diff --git a/uasyncio_iostream/README.md b/uasyncio_iostream/README.md
index 6ac839e..1cfad6e 100644
--- a/uasyncio_iostream/README.md
+++ b/uasyncio_iostream/README.md
@@ -1,34 +1,40 @@
 # Changes to usayncio
 
+This archive contains suggestions for changes to new `uasyncio`:
+
  1. Implement as a Python package.
  2. Implement synchronisation primitives as package modules to conserve RAM.
- 3. Add .priority method to Stream class. Enables I/O to be handled at high
+ 3. Add `.priority` method to `Stream` class. Enables I/O to be handled at high
  priority on a per-device basis.
- 4. Rename task queue class TQueue to avoid name clash with Queue primitive.
- 5. Rename task queue instance to tqueue as it is used by primitives.
+ 4. Rename task queue class `TQueue` to avoid name clash with Queue primitive.
+ 5. Rename task queue instance to `tqueue` as it is used by primitives.
 
 ## Minor changes
 
- 1. Move StreamReader and StreamWriter assignments out of legacy section of code.
- 2. CreateTask produces an assertion fail if called with a generator function.
+ 1. Move `StreamReader` and `StreamWriter` assignments out of legacy section of
+ code: these classes exist in `asyncio` 3.8.
+ 2. `.CreateTask` produces an assertion fail if called with a generator function.
  Avoids obscure traceback if someone omits the parens.
- 3. Add machine readable version.
+ 3. Add machine readable version info. Useful in testing.
 
 # CPython-compatible synchronisation primitives
 
-These have been adapted to work efficiently with the new version.
+The ones I implemented are adapted to work efficiently with the new version.
+All are separate modules to conserve RAM.
 
- 1. `Event`: moved to separate module for consistency with other primitives.
+ 1. `Event`: just moved to separate module.
  2. `Lock`: Kevin Köck's solution.
  3. `Queue`: Paul's solution adapted for efficiency.
- 4. `Semaphore`: Also implements BoundedSemaphore.
+ 4. `Semaphore`: Also implements `BoundedSemaphore`.
  5. `Condition`.
 
 # Other primitives
 
+Included as examples of user-contributed primitives.
+
  1. `Message`: Awaitable `Event` subclass with a data payload.
- 2. `Barrier`: Multiple tasks wait until all reach a Barrier instance. Or some tasks
- wait until others have triggered the Barrier instance.
+ 2. `Barrier`: Multiple tasks wait until all reach a Barrier instance. Or some
+ tasks wait until others have triggered the Barrier instance.
 
 # Test scripts
 
@@ -40,6 +46,18 @@ Hopefully these are self-documenting on import.
  3. `ms_timer.py` and `ms_timer_test.py` A practical use of priority scheduling to
  implement a timer with higher precision than `asyncio.sleep_ms`. Runs on Pyboard.
 
-# Note
+# CPython compatibility
 
-Use of I/O is still incompatible with Unix.
+`prim_test.py` runs on MicroPython or CPython 3.8, demonstrating that MicroPython
+primitives behave similarly to the native CPython ones.
+
+`Message` is common to CPython and MicroPython.
+There are two implementations of `Barrier` with the same functionality: a CPython
+version and a MicroPython version with specific optimisations. The `Barrier` class
+is loosely based on
+[a Microsoft concept](https://docs.microsoft.com/en-us/windows/win32/sync/synchronization-barriers).
+
+## Directory structure
+
+MicroPython optimised primitives are in `uasyncio/`. Primitives compatible with
+`asyncio` are in `primitives/`.
diff --git a/uasyncio_iostream/prim_test.py b/uasyncio_iostream/prim_test.py
index 34f28c1..c4f70ab 100644
--- a/uasyncio_iostream/prim_test.py
+++ b/uasyncio_iostream/prim_test.py
@@ -23,13 +23,22 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 
-import uasyncio as asyncio
-import uasyncio.lock
-import uasyncio.event
-import uasyncio.barrier
-import uasyncio.semaphore
-import uasyncio.condition
-from uasyncio.queue import Queue  # Name collision in __init__.py
+try:
+    import asyncio
+except ImportError:
+    # Specific imports under MicroPython to conserve RAM
+    import uasyncio as asyncio
+    import uasyncio.lock
+    import uasyncio.event
+    import uasyncio.semaphore
+    import uasyncio.condition
+    import uasyncio.queue
+    from uasyncio.barrier import Barrier  # MicroPython optimised
+else:
+    from primitives.barrier import Barrier  # CPython generic
+from primitives.message import Message  # Portable
+
+
 
 def print_tests():
     st = '''Available functions:
@@ -69,7 +78,7 @@ async def event_wait(message, ack_event, n):
     ack_event.set()
 
 async def run_ack():
-    message = asyncio.Message()
+    message = Message()
     ack1 = asyncio.Event()
     ack2 = asyncio.Event()
     count = 0
@@ -121,7 +130,7 @@ Cleared message
 I've seen attack ships burn on the shoulder of Orion...
 Time to die...
 ''', 10)
-    asyncio.run(ack_coro(10))
+    asyncio.get_event_loop().run_until_complete(ack_coro(10))
 
