frame1.set_value(t2, (self.frame_number & 2) >> 1)
-            self.pdq.frame2.set_value(t2, (self.frame_number & 4) >> 2)
+            at_mu(trigger_start_t - seconds_to_mu(frame_setup))
+            self.pdq.frame0.set_o(bool(self.frame_number & 1))
+            self.pdq.frame1.set_o(bool((self.frame_number & 2) >> 1))
+            self.pdq.frame2.set_o(bool((self.frame_number & 4) >> 2))
 
-        self.pdq.trigger.on(t)
-        self.pdq.trigger.off(t + time_to_cycles(trigger_duration))
+        at_mu(trigger_start_t)
+        self.pdq.trigger.pulse(trigger_duration)
 
-        delay(cycles_to_time(self.segment_delays[self.pdq.next_segment]))
+        at_mu(call_t)
+        delay_mu(self.segment_delays[self.pdq.next_segment])
         self.pdq.next_segment += 1
 
         # test for end of frame
@@ -157,19 +159,15 @@ class CompoundPDQ2(AutoDB):
     class DBKeys:
         core = Device()
         pdq2_devices = Argument()
-        rtio_trigger = Argument()
-        rtio_frame = Argument()
+        trigger_device = Argument()
+        frame_devices = Argument()
 
     def build(self):
         self.pdq2s = [self.dbh.get_device(d) for d in self.pdq2_devices]
-        self.trigger = ttl.LLTTLOut(
-            core=self.core, channel=self.rtio_trigger)
-        self.frame0 = ttl.LLTTLOut(
-            core=self.core, channel=self.rtio_frame[0])
-        self.frame1 = ttl.LLTTLOut(
-            core=self.core, channel=self.rtio_frame[1])
-        self.frame2 = ttl.LLTTLOut(
-            core=self.core, channel=self.rtio_frame[2])
+        self.trigger = self.dbh.get_device(self.trigger_device)
+        self.frame0 = self.dbh.get_device(self.frame_devices[0])
+        self.frame1 = self.dbh.get_device(self.frame_devices[1])
+        self.frame2 = self.dbh.get_device(self.frame_devices[2])
 
         self.frames = []
         self.current_frame = -1
diff --git a/artiq/language/core.py b/artiq/language/core.py
index 424fd07cc..340ea2374 100644
--- a/artiq/language/core.py
+++ b/artiq/language/core.py
@@ -28,7 +28,6 @@ class int64(int):
     True
     >>> a + b
     6
-
     """
     pass
 
@@ -62,7 +61,6 @@ def round64(x):
     This function is equivalent to ``int64(round(x))`` but, when targeting
     static compilation, prevents overflow when the rounded value is too large
     to fit in a 32-bit integer.
-
     """
     return int64(round(x))
 
@@ -88,7 +86,6 @@ def kernel(arg):
 
     The decorator takes an optional parameter that defaults to ``core`` and
     specifies the name of the attribute to use as core device driver.
-
     """
     if isinstance(arg, str):
         def real_decorator(k_function):
@@ -117,7 +114,6 @@ def portable(f):
     host will be executed on the host (no compilation and execution on the
     core device). A decorated function called from a kernel will be executed
     on the core device (no RPC).
-
     """
     f.k_function_info = _KernelFunctionInfo(core_name="", k_function=f)
     return f
@@ -131,9 +127,10 @@ class _DummyTimeManager:
     enter_sequential = _not_implemented
     enter_parallel = _not_implemented
     exit = _not_implemented
+    take_time_mu = _not_implemented
+    get_time_mu = _not_implemented
+    set_time_mu = _not_implemented
     take_time = _not_implemented
-    get_time = _not_implemented
-    set_time = _not_implemented
 
 _time_manager = _DummyTimeManager()
 
@@ -143,7 +140,6 @@ def set_time_manager(time_manager):
     directly inside the Python interpreter. The time manager responds to the
     entering and leaving of parallel/sequential blocks, delays, etc. and
     provides a time-stamped logging facility for events.
-
     """
     global _time_manager
     _time_manager = time_manager
@@ -160,7 +156,6 @@ _syscall_manager = _DummySyscallManager()
 def set_syscall_manager(syscall_manager):
     """Set the system call manager used for simulating the core device's
     runtime in the Python interpreter.
-
     """
     global _syscall_manager
     _syscall_manager = syscall_manager
@@ -168,7 +163,8 @@ def set_syscall_manager(syscall_manager):
 # global namespace for kernels
 
 kernel_globals = ("sequential", "parallel",
-    "delay", "now", "at", "time_to_cycles", "cycles_to_time",
+    "delay_mu", "now_mu", "at_mu", "delay",
+    "seconds_to_mu", "mu_to_seconds",
     "syscall", "watchdog")
 
