[USRP-users] e310, RFNOC, GNURadio Full Duplex, Custom RFNOC Block

Andrew Payne wandrewp at gmail.com
Wed Jul 8 19:25:23 EDT 2020

Actually I have found a clue! In
usrp3/lib/rfnoc/noc_block_keep_one_in_n.v, axi_wrapper simple_mode is
set to off, instead opting to use cvita_hdr_modify.  I opted to use
keep_one_in_n.v in my custom noc_block, BUT, I have set simple mode to
1.  And if I go into usrp3/lib/rfnoc/axi_wrapper.v, at the top the
comments for SIMPLE_MODE say "Automatically handle header
(s_axis_data_tuser), packets must be consumed / produced 1-to-1".
What does this mean?  That the CEs installed at the crossbar are all
beholden to the rate of this CE?  Because remember with my issue, my
custom RFNOC block (which incorporates keep_one_in_n.v with simple
mode enabled) works well, the TX with DUC alone works well, but TX
with DUC and FIFO plus my custom RFNOC block seems to greatly
attenuate TX.  Could the TX stream be slowed down by my custom RFNOC

On Wed, Jul 8, 2020 at 4:37 PM Andrew Payne <wandrewp at gmail.com> wrote:
> I have an issue with my setup I'm hoping to solve.
> I have an e310 running the UHD 3.15 LTS image.
> I have created one custom RFNOC block, which has 2 RX streams, and it
> is composed of the following chain: complex to magnitude ---> moving
> sum ---> keep one in n (n=2048) ---> FIFO with input parameter SIZE=5,
> so then I don't need the RFNOC FIFO block to save space when
> generating the FPGA image file.  The moving sum block generates a sum
> from a power of 2 samples, then I feed the keep one in n block with a
> resulting sum whose LSBs are truncated, effectively dividing by a
> power of 2 to effectively generate a moving average. I am using the
> AXI Wrapper with Simple Mode, noc shell, etc, all generated from the
> rfnoc mod tool.
> It works great, but I also have a TX output signal, just a sine wave,
> in my gnuradio flowgraph.  Its output, depending on the RF center
> frequency, is greatly attenuated (the greatest I can get it is like
> -39dBm, but it falls off to -55).  But if I just have the TX output
> alone without my RX RFNOC block, I can get the output over 0dBm or
> more, haven't tried going higher than that.
> My question is, how can I get the TX signal higher with my full duplex
> RFNOC setup?  Could anything about the RX chain be affecting my TX
> samples, like could it be somehow deleting samples?  Do I need to tag
> the streams in GNURadio so they don't interfere or something?
> Thanks,
> Andrew

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