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diff --git a/docs/howto-write-a-block/howto-write-a-block.xml b/docs/howto-write-a-block/howto-write-a-block.xml deleted file mode 100644 index f8027b456..000000000 --- a/docs/howto-write-a-block/howto-write-a-block.xml +++ /dev/null @@ -1,959 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" - "docbookx.dtd" [ - <!ENTITY gnuradio "<application>GNU Radio</application>"> - <!ENTITY SWIG "<application>SWIG</application>"> - <!ENTITY gr_block "<classname>gr_block</classname>"> - <!ENTITY square "<classname>howto_square_ff</classname>"> - - <!ENTITY were "we're"> - <!ENTITY well "we'll"> - <!ENTITY thats "that's"> - <!ENTITY its "it's"> - <!ENTITY lets "let's"> - <!ENTITY youre "you're"> - - <!ENTITY gr_block_listing SYSTEM "gr_block.h.xml"> - <!ENTITY qa_howto_1_listing SYSTEM "qa_howto_1.py.xml"> - <!ENTITY howto_square_ff_h_listing SYSTEM "howto_square_ff.h.xml"> - <!ENTITY howto_square_ff_cc_listing SYSTEM "howto_square_ff.cc.xml"> - <!ENTITY howto_square2_ff_h_listing SYSTEM "howto_square2_ff.h.xml"> - <!ENTITY howto_square2_ff_cc_listing SYSTEM "howto_square2_ff.cc.xml"> - <!ENTITY howto_1_i_listing SYSTEM "howto_1.i.xml"> - <!ENTITY src_lib_Makefile_1_am_listing SYSTEM "src_lib_Makefile_1.am.xml"> - <!ENTITY src_lib_Makefile_2_am_listing SYSTEM "src_lib_Makefile_2.am.xml"> - -]> - -<article> - -<articleinfo> -<title>How to Write a Signal Processing Block</title> -<author> - <firstname>Eric</firstname> - <surname>Blossom</surname> - <affiliation> - <address> - <email>eb@comsec.com</email> - </address> - </affiliation> -</author> - -<revhistory> - <revision> - <revnumber>0.1</revnumber> - <date>2005-01-20</date> - </revision> - <revision> - <revnumber>0.2</revnumber> - <date>2005-02-02</date> - <revremark>Updated for SWIG 1.3.24</revremark> - </revision> - <revision> - <revnumber>0.3</revnumber> - <date>2006-07-21</date> - <revremark>Clarification of 1:1 fixed rate vs item size</revremark> - </revision> -</revhistory> - -<copyright> - <year>2004</year> - <year>2005</year> - <holder>Free Software Foundation, Inc.</holder> -</copyright> - -<abstract><para>This article explains how to write signal -processing blocks for <application>GNU Radio</application>. -</para></abstract> - -</articleinfo> - -<sect1 id="prereqs"><title>Prerequisites</title> -<para>This article assumes that the reader has basic familiarity with -GNU Radio and has read and understood -<ulink url="http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html"> -<citetitle>Exploring GNU Radio</citetitle></ulink>. -</para> - -<para>There is a tarball of files that accompany this article. It -includes the examples, DocBook source for the article and all the -Makefiles etc it takes to make it work. Grab it at <ulink -url="ftp://ftp.gnu.org/gnu/gnuradio"> -ftp://ftp.gnu.org/gnu/gnuradio</ulink> or one of the mirrors. The -file you want is -<filename>gr-howto-write-a-block-X.Y.tar.gz</filename>. Pick the one -with the highest version number. -See <ulink url="http://comsec.com/wiki?CvsAccess"> -http://comsec.com/wiki?CvsAccess</ulink> for CVS Access. -</para> - - -</sect1> - -<sect1 id="intro"><title>Introduction</title> -<para>&gnuradio; provides a framework for building software radios. -Waveforms -- signal processing applications -- are built using a -combination of Python code for high level organization, policy, GUI and -other non performance-critical functions, while performance critical -signal processing blocks are written in C++.</para> - -<para>From the Python point of view, &gnuradio; provides a data flow -abstraction. The fundamental concepts are signal processing -blocks and the connections between them. This abstraction is -implemented by the Python <classname>gr.flow_graph</classname> class. -Each block has a set of input ports and output ports. Each port has -an associated data type. The most common port types are -<classname>float</classname> and <classname>gr_complex</classname> -(equivalent to std::complex<float>), though other types are used, -including those representing structures, arrays or other types of -packetized data.