 
@@ -190,7 +186,6 @@ class _Parallel:
     The execution time of a parallel block is the execution time of its longest
     statement. A parallel block may contain sequential blocks, which themselves
     may contain parallel blocks, etc.
-
     """
     def __enter__(self):
         _time_manager.enter_parallel()
@@ -200,50 +195,49 @@ class _Parallel:
 parallel = _Parallel()
 
 
-def delay(duration):
-    """Increases the RTIO time by the given amount.
+def delay_mu(duration):
+    """Increases the RTIO time by the given amount (in machine units)."""
+    _time_manager.take_time_mu(duration)
 
-    """
+
+def now_mu():
+    """Retrieves the current RTIO time, in machine units."""
+    return _time_manager.get_time_mu()
+
+
+def at_mu(time):
+    """Sets the RTIO time to the specified absolute value, in machine units."""
+    _time_manager.set_time_mu(time)
+
+
+def delay(duration):
+    """Increases the RTIO time by the given amount (in seconds)."""
     _time_manager.take_time(duration)
 
 
-def now():
-    """Retrieves the current RTIO time, in seconds.
+def seconds_to_mu(seconds, core=None):
+    """Converts seconds to the corresponding number of machine units
+    (RTIO cycles).
 
-    """
-    return _time_manager.get_time()
-
-
-def at(time):
-    """Sets the RTIO time to the specified absolute value.
-
-    """
-    _time_manager.set_time(time)
-
-
-def time_to_cycles(time, core=None):
-    """Converts time to the corresponding number of RTIO cycles.
-
-    :param time: Time (in seconds) to convert.
-    :param core: Core device for which to perform the conversion. Specify only
-        when running in the interpreter (not in kernel).
-
-    """
-    if core is None:
-        raise ValueError("Core device must be specified for time conversion")
-    return round64(time//core.ref_period)
-
-
-def cycles_to_time(cycles, core=None):
-    """Converts RTIO cycles to the corresponding time.
-
-    :param time: Cycle count to convert.
-    :param core: Core device for which to perform the conversion. Specify only
+    :param seconds: time (in seconds) to convert.
+    :param core: core device for which to perform the conversion. Specify only
         when running in the interpreter (not in kernel).
     """
     if core is None:
         raise ValueError("Core device must be specified for time conversion")
-    return cycles*core.ref_period
+    return round64(seconds//core.ref_period)
+
+
+def mu_to_seconds(mu, core=None):
+    """Converts machine units (RTIO cycles) to seconds.
+
+    :param mu: cycle count to convert.
+    :param core: core device for which to perform the conversion. Specify only
+        when running in the interpreter (not in kernel).
+    """
+    if core is None:
+        raise ValueError("Core device must be specified for time conversion")
+    return mu*core.ref_period
 
 
 def syscall(*args):
diff --git a/artiq/sim/devices.py b/artiq/sim/devices.py
index c5900a405..25fc934f5 100644
--- a/artiq/sim/devices.py
+++ b/artiq/sim/devices.py
@@ -7,13 +7,15 @@ from artiq.sim import time
 
 
 class Core(AutoDB):
-    _level = 0
+    def build(self):
+        self.ref_period = 1
+        self._level = 0
 
     def run(self, k_function, k_args, k_kwargs):
-        Core._level += 1
+        self._level += 1
         r = k_function(*k_args, **k_kwargs)
-        Core._level -= 1
-        if Core._level == 0:
+        self._level -= 1
+        if self._level == 0:
             print(time.manager.format_timeline())
         return r
 
diff --git a/artiq/sim/time.py b/artiq/sim/time.py
index 3ae01a073..72cd3313f 100644
--- a/artiq/sim/time.py
+++ b/artiq/sim/time.py
@@ -30,37 +30,39 @@ class Manager:
         self.timeline = []
 
     def enter_sequential(self):
-        new_context = SequentialTimeContext(self.get_time())
+        new_context = SequentialTimeContext(self.get_time_mu())
         self.stack.append(new_context)
 
     def enter_parallel(self):
-        new_context = ParallelTimeContext(self.get_time())
+        new_context = ParallelTimeContext(self.get_time_mu())
         self.stack.append(new_context)
 
     def exit(self):
         old_context = self.stack.pop()
         self.take_time(old_context.block_duration)
 