 # ************ Test Message class ************
 
@@ -132,7 +141,7 @@ async def wait_message(message):
     print('Got message {}'.format(msg))
 
 async def run_message_test():
-    message = asyncio.Message()
+    message = Message()
     asyncio.create_task(wait_message(message))
     await asyncio.sleep(1)
     message.set('Hello world')
@@ -143,7 +152,7 @@ def message_test():
 Waiting for message
 Got message Hello world
 ''', 2)
-    asyncio.run(run_message_test())
+    asyncio.get_event_loop().run_until_complete(run_message_test())
 
 # ************ Test Lock and Event classes ************
 
@@ -199,11 +208,14 @@ got event
 Event status OK
 Tasks complete
 ''', 5)
-    asyncio.run(run_event_test())
+    asyncio.get_event_loop().run_until_complete(run_event_test())
 
 # ************ Barrier test ************
 
-async def killer(duration):
+async def main(duration):
+    barrier = Barrier(3, callback, ('Synch',))
+    for _ in range(3):
+        asyncio.create_task(report(barrier))
     await asyncio.sleep(duration)
 
 def callback(text):
@@ -221,10 +233,7 @@ def barrier_test():
 3 3 3 Synch
 4 4 4 Synch
 ''')
-    barrier = asyncio.Barrier(3, callback, ('Synch',))
-    for _ in range(3):
-        asyncio.create_task(report(barrier))
-    asyncio.run(killer(2))
+    asyncio.get_event_loop().run_until_complete(main(2))
 
 # ************ Semaphore test ************
 
@@ -239,7 +248,7 @@ async def run_sema(n, sema, barrier):
 
 async def run_sema_test(bounded):
     num_coros = 5
-    barrier = asyncio.Barrier(num_coros + 1)
+    barrier = Barrier(num_coros + 1)
     if bounded:
         semaphore = asyncio.BoundedSemaphore(3)
     else:
@@ -291,7 +300,7 @@ run_sema 4 has released semaphore
 
 Exact sequence of acquisition may vary when 3 and 4 compete for semaphore.'''
     printexp(exp, 3)
-    asyncio.run(run_sema_test(bounded))
+    asyncio.get_event_loop().run_until_complete(run_sema_test(bounded))
 
 # ************ Condition test ************
 
@@ -343,20 +352,20 @@ async def cond04(n, cond, barrier):
 async def cond_go():
     cond = asyncio.Condition()
     ntasks = 7
-    barrier = asyncio.Barrier(ntasks + 1)
+    barrier = Barrier(ntasks + 1)
     t1 = asyncio.create_task(cond01_new(cond))
     t3 = asyncio.create_task(cond03_new())
     for n in range(ntasks):
         asyncio.create_task(cond02(n, cond, barrier))
     await barrier  # All instances of cond02 have completed
     # Test wait_for
-    barrier = asyncio.Barrier(2)
+    barrier = Barrier(2)
     asyncio.create_task(cond04(99, cond, barrier))
     await barrier
     # cancel continuously running coros.
     t1.cancel()
     t3.cancel()
-    await asyncio.sleep_ms(0)
+    await asyncio.sleep(0)
     print('Done.')
 
 def condition_test():
@@ -378,7 +387,7 @@ cond04 99 Awaiting notification and predicate.
 cond04 99 triggered. tim = 9
 Done.
 ''', 13)
-    asyncio.run(cond_go())
+    asyncio.get_event_loop().run_until_complete(cond_go())
 
 # ************ Queue test ************
 
@@ -395,7 +404,7 @@ async def mtq(myq):
         await asyncio.sleep(0.2)
 
 async def queue_go():
-    myq = Queue(5)
+    myq = asyncio.Queue(5)
     asyncio.create_task(fillq(myq))
     await mtq(myq)
 