</para> - -<para>From the high level point-of-view, infinite streams of data flow -through the ports. At the C++ level, streams are dealt with in -convenient sized pieces, represented as contiguous arrays of the -underlying type.</para> - -</sect1> - -<sect1 id="overview"><title>The View from 30,000 Feet</title> - -<para>This article will walk through the construction of several -simple signal processing blocks, and explain the techniques and idioms -used. Later sections cover debugging signal processing blocks in the -mixed Python/C++ environment and performance measurement and -optimization.</para> - -<para>The example blocks will be built in the style of all &gnuradio; -extensions. That is, they are built outside of the gnuradio-core build -tree, and are constructed as shared libraries that may be dynamically -loaded into Python using the "import" mechanism. &SWIG;, the -Simplified Wrapper and Interface Generator, is used to generate the -glue that allows our code to be used from Python.</para> - -</sect1> - - -<sect1 id="gr_block"><title></title> - -<para>The C++ class &gr_block; is the base of all signal processing -blocks in &gnuradio;. Writing a new signal processing block involves -creating 3 files: The .h and .cc files that define the new class and -the .i file that tells &SWIG; how to generate the glue that binds the -class into Python. The new class must derive from &gr_block; or -one of it's subclasses.</para> - -<para>Our first examples will derive directly from &gr_block;. Later -we will look at some other subclasses that simplify the process for -common cases.</para> - -</sect1><!-- end gr_block sect1 --> - - - -<!-- ================================================================ --> - -<sect1 id="autotools"><title>Autotools, Makefiles, and Directory Layout</title> - -<para>Before we dive into the code, &lets; talk a bit about the -overall build environment and the directory structure that &well; -be using.</para> - -<para>To reduce the amount of Makefile hacking that we have to do, and -to facilitate portability across a variety of systems, we use the GNU -<application>autoconf</application>, -<application>automake</application>, and -<application>libtool</application> tools. These are collectively -referred to as the autotools, and once you get over the initial -shock, they will become your friends. (The good news is that we -provide boilerplate that can be used pretty much as-is.)</para> - -<variablelist> - -<varlistentry><term>automake</term> - -<listitem><para>automake and configure work together to generate GNU -compliant Makefiles from a much higher level description contained in -the corresponding Makefile.am file. <filename>Makefile.am</filename> -specifies the libraries and programs to build and the source files -that compose each. Automake reads <filename>Makefile.am</filename> -and produces <filename>Makefile.in</filename>. Configure reads -<filename>Makefile.in</filename> and produces -<filename>Makefile</filename>. The resulting Makefile contains a -zillion rules that do the right right thing to build, check and -install your code. It is not uncommon for the the resulting -<filename>Makefile</filename> to be 5 or 6 times larger than -<filename>Makefile.am</filename>.</para> - -</listitem> -</varlistentry> - -<varlistentry><term>autoconf</term> -<listitem><para>autoconf reads <filename>configure.ac</filename> -and produces the <filename>configure</filename> shell -script. <filename>configure</filename> automatically tests for -features of the underlying system and sets a bunch of variables and -defines that can be used in the Makefiles and your C++ code to -conditionalize the build. If features are required but not found, -configure will output an error message and stop.</para> -</listitem> -</varlistentry> - -<varlistentry><term>libtool</term> -<listitem><para>libtool works behind the scenes and provides the magic -to construct shared libraries on a wide variety of systems.</para> -</listitem> -</varlistentry> - -</variablelist> - -<para><xref linkend="dir-layout"/> shows the directory layout and -common files &well; be using. After renaming the -<replaceable>topdir</replaceable> directory, use it in your projects -too. We'll talk about particular files as they come up later.