diff --git a/core/embed/extmod/modtrezorutils/modtrezorutils.c b/core/embed/extmod/modtrezorutils/modtrezorutils.c
index 81287990a..04e9c2003 100644
--- a/core/embed/extmod/modtrezorutils/modtrezorutils.c
+++ b/core/embed/extmod/modtrezorutils/modtrezorutils.c
@@ -58,15 +58,16 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorutils_consteq_obj,
                                  mod_trezorutils_consteq);
 
 /// def memcpy(
-///     dst: bytearray, dst_ofs: int, src: bytes, src_ofs: int, n: int
+///     dst: bytearray, dst_ofs: int, src: bytes, src_ofs: int, n: int = None
 /// ) -> int:
 ///     """
 ///     Copies at most `n` bytes from `src` at offset `src_ofs` to
-///     `dst` at offset `dst_ofs`.  Returns the number of actually
-///     copied bytes.
+///     `dst` at offset `dst_ofs`. Returns the number of actually
+///     copied bytes. If `n` is not specified, tries to copy
+///     as much as possible.
 ///     """
 STATIC mp_obj_t mod_trezorutils_memcpy(size_t n_args, const mp_obj_t *args) {
-  mp_arg_check_num(n_args, 0, 5, 5, false);
+  mp_arg_check_num(n_args, 0, 4, 5, false);
 
   mp_buffer_info_t dst;
   mp_get_buffer_raise(args[0], &dst, MP_BUFFER_WRITE);
@@ -76,7 +77,12 @@ STATIC mp_obj_t mod_trezorutils_memcpy(size_t n_args, const mp_obj_t *args) {
   mp_get_buffer_raise(args[2], &src, MP_BUFFER_READ);
   uint32_t src_ofs = trezor_obj_get_uint(args[3]);
 
-  uint32_t n = trezor_obj_get_uint(args[4]);
+  uint32_t n = 0;
+  if (n_args > 4) {
+    n = trezor_obj_get_uint(args[4]);
+  } else {
+    n = src.len;
+  }
 
   size_t dst_rem = (dst_ofs < dst.len) ? dst.len - dst_ofs : 0;
   size_t src_rem = (src_ofs < src.len) ? src.len - src_ofs : 0;
@@ -86,7 +92,7 @@ STATIC mp_obj_t mod_trezorutils_memcpy(size_t n_args, const mp_obj_t *args) {
 
   return mp_obj_new_int(ncpy);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorutils_memcpy_obj, 5, 5,
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorutils_memcpy_obj, 4, 5,
                                            mod_trezorutils_memcpy);
 
 /// def halt(msg: str = None) -> None:
diff --git a/core/mocks/generated/trezorutils.pyi b/core/mocks/generated/trezorutils.pyi
index aed9911c0..26746e2d2 100644
--- a/core/mocks/generated/trezorutils.pyi
+++ b/core/mocks/generated/trezorutils.pyi
@@ -13,12 +13,13 @@ def consteq(sec: bytes, pub: bytes) -> bool:
 
 # extmod/modtrezorutils/modtrezorutils.c
 def memcpy(
-    dst: bytearray, dst_ofs: int, src: bytes, src_ofs: int, n: int
+    dst: bytearray, dst_ofs: int, src: bytes, src_ofs: int, n: int = None
 ) -> int:
     """
     Copies at most `n` bytes from `src` at offset `src_ofs` to
-    `dst` at offset `dst_ofs`.  Returns the number of actually
-    copied bytes.
+    `dst` at offset `dst_ofs`. Returns the number of actually
+    copied bytes. If `n` is not specified, tries to copy
+    as much as possible.
     """
 
 
diff --git a/core/src/protobuf.py b/core/src/protobuf.py
index 74e91603d..ff568d44d 100644
--- a/core/src/protobuf.py
+++ b/core/src/protobuf.py
@@ -9,14 +9,14 @@ if False:
     from typing import Any, Dict, Iterable, List, Optional, Type, TypeVar, Union
     from typing_extensions import Protocol
 
