Hello Marcus,
Thank you for your detailed explanation. I was able to fix the problem now: I
updated GNU Radio from 3.10.5 (installed over apt) to 3.10.7 (installed from
source). With the newer version the FFT block now correctly displays a noise
floor.
So far so good, the FFT resolution is still low as I cannot set the size higher
than 256 (Error “samples per package must not be smaller than atomic item
size”). As far as I understood, the size should be able to go as high as 2048
when using 10Gbit streaming.
My current configuration should enable that:
- MTU on my interface is set to 9000
- Parameter spp of RFNoC RX Radio is set to 2048
- Current FPGA image is of XG type
In case it’s helpful, here’s the relevant output of `ip a` of my devices:
Host:
4: enp9s0f1np1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc
mq state UP group default qlen 1000
link/ether 9c:6b:00:16:8e:96 brd ff:ff:ff:ff:ff:ff
inet 192.168.10.3/24 scope global enp9s0f1np1
valid_lft forever preferred_lft forever
USRP:
3: sfp0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc
pfifo_fast qlen 1000
link/ether 00:80:2f:31:28:42 brd ff:ff:ff:ff:ff:ff
inet 192.168.10.2/24 brd 192.168.10.255 scope global sfp0
valid_lft forever preferred_lft forever
Von: Marcus D. Leech <patchvonbr...@gmail.com>
Gesendet: Montag, 4. September 2023 17:09
An: Bachmaier, Luca <luca.bachma...@iis.fraunhofer.de>;
usrp-users@lists.ettus.com
Cc: Nieland, Michael <michael.niel...@iis.fraunhofer.de>
Betreff: Re: AW: AW: [USRP-users] Re: RFNoC: strange behavior of FFT block
On 04/09/2023 04:32, Bachmaier, Luca wrote:
Hello Marcus,
I’m currently using a USRP N310. Could you please explain what you wrote a
little more? Where can I set the “fft_scaling” parameter, directly in GNU
Radio, over the Python API, …? How do I set it there?
Thank you and regards
Luca
In "Block Args" you would specify:
"fft_scaling=<number>"
Where <number> is a decimal constant corresponding to the desired scaling
schedule as described in the document
I referred to from Xilinx.
That's about as much as I know. You should probably spend some time with that
Xilinx document.
Von: Marcus D. Leech <patchvonbr...@gmail.com><mailto:patchvonbr...@gmail.com>
Gesendet: Mittwoch, 23. August 2023 17:10
An: Bachmaier, Luca
<luca.bachma...@iis.fraunhofer.de><mailto:luca.bachma...@iis.fraunhofer.de>;
usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com>
Betreff: Re: AW: [USRP-users] Re: RFNoC: strange behavior of FFT block
On 23/08/2023 08:47, Bachmaier, Luca wrote:
Are you talking about the gain of the “RFNoC Rx Radio” block or a software gain
block before the FFT? Even with the highest possible hardware gain it doesn’t
seem to work.
So, the "fft_scaling" parameter is actually a kind of bit-mapped value,
described here:
https://support.xilinx.com/s/article/1160838?language=en_US
Von: Marcus D. Leech <patchvonbr...@gmail.com><mailto:patchvonbr...@gmail.com>
Gesendet: Montag, 21. August 2023 16:49
An: usrp-users@lists.ettus.com<mailto:usrp-users@lists.ettus.com>
Betreff: [USRP-users] Re: RFNoC: strange behavior of FFT block
On 21/08/2023 09:04, Bachmaier, Luca wrote:
Hello everyone,
I’m currently running into issues while trying to use the RFNoC FFT block in
GNU Radio. A picture of my GNU Radio flowgraph and its QT GUI Vector Sink
output are attached.
The configuration of UHD / my USRP should be correct as there are no problems
when I stream the RFNoC RX Radio Data to my host and calculate the FFT on the
host. However, when I try calculating the FFT on the FPGA, the output seems to
make no sense. I can’t see a noise floor or any proper signals. There’s just a
randomly appearing and disappearing DC spike. Other than that, the spectrum is
just a flat line (see vector_sink.png).
I think that this problem comes from some faulty configuration of the RFNoC FFT
block. Unfortuantely, I haven’t been able to find any helpful and up-to-date
information about its usage online. I would be very glad to get some help from
this mailing list.
Thank you and regards
Luca
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You could try increasing the gain--it may be that due to the integer
implementation of the FFT, the signal levels are dropping below
the minimum quantization.
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