-    def take_time(self, duration):
+    def take_time_mu(self, duration):
         self.stack[-1].take_time(duration)
 
-    def get_time(self):
+    def get_time_mu(self):
         return self.stack[-1].current_time
 
-    def set_time(self, t):
-        dt = t - self.get_time()
+    def set_time_mu(self, t):
+        dt = t - self.get_time_mu()
         if dt < 0*s:
             raise ValueError("Attempted to go back in time")
         self.take_time(dt)
 
+    take_time = take_time_mu
+
     def event(self, description):
-        self.timeline.append((self.get_time(), description))
+        self.timeline.append((self.get_time_mu(), description))
 
     def format_timeline(self):
         r = ""
         prev_time = 0*s
         for time, description in sorted(self.timeline, key=itemgetter(0)):
-            r += "@{:10} (+{:10}) ".format(str(time), str(time-prev_time))
+            r += "@{:.9f} (+{:.9f}) ".format(time, time-prev_time)
             for item in description:
                 r += "{:16}".format(str(item))
             r += "\n"
diff --git a/artiq/test/full_stack.py b/artiq/test/full_stack.py
index a75a73fcd..ad819827c 100644
--- a/artiq/test/full_stack.py
+++ b/artiq/test/full_stack.py
@@ -74,17 +74,20 @@ class _PulseLogger(AutoDB):
             self.first_timestamp = t
         self.output_list.append((self.name, t-self.first_timestamp, l, f))
 
+    def int_usec(self, mu):
+        return round(mu_to_seconds(mu, self.core)*1000000)
+
     def on(self, t, f):
-        self._append(t, True, f)
+        self._append(self.int_usec(t), True, f)
 
     def off(self, t):
-        self._append(t, False, 0)
+        self._append(self.int_usec(t), False, 0)
 
     @kernel
     def pulse(self, f, duration):
-        self.on(round(now()*1000000000), f)
+        self.on(now_mu(), f)
         delay(duration)
-        self.off(round(now()*1000000000))
+        self.off(now_mu())
 
 
 class _Pulses(AutoDB):
@@ -288,9 +291,9 @@ class _RTIOSequenceError(AutoDB):
 
     @kernel
     def run(self):
-        t = now()
+        t = now_mu()
         self.o.pulse(25*us)
-        at(t)
+        at_mu(t)
         self.o.pulse(25*us)
 
 
diff --git a/artiq/test/transforms.py b/artiq/test/transforms.py
index 31d77bd63..75af1b2dc 100644
--- a/artiq/test/transforms.py
+++ b/artiq/test/transforms.py
@@ -10,7 +10,7 @@ optimize_in = """
 
 def run():
     dds_sysclk = Fraction(1000000000, 1)
-    n = time_to_cycles((1.2345 * Fraction(1, 1000000000)))
+    n = seconds_to_mu((1.2345 * Fraction(1, 1000000000)))
     with sequential:
         frequency = 345 * Fraction(1000000, 1)
         frequency_to_ftw_return = int((((2 ** 32) * frequency) / dds_sysclk))
@@ -19,7 +19,7 @@ def run():
         ftw2 = ftw
         ftw_to_frequency_return = ((ftw2 * dds_sysclk) / (2 ** 32))
     f = ftw_to_frequency_return
-    phi = ((1000 * cycles_to_time(n)) * f)
+    phi = ((1000 * mu_to_seconds(n)) * f)
     do_something(int(phi))
 """
 
