diff --git a/bluetooth/hci_protocol.cc b/bluetooth/hci_protocol.cc
new file mode 100644
index 0000000..cd709b4
--- /dev/null
+++ b/bluetooth/hci_protocol.cc
@@ -0,0 +1,74 @@
+//
+// Copyright 2017 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include "hci_protocol.h"
+
+#define LOG_TAG "android.hardware.bluetooth-hci-hci_protocol"
+#include <android-base/logging.h>
+#include <assert.h>
+#include <fcntl.h>
+#include <utils/Log.h>
+
+namespace {
+
+const size_t preamble_size_for_type[] = {
+    0, HCI_COMMAND_PREAMBLE_SIZE, HCI_ACL_PREAMBLE_SIZE, HCI_SCO_PREAMBLE_SIZE,
+    HCI_EVENT_PREAMBLE_SIZE};
+const size_t packet_length_offset_for_type[] = {
+    0, HCI_LENGTH_OFFSET_CMD, HCI_LENGTH_OFFSET_ACL, HCI_LENGTH_OFFSET_SCO,
+    HCI_LENGTH_OFFSET_EVT};
+
+size_t HciGetPacketLengthForType(HciPacketType type, const uint8_t* preamble) {
+  size_t offset = packet_length_offset_for_type[type];
+  if (type != HCI_PACKET_TYPE_ACL_DATA) return preamble[offset];
+  return (((preamble[offset + 1]) << 8) | preamble[offset]);
+}
+
+}  // namespace
+
+namespace android {
+namespace hardware {
+namespace bluetooth {
+namespace hci {
+
+size_t HciProtocol::WriteSafely(int fd, const uint8_t* data, size_t length) {
+  size_t transmitted_length = 0;
+  while (length > 0) {
+    ssize_t ret =
+        TEMP_FAILURE_RETRY(write(fd, data + transmitted_length, length));
+
+    if (ret == -1) {
+      if (errno == EAGAIN) continue;
+      ALOGE("%s error writing to UART (%s)", __func__, strerror(errno));
+      break;
+
+    } else if (ret == 0) {
+      // Nothing written :(
+      ALOGE("%s zero bytes written - something went wrong...", __func__);
+      break;
+    }
+
+    transmitted_length += ret;
+    length -= ret;
+  }
+
+  return transmitted_length;
+}
+
+}  // namespace hci
+}  // namespace bluetooth
+}  // namespace hardware
+}  // namespace android