On 14/03/2011 9:42 AM, Scott Johnston wrote:
Hello Mark,
Is there anyway you could post your code or a link to it on the forum?
I am interested in full duplex communications.
Rest of the gnuradio world,
Does anybody have an example of how to setup a full duplex app?
I am using the uhd with the USRP n210.
TIA
Scott
Marc Epard wrote:
I've been attempting to do a full duplex send/recv using UHD on a
USRP2 with an XCVR2450.
The major problem I had was that issue_stream_cmd nearly always
resulted in a runtime error of "usrp2 no control response". It worked
fine if I transmitted w/o receiving or received w/o transmitting. The
same code also worked when using a 2nd USRP2 for receiving.
After a session with Wireshark and the UHD host source, I had my
"Well, duh" moment. When you call send, the data starts streaming to
the USRP2 right away -- even if you specify a timestamp in the
future. The USRP2 starts sending back PAUSE frames almost
immediately, which throttles not only additional send data, but also
any commands to the control port.
The solution is to call issue_stream_cmd first (and start the recv
thread), then start the send thread. This was simple enough in my app
because I was specifying start times in the future anyway. It does
prevent a method I was going to use on a WBX where I start the send
thread once and scan through several receive frequencies before
stoping the send thread.
Perhaps most of you knew about this gotcha already, but I hope this
will help someone else who encounters the problem. Anyway, it was fun
investigating and I learned a lot more about the UHD host code and
protocols
-Marc
Marc:
The XCVR2450 *hardware* doesn't support full-duplex at all, so no amount
of cleverness on the software side can change that.
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