WA4430+FIT模式Console启动时Ctrl-B按键无效

​想将FIT模式刷成FAT模式，通过Console口启动时，按Ctrl+B无效，这里的B不区分大小写吧？

启动日志（在加粗提示出现后按Ctrl+B无效，启动到最后Console就没有反应了，Enter键按了也没有任何反应）：

System is starting... Press Ctrl+D to access BASIC-BOOTWARE MENU Booting Normal Extend BootWare The Extend BootWare is self-decompressing....................Done! **************************************************************************** * * * H3C WA4330-ACN BootWare, Version 1.15 * * * **************************************************************************** Copyright (c) 2004-2017 New H3C Technologies Co., Ltd. Compiled Date : Mar 27 2017 CPU Type : ATHEROS AR9557 CPU L1 Cache : 32KB CPU Clock Speed : 720MHz Memory Type : SDRAM Memory Size : 256MB Memory Speed : 560MHz BootWare Size : 512KB Flash Size : 32MB PCB Version : Ver.B BootWare Validating... Press Ctrl+B to enter extended boot menu... Starting to get the main application file--flash:/wa4300_fit.bin!........... ............................................................................ ................................. The main application file is self-decompressing............................. ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ ............................................................................ .........................................................Done! System application is starting... Startup configuration file does not exist. User interface con0 is available. 

 Press ENTER to get started.