[Discuss-gnuradio] register io

[Zhuocheng Yang]

So I took a look at serial_io.v. I understand the idea now, you just shift in 
the serial_addr first and then shift in the serial_data if you want to write. 
Upon read, the highest bit of serial_addr should be set to one. In 
usrp_inband_usb.v, inputs to serial_io.v is set to be inputs of the higher 
level file. Is it ok for me to change those inputs to be outputs of my own 
logic block? I am not sure if that will cause any problem.

Leo