Wednesday, November 30, 2011

Re: [Discuss-gnuradio] Raw Samples from Receiver

Hi Josh,

Thank you for the answer... I can now see the data of interest in my C++
code.

Your comments, and Marcus', have raised a few question...

Is the item32 data the same before the type conversion regardless of
which type is specified for the source in Python.

By that I mean, if I use gr.COMPLEX_INT16 rather than gr.COMPLEX_FLOAT32
will the system operate the same or does it affect other aspects of the
system? Is the only difference that the IQ samples in the (initial) C++
block will be between -32767 to 32768 rather than in the {+1.0, -1.0}
set.

As background, I have 10 32-bit words of "metadata" prefixed to a burst
of complex samples and I need to extract (and remove) them. I noticed
recently that the trunk has some code related to tagging; in your
opinion would the transport of my "metadata" be better done using
tagging or is there an alternative method you can suggest. It is
important that the "metadata" remain associated exactly with the burst
samples.

Kind regards,

Lukasz

-----Original Message-----
From: discuss-gnuradio-bounces+lukasz.suleja=roke.co.uk@gnu.org
[mailto:discuss-gnuradio-bounces+lukasz.suleja=roke.co.uk@gnu.org] On
Behalf Of Josh Blum
Sent: 30 November 2011 14:26
To: discuss-gnuradio@gnu.org
Subject: Re: [Discuss-gnuradio] Raw Samples from Receiver


> Is there a way of transferring the 32-bit words from the FPGA to a C++
> GR block without the UHD code modifying it?
>
>

You can use the sc16 data type, this will involve a conversion from
item32 to complex<int16> which is basically a byte swap.

You can also use the item32 data type which will just perform endianess
conversion.

Also, both options are available in GRC.

>
> Using wireshark I can see the bytes of interested, but I cannot see
> these in the UHD item32_to_fc32 function. Should I not be able to see
> the bytes as seen in wireshark (UDP payload minus VITA framing) within
> this function?
>
>

All vita payload words pass through the converter function.

-josh

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