[USRP-users] Description of Timestamp & I/Q samples out of the radio & CHDR

Sebastian.Fenn at l-3com.com Sebastian.Fenn at l-3com.com
Wed Dec 10 05:22:16 EST 2014


Can someone please refer me to some accurate documentation, or describe, the structure of (CHDR) data coming out of the radio and into the RFNoC network. In particular:

a) What is the format of the timestamp
b) Where is the timestamp is the packet
c) How the I and Q samples are arranged in the 64  bit words
d) Size and coding of the I/Q samples (e.g. 16 bit signed?)
e) What is a trailer (as indicated by bit 62 in the header)

I am coding up blocks to include in the FPGA fabric, not writing software.

And is there more information on CHDR? I have gleaned some from simulations and the paper "Simplifying FPGA Design with a Novel Network on Chip Architecture". But could do with some more complete descriptions. For example I don't understand why the Packet Size field in Context Packets in various testbenches (e.g. noc_shell_tb.v) is set to 16. And there seems to be a three word acknowledgment of a write to the NoC Shell address space. What is the meaning of the data in these words, I have guessed some of it , but would like confirmation.

I have seen https://github.com/EttusResearch/uhd/wiki/RFNoC:--Specification , but more information would be welcomed. For example is there any guidance on the usage of the "Upstream Flow Control: Cycles per ACK" and "Downstream Flow Control: Buffer size" registers? Some of this information seems inaccurate, for example the " Upstream Flow Control: Packets per ACK" register seems to be tied low.

Thanks in advance. The RFNoC approach seems a great innovation but working out how to add my own logic is proving something of a slog at the moment and I'd welcome more documentation.



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