[USRP-users] Timed command in GR (stream TX and command port RX) simulaneous

LEMENAGER Claude claude.lemenager at thalesgroup.com
Tue Nov 14 09:14:08 EST 2017


Hello,

I  try to send frequency radio tuning commands to TX (USRP_SINK) and RX (USRP_SOURCE) in the same Gnu Radio companion design using the same usrp (N210 or X310 for TX and RX.
The USRP_SINK block is feed by a stream which has tags tx_eob and tx_sob associated with tx_time and tx_freq tags (are tx_lo_freq and tx_dsp_freq usable)?.
The URSP_SOURCE receives "command" message with time and dsp_freq, lo_freq keys and pmt values.
The time key of the USRP_SOURCE message has a value delayed (adjustable ) with respect of tx_time tagged in the stream of USRP_SINK.
I can check that, without RX command, TX is OK (external scope and specrum analyzer)
That's not the case when I issue the commands to RX, even when I sleep the delay to send the message and L characters appear (late command error seen by UHD, more delay==> more L).
Remembering that the FIFO of timed command of is common for the board (no TX or RX specific FIFO) the question is :
how to avoid discrepancy in the time between TX stream (or PDU-tagged stream Block) and RX commands? (I think my RX command arrives in the FIFO before the tx_sob/tx_freq tag)

is it possible to put a tx_freq tag with a tx_eob tag on a stream (is then the lo prepositioned?)?

Excuse me is somebody asked about the same problem before (I don't find tracks about that).

Can anybody help?

Thanks for support

Claude Leménager

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