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Re: GRC max sample rate

From: Marcus Müller
Subject: Re: GRC max sample rate
Date: Sat, 25 Jul 2020 11:00:46 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0

Also, it would be super awesome if you could avoid posting question both
here and on usrp-users without telling the other list; that can save
people time not duplicating answers others have given already.

On 25.07.20 10:42, Paul Boven wrote:
> Hi Koyel,
> I was attempting to explain why the output of the USRP block (Complex
> Int16) doesn't directly connect to other blocks. Although no other
> block in GNU radio seems to use the type 'Complex Int16', it is
> actually just a vector of size 2, containing the I and Q samples as 16
> bits int.
> It is possible to connect the USRP source block directly to the File
> Sink block: you just need to set Vec Length to 2 in the File Sink
> block, and set the data type to 'short'.
> Other blocks in GNU Radio can use either the 'Short' or the 'IShort'
> data type, where the latter stands for 'Interleaved Short'. Using the
> 'Vector to Stream' block as described in my previous mail, you can
> convert the vector shorts from the USRP block into interleaved shorts
> which can then be converted into e.g. floats.
> Regards, Paul Boven.
> On 7/25/20 10:22 AM, Koyel Das (Vehere) wrote:
>> Hi Paul,
>> Thanks for your help. Can you please give an example? Like if usrp
>> source outputs 16 bit complex as I Q I Q I Q I Q for 4 IQ samples
>> where I and Q are 16 bit complex then what will be the change in the
>> format after vector to stream conversion? I understood that usrp
>> source block already gives binary file where I and Q are written
>> alternately as above or interleaved. So I am unable to understand
>> when you say vector to stream will interleave I and Q samples.
>> Regards,
>> Koyel
>> Get Outlook for iOS <https://aka.ms/o0ukef>
>> ------------------------------------------------------------------------
>> *From:* Discuss-gnuradio
>> <discuss-gnuradio-bounces+koyel.das=vehere.com@gnu.org> on behalf of
>> Paul Boven <p.boven@xs4all.nl>
>> *Sent:* Saturday, July 25, 2020 1:31:20 PM
>> *To:* discuss-gnuradio@gnu.org <discuss-gnuradio@gnu.org>
>> *Subject:* Re: GRC max sample rate
>> Hi Koyel,
>> On 7/25/20 9:19 AM, Koyel Das (Vehere) wrote:
>>> Will there be packet drops if USRP source is set at 32 bit complex
>>> float in grc when receiving at 100 MSPS each from two channels? That
>>> makes 2*100e6*64 (32 bit I and 32 bit Q) = 12800e6 or 12.8 gbps. I
>>> am unable to set usrp source block to 16 bit complex as then the
>>> usrp source block is not compatible with file sink which doesn’t
>>> have option for 16 bit complex.
>> The USRP block is (as far as I could find) the only block in all of GNU
>> Radio that uses the 'Complex Int16' type. Which is a bit confusing, but
>> it is just a vector with a length of 2, alternating the I and Q channels
>> as 16 bit shorts.
>> You can simply convert it to interleaved int16 by using a 'Vector to
>> Stream' block, with these settings:
>> io_type: short
>> num_items: 2
>> vec_length: 1
>> These 16 bit integers can then be written to disk (if it can keep up),
>> memory, transferred over the network, or turned into floats for further
>> processing.
>> We use this to efficiently stream raw samples over the internet using a
>> ZMQ Pub Sink.
>> Regards, Paul Boven.

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