[USRP-users] GPIO with X310

Marcus D. Leech mleech at ripnet.com
Thu Dec 4 16:04:10 EST 2014

On 12/04/2014 04:01 PM, Andy Walls via USRP-users wrote:
> On Thu, 2014-12-04 at 15:37 -0500, Robert Kossler via USRP-users wrote:
>> Hi,
>> 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?
> There are 4 ATR indicators that can be mapped to a GPIO:  Idle, Rx, Tx,
> and Tx+Rx.  In my testing, they all appear to be mutually exclusive.
> So, if you want a "1" value when the transmit is ongoing, regardless of
> receive, you need both the Tx and Tx+Rx indicator mapped to that GPIO
> pin.
One could (please don't shoot me) use an old-school solution to this 
class of problem and insert a COR-type device to turn your bits on and 

>>    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.
> Good question.   Looking at the FPGA source code, it looks like the
> Front Panel GPIO is propagated up from radio 0 (the first daughter card)
> and not at all from radio 1 (the second daughter card).
> Obviously a quick test with a DVM or oscilloscope can be used to verify
> that.
>> 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?
> Another good question.  I can't help here.
>> 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?
> There is no existing GNURadio block.  I had to write my own block for
> GNURadio and GRC.  It is possible.
> Regards,
> Andy
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Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium

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