</para> - - -<table id="dir-layout"><title>Directory Layout</title> -<tgroup cols="2"> - -<thead><row> -<entry>File/Dir Name</entry> -<entry>Comment</entry> -</row> -</thead> - -<tbody> - -<row> -<entry><replaceable>topdir</replaceable>/Makefile.am</entry> -<entry>Top level Makefile.am</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/Makefile.common</entry> -<entry>Common fragment included in sub-Makefiles</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/bootstrap</entry> -<entry>Runs autoconf, automake, libtool first time through</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/config</entry> -<entry>Directory of m4 macros used by configure.ac</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/configure.ac</entry> -<entry>Input to autoconf</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/src</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/src/lib</entry> -<entry>C++ code goes here</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/src/lib/Makefile.am</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/src/python</entry> -<entry>Python code goes here</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/src/python/Makefile.am</entry> -</row> -<row> -<entry><replaceable>topdir</replaceable>/src/python/run_tests</entry> -<entry>Script to run tests in the build tree</entry> -</row> - -</tbody> -</tgroup> -</table> - -</sect1> - -<!-- ================================================================ --> - -<sect1 id="naming"><title>Naming Conventions</title> - -<para>&gnuradio; uses a set of naming conventions to assist in -comprehending the code base and gluing C++ and Python together. -Please follow them.</para> - -<sect2 id="camel-case"><title><emphasis>Death to CamelCaseNames!</emphasis></title> - -<para>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.</para> - -<para>With the exception of macros and other constant values, all -identifiers shall be lower case with <literal>words_separated_like_this</literal>.</para> - -<para>Macros and constant values (e.g., enumerated values, -<literal>static const int FOO = 23</literal>) shall be in <literal>UPPER_CASE</literal>.</para> - -</sect2> - -<sect2 id="global_names"><title>Global Names</title> - -<para>All globally visible names (types, functions, variables, consts, etc) -shall begin with a "package prefix", followed by an underscore. The bulk of -the code in GNU Radio belongs to the "gr" package, hence -names look like <literal>gr_open_file (...)</literal>.</para> - -<para>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.</para> - -</sect2> - -<sect2 id="package_prefixes"><title>Package Prefixes</title> - -<para>These are the current package prefixes: - -<variablelist> - -<varlistentry><term>gr_</term> -<listitem><para>Almost everything.</para></listitem> -</varlistentry> - -<varlistentry><term>gri_</term> -<listitem><para> -Implementation primitives. Sometimes we -have both a gr_<replaceable>foo</replaceable> and a gri_<replaceable>foo</replaceable>. In that case, -gr_<replaceable>foo</replaceable> would be derived from gr_block and gri_<replaceable>foo</replaceable> -would be the low level guts of the function.</para></listitem> -</varlistentry> - -<varlistentry><term>atsc_</term> -<listitem><para>Code related to the Advanced Television Standards Committee HDTV implementation -</para></listitem> -</varlistentry> - -<varlistentry><term>usrp_</term> -<listitem><para>Universal Software Radio Peripheral.</para></listitem> -</varlistentry> - -<varlistentry><term>qa_</term> -<listitem><para>Quality Assurance (Test code.)</para></listitem> -</varlistentry> - -</variablelist> - -</para> -</sect2> - -<sect2 id="class-data-members"><title>Class Data Members (instance variables)</title> - -<para>All class data members shall begin with d_<replaceable>foo</replaceable>.