[Discuss-gnuradio] tune_request feature for UHD's USRP blocks in GRC

[Josh Blum]

A few people have mentioned wanting to tune the UHD's USRP source/sink
block without any tune error correction in the FPGA DSP. Described here:
http://files.ettus.com/uhd_docs/manual/html/general.html#tuning-notes


So you can do this in python with tune_request as follows:
tr = uhd.tune_request(target_freq)
tr.dsp_freq = 0
tr.dsp_freq_policy = uhd.tune_request.POLICY_MANUAL
usrp.set_center_freq(tr)


However, this is cumbersome to setup the struct inside GRC. So, I added
a convenience constructor that initializes the struct using **kwargs:
Inside the tune frequency parameter, use this one-liner instead:
uhd.tune_request(target_freq, dsp_freq=0,
dsp_freq_policy=uhd.tune_request.POLICY_MANUAL)


If you want to use this feature, go ahead and cherry-pick this change. I
tested out that the constructor works but have not yet given it a live
run:
http://gnuradio.org/cgit/jblum.git/commit/?h=uhd_tune_req_kwargs&id=fe4a627dee67cc05e1516fdbacd977a8cbca89a6

-Josh