diff --git a/zaf_ecode.h b/zaf_ecode.h
index 64954a7..d984dda 100644
--- a/zaf_ecode.h
+++ b/zaf_ecode.h
@@ -10,3 +10,28 @@ typedef enum {
   kxs_ec_lose_connect               = 7,
   kxs_ec_param_error                = 8,
 } zaf_error_code_t;
+
+static const char *zaf_ecode_to_string(zaf_error_code_t ecode) {
+  switch (ecode) {
+    case kxs_ec_success:
+      return "success";
+    case kxs_ec_overtime:
+      return "overtime";
+    case kxs_ec_socket_fail:
+      return "socket fail";
+    case kxs_ec_bind_fail:
+      return "bind fail";
+    case kxs_ec_send_fail:
+      return "send fail";
+    case kxs_ec_receive_fail:
+      return "receive fail";
+    case kxs_ec_setsockopt_rx_timeout_fail:
+      return "setsockopt rx timeout fail";
+    case kxs_ec_lose_connect:
+      return "lose connect";
+    case kxs_ec_param_error:
+      return "param error";
+    default:
+      return "unknown";
+  }
+}
diff --git a/zaf_protocol.h b/zaf_protocol.h
index 53a8dd0..f580c00 100644
--- a/zaf_protocol.h
+++ b/zaf_protocol.h
@@ -9,9 +9,9 @@
 
 #define VERSION(main, sub, fix) (main << 16 | sub << 8 | fix << 0)
 
-#define VERSION_MAIN(v)         ((v >> 16) & 0xFF)
-#define VERSION_SUB(v)          ((v >> 8) & 0xFF)
-#define VERSION_FIX(v)          ((v >> 0) & 0xFF)
+#define VERSION_MAIN(v) ((v >> 16) & 0xFF)
+#define VERSION_SUB(v)  ((v >> 8) & 0xFF)
+#define VERSION_FIX(v)  ((v >> 0) & 0xFF)
 
 #define PACKET_HEADER 0x5A5A
 #define PACKET_TAIL   0xA5A5
@@ -44,6 +44,7 @@ typedef enum {
   kzaf_packet_type_cmd     = 0,
   kzaf_packet_type_receipt = 1,
   kzaf_packet_type_report  = 2,
+  kzaf_packet_type_heart   = 3,
 } zaf_protocol_packet_type_t;
 
 typedef enum {