</para> - -<para>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_. </para> - -<literallayout> -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) - { - ... - } - ... -}; -</literallayout> - -</sect2> - -<sect2 id="static-data-members"><title>Class Static Data Members (class variables)</title> - -<para> -All class static data members shall begin with s_<replaceable>foo</replaceable>. -</para> - -</sect2> - -<sect2 id="file-names"><title>File Names</title> - -<para>Each significant class shall be contained in its own file. The -declaration of class <classname>gr_foo</classname> shall be in -<filename>gr_foo.h</filename> and the definition in -<filename>gr_foo.cc</filename>.</para> -</sect2> - - -<sect2><title>Suffixes</title> - -<para>By convention, we encode the input and output types of signal -processing blocks in their name using suffixes. The suffix is -typically one or two characters long. Source and sinks have single -character suffixes. Regular blocks that have both inputs and outputs -have two character suffixes. The first character indicates the type -of the input streams, the second indicates the type of the output -streams. FIR filter blocks have a three character suffix, indicating -the type of the inputs, outputs and taps, respectively.</para> - -<para>These are the suffix characters and their interpretations: -<itemizedlist> -<listitem><para>f - single precision floating point</para></listitem> -<listitem><para>c - complex<float></para></listitem> -<listitem><para>s - short (16-bit integer)</para></listitem> -<listitem><para>i - integer (32-bit integer)</para></listitem> -</itemizedlist> -</para> - -<para>In addition, for those cases where the block deals with streams -of vectors, we use the character 'v' as the first character of the -suffix. An example of this usage is -<classname>gr_fft_vcc</classname>. The FFT block takes a vector of -complex numbers on its input and produces a vector of complex -numbers on its output.</para> - -</sect2> - -</sect1> - - - - -<sect1 id="square"><title>First Block: □</title> - -<para>For our first example &well; create a block that computes -the square of its single float input. This block will accept a single -float input stream and produce a single float output stream.</para> - -<para>Following the naming conventions, &well; use -<literal>howto</literal> as our package prefix, and the block will -be called <classname>howto_square_ff</classname>.</para> - -<para>We are going to arrange that this block, as well as the others -that we write in this article, end up in the -<literal>gnuradio.howto</literal> Python module. This will allow us -to access it from Python like this: -<programlisting> -from gnuradio import howto -sqr = howto.square_ff () -</programlisting> -</para> - - -<sect2 id="test_driven"><title>Test Driven Programming</title> - -<para>We could just start banging out the C++ code, but being highly -evolved modern programmers, &were; going to write the test code first. -After all, we do have a good spec for the behavior: take a single -stream of floats as the input and produce a single stream of floats as -the output. The output should be the square of the input.</para> - -<para>How hard could this be? Turns out that this is easy! Check out -<xref linkend="qa_howto_1.py"/>.</para> - -<example id="qa_howto_1.py"> -<title><filename>qa_howto.py</filename> (first version)</title> -&qa_howto_1_listing; -</example> - -<para> -<classname>gr_unittest</classname> is an extension to the standard -python module <classname>unittest</classname>. -<classname>gr_unittest</classname> adds support for checking -approximate equality of tuples of float and complex numbers. -Unittest uses Python's reflection mechanism to find all methods that start with -<methodname>test_</methodname> and runs them. Unittest wraps each call -to <methodname>test_*</methodname> with matching calls to -<methodname>setUp</methodname> and <methodname>tearDown</methodname>. -See the python <ulink url="http://docs.python.org/lib/module-unittest.html"> -unittest</ulink> documentation for details. -</para> - -<para>When we run the test, -gr_unittest.main is going to invoke -<methodname>setUp</methodname>, -<methodname>test_001_square_ff</methodname>, and -<methodname>tearDown</methodname>.</para> -<para> -<methodname>test_001_square_ff</methodname> builds a small graph that -contains three nodes. gr.vector_source_f(src_data) will source the -elements of src_data and then say that &its; finished. howto.square_ff is the block -&were; testing. gr.vector_sink_f gathers the output of -howto.square_ff.