-    class AsyncReader(Protocol):
-        async def areadinto(self, buf: bytearray) -> int:
+    class Reader(Protocol):
+        def readinto(self, buf: bytearray) -> int:
             """
             Reads `len(buf)` bytes into `buf`, or raises `EOFError`.
             """
 
-    class AsyncWriter(Protocol):
-        async def awrite(self, buf: bytes) -> int:
+    class Writer(Protocol):
+        def write(self, buf: bytes) -> int:
             """
             Writes all bytes from `buf`, or raises `EOFError`.
             """
@@ -25,20 +25,20 @@ if False:
 _UVARINT_BUFFER = bytearray(1)
 
 
-async def load_uvarint(reader: AsyncReader) -> int:
+def load_uvarint(reader: Reader) -> int:
     buffer = _UVARINT_BUFFER
     result = 0
     shift = 0
     byte = 0x80
     while byte & 0x80:
-        await reader.areadinto(buffer)
+        reader.readinto(buffer)
         byte = buffer[0]
         result += (byte & 0x7F) << shift
         shift += 7
     return result
 
 
-async def dump_uvarint(writer: AsyncWriter, n: int) -> None:
+def dump_uvarint(writer: Writer, n: int) -> None:
     if n < 0:
         raise ValueError("Cannot dump signed value, convert it to unsigned first.")
     buffer = _UVARINT_BUFFER
@@ -46,7 +46,7 @@ async def dump_uvarint(writer: AsyncWriter, n: int) -> None:
     while shifted:
         shifted = n >> 7
         buffer[0] = (n & 0x7F) | (0x80 if shifted else 0x00)
-        await writer.awrite(buffer)
+        writer.write(buffer)
         n = shifted
 
 
@@ -165,15 +165,15 @@ class MessageType:
 
 
 class LimitedReader:
-    def __init__(self, reader: AsyncReader, limit: int) -> None:
+    def __init__(self, reader: Reader, limit: int) -> None:
         self.reader = reader
         self.limit = limit
 
-    async def areadinto(self, buf: bytearray) -> int:
+    def readinto(self, buf: bytearray) -> int:
         if self.limit < len(buf):
             raise EOFError
         else:
-            nread = await self.reader.areadinto(buf)
+            nread = self.reader.readinto(buf)
             self.limit -= nread
             return nread
 
@@ -184,8 +184,8 @@ if False:
     LoadedMessageType = TypeVar("LoadedMessageType", bound=MessageType)
 
 
-async def load_message(
-    reader: AsyncReader, msg_type: Type[LoadedMessageType]
+def load_message(
+    reader: Reader, msg_type: Type[LoadedMessageType]
 ) -> LoadedMessageType:
     fields = msg_type.get_fields()
     msg = msg_type()
@@ -197,7 +197,7 @@ async def load_message(
 
     while True:
         try:
-            fkey = await load_uvarint(reader)
+            fkey = load_uvarint(reader)
         except EOFError:
             break  # no more fields to load
 
@@ -208,10 +208,10 @@ async def load_message(
 
         if field is None:  # unknown field, skip it
             if wtype == 0:
-                await load_uvarint(reader)
+                load_uvarint(reader)
             elif wtype == 2:
-                ivalue = await load_uvarint(reader)
-                await reader.areadinto(bytearray(ivalue))
+                ivalue = load_uvarint(reader)
+                reader.readinto(bytearray(ivalue))
             else:
                 raise ValueError
             continue
@@ -220,7 +220,7 @@ async def load_message(
         if wtype != ftype.WIRE_TYPE:
             raise TypeError  # parsed wire type differs from the schema
 
