diff --git a/i2c/asi2c.py b/i2c/asi2c.py
index ade4ea4..995c3eb 100644
--- a/i2c/asi2c.py
+++ b/i2c/asi2c.py
@@ -27,6 +27,10 @@
 import utime
 from micropython import const, schedule
 import io
+import gc
+
+import micropython
+micropython.alloc_emergency_exception_buf(100)
 
 _MP_STREAM_POLL_RD = const(1)
 _MP_STREAM_POLL_WR = const(4)
@@ -36,6 +40,8 @@
 # between Initiator setting a pin and initiating an I2C transfer: ensure
 # Initiator sets up first.
 _DELAY = const(20)  # μs
+# bytes objects are transmitted in blocks of size 16N where N is an integer
+upsize = lambda x : (x + 15) & ~15
 
 # Base class provides user interface and send/receive object buffers
 class Channel(io.IOBase):
@@ -52,8 +58,12 @@ def __init__(self, i2c, own, rem, verbose, rxbufsize):
         self.txbyt = b''  # Data to send
         self.txsiz = bytearray(2)  # Size of .txbyt encoded as 2 bytes
         self.rxbyt = b''
-        self.rxbuf = bytearray(rxbufsize)
+        self.rxbuf = bytearray(upsize(rxbufsize))  # Hold an integer no. of blocks
         self.rx_mv = memoryview(self.rxbuf)
+        self.lstmv = []
+        for n in range(16, len(self.rxbuf) + 16, 16):  # Preallocate memoryviews
+            self.lstmv.append(self.rx_mv[0 : n])  # for all data lengths
+        self.nrx = 0  # No. of bytes received (ignoring padding)
         self.cantx = True  # Remote can accept data
 
     async def _sync(self):
@@ -72,7 +82,7 @@ def waitfor(self, val):  # Initiator overrides
 
     # Get incoming bytes instance from memoryview.
     def _handle_rxd(self, msg):
-        self.rxbyt = bytes(msg)
+        self.rxbyt = bytes(msg[:self.nrx])
 
     def _txdone(self):
         self.txbyt = b''
@@ -122,7 +132,8 @@ def write(self, buf, off, sz):
                 d = buf[off : off + sz]
             d = d.encode()
             l = len(d)
-            self.txbyt = d
+            # Pad to integer no. of blocks
+            self.txbyt = b''.join((d, bytes(upsize(l) - l)))
             self.txsiz[0] = l & 0xff
             self.txsiz[1] = l >> 8
             return l
@@ -148,19 +159,24 @@ class Responder(Channel):
     rxbufsize = 200
     def __init__(self, i2c, pin, pinack, verbose=True):
         super().__init__(i2c, pinack, pin, verbose, self.rxbufsize)
+        self._handle_rxd_ref = self._handle_rxd  # Alocate RAM here
+        self._handler_ref = self._handler
         loop = asyncio.get_event_loop()
         loop.create_task(self._run())
 
     async def _run(self):
         await self._sync()  # own pin ->0, wait for remote pin == 0
-        self.rem.irq(handler = self._handler, trigger = machine.Pin.IRQ_RISING)
+        self.rem.irq(handler = self._handler, trigger = machine.Pin.IRQ_RISING) #, hard = True)
+        while True:
+            await asyncio.sleep(1)
+            gc.collect()
 
     # Request was received: immediately read payload size, then payload
     # On Pyboard blocks for 380μs to 1.2ms for small amounts of data
     def _handler(self, _, sn=bytearray(2), txnull=bytearray(2)):
 #        tstart = utime.ticks_us()  # TEST
         addr = Responder.addr
-        self.rem.irq(handler = None, trigger = machine.Pin.IRQ_RISING)
+        self.rem.irq(handler = None, trigger = machine.Pin.IRQ_RISING) #, hard = True)
         utime.sleep_us(_DELAY)  # Ensure Initiator has set up to write.
         self.i2c.readfrom_into(addr, sn)
         self.own(1)
@@ -171,12 +187,13 @@ def _handler(self, _, sn=bytearray(2), txnull=bytearray(2)):
         if n:
             self.waitfor(1)
             utime.sleep_us(_DELAY)
-            mv = memoryview(self.rx_mv[0 : n])  # allocates
+            mv = self.lstmv[(n >> 4)]
             self.i2c.readfrom_into(addr, mv)
             self.own(1)
             self.waitfor(0)
             self.own(0)
-            schedule(self._handle_rxd, mv)  # Postpone allocation
+            self.nrx = n
+            schedule(self._handle_rxd_ref, mv)  # Postpone allocation
 
         self.own(1)  # Request to send
         self.waitfor(1)
@@ -198,5 +215,5 @@ def _handler(self, _, sn=bytearray(2), txnull=bytearray(2)):
             self.own(0)
             self.waitfor(0)
             self._txdone()  # Invalidate source
-        self.rem.irq(handler = self._handler, trigger = machine.Pin.IRQ_RISING)
+        #self.rem.irq(handler = self._handler_ref, trigger = machine.Pin.IRQ_RISING) #, hard = True)
 #        print('Time: ', utime.ticks_diff(utime.ticks_us(), tstart))
diff --git a/i2c/asi2c_i.py b/i2c/asi2c_i.py
index 2a08735..c8f7bdb 100644
--- a/i2c/asi2c_i.py
+++ b/i2c/asi2c_i.py
@@ -28,7 +28,7 @@
 import utime
 import gc
 from micropython import schedule
-from asi2c import Channel
+from asi2c import Channel, upsize
 
 # The initiator is an I2C slave. It runs on a Pyboard. I2C uses pyb for slave
 # mode, but pins are instantiated using machine.
@@ -85,8 +85,9 @@ async def _run(self):
                 except OSError:
                     break
                 await asyncio.sleep_ms(Initiator.t_poll)
-                self.block_max = max(self.block_max, t)  # self measurement
                 self.block_cnt += 1
+                if self.block_cnt > 2:  # Avoid any start-up effects
+                    self.block_max = max(self.block_max, t)  # self measurement
                 self.block_sum += t
             self.nboots += 1
             if self.reset is None:  # No means of recovery
@@ -128,10 +129,12 @@ def _sendrx(self, rxbusy, sn=bytearray(2), txnull=bytearray(2)):
         if n:
             self.waitfor(1)  # Wait for responder to request send
             self.own(1)  # Acknowledge
-            mv = memoryview(self.rx_mv[0 : n])
+            mv = self.lstmv[(n >> 4)]
+#            mv = memoryview(self.rx_mv[0 : upsize(n)])
             self.i2c.recv(mv, timeout=to)
             self.waitfor(0)
             self.own(0)
+            self.nrx = n
             schedule(self._handle_rxd, mv) # Postpone allocation
             return True
         return False