</para> - -<para>The <methodname>run</methodname> method runs the graph until all -the blocks indicate they are finished. Finally, we check that the -result of executing square_ff on src_data matches what we expect. -</para> - -</sect2> - -<sect2 id="build_vs_install"><title>Build Tree vs. Install Tree</title> - -<para>The build tree is everything from <replaceable>topdir</replaceable> -(the one containing configure.ac) down. The path to the install tree is -<filename> -<replaceable>prefix</replaceable>/lib/python<replaceable>version</replaceable>/site-packages</filename>, -where <replaceable>prefix</replaceable> is the <literal>--prefix</literal> -argument to configure (default <filename>/usr/local</filename>) and -<replaceable>version</replaceable> is the installed version of -python. A typical value is -<filename>/usr/local/lib/python2.3/site-packages</filename>.</para> - - -<para>We normally set our PYTHONPATH environment variable to point at -the install tree, and do this in <filename>~/.bash_profile</filename> -or <filename>~/.profile</filename>. -This allows our python apps to access all the standard python -libraries, plus our locally installed stuff like GNU Radio.</para> - -<para>We write our applications such that they access the code and -libraries in the install tree. On the other hand, we want our test -code to run on the build tree, where we can detect problems before -installation.</para> - -</sect2> - -<sect2 id="make_check"><title>make check</title> - - -<para>We use <command>make check</command> to run our tests. -Make check invokes the <command>run_tests</command> shell script which -sets up the PYTHONPATH environment variable so that -our tests use the build tree versions of our code and libraries. -It then runs all files -which have names of the form <filename>qa_*.py</filename> and reports -the overall success or failure.</para> - -<para>There is quite a bit of behind-the-scenes action required to use -the non-installed versions of our code (look at -<filename>runtest</filename> for a cheap thrill.)</para> - -<para>Finally, running <command>make check</command> in the python -directory produces this result: -<literallayout> - [eb@bufo python]$ make check - make check-TESTS - make[1]: Entering directory `/home/eb/gr-build/gr-howto-write-a-block/src/python' - Traceback (most recent call last): - File "./qa_howto.py", line 24, in ? - import howto - ImportError: No module named howto - Traceback (most recent call last): - File "./qa_howto_1.py", line 24, in ? - import howto - ImportError: No module named howto - FAIL: run_tests - =================== - 1 of 1 tests failed - =================== - make[1]: *** [check-TESTS] Error 1 - make[1]: Leaving directory `/home/eb/gr-build/gr-howto-write-a-block/src/python' - make: *** [check-am] Error 2 - [eb@bufo python]$ -</literallayout> -Excellent! Our test failed, just as we expected. The ImportError -indicates that it can't find the module named -<classname>howto</classname>. No surprise, since we haven't written it yet. -</para> - -</sect2> - -<sect2><title>The C++ code</title> -<para>Now that we've got a test case written that successfully fails, -let's write the C++ code. As we mentioned earlier, all signal -processing blocks are derived from <classname>gr_block</classname> or -one of its subclasses. Let's take a look at -<xref linkend="gr_block.h"/>.</para> - -<example id="gr_block.h"> -<title><filename>gr_block.h</filename></title> -&gr_block_listing; -</example> - -<para>A quick scan of <filename>gr_block.h</filename> reveals that -since <methodname>general_work</methodname> is pure virtual, we -definitely need to override that. -<methodname>general_work</methodname> is the method that does the -actual signal processing. For our squaring example we'll -need to override <methodname>general_work</methodname> and provide a -constructor and destructor and a bit of stuff to take advantage of -the <ulink url="http://www.boost.org">boost</ulink> -<ulink url="http://www.boost.org/libs/smart_ptr/smart_ptr.htm"> -<classname>shared_ptr</classname>s.