-        ivalue = await load_uvarint(reader)
+        ivalue = load_uvarint(reader)
 
         if ftype is UVarintType:
             fvalue = ivalue
@@ -232,13 +232,13 @@ async def load_message(
             fvalue = ftype.validate(ivalue)
         elif ftype is BytesType:
             fvalue = bytearray(ivalue)
-            await reader.areadinto(fvalue)
+            reader.readinto(fvalue)
         elif ftype is UnicodeType:
             fvalue = bytearray(ivalue)
-            await reader.areadinto(fvalue)
+            reader.readinto(fvalue)
             fvalue = bytes(fvalue).decode()
         elif issubclass(ftype, MessageType):
-            fvalue = await load_message(LimitedReader(reader, ivalue), ftype)
+            fvalue = load_message(LimitedReader(reader, ivalue), ftype)
         else:
             raise TypeError  # field type is unknown
 
@@ -257,9 +257,7 @@ async def load_message(
     return msg
 
 
-async def dump_message(
-    writer: AsyncWriter, msg: MessageType, fields: Dict = None
-) -> None:
+def dump_message(writer: Writer, msg: MessageType, fields: Dict = None) -> None:
     repvalue = [0]
 
     if fields is None:
@@ -281,39 +279,39 @@ async def dump_message(
         ffields = None  # type: Optional[Dict]
 
         for svalue in fvalue:
-            await dump_uvarint(writer, fkey)
+            dump_uvarint(writer, fkey)
 
             if ftype is UVarintType:
-                await dump_uvarint(writer, svalue)
+                dump_uvarint(writer, svalue)
 
             elif ftype is SVarintType:
-                await dump_uvarint(writer, sint_to_uint(svalue))
+                dump_uvarint(writer, sint_to_uint(svalue))
 
             elif ftype is BoolType:
-                await dump_uvarint(writer, int(svalue))
+                dump_uvarint(writer, int(svalue))
 
             elif isinstance(ftype, EnumType):
-                await dump_uvarint(writer, svalue)
+                dump_uvarint(writer, svalue)
 
             elif ftype is BytesType:
                 if isinstance(svalue, list):
-                    await dump_uvarint(writer, _count_bytes_list(svalue))
+                    dump_uvarint(writer, _count_bytes_list(svalue))
                     for sub_svalue in svalue:
-                        await writer.awrite(sub_svalue)
+                        writer.write(sub_svalue)
                 else:
-                    await dump_uvarint(writer, len(svalue))
-                    await writer.awrite(svalue)
+                    dump_uvarint(writer, len(svalue))
+                    writer.write(svalue)
 
             elif ftype is UnicodeType:
                 svalue = svalue.encode()
-                await dump_uvarint(writer, len(svalue))
-                await writer.awrite(svalue)
+                dump_uvarint(writer, len(svalue))
+                writer.write(svalue)
 
             elif issubclass(ftype, MessageType):
                 if ffields is None:
                     ffields = ftype.get_fields()
-                await dump_uvarint(writer, count_message(svalue, ffields))
-                await dump_message(writer, svalue, ffields)
+                dump_uvarint(writer, count_message(svalue, ffields))
+                dump_message(writer, svalue, ffields)
 
             else:
                 raise TypeError
diff --git a/core/src/trezor/wire/__init__.py b/core/src/trezor/wire/__init__.py
index c64927b4e..f79b5cc16 100644
--- a/core/src/trezor/wire/__init__.py
+++ b/core/src/trezor/wire/__init__.py
@@ -138,6 +138,7 @@ class Context:
     def __init__(self, iface: WireInterface, sid: int) -> None:
         self.iface = iface
         self.sid = sid
+        self.buffer_io = codec_v1.BytesIO(bytearray(8192))
 
     async def call(
         self, msg: protobuf.MessageType, expected_type: Type[protobuf.LoadedMessageType]
@@ -153,11 +154,13 @@ class Context:
         del msg
         return await self.read_any(expected_wire_types)
 
