root/gnuradio/trunk/README.hacking

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Random notes on coding conventions, some explanations about why things
aren't done differently, etc, etc,


* C++ and Python

GNU Radio is now a hybrid system.  Some parts of the system are built
in C++ and some of it in Python.  In general, prefer Python to C++.
Signal processing primitives are still built in C++ for performance.

It is no longer possible to build user applications entirely in C++.
Essential parts of the runtime system have been moved into Python.


* C++ namespaces

In the cleanup process, I considered putting everything in the
gnuradio namespace and dropping the Gr|gr prefix.  In fact, I think
it's probably the right idea, but when I tested it out, I ran into
problems with SWIG's handling of namespaces.  Bottom line, SWIG
(1.3.21) got confused and generated bad code when I started playing
around with namespaces in a not particularly convoluted way.  I saw
problems using the boost::shared_ptr template in combination with
classes defined in the gnuradio namespace.  It wasn't pretty...


* Naming conventions

Death to CamelCaseNames!  We've returned to a kinder, gentler era.
We're now using the "STL style" naming convention with a couple of
modifications since we're not using namespaces.

With the exception of macros and other constant values, all
identifiers shall be lower case with words_separated_like_this.

Macros and constant values (e.g., enumerated values,
static const int FOO = 23) shall be in UPPER_CASE.


** Global names

All globally visible names (types, functions, variables, consts, etc)
shall begin with a "package prefix", followed by an '_'.  The bulk of
the code in GNU Radio logically belongs to the "gr" package, hence
names look like gr_open_file (...).

Large coherent bodies of code may use other package prefixes, but
let's try to keep them to a well thought out list.  See the list
below.

*** Package prefixes

These are the current package prefixes:

    gr_         Almost everything

    gri_        Implementation primitives.  Sometimes we
                have both a gr_<foo> and a gri_<foo>.  In that case,
                gr_<foo> would be derived from gr_block and gri_<foo>
                would be the low level guts of the function.

    atsc_       Code related to the Advanced Television
                Standards Committee HDTV implementation

    usrp_       Universal Software Radio Peripheral

    qa_         Quality Assurance.  Test code.


** Class data members (instance variables)

All class data members shall begin with d_<foo>.

The big win is when you're staring at a block of code it's obvious
which of the things being assigned to persist outside of the block.
This also keeps you from having to be creative with parameter names
for methods and constructors.  You just use the same name as the
instance variable, without the d_. 

class gr_wonderfulness {
  std::string   d_name;
  double        d_wonderfulness_factor;

public:
  gr_wonderfulness (std::string name, double wonderfulness_factor)
    : d_name (name), d_wonderfulness_factor (wonderfulness_factor)
  {
    ...
  }
  ...
};


** Class static data members (class variables)

All class static data members shall begin with s_<foo>.


** File names

Each significant class shall be contained in it's own file.  The
declaration of class gr_foo shall be in gr_foo.h, the definition in
gr_foo.cc.



* Storage management

Strongly consider using the boost smart pointer templates, scoped_ptr
and shared_ptr.  scoped_ptr should be used for locals that contain
pointers to objects that we need to delete when we exit the current
scope.  shared_ptr implements transparent reference counting and is a
major win.  You never have to worry about calling delete.  The right
thing happens.

See http://www.boost.org/libs/smart_ptr/smart_ptr.htm


* Unit tests

Build unit tests for everything non-trivial and run them after every
change.  Check out Extreme Programming: 
http://c2.com/cgi/wiki?ExtremeProgrammingRoadmap

Unit tests should also be written for all examples.  This should kill
off the bit rot we've been plagued with.

** C++ unit tests

For C++ we're using the cppunit framework.  cppunit has its bad
smells, but it's mostly workable.  http://cppunit.sf.net

Currently each directory <dirname> contains files qa_<dirname>.{h,cc}
that bring together all the qa_<foo> test suites in the directory.
We ought to be able to automate this without too much trouble.

The directory gnuradio-core/src/tests contains programs that run
the tests.  test_all runs all of the registered C++ unit tests.

As far as I can tell, the cppunit TestFactoryRegistry maybe able to be
tricked into doing what we want.  As is, I don't think it's enough by
itself, since there's nothing dragging the qa* files out of the
library and into the program.   I haven't tested out this idea.

** Python unit tests

We use the standard unittest package for unit testing of Python code.


