diff --git a/src/protobuf.py b/src/protobuf.py
index 7c0d166323..8174874954 100644
--- a/src/protobuf.py
+++ b/src/protobuf.py
@@ -1,6 +1,24 @@
 '''
 Extremely minimal streaming codec for a subset of protobuf.  Supports uint32,
 bytes, string, embedded message and repeated fields.
+
+For de-sererializing (loading) protobuf types, object with `AsyncReader`
+interface is required:
+
+    class AsyncReader:
+        async def areadinto(self, buffer):
+            """
+            Reads `len(buffer)` bytes into `buffer`, or raises `EOFError`.
+            """
+
+For serializing (dumping) protobuf types, object with `AsyncWriter` interface is
+required:
+
+    class AsyncWriter:
+        async def awrite(self, buffer):
+            """
+            Writes all bytes from `buffer`, or raises `EOFError`.
+            """
 '''
 
 from micropython import const
diff --git a/src/trezor/loop.py b/src/trezor/loop.py
index 88826788a3..56be3f98a2 100644
--- a/src/trezor/loop.py
+++ b/src/trezor/loop.py
@@ -120,16 +120,19 @@ def _step_task(task, value):
         else:
             result = task.send(value)
     except StopIteration as e:
-        log.debug(__name__, '%s finished', task)
+        if __debug__:
+            log.debug(__name__, 'finish: %s', task)
     except Exception as e:
-        log.exception(__name__, e)
+        if __debug__:
+            log.exception(__name__, e)
     else:
         if isinstance(result, Syscall):
             result.handle(task)
         elif result is None:
             schedule_task(task)
         else:
-            log.error(__name__, '%s is unknown syscall', result)
+            if __debug__:
+                log.error(__name__, 'unknown syscall: %s', result)
         if after_step_hook:
             after_step_hook()
 
diff --git a/src/trezor/wire/__init__.py b/src/trezor/wire/__init__.py
index 7c5785136e..d39ce22177 100644
--- a/src/trezor/wire/__init__.py
+++ b/src/trezor/wire/__init__.py
@@ -46,6 +46,10 @@ class Context:
         '''
         reader = self.getreader()
 
+        if __debug__:
+            log.debug(__name__, '%s:%x read: %s',
+                      self.iface.iface_num(), self.sid, types)
+
         await reader.aopen()  # wait for the message header
 
         # if we got a message with unexpected type, raise the reader via
@@ -63,6 +67,10 @@ class Context:
         '''
         writer = self.getwriter()
 
+        if __debug__:
+            log.debug(__name__, '%s:%x write: %s',
+                      self.iface.iface_num(), self.sid, msg)
+
         # get the message size
         counter = protobuf.CountingWriter()
         await protobuf.dump_message(counter, msg)
diff --git a/src/trezor/wire/codec_v1.py b/src/trezor/wire/codec_v1.py
index 488a81a0af..01f1553197 100644
--- a/src/trezor/wire/codec_v1.py
+++ b/src/trezor/wire/codec_v1.py
@@ -100,7 +100,7 @@ class Writer:
         self.ofs = 0
 
     def __repr__(self):
-        return '<WriterV2: type=%d size=%dB>' % (self.type, self.size)
+        return '<WriterV1: type=%d size=%dB>' % (self.type, self.size)
 
     def setheader(self, mtype, msize):
         '''
diff --git a/src/trezor/wire/codec_v2.py b/src/trezor/wire/codec_v2.py
index 31176e49b0..afe88032c0 100644
--- a/src/trezor/wire/codec_v2.py
+++ b/src/trezor/wire/codec_v2.py
@@ -124,6 +124,9 @@ class Writer:
         self.ofs = 0
         self.seq = 0
 
+    def __repr__(self):
+        return '<WriterV2: type=%d size=%dB>' % (self.type, self.size)
+
     def setheader(self, mtype, msize):
         '''
         Reset the writer state and load the message header with passed type and