[Discuss-gnuradio] Create a discontinuous and timed Tx/Rx stream from/to XCVR2450

[Jorge Miguel]

Dear all,

I would like to build an application that:

Between T0 and T1: Transmit my wave
Between T2 and T3: Receive data
Between T4 and T5 Transmit my wave
Between T6 and T7 Receive data
....
Where Tx should be totally defined and controlled (from the minimum possible value to any other value)

Hardware: ONE USRP2 + ONE XCVR2450 daughterboard (which is half-duplex)
Software: Ubuntu 10.10 + (??)

Since the board is half-duplex, I am only worried about switching the XCVR2450 between transmission and reception in the same model and as fast as possible.
Is it possible to do it straightforward in any software platform? From what I learn from my experience and experience of mailing list users:

1) GNU Radio: Aimed at a streaming model as well. 
  I read some information about valve blocks. I use them but I couldn't go further than 200-300ms from T1 to T2 (being my transmitted wave a short pulse).
  Is there anything else than can be done?

  Is it possible to write a C++ block that performs the switching? How?

2) UHD: There are ways to send and receive finite numbers of samples because of the use of timestamps. Is it my solution? What could be the switching time?

If under any of these software platforms my application can be built, what is the minimum expected time since the stop of the transmission to the start of the reception?

Can anybody give some tip?

Many thanks,
Jorge.