[USRP-users] Using multiple RX DDC chains on USRP2

Roy Thompson rthompso at gmail.com
Fri Feb 8 15:53:02 EST 2013


Is there any way to stream both channels with different rates into the
same flowgraph in GNURadio (i.e. 2 sources)?   From what I can tell,
the answer is no but I figured I'd ask before trying to come up with a
hack for it.

Thanks,
Roy

On Thu, Feb 7, 2013 at 4:41 PM, Josh Blum <josh at ettus.com> wrote:
>
>
> On 02/07/2013 03:30 PM, Roy Thompson wrote:
>> Thanks, will that work if the chains have different sample rates?
>> There is a comment in multi_usrp.hpp stating that all channels must
>> have the same rate, but it's not clear what causes the limitation
>> since it looks like it is possible to set the rate for individual
>> channels with set_rx_rate().
>
> Yes, all the api calls take a channel number. So in this case, you would
> want a different rx_streamer for each channel, since they are at
> different rates.
>
> -josh
>
>>
>> -Roy
>>
>> On Thu, Feb 7, 2013 at 4:17 PM, Josh Blum <josh at ettus.com> wrote:
>>>
>>>
>>> On 02/07/2013 02:49 PM, Roy Thompson wrote:
>>>> I am starting to look through some of the FPGA code for the USRP2 and
>>>> I noticed that there are 2 RX DDC chains.  I would like to be able to
>>>> use one of the chains to do standard DDC processing, and I would like
>>>> to modify the second chain to do custom processing on the same A/D
>>>> channel.  The output sample rate for the second chain will be
>>>> different from the first. Is it possible to configure the UHD driver
>>>> to support this configuration and allow for receiving from both
>>>> chains?
>>>>
>>>
>>> The rx_multi_samples example can show you how to use two DDC chains. If
>>> you had a WBX for example with frontend (named 0), this would map
>>> frontend 0 located on the first and only daughterboard (named A) to DSP0
>>> and DSP1 --subdev="A:0 A:0"
>>>
>>> see the --help for more.
>>>
>>>> std::cout <<
>>>>         "    This is a demonstration of how to receive aligned data from multiple channels.\n"
>>>>         "    This example can receive from multiple DSPs, multiple motherboards, or both.\n"
>>>>         "    The MIMO cable or PPS can be used to synchronize the configuration. See --sync\n"
>>>>         "\n"
>>>>         "    Specify --subdev to select multiple channels per motherboard.\n"
>>>>         "      Ex: --subdev=\"0:A 0:B\" to get 2 channels on a Basic RX.\n"
>>>>         "\n"
>>>>         "    Specify --args to select multiple motherboards in a configuration.\n"
>>>>         "      Ex: --args=\"addr0=192.168.10.2, addr1=192.168.10.3\"\n"
>>>>         << std::endl;
>>>
>>>
>>> See this readme, there is a place where it should be convenient to
>>> replace the DDC with custom logic:
>>>
>>> http://code.ettus.com/redmine/ettus/projects/uhd/repository/revisions/master/entry/fpga/README.txt
>>>
>>> -josh
>>>
>>>> Thanks,
>>>> Roy
>>>>
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>>>
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