串口测试出问题？？

跟着step by step 做串口测试，出现如下现象：

Please press Enter to activate this console.
[root@EmbedSky /]# serial_test
readserailcfg
serialread.dev is /dev/tq2440_serial1
serialread.speed is 57600
serialread.databits is 8
serialread.stopbits is 1
serialread.parity is N
isatty success!
nwrite=20
之后就没反应了，是怎么回事啊，有懂的帮忙解决下。

顶楼上，我也遇到相同的问题“nwrite=15"之后，就什么没有~~求大侠指导~~