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

Josh Blum josh at ettus.com
Thu Feb 7 16:41:19 EST 2013



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
>>>
>>> _______________________________________________
>>> USRP-users mailing list
>>> USRP-users at lists.ettus.com
>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>>
>>
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