+    async def read_from_wire(self) -> codec_v1.Message:
+        self.buffer_io.seek(0)
+        return await codec_v1.read_message(self.iface, self.buffer_io.buffer)
+
     async def read(
         self, expected_type: Type[protobuf.LoadedMessageType]
     ) -> protobuf.LoadedMessageType:
-        reader = self.make_reader()
-
         if __debug__:
             log.debug(
                 __name__,
@@ -167,14 +170,13 @@ class Context:
                 expected_type,
             )
 
-        # Wait for the message header, contained in the first report.  After
-        # we receive it, we have a message type to match on.
-        await reader.aopen()
+        # Load the full message into a buffer, parse out type and data payload
+        msg = await self.read_from_wire()
 
-        # If we got a message with unexpected type, raise the reader via
+        # If we got a message with unexpected type, raise the message via
         # `UnexpectedMessageError` and let the session handler deal with it.
-        if reader.type != expected_type.MESSAGE_WIRE_TYPE:
-            raise UnexpectedMessageError(reader)
+        if msg.type != expected_type.MESSAGE_WIRE_TYPE:
+            raise UnexpectedMessageError(msg)
 
         if __debug__:
             log.debug(
@@ -187,14 +189,13 @@ class Context:
 
         workflow.idle_timer.touch()
 
-        # parse the message and return it
-        return await protobuf.load_message(reader, expected_type)
+        # look up the protobuf class and parse the message
+        pbtype = messages.get_type(msg.type)
+        return protobuf.load_message(msg.data, pbtype)
 
     async def read_any(
         self, expected_wire_types: Iterable[int]
     ) -> protobuf.MessageType:
-        reader = self.make_reader()
-
         if __debug__:
             log.debug(
                 __name__,
@@ -204,17 +205,16 @@ class Context:
                 expected_wire_types,
             )
 
-        # Wait for the message header, contained in the first report.  After
-        # we receive it, we have a message type to match on.
-        await reader.aopen()
+        # Load the full message into a buffer, parse out type and data payload
+        msg = await self.read_from_wire()
 
-        # If we got a message with unexpected type, raise the reader via
+        # If we got a message with unexpected type, raise the message via
         # `UnexpectedMessageError` and let the session handler deal with it.
-        if reader.type not in expected_wire_types:
-            raise UnexpectedMessageError(reader)
+        if msg.type not in expected_wire_types:
+            raise UnexpectedMessageError(msg)
 
         # find the protobuf type
-        exptype = messages.get_type(reader.type)
+        exptype = messages.get_type(msg.type)
 
         if __debug__:
             log.debug(
@@ -224,24 +224,20 @@ class Context:
         workflow.idle_timer.touch()
 
         # parse the message and return it
-        return await protobuf.load_message(reader, exptype)
+        return protobuf.load_message(msg.data, exptype)
 
     async def write(self, msg: protobuf.MessageType) -> None:
-        writer = self.make_writer()
-
         if __debug__:
             log.debug(
                 __name__, "%s:%x write: %s", self.iface.iface_num(), self.sid, msg
             )
 
-        # get the message size
-        fields = msg.get_fields()
-        size = protobuf.count_message(msg, fields)
-
         # write the message
-        writer.setheader(msg.MESSAGE_WIRE_TYPE, size)
-        await protobuf.dump_message(writer, msg, fields)
-        await writer.aclose()
+        self.buffer_io.seek(0)
+        protobuf.dump_message(self.buffer_io, msg)
+        await codec_v1.write_message(
+            self.iface, msg.MESSAGE_WIRE_TYPE, self.buffer_io.get_written()
+        )
 
     def wait(self, *tasks: Awaitable) -> Any:
         """
@@ -251,43 +247,35 @@ class Context:
         """
         return loop.race(self.read_any(()), *tasks)
 