diff --git a/artiq/transforms/interleave.py b/artiq/transforms/interleave.py
index 0a1b794a9..8aa9df838 100644
--- a/artiq/transforms/interleave.py
+++ b/artiq/transforms/interleave.py
@@ -28,13 +28,14 @@ def _get_duration(stmt):
             return -1
     elif isinstance(stmt, ast.Call):
         name = stmt.func.id
-        if name == "delay":
+        assert(name != "delay")
+        if name == "delay_mu":
             try:
                 da = eval_constant(stmt.args[0])
             except NotConstant:
                 da = -1
             return da
-        elif name == "at":
+        elif name == "at_mu":
             return -1
         else:
             return 0
@@ -69,7 +70,7 @@ def _interleave_timelines(timelines):
                     ref_stmt = stmt.stmt
             delay_stmt = ast.copy_location(
                 ast.Expr(ast.Call(
-                    func=ast.Name("delay", ast.Load()),
+                    func=ast.Name("delay_mu", ast.Load()),
                     args=[value_to_ast(dt)],
                     keywords=[], starargs=[], kwargs=[])),
                 ref_stmt)
diff --git a/artiq/transforms/lower_time.py b/artiq/transforms/lower_time.py
index c2c779b84..5b3df0245 100644
--- a/artiq/transforms/lower_time.py
+++ b/artiq/transforms/lower_time.py
@@ -1,15 +1,15 @@
 """
-This transform implements time management functions (delay/now/at)
+This transform implements time management functions (delay_mu/now_mu/at_mu)
 using an accumulator 'now' and simple replacement rules:
 
-    delay(t) ->  now += t
-    now()    ->  now
-    at(t)    ->  now = t
+    delay_mu(t) ->  now += t
+    now_mu()    ->  now
+    at_mu(t)    ->  now = t
 
-Time parameters must be quantized to integers before running this transform.
+The function delay(), that uses seconds, must be lowered to delay_mu() before
+invoking this transform.
 The accumulator is initialized to an int64 value at the beginning of the
 output function.
-
 """
 
 import ast
@@ -17,7 +17,7 @@ import ast
 
 class _TimeLowerer(ast.NodeTransformer):
     def visit_Call(self, node):
-        if node.func.id == "now":
+        if node.func.id == "now_mu":
             return ast.copy_location(ast.Name("now", ast.Load()), node)
         else:
             self.generic_visit(node)
@@ -27,13 +27,13 @@ class _TimeLowerer(ast.NodeTransformer):
         r = node
         if isinstance(node.value, ast.Call):
             funcname = node.value.func.id
-            if funcname == "delay":
+            if funcname == "delay_mu":
                 r = ast.copy_location(
                     ast.AugAssign(target=ast.Name("now", ast.Store()),
                                   op=ast.Add(),
                                   value=node.value.args[0]),
                     node)
-            elif funcname == "at":
+            elif funcname == "at_mu":
                 r = ast.copy_location(
                     ast.Assign(targets=[ast.Name("now", ast.Store())],
                                value=node.value.args[0]),
diff --git a/artiq/transforms/quantize_time.py b/artiq/transforms/quantize_time.py
index 835dcd780..aad75069a 100644
--- a/artiq/transforms/quantize_time.py
+++ b/artiq/transforms/quantize_time.py
@@ -1,12 +1,12 @@
 """
-This transform turns calls to delay/now/at that use non-integer time
-expressed in seconds into calls that use int64 time expressed in multiples of
-ref_period.
+This transform turns calls to delay() that use non-integer time
+expressed in seconds into calls to delay_mu() that use int64 time
+expressed in multiples of ref_period.
 
 It does so by inserting multiplication/division/rounding operations around
 those calls.
 
-The time_to_cycles and cycles_to_time core language functions are also
+The seconds_to_mu and mu_to_seconds core language functions are also
 implemented here, as well as watchdog to syscall conversion.
 """
 
@@ -15,14 +15,7 @@ import ast
 from artiq.transforms.tools import value_to_ast
 
 
-def _call_now(node):
-    return ast.copy_location(
-        ast.Call(func=ast.Name("now", ast.Load()),
-                 args=[], keywords=[], starargs=[], kwargs=[]),
-        node)
-
-
-def _time_to_cycles(ref_period, node):
+def _seconds_to_mu(ref_period, node):
     divided = ast.copy_location(
         ast.BinOp(left=node,
                   op=ast.Div(),
@@ -35,7 +28,7 @@ def _time_to_cycles(ref_period, node):
         divided)
 
