[USRP-users] GPIO with X310

Robert Kossler Robert.D.Kossler.3 at nd.edu
Thu Dec 4 15:37:19 EST 2014

I would like to trigger some external instrumentation when my X310 begins
transmitting.  I have reviewed the GPIO documentation and it seems that the
ATR functionality with the GPIO pins would work well for me.  However, I
have a few questions:
1) I see that I can set a particular GPIO pin to output a "1" during
transmit, but what does "transmit" mean?  Since there are two channels,
does it mean transmit on either channel?  I don't see a way to specify this
behavior as a function of the transmit channel.
2) I am not looking for really precise accuracy (really, about 1 msec is
good enough), but I would like for this transmit bit rising edge to occur
at the same time as the RF signal appears at the SMA connector.  Does this
seem possible?  If not, perhaps there would at least be a "fixed" delay
between the onset of the transmit bit and the RF?
3) I see how this is called from C++ using set_gpio_attr.  However, I would
like to do this from GNU radio.  Is this possible?  Are there any examples?

Thank you.
Rob Kossler
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