cc2538 znp 的linux u***驱动，出现input/output error，请问是怎么回事？

在Z-Stack Home 1.2.2.42930上，2538的平台，选znp 用u***模拟串口，编译下载后，挂接到linux（2.6.31）下，但cat /dev/ttyACM0，出现input/output error，请问是怎么回事？
/lib/modules/2.6.31/u*** # u*** 1-1: new full speed USB device using ar7240-ehci and address 2
u*** 1-1: New USB device found, idVendor=0451, idProduct=16c8
u*** 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
u*** 1-1: Product: CC2538 USB CDC
u*** 1-1: Manufacturer: Texas Instruments
u*** 1-1: configuration #1 chosen from 1 choice
cdc_acm 1-1:1.0: ttyACM0: USB ACM device

cat: /dev/ttyACM0: Input/output error