-    def make_reader(self) -> codec_v1.Reader:
-        return codec_v1.Reader(self.iface)
-
-    def make_writer(self) -> codec_v1.Writer:
-        return codec_v1.Writer(self.iface)
-
 
 class UnexpectedMessageError(Exception):
-    def __init__(self, reader: codec_v1.Reader) -> None:
-        self.reader = reader
+    def __init__(self, msg: codec_v1.Message) -> None:
+        self.msg = msg
 
 
 async def handle_session(
     iface: WireInterface, session_id: int, use_workflow: bool = True
 ) -> None:
     ctx = Context(iface, session_id)
-    next_reader = None  # type: Optional[codec_v1.Reader]
+    next_msg = None  # type: Optional[codec_v1.Message]
     res_msg = None  # type: Optional[protobuf.MessageType]
-    req_reader = None
     req_type = None
     req_msg = None
     while True:
         try:
-            if next_reader is None:
+            if next_msg is None:
                 # We are not currently reading a message, so let's wait for one.
                 # If the decoding fails, exception is raised and we try again
                 # (with the same `Reader` instance, it's OK).  Even in case of
                 # de-synchronized wire communication, report with a message
                 # header is eventually received, after a couple of tries.
-                req_reader = ctx.make_reader()
-                await req_reader.aopen()
+                msg = await ctx.read_from_wire()
 
                 if __debug__:
                     try:
-                        msg_type = messages.get_type(req_reader.type).__name__
+                        msg_type = messages.get_type(msg.type).__name__
                     except KeyError:
-                        msg_type = "%d - unknown message type" % req_reader.type
+                        msg_type = "%d - unknown message type" % msg.type
                     log.debug(
                         __name__,
                         "%s:%x receive: <%s>",
@@ -298,8 +286,8 @@ async def handle_session(
             else:
                 # We have a reader left over from earlier.  We should process
                 # this message instead of waiting for new one.
-                req_reader = next_reader
-                next_reader = None
+                msg = next_msg
+                next_msg = None
 
             # Now we are in a middle of reading a message and we need to decide
             # what to do with it, based on its type from the message header.
@@ -312,13 +300,11 @@ async def handle_session(
 
             # We need to find a handler for this message type.  Should not
             # raise.
-            handler = find_handler(iface, req_reader.type)
+            handler = find_handler(iface, msg.type)
 
             if handler is None:
                 # If no handler is found, we can skip decoding and directly
-                # respond with failure, but first, we should read the rest of
-                # the message reports.  Should not raise.
-                await read_and_throw_away(req_reader)
+                # respond with failure.  Should not raise.
                 res_msg = unexpected_message()
 
             else:
@@ -332,11 +318,11 @@ async def handle_session(
                 try:
                     # Find a protobuf.MessageType subclass that describes this
                     # message.  Raises if the type is not found.
-                    req_type = messages.get_type(req_reader.type)
+                    req_type = messages.get_type(msg.type)
 
                     # Try to decode the message according to schema from
                     # `req_type`. Raises if the message is malformed.
-                    req_msg = await protobuf.load_message(req_reader, req_type)
+                    req_msg = protobuf.load_message(msg.data, req_type)
 
                     # At this point, message reports are all processed and
                     # correctly parsed into `req_msg`.
@@ -364,7 +350,7 @@ async def handle_session(
                     # TODO:
                     # We might handle only the few common cases here, like
                     # Initialize and Cancel.
-                    next_reader = exc.reader
+                    next_msg = exc.msg
                     res_msg = None
 
                 except Exception as exc:
@@ -401,7 +387,6 @@ async def handle_session(
 
             # Cleanup, so garbage collection triggered after un-importing can
             # pick up the trash.
-            req_reader = None
             req_type = None
             req_msg = None
             res_msg = None
diff --git a/core/src/trezor/wire/codec_v1.py b/core/src/trezor/wire/codec_v1.py
index 8a92a5aca..af0526d2c 100644
--- a/core/src/trezor/wire/codec_v1.py
+++ b/core/src/trezor/wire/codec_v1.py
@@ -18,143 +18,112 @@ SESSION_ID = const(0)
 INVALID_TYPE = const(-1)
 