</ulink> - -</para> - - -<para><xref linkend="howto_square_ff.h"/> -and <xref linkend="howto_square_ff.cc"/> are the header and c++ -source.</para> - -<example id="howto_square_ff.h"> -<title><filename>howto_square_ff.h</filename></title> -&howto_square_ff_h_listing; -</example> - -<example id="howto_square_ff.cc"> -<title><filename>howto_square_ff.cc</filename></title> -&howto_square_ff_cc_listing; -</example> - -<para>Now we need a Makefile.am to get all this to build. -<xref linkend="src_lib_Makefile_1"/> -is enough to build a shared library from our source file. We'll be -adding additional rules to use &SWIG; in just a bit. If you haven't -already, this is a good time to browse all the Makefile.am's in -the build tree and get an idea for how it all hangs together.</para> - -<example id="src_lib_Makefile_1"> -<title><filename>src/lib/Makefile.am</filename> (no &SWIG;)</title> -&src_lib_Makefile_1_am_listing; -</example> - -</sect2> - - -<!-- ============================== - -<sect2 id="io_sig"><title><classname>gr_io_signature</classname></title> -<para></para> -</sect2> - -<sect2 id="forecast"><title><methodname>forecast</methodname></title> -<para></para> -</sect2> - -<sect2 id="output_multiple"> -<title><methodname>set_output_multiple</methodname></title> -<para></para> -</sect2> - - ============================== --> - - -<sect2 id="swig"><title>The &SWIG; .i file</title> - -<para>Now that we've got something that will compile, we need to write -the &SWIG; .i file. This is a pared-down version of the .h file, plus -a bit of magic that has python work with the boost shared_ptr's. -To reduce code bloat, we only declare methods that &well; want to -access from Python.</para> - -<para>We're going to call the .i file -<filename>howto.i</filename>, and use it to hold the &SWIG; -declarations for all classes from <literal>howto</literal> that will -be accessible from python. It's quite small: -&howto_1_i_listing; -</para> - -</sect2> - -<sect2><title>Putting it all together</title> -<para> -Now we need to modify <filename>src/lib/Makefile.am</filename> -to run &SWIG; and to add the glue it generates to the shared library.</para> - -<example id="src_lib_Makefile_2"> -<title><filename>src/lib/Makefile.am</filename> (with &SWIG;)</title> -&src_lib_Makefile_2_am_listing; -</example> - -<para><command>make</command> now builds everything successfully. We get a -few warnings, but &thats; OK.</para> - -<para>Changing directories back to the python directory we try -<command>make check</command> again: -<literallayout> - [eb@bufo python]$ make check - make check-TESTS - make[1]: Entering directory `/home/eb/gr-build/gr-howto-write-a-block/src/python' - . - ---------------------------------------------------------------------- - Ran 1 test in 0.004s - - OK - PASS: run_tests - ================== - All 1 tests passed - ================== - make[1]: Leaving directory `/home/eb/gr-build/gr-howto-write-a-block/src/python' - [eb@bufo python]$ -</literallayout> -<emphasis>Victory! Our new block works!</emphasis> -</para> - -</sect2> - -</sect1><!-- end First Block: square --> - -<sect1 id="additional_methods"><title>Additional gr_block methods</title> - -<para>In our <classname>howto_square_ff</classname> example above, we only -had to override the <methodname>general_work</methodname> method to -accomplish our goal. <classname>gr_block</classname> provides a few other -methods that are sometimes useful.</para> - -<sect2 id="forecast"><title>forecast</title> - -<para>Looking at <methodname>general_work</methodname> you may -have wondered how the system knows how much data it needs to -ensure is valid in each of the input arrays. The -<methodname>forecast</methodname> method provides this -information.