Re: [Discuss-gnuradio] Need help: How to extract timestamps of data for UHD mimo source block?

[Josh Blum]

> 1). I read the codes in the work function. The metadata is defined by:
>       uhd::rx_metadata_t metadata;
>
>      Does "uhd::rx_metadata_t" define the data type or give values to
> metadata?  And in which C++ file may I find that the "uhd::rx_metadata_t" is
> created ?

http://www.ettus.com/uhd_docs/doxygen/html/structuhd_1_1rx__metadata__t.html

> 2). Is metadata a scaler or vector? I use 4 USRP2 boards for MIMO receiver
> system. Does metadata contain 4 groups of timestamps for each 4 USRP2 boards
> or just 1 group of timestamps for the whole synchronised data?

"scalar" that is 1 metadata struct for all N aligned channels.

> 3). When I use the UHD MIMO Source block, GNU Radio Companion shows the
> following sentences:
>
>     Current recv sock buff size: 50000000 bytes
>     Current recv sock buff size: 50000000 bytes
>     Current recv sock buff size: 50000000 bytes
>     Current recv sock buff size: 50000000 bytes
>     Using: Flex 2400 MIMO B RX (0x0027)
>     Using: Flex 2400 MIMO B TX (0x002b)
>     Using: Flex 2400 MIMO B RX (0x0027)
>     Using: Flex 2400 MIMO B TX (0x002b)
>     Using: Flex 2400 MIMO B RX (0x0027)
>     Using: Flex 2400 MIMO B TX (0x002b)
>     Using: Flex 2400 MIMO B RX (0x0027)
>     Using: Flex 2400 MIMO B TX (0x002b)
>     RX samples per packet: 362
>     TX samples per packet: 363
>     Recv pirate num frames: 33967
>     Set time with unknown pps edge:
>         1) set times next pps (race condition)
>         2) catch seconds rollover at pps edge
>         3) set times next pps (synchronously)
>     Time was reset successfully on board 1 relative to board 0
>     Time was reset successfully on board 2 relative to board 0
>     Time was reset successfully on board 3 relative to board 0
>
> Do they mean that 4 boards are synchronised and have the same timestamps? In
> which C++ script may I find this sentence :" Time was reset successfully on
> board 1 relative to board 0" ?

Yes, it means that all N boards have the same time in their time 
registers. The code here:

http://ettus-apps.sourcerepo.com/redmine/ettus/projects/uhd/repository/revisions/master/entry/host/lib/usrp/mimo_usrp.cpp#L116

I cannot say where "Time was reset" is in the code, I am surprised to 
see those last 3 lines.

-Josh