[Discuss-gnuradio] set_auto_tr(), gr_stall, and PTT

[Michael Dickens]

This email is to verify 2 items:

A) As per emails (1) and (2) below, in order to use the set_auto_tr()  
feature on RFX boards, I need to stall the TX path somehow since - 
any- input on the TX path will result in no RX (even all 0's).

B) After searching through gnuradio-core/src/lib, I find no  
"gr_stall" or similar.  Does this block exist anywhere, and if not,  
is there a simple way around it or should I just write the block  
(it's not difficult, but why reinvent the wheel)?  Or does someone  
have an implementation that I can leverage?

The "set_auto_tr()" method sounds from my reading to be a great way  
to go, but the examples I've found in gnuradio-examples instead use  
"subdev.set_enable()" instead ... which from reading through the GNU  
Radio email archives is quite a bit slower than the former.  Thus my  
wondering if anyone is using the former, and if so, how?

Thanks! - MLD

1: < http://lists.gnu.org/archive/html/discuss-gnuradio/2006-09/ 
msg00233.html >
==========================
From: Eric Blossom <address@hidden>
Date: September 23, 2006 6:30:33 PM EDT
To: Bdale Garbee <address@hidden>
Cc: address@hidden
Subject: Re: [Discuss-gnuradio] USRP push-to-talk?

[snip]

(2) Take advantage of the hooks for "auto T/R switching".
The RFX boards use this, but it's ignored by the basic tx and rx.

[snip]

all this depends on your application "stalling" the
transmit path unless it's got something to do.  I seem to recall
that somebody built a "stall" block, but in looking through "general",
I don't see it.  Does this sound familiar to anyone?  Johnathan,
weren't you looking at this?  (It might have been a mute/squelch
block, with the same idea).

As I recall it was going to work like this:

  stall = gr.stall(sizeof_item)

  ...
  stall.set_stall(True)       # Causes the block to consume all input,
                              # but produce no output
  ...
  stall.set_stall(False)      # block copies input to output, producing
                              # and consuming in the normal way

Then your "push to talk" button would just call the set_stall method
as appropriate.

2: < http://lists.gnu.org/archive/html/discuss-gnuradio/2006-11/ 
msg00234.html >
==========================
From: Eric Blossom <address@hidden>
Date: November 14, 2006 10:34:56 PM EST
To: address@hidden
Cc: gnuradio mailing list <address@hidden>
Subject: Re: [Discuss-gnuradio] Re: USRP push-to-talk?

On Mon, Nov 13, 2006 at 09:39:30PM -0500, address@hidden wrote:
[snip]
> 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 ;-)

If you stall the transmit pipeline unless the user is pressing the PTT
button, then Auto T/R is what you want.  In that case, the receiver is
always running, but the transmitter is only producing output when it's
not stalled.

If Tom's around, check with him.  He and I talked about ways to do this.

Eric