About tunnel.py

Hi all,
I want to use tunnel.py to make a usrp with two daughter boards work
as two pieces of wireless cards. The first time I run tunnel.py, it
works well, and generate gr0. But when I run tunnel.py for the second
time (in another terminal) to configure the other daughter board, it
turned out error “Unable to find usrp1”.
Is it possible to generate two wireless cards with only one usrp with
two doughter boards instead of with two usrps? If it is, what should I
Thank you!