Re: [Discuss-gnuradio] Modulation/Demodulation Blocks' Function details

[Christian Gagneraud]

On 09/08/12 18:55, Frederick Lee wrote:
> Hi GNURadio community,
>
> I'm looking into how the modulation and demodulation blocks work.
> Specifically the BPSK mod and demod blocks. Here is a list of the files
> I looked through and the location:
>
> generic_mod_demod.py - */gr-digital/python
> modulation_utils.py - */gr-digital/python
> bpsk.py - */gr-digital/python
> digital_constellation.h - */gr-digital/include
> digital_constellation.cc - */gr-digital/lib
> digital_swig.py - */build/gr-digital/swig
>
> gr_phase_modulator_fc.h - */gnuradio-core/src/lib/general
> gr_phase_modulator_fc.cc - */gnuradio-core/src/lib/general
>
> digital_gmskmod_bc.h - */gr-digital/include
> digital_gmskmod_bc.cc - */gr-digital/lib
>
> gr_diff_encoder_bb.h - */gnuradio-core/src/lib/general        for
> differntialBPSK
> gr_diff_encoder_bb.cc - */gnuradio-core/src/lib/general        for
> differntialBPSK
>
> gr_unpack_k_bits_bb.h - */gnuradio-core/src/lib/general
> gr_unpack_k_bits_bb.cc - */gnuradio-core/src/lib/general
>
> Are there any other files I should look at the get an understanding what
> happens to the bits?
>
> In the generic_mod_demod.py file, I come across functions like
> digital.map_bb(mod_codes.invert_code(self._constellation.pre_diff_code()))
> and I find the function map_bb in the digital_swig.py file. But the only
> code there is
> return _digital_swig.map_bb(*args, **kwargs)
> I can't find anything on _digital_swig no matter where I look.
> _digital_swig was set to something at the beginning of the file, but I
> couldn't understand it. Can someone tell me where to look to find the
> source code for the _digital_swig.maps_bb() and the
> _digital_swig.pfb_clock_sync_ccf() functions?

Swig stuff are python bindings to C or C++ code. So in your example 
pfb_clock_sync_ccf() has been coded in C++, and 
_digital_swig.pfb_clock_sync_ccf() is the generated python wrapper to 
access the C++ pfb_clock_sync_ccf() from a python script.
The C++ code is in include/ and lib/, swig bindings are in swig/ and 
pure python code is in python/

See http://gnuradio.org/redmine/projects/gnuradio/wiki/Coding_guide_impl


> Also another thing I've been wondering is why is there the DIGITAL_API
> in some lines. For example,
> class DIGITAL_API digital_constellation : public
> boost::enable_shared_from_this<digital_constellation>
> What is the point of DIGITAL_API?
This is a standard way to import/export symbols from/to .so or .dll in a 
platform/OS agnostic way.
Look at gr-digital/include/digital_api.h

Hope this help.
Chris

> Thanks a lot,
> Frederick
>
>
> This body part will be downloaded on demand.


--
Christian Gagneraud,
Embedded systems engineer.
Techworks Marine
1 Harbour road
Dun Laoghaire
Co. Dublin
Ireland
Tel: + 353 (0) 1 236 5990
Web: http://www.techworks.ie/