Experimental Physics and
Industrial Control System

I try to make epics control system for dg812(Rf signal generator of RIGOL).
The dg812 supported usb commuincation but the protocol is usbtmc so I used drvAsynusbtmc module of asyn. 
However, I faced  some error like below. 

I did the test in centos7 enviroment and the version of asyn is 4-26 and the version of base is 3.14.12.5 .
I also did the test with rasberrypi3 enviroment with same asyn and base version but it shows same error message. 

'Can clear buffer ~' and 'Can't get device capabilities ~'

The most strange thing is about usb mount. When I plug in the usb cable and check the usb mount at /dev, I can check that the usb is succesfully mounted with name 'usbtmc0'. 
However, after I run epics and see the above error, the usb is diconnected so I can't see the 'usbtmc0' at /dev directory.

 That thing happens at centos 7 environment and also in rasberrypi enviroment. 
Can you give me some advice about this error?

Best Regards 

SeokHoMoon