[Discuss-gnuradio] Re: USRP push-to-talk?

[scaperot]

all,

I am interested in controlling the USRP to do a half duplex operation: (when I
say transmit, stop receiving, and when I say receive, stop transmit).  I have
been reading about the output enable registers, and in a previous discussion,
you suggested doing something like:

u_rx = usrp.source_c()
u_rx.subdev = ...

u_tx = usrp_sink_c()
u_tx.subdev = ...

and for a transmit only you might do: u_tx._write_oe(u_tx.subdev._which, 0xffff,
0xffff)
and likewise for the receive only.

I am nervous about this option after reading the in the comments: "Using this
method incorrectly will kill your USRP motherboard and / or daughterboard." 
I'm guessing that the way in which you have suggested above is sufficient, but
are there some caviats that I should be aware of the would make me break the
USRP?  Also, the first arguement in the _write_oe method is the "value" and the
second is the "mask".  I'm a bit confused as to  what is meant by the two.  are
there ever cases where the "value" and the "mask" are different?  From the
comments I know that value is "value to write into register" and mask is "which
bits of value to write into reg."  During default operation (or in auto
switching), I'm guessing that the mask is changed to allow for flexible changes
in the data flow in Transmit and Receive (Am I close??).  Is it dangerous to
write to the write_oe register often?? There may be times where it would be
helpful for it to change from TX to RX to TX in under a second...

Also, in a previous e-mail you suggested using Auto T/R in a push-to-talk case. 
Would this help in the situation where I want just a half-duplex system?  My
understanding of the Auto T/R says no, but that doesn't mean that I'm right ;-)

Thanks!

David Scaperoth