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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