diff --git a/protocol.h b/protocol.h
index baa9232..e8598d5 100644
--- a/protocol.h
+++ b/protocol.h
@@ -112,8 +112,6 @@ typedef struct {
   } data;
 } hand_acid_ble_proto_t;
 
-#pragma pack()
-
 static inline bool hand_acid_ble_proto_check_packet(hand_acid_ble_proto_t *packet) {
   uint8_t *pu8 = (uint8_t *)packet;
 
@@ -138,6 +136,29 @@ static inline bool hand_acid_ble_proto_check_packet(hand_acid_ble_proto_t *packe
   return true;
 }
 
+static inline uint8_t hand_acid_ble_proto_sum(hand_acid_ble_proto_t *packet) {
+  uint8_t *_packet = (uint8_t *)packet;
+  uint8_t  sum     = 0;
+  for (int i = 0; i < packet->packetlen - 2; i++) {
+    sum += _packet[i];
+  }
+  return sum;
+}
+
+#define PACKET_SET_TAIL(packet)                        \
+  {                                                    \
+    uint8_t *__data               = (uint8_t *)packet; \
+    __data[packet->packetlen - 1] = PACKET_TAIL;       \
+  }
+
+#define PACKET_SET_CHECKSUM(packet)                                  \
+  {                                                                  \
+    uint8_t *__data               = (uint8_t *)packet;               \
+    __data[packet->packetlen - 2] = hand_acid_ble_proto_sum(packet); \
+  }
+
+#pragma pack()
+
 #ifdef __cplusplus
 }
 #endif