@@ -418,4 +427,4 @@ Retrieved 5 from queue
 Retrieved 6 from queue
 Retrieved 7 from queue
 ''', 3)
-    asyncio.run(queue_go())
+    asyncio.get_event_loop().run_until_complete(queue_go())
diff --git a/uasyncio_iostream/primitives/__init__.py b/uasyncio_iostream/primitives/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/uasyncio_iostream/primitives/barrier.py b/uasyncio_iostream/primitives/barrier.py
new file mode 100644
index 0000000..2cb91ee
--- /dev/null
+++ b/uasyncio_iostream/primitives/barrier.py
@@ -0,0 +1,73 @@
+# Generic Barrier class: runs under CPython 3.8
+
+# A Barrier synchronises N coros. In normal use each issues await barrier.
+# Execution pauses until all other participant coros are waiting on it.
+# At that point the callback is executed. Then the barrier is 'opened' and
+# execution of all participants resumes.
+# .trigger enables a coro to signal it has passed the barrier without waiting.
+
+import asyncio
+
+# Ignore "coroutine '_g' was never awaited" warning.
+async def _g():
+    pass
+type_coro = type(_g())
+
+# If a callback is passed, run it and return.
+# If a coro is passed initiate it and return.
+# coros are passed by name i.e. not using function call syntax.
+
+def launch(func, tup_args):
+    res = func(*tup_args)
+    if isinstance(res, type_coro):
+        asyncio.create_task(res)
+
+
+
+class Barrier():
+    def __init__(self, participants, func=None, args=()):
+        self._participants = participants
+        self._func = func
+        self._args = args
+        self._reset(True)
+
+    def __await__(self):
+        self._update()
+        if self._at_limit():  # All other threads are also at limit
+            if self._func is not None:
+                launch(self._func, self._args)
+            self._reset(not self._down)  # Toggle direction to release others
+            return
+
+        direction = self._down
+        while True:  # Wait until last waiting thread changes the direction
+            if direction != self._down:
+                return
+            yield
+
+    def trigger(self):
+        self._update()
+        if self._at_limit():  # All other threads are also at limit
+            if self._func is not None:
+                launch(self._func, self._args)
+            self._reset(not self._down)  # Toggle direction to release others
+
+    def _reset(self, down):
+        self._down = down
+        self._count = self._participants if down else 0
+
+    def busy(self):
+        if self._down:
+            done = self._count == self._participants
+        else:
+            done = self._count == 0
+        return not done
+
+    def _at_limit(self):  # Has count reached up or down limit?
+        limit = 0 if self._down else self._participants
+        return self._count == limit
+
+    def _update(self):
+        self._count += -1 if self._down else 1
+        if self._count < 0 or self._count > self._participants:
+            raise ValueError('Too many tasks accessing Barrier')
diff --git a/uasyncio_iostream/primitives/message.py b/uasyncio_iostream/primitives/message.py
new file mode 100644
index 0000000..86eb9d6
--- /dev/null
+++ b/uasyncio_iostream/primitives/message.py
@@ -0,0 +1,34 @@
+# message.py
+# A coro waiting on a message issues msg = await message_instance
+# A coro rasing the message issues message_instance.set(msg)
+# When all waiting coros have run
+# message_instance.clear() should be issued
+
+try:
+    import asyncio
+except ImportError:
+    import uasyncio as asyncio
+
+
+class Message(asyncio.Event):
+    def __init__(self):
+        super().__init__()
+        self._data = None
+
+    def clear(self):
+        super().clear()
+
+    def __await__(self):
+        yield from self.wait().__await__()  # CPython
+        return self._data
+
+    def __iter__(self):
+        yield from self.wait()  # MicroPython
+        return self._data
+
+    def set(self, data=None):
+        super().set()
+        self._data = data
+
+    def value(self):
+        return self._data
diff --git a/uasyncio_iostream/uasyncio/barrier.py b/uasyncio_iostream/uasyncio/barrier.py
index 827fdb9..09d574e 100644
--- a/uasyncio_iostream/uasyncio/barrier.py
+++ b/uasyncio_iostream/uasyncio/barrier.py
@@ -1,11 +1,16 @@
-# barrier.py
+# barrier.py MicroPython optimised version
 
-# A Barrier synchronises N coros. Each issues await barrier.
+# A Barrier synchronises N coros. In normal use each issues await barrier.
 # Execution pauses until all other participant coros are waiting on it.
 # At that point the callback is executed. Then the barrier is 'opened' and
 # execution of all participants resumes.
+# .trigger enables a coro to signal it has passed the barrier without waiting.
 
-import uasyncio
+try:
+    import asyncio
+    raise RuntimeError('This version of barrier is MicroPython specific')
+except ImportError:
+    import uasyncio
 
 async def _g():
     pass
@@ -37,7 +42,7 @@ class Barrier():
             while self.waiting.next:
                 uasyncio.tqueue.push_head(self.waiting.pop_head())
 
-    def __iter__(self):
+    def __iter__(self):  # MicroPython
         self._update()
         if self._at_limit():  # All other coros are also at limit
             if self._func is not None:
@@ -72,5 +77,3 @@ class Barrier():
         self._count += -1 if self._down else 1
         if self._count < 0 or self._count > self._participants:
             raise ValueError('Too many tasks accessing Barrier')
-
-uasyncio.Barrier = Barrier
diff --git a/uasyncio_iostream/uasyncio/event.py b/uasyncio_iostream/uasyncio/event.py
index 610067a..e5a5304 100644
--- a/uasyncio_iostream/uasyncio/event.py
+++ b/uasyncio_iostream/uasyncio/event.py
@@ -24,28 +24,3 @@ class Event:
         return True
 
 uasyncio.Event = Event
-
-# A coro waiting on a message issues msg = await Message_instance
-# A coro rasing the message issues event.set(msg)
-# When all waiting coros have run
-# Message.clear() should be issued
-class Message(uasyncio.Event):
-    def __init__(self, delay_ms=0):
-        super().__init__()
-        self._data = None
-
-    def clear(self):
-        super().clear()
-
-    def __iter__(self):
-        await self.wait()
-        return self._data
-
-    def set(self, data=None):
-        super().set()
-        self._data = data
-
-    def value(self):
-        return self._data
-
-uasyncio.Message = Message