Re: [Discuss-gnuradio] gr-uhd: rx_freq tag and lo_locked

[Martin Braun]

On 01.04.2015 10:49, Anderson, Douglas J. wrote:
> Martin,
>
> I think we could have the same effect with a much simpler solution:
>
> What about adding an lo_locked metadata tag to the stream of
> samples?

This would require the FPGA to automatically send some kind of 
notification that the LO has locked (our packet format doesn't have such 
a field), and the USRP sink to parse async messages or something like 
that for every sample (at least, every sample after an rx_freq tag). 
This would mean both architectural changes and added processing load.

My assertion 'depends on everything' also was a bit pessimistic. Tune 
time depends on certain parameters, such as devices used (mboard/dboard) 
and some DSP settings; possibly even temperature and other analogs. For 
a given setup, it won't change massively during operation.

So you're right that we're pushing this to the user, but without a 
really tight coupling between the app and the analog front-end (and I 
consider USB or Ethernet not fall into this category), there's not a 
simple solution -- unless you count measuring the delay between the 
first sample with the rx_freq tag and the end of the transition, and 
then statically adding another tag after X many samples, which I don't 
think you were asking for.

Cheers,
M