[Discuss-gnuradio] Where is the gain control in cmu_macs?

[David Knox]

I am using the following code: 
https://www.cgran.org/browser/projects/cmu_macs
https://www.cgran.org/browser/projects/cmu_macs  and this is a request for
help with anyone with experience with that code.  I have spent a fair bit of
time looking through gmsk.cc, cmac.cc, .... but I cannot find the parts that
control the gain of the VGA on USRP1.  There are some gain settings but they
seem to be for filters.  The CMAC code makes use of (now deprecated) mblock
messaging, but I am assuming that it is still built on top of the normal
gnuradio base (I believe with a patch to permit mblocks).  

How do I determine which gain control blocks (e.g. AGC/AGC2/..) that it is
using, if any?  George Nychis worked on the project but is less familiar
with the physical layer code, since his project is at a higher MAC layer. 
Does anyone else out there know this off the top of their head?  When I look
at data being received from transmitters placed at long and then short
distances from the USRP using 
https://www.cgran.org/browser/projects/cmu_macs/trunk/src/apps/rx_file.cc
https://www.cgran.org/browser/projects/cmu_macs/trunk/src/apps/rx_file.cc ,
the amplitude of the IQ data, as seen in gmsk.cc, is relatively constant. 
This must be a sign of adaptive gain control (somewhere?) or of saturating
elements in the RF to baseband path, right?

Alternatively, could anyone suggest a method to query and/or control the
gain settings of the USRP1 from C++ source code?  As an alternative to using
the cmu-macs code, I'd also be interested in any working gnuradio companion
implementations of a QPSK/MSK demodulator too.  This would enable me to use
explicit gain control elements (like the AGC blocks) although I am quite
familiar with the c++ source code in the cmu_macs project now and don't
really want to abandon it given the time I've invested already.

Thanks, in advance,
/ David Knox 
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