 
-class Reader:
-    """
-    Decoder for a wire codec over the HID (or UDP) layer.  Provides readable
-    async-file-like interface.
-    """
-
-    def __init__(self, iface: WireInterface) -> None:
-        self.iface = iface
-        self.type = INVALID_TYPE
-        self.size = 0
-        self.ofs = 0
-        self.data = bytes()
-
-    def __repr__(self) -> str:
-        return "<Reader type: %s>" % self.type
-
-    async def aopen(self) -> None:
-        """
-        Start reading a message by waiting for initial message report.  Because
-        the first report contains the message header, `self.type` and
-        `self.size` are initialized and available after `aopen()` returns.
-        """
-        read = loop.wait(self.iface.iface_num() | io.POLL_READ)
-        while True:
-            # wait for initial report
-            report = await read
-            marker = report[0]
-            if marker == _REP_MARKER:
-                _, m1, m2, mtype, msize = ustruct.unpack(_REP_INIT, report)
-                if m1 != _REP_MAGIC or m2 != _REP_MAGIC:
-                    raise ValueError
-                break
+class CodecError(Exception):
+    pass
 
-        # load received message header
-        self.type = mtype
-        self.size = msize
-        self.data = report[_REP_INIT_DATA : _REP_INIT_DATA + msize]
-        self.ofs = 0
-
-    async def areadinto(self, buf: bytearray) -> int:
-        """
-        Read exactly `len(buf)` bytes into `buf`, waiting for additional
-        reports, if needed.  Raises `EOFError` if end-of-message is encountered
-        before the full read can be completed.
-        """
-        if self.size < len(buf):
-            raise EOFError
 
-        read = loop.wait(self.iface.iface_num() | io.POLL_READ)
-        nread = 0
-        while nread < len(buf):
-            if self.ofs == len(self.data):
-                # we are at the end of received data
-                # wait for continuation report
-                while True:
-                    report = await read
-                    marker = report[0]
-                    if marker == _REP_MARKER:
-                        break
-                self.data = report[_REP_CONT_DATA : _REP_CONT_DATA + self.size]
-                self.ofs = 0
-
-            # copy as much as possible to target buffer
-            nbytes = utils.memcpy(buf, nread, self.data, self.ofs, len(buf))
-            nread += nbytes
-            self.ofs += nbytes
-            self.size -= nbytes
+class BytesIO:
+    def __init__(self, buffer: bytearray) -> None:
+        self.buffer = buffer
+        self.offset = 0
 
+    def seek(self, offset: int) -> None:
+        offset = min(offset, len(self.buffer))
+        offset = max(offset, 0)
+        self.offset = offset
+
+    def readinto(self, dst: bytearray) -> int:
+        buffer = self.buffer
+        offset = self.offset
+        if len(dst) > len(buffer) - offset:
+            raise EOFError
+        nread = utils.memcpy(dst, 0, buffer, offset)
+        self.offset += nread
         return nread
 
+    def write(self, src: bytes) -> int:
+        buffer = self.buffer
+        offset = self.offset
+        if len(src) > len(buffer) - offset:
+            raise EOFError
+        nwrite = utils.memcpy(buffer, offset, src, 0)
+        self.offset += nwrite
+        return nwrite
+
+    def get_written(self) -> bytes:
+        return memoryview(self.buffer)[: self.offset]
+
 