* Subversion line ending styles

All text files in the tree should have the subversion property 
'svn:eol-style' set to 'native', with the following exceptions:

config/*.m4
configure.ac
gr-howto-write-a-block/config/*.m4
gr-howto-write-a-block/configure.ac

The easiest way to ensure this is to add or edit the following lines in
your svn client configuration file (~/.subversion/config):

enable-auto-props=yes

[auto-props]
*.c = svn:eol-style=native
*.cc = svn:eol-style=native  
*.i = svn:eol-style=native
*.h = svn:eol-style=native
*.am = svn:eol-style=native
*.py = svn:eol-style=native
*.ac = svn:eol-style=LF
*.m4 = svn:eol-style=LF

* Misc tips

ccache, a compiler cache, can really speed up your builds.
See http://ccache.samba.org/

Be sure to create links for gcc and g++


* Standard command line options

When writing programs that are executable from the command line,
please follow these guidelines for command line argument names (short
and long) and types of the arguments.  We list them below using the
Python optparse syntax.  In general, the default value should be coded
into the help string using the "... [default=%default]" syntax.

** Mandatory options by gr_block

*** USRP source

Any program using a USRP source (usrp.source_*) shall include:

  add_option("", "--which-usrp", type="intx", default=0,
             help="select which USRP to use [default=%default]")

  add_option("-R", "--rx-subdev-spec", type="subdev", default=(0, 0),
             help="select USRP Rx side A or B [default=A]")

You are free to change the default if it makes sense in your application.


*** USRP sink

Any program using a USRP sink (usrp.sink_*) shall include:

  add_option("", "--which-usrp", type="intx", default=0,
             help="select which USRP to use [default=%default]")

  add_option("-T", "--tx-subdev-spec", type="subdev", default=(0, 0),
             help="select USRP Tx side A or B [default=A]")

You are free to change the default if it makes sense in your application.


*** Audio source

Any program using an audio source shall include:

  add_option("-I", "--audio-input", type="string", default="",
             help="pcm input device name.  E.g., hw:0,0 or /dev/dsp")

The default must be "".  This allows an audio module-dependent default
to be specified in the user preferences file.


*** Audio sink

  add_option("-O", "--audio-output", type="string", default="",
             help="pcm output device name.  E.g., hw:0,0 or /dev/dsp")

The default must be "".  This allows an audio module-dependent default
to be specified in the user preferences file.


** Standard options names by parameter

Whenever you want an integer, use the "intx" type.  This allows the
user to input decimal, hex or octal numbers.  E.g., 10, 012, 0xa.

Whenever you want a float, use the "eng_float" type.  This allows the
user to input numbers with SI suffixes.  E.g, 10000, 10k, 10M, 10m, 92.1M

If your program allows the user to specify values for any of the
following parameters, please use these options to specify them:


To specify a frequency (typically an RF center frequency) use:

  add_option("-f", "--freq", type="eng_float", default=<your-default-here>,
             help="set frequency to FREQ [default=%default]")


To specify a decimation factor use:

  add_option("-d", "--decim", type="intx", default=<your-default-here>,
             help="set decimation rate to DECIM [default=%default]")


To specify an interpolation factor use:

  add_option("-i", "--interp", type="intx", default=<your-default-here>,
             help="set interpolation rate to INTERP [default=%default]")


To specify a gain setting use:

  add_option("-g", "--gain", type="eng_float", default=<your-default-here>,
             help="set gain in dB [default=%default]")


If your application specifies both a tx and an rx gain, use:

  add_option("", "--rx-gain", type="eng_float", default=<your-default-here>,
             help="set receive gain in dB [default=%default]")

  add_option("", "--tx-gain", type="eng_float", default=<your-default-here>,
             help="set transmit gain in dB [default=%default]")


To specify the number of channels of something use:

  add_option("-n", "--nchannels", type="intx", default=1,
             help="specify number of channels [default=%default]")


To specify an output filename use:

  add_option("-o", "--output-filename", type="string", default=<your-default-here>,
             help="specify output-filename [default=%default]")


To specify a rate use:

  add_option("-r", "--bit-rate", type="eng_float", default=<your-default-here>,
             help="specify bit-rate [default=%default]")
     or

  add_option("-r", "--sample-rate", type="eng_float", default=<your-default-here>,
             help="specify sample-rate [default=%default]")
  

If your application has a verbose option, use:

  add_option('-v', '--verbose', action="store_true", default=False,
             help="verbose output")


If your application allows the user to specify the "fast USB" options, use: 

  add_option("", "--fusb-block-size", type="intx", default=0,
             help="specify fast usb block size [default=%default]")

  add_option("", "--fusb-nblocks", type="intx", default=0,
             help="specify number of fast usb blocks [default=%default]")