</para> - -<para>The default implementation of <methodname>forecast</methodname> -says there is a 1:1 relationship between noutput_items and the -requirements for each input stream. The size of the items is defined by -<classname>gr_io_signature</classname>s in the constructor of -<classname>gr_block</classname>. The sizes of the input and output items -can of course differ; this still qualifies as a 1:1 relationship. -<programlisting> - // default implementation: 1:1 - - void - gr_block::forecast (int noutput_items, - gr_vector_int &ninput_items_required) - { - unsigned ninputs = ninput_items_required.size (); - for (unsigned i = 0; i < ninputs; i++) - ninput_items_required[i] = noutput_items; - } -</programlisting> -</para> - -<para>Although the 1:1 implementation worked for howto_square_ff, it -wouldn't be appropriate for interpolators, decimators, or blocks -with a more complicated relationship between noutput_items and the -input requirements. That said, by deriving your classes from -<classname>gr_sync_block</classname>, -<classname>gr_sync_interpolator</classname> or -<classname>gr_sync_decimator</classname> instead of -<classname>gr_block</classname>, you can often avoid -implementing <methodname>forecast</methodname>.</para> - -</sect2> - -<sect2 id="set_output_multiple"><title>set_output_multiple</title> - -<para>When implementing your <methodname>general_work</methodname> -routine, &its; occasionally convenient to have the run time system -ensure that you are only asked to produce a number of output items -that is a multiple of some particular value. This might occur if your -algorithm naturally applies to a fixed sized block of data. -Call <methodname>set_output_multiple</methodname> in your constructor -to specify this requirement. The default output multiple is 1.</para> - -</sect2> - -</sect1> - - -<sect1 id="common_patterns"> -<title>Subclasses for common patterns</title> - -<para><classname>gr_block</classname> allows tremendous flexibility -with regard to the consumption of input streams and the production of -output streams. Adroit use of <methodname>forecast</methodname> and -<methodname>consume</methodname> allows variable rate blocks to be -built. It is possible to construct blocks that consume data at -different rates on each input, and produce output at a rate that -is a function of the contents of the input data.</para> - -<para>On the other hand, it is very common for signal processing -blocks to have a fixed relationship between the input rate and the -output rate. Many are 1:1, while others have 1:N or N:1 -relationships.</para> - -<para>Another common requirement is the need to examine more than one -input sample to produce a single output sample. This is orthogonal to -the relationship between input and output rate. For example, a -non-decimating, non-interpolating FIR filter needs to examine N input -samples for each output sample it produces, where N is the number of -taps in the filter. However, it only consumes a single input sample -to produce a single output. We call this concept "history", but you -could also think of it as "look-ahead".</para> - -<sect2 id="gr_sync_block"><title><classname>gr_sync_block</classname></title> - -<para> -<ulink url="http://www.gnu.org/software/gnuradio/doc/classgr__sync__block.html"> -<classname>gr_sync_block</classname></ulink> -is derived from -<ulink url="http://www.gnu.org/software/gnuradio/doc/classgr__block.html"> -<classname>gr_block</classname></ulink> -and implements a 1:1 block with -optional history. Given that we know the input to output rate, -certain simplifications are possible. From the implementor's -point-of-view, the primary change is that we define a -<methodname>work</methodname> method instead of -<methodname>general_work</methodname>. <methodname>work</methodname> -has a slightly different calling sequence; -It omits the unnecessary ninput_items parameter, and arranges for -<methodname>consume_each</methodname> to be called on our -behalf.</para> -<programlisting> - /*! - * \brief Just like gr_block::general_work, only this arranges to - * call consume_each for you. - * - * The user must override work to define the signal processing code - */ - virtual int work (int noutput_items, - gr_vector_const_void_star &input_items, - gr_vector_void_star &output_items) = 0; -</programlisting> - -<para>This gives us fewer things to worry about, and less code to -write. If the block requires history greater than 1, call -<methodname>set_history</methodname> in the constructor, or any time -the requirement changes.