diff --git a/errorcode.cpp b/errorcode.c
similarity index 93%
rename from errorcode.cpp
rename to errorcode.c
index 1151b67..db148c2 100644
--- a/errorcode.cpp
+++ b/errorcode.c
@@ -1,11 +1,9 @@
-#include "errorcode.hpp"
+#include "errorcode.h"
 
 #define ERR2STR(code) \
   case code:          \
     return #code;
 
-namespace iflytop {
-namespace err {
 
 #define ERR_ITERM(enum) \
   { enum, #enum }
@@ -53,5 +51,3 @@ const char* error2str(int32_t code) {
 ecode_table_item_t* error_get_table() { return table; }
 int                 error_get_table_size() { return sizeof(table) / sizeof(table[0]); }
 
-}  // namespace err
-}  // namespace iflytop
diff --git a/errorcode.hpp b/errorcode.h
similarity index 94%
rename from errorcode.hpp
rename to errorcode.h
index 4cd217a..b5f8d4a 100644
--- a/errorcode.hpp
+++ b/errorcode.h
@@ -1,9 +1,9 @@
 #pragma once
 #include <stdint.h>
 
-namespace iflytop {
-namespace err {
-using namespace std;
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 #define ERROR_CODE(errortype, suberrorcode) (errortype + suberrorcode)
 
@@ -50,5 +50,6 @@ const char* error2str(int32_t code);
 ecode_table_item_t* error_get_table();
 int                 error_get_table_size();
 
-}  // namespace err
-}  // namespace iflytop
\ No newline at end of file
+#ifdef __cplusplus
+}
+#endif
diff --git a/protocol.h b/protocol.h
new file mode 100644
index 0000000..ab47f7b
--- /dev/null
+++ b/protocol.h
@@ -0,0 +1,95 @@
+#pragma once
+#include <stdint.h>
+
+#include "errorcode.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define HAND_ACID_BLE_BASE_SIZE 3
+typedef enum {
+  kproto_cmd           = 1,
+  kproto_cmd_receipt   = 2,
+  kproto_report        = 3,
+  kproto_error_receipt = 4,
+} hand_acid_ble_proto_packet_type_t;
+
+typedef enum {
+  kproto_cmd_set_state           = 1,  // set_state
+  kproto_cmd_reset               = 2,  //
+  kproto_cmd_setlong_key_delayms = 3,  //
+
+  kproto_cmd_ble_master_start_scan = 50,  // process by ble master ble_master_start_scan
+  kproto_cmd_ble_master_enter_dfu  = 51,  // process by ble master ble_master_enter_dfu
+  kproto_cmd_ble_master_reset      = 52,  // process by ble master
+
+  kproto_report_key_event       = 101,  // key_event
+  kproto_report_connected_event = 102,  // generater by ble master and slave
+  kproto_report_heart           = 104,  //
+} hand_acid_ble_proto_cmd_t;
+
+typedef enum {
+  khand_acid_m_unset_mode      = 0,  // unset_mode
+  khand_acid_m_jog_mode        = 1,  // jog_mode
+  khand_acid_m_continuous_mode = 2,  // continuous_mode
+} hand_acid_mode_t;
+
+typedef enum {
+  khand_acid_pump_is_idle    = 0,  //
+  khand_acid_pump_is_working = 1,  //
+} hand_pump_working_state_t;
+
+typedef enum {
+  kkey_short_press_event = 0,  //
+  kkey_long_press_event  = 1,  //
+} key_event_t;
+
+typedef enum {
+  kkey_id_mode_and_action_butt,
+  kkey_id_liquid_reflux_butt,
+} key_id_t;
+
+#pragma pack(1)
+typedef struct {
+  uint8_t frame_type;
+  uint8_t frame_index;
+  uint8_t cmd;
+  union {
+    struct {
+      uint8_t hand_acid_mode;           // hand_acid_mode_t
+      uint8_t hand_pump_working_state;  // hand_pump_working_state_t
+    } set_state;
+    //
+    struct {
+      uint8_t scanid[20];  // scan id
+    } ble_master_start_scan;
+
+    struct {
+      uint8_t keyid;     // key_id_t
+      uint8_t keyevent;  // key_event_t
+    } key_event;
+
+    struct {
+      uint8_t connected;
+      uint8_t from_ble_master;
+    } connected_event;
+
+    struct {
+      uint8_t powerlevel;
+    } heart;
+
+    struct {
+      uint32_t longkeydelay;
+    } setlong_key_delayms;
+
+    struct {
+      int32_t ecode;
+    } errreceipt;
+  } data;
+} hand_acid_ble_proto_t;
+#pragma pack()
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/protocol.hpp b/protocol.hpp
deleted file mode 100644
index 819c9b6..0000000
--- a/protocol.hpp
+++ /dev/null
@@ -1,3 +0,0 @@
-#pragma once
-
-#include "errorcode.hpp"