 
-def _cycles_to_time(ref_period, node):
+def _mu_to_seconds(ref_period, node):
     return ast.copy_location(
         ast.BinOp(left=node,
                   op=ast.Mult(),
@@ -50,29 +43,22 @@ class _TimeQuantizer(ast.NodeTransformer):
 
     def visit_Call(self, node):
         funcname = node.func.id
-        if funcname == "now":
-            return _cycles_to_time(self.ref_period, _call_now(node))
-        elif funcname == "delay" or funcname == "at":
+        if funcname == "delay":
+            node.func.id = "delay_mu"
             if (isinstance(node.args[0], ast.Call)
-                    and node.args[0].func.id == "cycles_to_time"):
+                    and node.args[0].func.id == "mu_to_seconds"):
                 # optimize:
-                # delay/at(cycles_to_time(x)) -> delay/at(x)
+                # delay(mu_to_seconds(x)) -> delay_mu(x)
                 node.args[0] = self.visit(node.args[0].args[0])
             else:
-                node.args[0] = _time_to_cycles(self.ref_period,
-                                               self.visit(node.args[0]))
+                node.args[0] = _seconds_to_mu(self.ref_period,
+                                              self.visit(node.args[0]))
             return node
-        elif funcname == "time_to_cycles":
-            if (isinstance(node.args[0], ast.Call)
-                    and node.args[0].func.id == "now"):
-                # optimize:
-                # time_to_cycles(now()) -> now()
-                return _call_now(node)
-            else:
-                return _time_to_cycles(self.ref_period,
+        elif funcname == "seconds_to_mu":
+                return _seconds_to_mu(self.ref_period,
                                        self.visit(node.args[0]))
-        elif funcname == "cycles_to_time":
-            return _cycles_to_time(self.ref_period,
+        elif funcname == "mu_to_seconds":
+            return _mu_to_seconds(self.ref_period,
                                    self.visit(node.args[0]))
         else:
             self.generic_visit(node)
@@ -123,6 +109,5 @@ class _TimeQuantizer(ast.NodeTransformer):
         return node
 
 
-
 def quantize_time(func_def, ref_period):
     _TimeQuantizer(ref_period).visit(func_def)
diff --git a/artiq/transforms/tools.py b/artiq/transforms/tools.py
index 1b68fd0f3..97d596d2b 100644
--- a/artiq/transforms/tools.py
+++ b/artiq/transforms/tools.py
@@ -6,8 +6,9 @@ from artiq.language import units
 
 
 embeddable_funcs = (
-    core_language.delay, core_language.at, core_language.now,
-    core_language.time_to_cycles, core_language.cycles_to_time,
+    core_language.delay_mu, core_language.at_mu, core_language.now_mu,
+    core_language.delay,
+    core_language.seconds_to_mu, core_language.mu_to_seconds,
     core_language.syscall, core_language.watchdog,
     range, bool, int, float, round, len,
     core_language.int64, core_language.round64,
@@ -92,7 +93,7 @@ def eval_constant(node):
 _replaceable_funcs = {
     "bool", "int", "float", "round",
     "int64", "round64", "Fraction",
-    "time_to_cycles", "cycles_to_time"
+    "seconds_to_mu", "mu_to_seconds"
 }
 
 
diff --git a/examples/master/ddb.pyon b/examples/master/ddb.pyon
index ff6772fcb..81903fca5 100644
--- a/examples/master/ddb.pyon
+++ b/examples/master/ddb.pyon
@@ -43,6 +43,12 @@
         "class": "TTLOut",
         "arguments": {"channel": 4}
     },
+    "ttl3": {
+        "type": "local",
+        "module": "artiq.coredevice.ttl",
+        "class": "TTLOut",
+        "arguments": {"channel": 5}
+    },
     "led": {
         "type": "local",
         "module": "artiq.coredevice.ttl",
@@ -113,10 +119,9 @@
         "class": "CompoundPDQ2",
         "arguments": {
             "pdq2_devices": ["qc_q1_0", "qc_q1_1", "qc_q1_2", "qc_q1_3"],
-            "rtio_trigger": 7,
-            "rtio_frame": [2, 3, 4]
-        },
-        "comment": "Uses ttl 0, 1, 2 and 5"
+            "trigger_device": "ttl3",
+            "frame_devices": ["ttl0", "ttl1", "ttl2"]
+        }
     },
 
     "lda": {