Re: [Discuss-gnuradio] recording data from 2 USRP daughterboards simultaneously

[Eric Blossom]

On Tue, Aug 21, 2007 at 03:49:30PM -0400, Brent M. Ledvina wrote:
> Hi,
> 
> I am trying to record I/Q data from two daughterboards (currently a  
> TVRX and a RFX400) on one USRP simultaneously. I have no trouble  
> recording data from either of these daughterboards independently, but  
> when I try to record data simultaneously, I receive the following error:
> 
> ------------------------------------------------------------------------ 
> ------
> 
> #./usrp_rx_cfile.py  -R A -d 10 -g 65 -f 491e6 data
> usrp_open_interface:usb_claim_interface: failed interface 2
> could not claim interface 2: Device or resource busy
> usrp_basic_rx: can't open rx interface
> Traceback (most recent call last):
>   File "./usrp_rx_cfile.py", line 105, in ?
>     my_graph().run()
>   File "./usrp_rx_cfile.py", line 61, in __init__
>     self.u = usrp.source_c(decim_rate=options.decim)
>   File "/usr/local/lib/python2.4/site-packages/gnuradio/usrp.py",  
> line 248, in __init__
>     fpga_filename, firmware_filename)
>   File "/usr/local/lib/python2.4/site-packages/gnuradio/usrp1.py",  
> line 1232, in source_c
>     return _usrp1.source_c(*args)
> RuntimeError: can't open usrp1
> 
> 
> ------------------------------------------------------------------------ 
> ------
> 
> This seems to be an inability to open the USB port on the second call  
> to usrp_rx_cfile.py. Is there a simple workaround to this problem?
> 
> Regards,
> Brent

Hi Brent,

You'll need to write a small bit of code.  The Rx side of a USRP can
only be opened once.  Thus, you need a single program that reads input
from both daughterboardsd at the same time.

Take a look at gnuradio-examples/python/multi-antenna/multi_file.py.
It handles 4 simultaneous inputs.  Your case will be similar, only
using 2.  Also, when using 2 inputs, there's no need to load special
fpga firmware.  The standard file works fine.  The channel filter
won't be required either.  We needed it for our application.

Eric