-class Writer:
-    """
-    Encoder for a wire codec over the HID (or UDP) layer.  Provides writable
-    async-file-like interface.
-    """
-
-    def __init__(self, iface: WireInterface):
-        self.iface = iface
-        self.type = INVALID_TYPE
-        self.size = 0
-        self.ofs = 0
-        self.data = bytearray(_REP_LEN)
-
-    def setheader(self, mtype: int, msize: int) -> None:
-        """
-        Reset the writer state and load the message header with passed type and
-        total message size.
-        """
+class Message:
+    def __init__(self, mtype: int, mdata: BytesIO) -> None:
         self.type = mtype
-        self.size = msize
-        ustruct.pack_into(
-            _REP_INIT, self.data, 0, _REP_MARKER, _REP_MAGIC, _REP_MAGIC, mtype, msize
-        )
-        self.ofs = _REP_INIT_DATA
-
-    async def awrite(self, buf: bytes) -> int:
-        """
-        Encode and write every byte from `buf`.  Does not need to be called in
-        case message has zero length.  Raises `EOFError` if the length of `buf`
-        exceeds the remaining message length.
-        """
-        if self.size < len(buf):
-            raise EOFError
+        self.data = mdata
+
+
+async def read_message(iface: WireInterface, buffer: bytearray) -> Message:
+    read = loop.wait(iface.iface_num() | io.POLL_READ)
+
+    # wait for initial report
+    report = await read
+    if report[0] != _REP_MARKER:
+        raise CodecError("Invalid magic")
+    _, magic1, magic2, mtype, msize = ustruct.unpack(_REP_INIT, report)
+    if magic1 != _REP_MAGIC or magic2 != _REP_MAGIC:
+        raise CodecError("Invalid magic")
+
+    throw_away = False
+    if msize > len(buffer):
+        throw_away = True
+
+    # prepare the backing buffer
+    mdata = memoryview(buffer)[:msize]
+
+    # buffer the initial data
+    nread = utils.memcpy(mdata, 0, report, _REP_INIT_DATA)
+
+    while nread < msize:
+        # wait for continuation report
+        report = await read
+        if report[0] != _REP_MARKER:
+            raise CodecError("Invalid magic")
+
+        # buffer the continuation data
+        if not throw_away:
+            nread += utils.memcpy(mdata, nread, report, _REP_CONT_DATA)
+
+    if throw_away:
+        raise CodecError("Message too large")
+
+    return Message(mtype, BytesIO(mdata))
+
+
+async def write_message(iface: WireInterface, mtype: int, mdata: bytearray) -> None:
+    write = loop.wait(iface.iface_num() | io.POLL_WRITE)
+
+    # gather data from msg
+    msize = len(mdata)
+
+    # prepare the report buffer with header data
+    report = bytearray(_REP_LEN)
+    repofs = _REP_INIT_DATA
+    ustruct.pack_into(
+        _REP_INIT, report, 0, _REP_MARKER, _REP_MAGIC, _REP_MAGIC, mtype, msize
+    )
+
+    nwritten = 0
+    while True:
+        # copy as much as possible to the report buffer
+        nwritten += utils.memcpy(report, repofs, mdata, nwritten)
+
+        # write the report
+        while True:
+            await write
+            n = iface.write(report)
+            if n == len(report):
+                break
 
-        write = loop.wait(self.iface.iface_num() | io.POLL_WRITE)
-        nwritten = 0
-        while nwritten < len(buf):
-            # copy as much as possible to report buffer
-            nbytes = utils.memcpy(self.data, self.ofs, buf, nwritten, len(buf))
-            nwritten += nbytes
-            self.ofs += nbytes
-            self.size -= nbytes
-
-            if self.ofs == _REP_LEN:
-                # we are at the end of the report, flush it
-                while True:
-                    await write
-                    n = self.iface.write(self.data)
-                    if n == len(self.data):
-                        break
-                self.ofs = _REP_CONT_DATA
-
-        return nwritten
-
-    async def aclose(self) -> None:
-        """Flush and close the message transmission."""
-        if self.ofs != _REP_CONT_DATA:
-            # we didn't write anything or last write() wasn't report-aligned,
-            # pad the final report and flush it
-            while self.ofs < _REP_LEN:
-                self.data[self.ofs] = 0x00
-                self.ofs += 1
-
-            write = loop.wait(self.iface.iface_num() | io.POLL_WRITE)
-            while True:
-                await write
-                n = self.iface.write(self.data)
-                if n == len(self.data):
-                    break
+        # if we have more data to write, use continuation reports for it
+        if nwritten < msize:
+            repofs = _REP_CONT_DATA
+        else:
+            break