I am targeting the X440 with a design that has a CHDR_W of 512 and I'd like to use the metadata inside my AXIS stream associated with it. In the RFNoC specification ( https://files.ettus.com/app_notes/RFNoC_Specification.pdf), table 1 shows the CHDR packet with the Metadata being CHDR_W wide. I see the metadata listed in the chdr_packet here is a vector of uint64_t: https://files.ettus.com/manual/classuhd_1_1utils_1_1chdr_1_1chdr__packet.html#aa294b5e5291ae8250dab05f2f0339d3f Are there any examples of building a chdr packet with custom metadata that I can reference? Especially one that might use a different CHDR_W than 64-bits and how that might affect things? Am I venturing into untested territory which may have a lot of potential issues? Any insights would be appreciated. Thanks, Brian

Hey Brian, I do not know of any examples of the top of my head that use metadata for higher CHDR_W’s.\ \ I suspect that on the Host side, 64bit is just the data type used because it is the lowest common denominator for all CHDR_W’s. In the CHDR header , the metadata is not counted in terms of bytes like the length is, but rather in words of CHDR_W. I would expect the UHD host driver to do the correct conversion if needed for your particular usrp image. I am assuming you are asking about how to get access to the metadata inside of a custom RFNoC block. If you have not already, maybe taking a look at the different RFNoC block data plane interface options in the RFNoC specification. Specifically **2.3.3.3 AXI-Stream Payload Context (Simple Interface)** might be useful for your use case. If you use this interface setting, you get separate data streams for payload and context, where context includes a stream of CHDR_W words of either header/timestamp information, or the metadata, with the axi user signals differentiating between the two: If this is not suited for your usecase, and want to implement your own solution, you can take the [chdr_to_axis_pyld_ctxt](https://github.com/EttusResearch/uhd/blob/master/fpga/usrp3/lib/rfnoc/core/chdr_to_axis_pyld_ctxt.v)(or [axis_pyld_ctxt_to_chdr](https://github.com/EttusResearch/uhd/blob/master/fpga/usrp3/lib/rfnoc/core/axis_pyld_ctxt_to_chdr.v) for the opposite direction) as an example of how the noc shell separates context and payload.\ \ Hope this helps, Regards, Niels --- I am targeting the X440 with a design that has a CHDR_W of 512 and I'd like \ to use the metadata inside my AXIS stream associated with it. In the RFNoC specification ( \ <https://files.ettus.com/app_notes/RFNoC_Specification.pdf>), table 1 shows \ the CHDR packet with the Metadata being CHDR_W wide. I see the metadata \ listed in the chdr_packet here is a vector of uint64_t: <https://files.ettus.com/manual/classuhd_1_1utils_1_1chdr_1_1chdr__packet.html#aa294b5e5291ae8250dab05f2f0339d3f> Are there any examples of building a chdr packet with custom metadata that \ I can reference? Especially one that might use a different CHDR_W than \ 64-bits and how that might affect things? Am I venturing into untested territory which may have a lot of potential \ issues? Any insights would be appreciated. Thanks, \ Brian