[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


Hi

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.

Regards

Seb


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