Hi, I just modified one of my RFNoC blocks to use metadata for the first time. The following remarks identify issues I encountered along the way and some suggestions that would make things a bit easier.
- You can't use axis_data (with sideband signals) if you want access to metadata. While I realize that Ettus has indicated that metadata is an "advanced" use case and that the axis_data interface is a "simple" interface model, it still seems like it wouldn't be that difficult to expand the axis_data model to accommodate some metadata capability - Along the same lines, any block that uses axis_data will discard any metadata from an upstream block. This is probably the bigger issue. For example, if the rx radio were to insert a metadata word, it would be discarded by the DDC since the DDC uses the axis_data model - There is no structure to the metadata. I fully understand that this is by intent. However, I did start to wonder if some skeleton structure would make sense. For example, maybe some bits of the metadata should be designated for the NOC_ID of the block that inserts it. Or, instead, maybe some bits could hold a unique WORD_ID that identifies the type of metadata word. Ettus could reserve some IDs for itself to allow for future use of metadata by Ettus blocks. - It would be nice if it was easier for a block to just "insert" a metadata word. With my own limited FPGA skills, I just decided to ignore any upstream metadata words and create 1 metadata word that gets sent to downstream blocks. But, that's not very friendly to the upstream blocks. If it were easier to do, I would have preferred to just add my block's metadata word to the incoming metadata words.
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