연결 직후 FW에서 먼저 MTU Exchange 요청

- 기존: central이 MTU Exchange Request를 보내면 FW에서 응답값 전달
 → central에서 요청하지 않는 경우 기본값 23 유지됨

src/ble/ble_service.c

@@ -78,6 +78,35 @@ static void att_mtu_updated(struct bt_conn *conn, uint16_t tx, uint16_t rx)
                (current_notify_mtu > 3U) ? (current_notify_mtu - 3U) : 0U);
 }
 
+
+/* MTU Exchange 연결 직후 요청 */
+static void mtu_exchange_cb(struct bt_conn *conn, uint8_t err, struct bt_gatt_exchange_params *params)
+{
+    uint16_t uatt;
+
+    ARG_UNUSED(params);
+
+    if (err)
+    {
+        DBG_ERR("[BLE] MTU exchange failed err=%u\r\n", err);
+        return;
+    }
+
+    uatt = bt_gatt_get_uatt_mtu(conn);
+    if (uatt != 0U)
+    {
+        current_notify_mtu = uatt;
+    }
+
+    DBG_PRINTF("[BLE] MTU exchange complete uatt=%u notify_payload=%u\r\n",
+               uatt,
+               (uatt > 3U) ? (uatt - 3U) : 0U);
+}
+
+static struct bt_gatt_exchange_params mtu_exchange_params =
+{
+    .func = mtu_exchange_cb,
+};
 static struct bt_gatt_cb gatt_callbacks =
 {
     .att_mtu_updated = att_mtu_updated,
@@ -416,6 +445,16 @@ static void connected(struct bt_conn *conn, uint8_t err)
     bt_addr_le_to_str(bt_conn_get_dst(conn), addr_str, sizeof(addr_str));
     DBG_CORE("[BLE] Peer: %s\r\n", addr_str); // 연결 정보 출력
 
+
+    err = bt_gatt_exchange_mtu(conn, &mtu_exchange_params);
+    if (err)
+    {
+        DBG_ERR("[BLE] MTU exchange request failed err=%d\r\n", err);
+    }
+    else
+    {
+        DBG_PRINTF("[BLE] MTU exchange requested\r\n");
+    }
     conn_param_update_attempts = 0U;
     last_rx_conn_param_update_ms = 0;