一边是平板 android3.1，作为device端
一边是pc机或者arm板，作为host端

他们之间通过usb线连接，虚拟串口来通信。现在host端发送数据过来，device总是出现丢弃1次数据，50%；而反过来，device发送给host倒是100%成功。
以下为logcat：

host上第1次发过来时情况，看上去device收到数据，但是中间好像卡了：
E/DataRouter( 236): Got command as string
E/DataRouter( 236): last char is 10
E/DataRouter( 236): last second char is 57
E/DataRouter( 236): IsDeviceManagerCmd buffer in usb = 123456789
E/DataRouter( 236):
E/DataRouter( 236): IsDeviceManagerCmd buffer in usb: return false
E/DataRouter( 236): DSR is OFF, can not send the packet to Modem
E/DataRouter( 236): write [19] bytes of data to USB fd[0]
E/DataRouter( 236): Before the usb select

host上第2次发过来时情况，看上去device收到的是第1次卡的数据：
E/DataRouter( 236): After the usb select
D/---JniLog---( 1068): callback len:10, buf:123456789
D/---JniLog---( 1068):
E/DataRouter( 236): Before checking the modem suspend state
E/DataRouter( 236): PDP is resumed now
E/DataRouter( 236): After checking the modem suspend state
D/BatteryService( 292): update start

host上第3次发过来时情况，重复轮回：
E/DataRouter( 236): Got command as string
E/DataRouter( 236): last char is 10
E/DataRouter( 236): last second char is 57
E/DataRouter( 236): IsDeviceManagerCmd buffer in usb = 123456789
E/DataRouter( 236):
E/DataRouter( 236): IsDeviceManagerCmd buffer in usb: return false
E/DataRouter( 236): DSR is OFF, can not send the packet to Modem
E/DataRouter( 236): write [19] bytes of data to USB fd[0]
E/DataRouter( 236): Before the usb select
D/BatteryService( 292): update start

host上第4次发过来时情况：
E/DataRouter( 236): After the usb select
D/---JniLog---( 1068): callback len:10, buf:123456789
D/---JniLog---( 1068):
E/DataRouter( 236): Before checking the modem suspend state
E/DataRouter( 236): PDP is resumed now
E/DataRouter( 236): After checking the modem suspend state