On 09/10/2023 10:56, Bachmaier, Luca wrote:
Hi all,
I’m currently implementing a GNU Radio flowgraph that makes use of the
RFNoC FFT block. After fixing a bug found out by Rob Kossler (mail in
this mailing list from September 14) in the UHD repository, the
original problem persists in GNU Radio: trying to use FFT lengths
greater than 256 throws the error “samples per package must not be
smaller than atomic item size”.
When trying to look closer into the problem I noticed that the spp
parameter is set differently when using the UHD python API directly
(script rfnoc_rx_to_file) and when using GNU Radio. I added debug
statements to the rfnoc_rx_streamer block that print the values of spp
and ais.get() (atomic item size). When calling the rfnoc_rx_to_file
script with a spp set to 1024 and an FFT length of 1024 I get the
following output:
[INFO] [0/LogPwr#0] Setting default MTU forward policy.
Using radio 0, channel 0 Attempting to connect FFT:0 to 0/Radio#0:0...
Requesting RX Freq: 0 MHz... Actual RX Freq: 1 MHz...
Waiting for "lo_locked": ++++++++++ locked.
Requesting samples per packet of: 1024
Actual samples per packet = 1024
Using streamer args:
[DEBUG] spp = 18446744073709551615
[DEBUG] ais.get() = 1
[DEBUG] spp = 2000
[DEBUG] ais.get() = 1
[DEBUG] spp = 2000
[DEBUG] ais.get() = 1024
[DEBUG] spp = 1024
[DEBUG] ais.get() = 1024
Since here spp is not smaller than ais.get(), the flowgraph is able to
run. When trying the same as a GNU Radio flowgraph, the output is the
following:
[INFO] [0/LogPwr#0] Setting default MTU forward policy.
[DEBUG] spp = 18446744073709551615
[DEBUG] ais.get() = 1
[DEBUG] spp = 2000
[DEBUG] ais.get() = 1
[DEBUG] spp = 2000
[DEBUG] ais.get() = 2048
[DEBUG] spp = 0
[DEBUG] ais.get() = 2048
For some reason, spp is finally set to zero and ais.get() is set to
2048. I do not understand why, and I also don’t get why the behavior
is different for GNU Radio at all. Is it possible that GNU Radio uses
its own version of UHD? Up until now I believed that GNU Radio simply
uses the already installed UHD implementation over the UHD Python API.
If this is not the case, how can I change this specific GNU Radio UHD
version? I tried looking into the source code of
gnuradio/gr-uhd/lib/rfnoc but I do not understand it unfortunately.
Regards
Luca
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If you installed Gnu Radio from the distros package, it will have been
linked against whatever version of the UHD was also
packaged by the distro.
If you then build UHD from source (with your fixes), Gnu Radio won't see
that version of UHD. What you might need to do is
having built your patched UHD from source, also build Gnu Radio from
source, having first removed the installed-by-the-distro
UHD and Gnu Radio packages.
This is just an emergent property of large complex software systems, the
semantics of compiled languages and linking, and
conflicts between built-from-source, and installed-from-the-distro
packages.
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