On 27/08/2024 01:16, Olo via USRP-users wrote:
I have an additional question related to my current project involving
RFNoC. Specifically, I need to implement as many narrowband channels
(DDC) as possible to record various parts of the spectrum as required.
I’m wondering if it would be more efficient to handle this through
RFNoC or directly on a GPU? Additionally, how many narrowband channels
of specific bandwidths could I implement using RFNoC, considering I
primarily intend to store (record) the data into memory? I have a
clear understanding of the memory and network interface requirements,
but I am uncertain about the implications for CPU usage and RAM.
Could you provide some guidance on this aspect?
My guess is that you wouldn't be able to create dozens of DDCs, due to
resource constraints in the FPGA, but adding a handful
more might not be that big a deal.
But I've never done this, so, just a roughly-educated guess.
Olo.
On Monday, August 26th, 2024 at 7:13 PM, Olo via USRP-users
<usrp-users@lists.ettus.com> wrote:
Thank you for your detailed responses to my previous questions. I
appreciate the information provided about the limitations and
potential issues related to FFT size and TwinRX configuration.
However, I noticed that there was no feedback regarding the YAML file
I attached in my original email. Could you please review it and let
me know if the configuration I've set up is correct?
Additionally, based on your recommendations, I plan to use a window
function (Window block) with a size of 1024, along with an FFT block
of the same size for the scanner (sweep spectrum) functionality.
Would this approach be correct given the current limitations and your
suggestions?
Your confirmation on these points would be invaluable to ensure that
I am on the right track with my project.
Thank you once again for your time and assistance. I look forward to
your response.
Best regards,
Olo.
On Monday, August 26th, 2024 at 18:04, Rob Kossler via USRP-users
<usrp-users@lists.ettus.com> wrote:
On Mon, Aug 26, 2024 at 10:24 AM Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 26/08/2024 10:21, Rob Kossler via USRP-users wrote:
Hi Olo,
On one point regarding an FFT length of 8192, there is likely
an issue with using the Ettus FFT block. In the past (I haven't
checked recently), this block was limited to a maximum FFT size
of 1024 because the entire FFT had to fit in one packet where
the maximum packet payload was about 2000 samples. It is
possible to use larger FFTs, but this requires some custom code
that divorces the FFT size from the packet size.
Rob
My understanding is that in recent RFNoC, the limit has been
raised to 2048:
https://files.ettus.com/manual/classuhd_1_1rfnoc_1_1fft__block__control.html
The xci file
<https://github.com/EttusResearch/uhd/blob/master/fpga/usrp3/lib/ip/axi_fft/axi_fft.xci>
still shows a transform length of 1024. Also, I think that the X300
MTU size is 10 which implies 2^10=1024 x 64bit is the max payload.
This implies 2048 32-bit words in the payload. But, because of a few
bytes of header, it is not possible to use an FFT of length 2048
unless the FFT length is divorced from the packet length.
Rob
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