</para> - -<para><classname>gr_sync_block</classname> provides a -version of <methodname>forecast</methodname> that handles the -history requirement.</para> - -</sect2> - -<sect2 id="gr_sync_decimator"><title><classname>gr_sync_decimator</classname></title> - -<para> -<ulink url="http://www.gnu.org/software/gnuradio/doc/classgr__sync__decimator.html"> -<classname>gr_sync_decimator</classname></ulink> -is derived from -<ulink url="http://www.gnu.org/software/gnuradio/doc/classgr__sync__block.html"> -<classname>gr_sync_block</classname></ulink> -and implements a N:1 block with optional history. -</para> - -</sect2> - -<sect2 id="gr_sync_interpolator"><title><classname>gr_sync_interpolator</classname></title> - -<para> -<ulink url="http://www.gnu.org/software/gnuradio/doc/classgr__sync__interpolator.html"> -<classname>gr_sync_interpolator</classname></ulink> -is derived from -<ulink url="http://www.gnu.org/software/gnuradio/doc/classgr__sync__block.html"> -<classname>gr_sync_block</classname></ulink> -and implements a 1:N block with optional history. -</para> - -</sect2> - - -</sect1> - -<sect1 id="square2"> -<title>Second Block: <classname>howto_square2_ff</classname></title> - -<para>Given that we now know about -<classname>gr_sync_block</classname>, the way -<classname>howto_square_ff</classname> should really be implemented is -by subclassing <classname>gr_sync_block</classname>.</para> - -<para>Here are the revised sources: <xref -linkend="howto_square2_ff.h"/>, -<xref linkend="howto_square2_ff.cc"/>. -The accompanying files contain the additional test code. -</para> - -<example id="howto_square2_ff.h"> -<title><filename>howto_square2_ff.h</filename></title> -&howto_square2_ff_h_listing; -</example> - -<example id="howto_square2_ff.cc"> -<title><filename>howto_square2_ff.cc</filename></title> -&howto_square2_ff_cc_listing; -</example> - -</sect1> - -<sect1 id="where_to"><title>Where to from Here?</title> - -<para>At this point, we've got a basic overview of how the system -goes together. For more insight, I suggest that you look at the code -of the system. The doxygen generated <ulink -url="http://www.gnu.org/software/gnuradio/doc/hierarchy.html"> class -hierarchy</ulink> is a useful way to find things that might interest -you.</para> - -</sect1> - - -<sect1 id="tips"><title>Miscellaneous Tips</title> - -<sect2 id="sources_and_sinks"><title>Sources and Sinks</title> - -<para>Sources and sinks are derived from -<classname>gr_sync_block</classname>. The only thing different about -them is that sources have no inputs and sinks have no outputs. This -is reflected in the <classname>gr_io_signature</classname>s that are -passed to the <classname>gr_sync_block</classname> constructor. -Take a look at <filename>gr_file_source.{h,cc}</filename> and -<filename>gr_file_sink.{h,cc}</filename> for some very straight-forward examples. -</para> - -</sect2> - -<sect2 id="debugging"> -<title>Debugging with <application>gdb</application></title> - -<para>If your block isn't working, and you can't sort it -out through python test cases or a few printfs in the code, you may want to -use <application>gdb</application> to debug it. The trick of course -is that all of &gnuradio;, including your new block, is dynamically -loaded into python for execution.</para> - -<para>Try this: In your python test code, after the relevant imports, -print out the process id and wait for a keystroke. In another -window run gdb and tell it to attach to the python process with the -given process id. At this point you can set breakpoints or whatever -in your code. Go back to the python window and hit Enter so -it'll continue.</para> - -<programlisting> - #!/usr/bin/env python - from gnuradio import gr - from gnuradio import my_buggy_module - - # insert this in your test code... - import os - print 'Blocked waiting for GDB attach (pid = %d)' % (os.getpid(),) - raw_input ('Press Enter to continue: ') - # remainder of your test code follows... -</programlisting> - -<para>Another SNAFU you might run into is that gdb 6.2 isn't -able to set breakpoints in the constructors or destructors generated -by g++ 3.4. In this case, insert a call to the nop function -gri_debugger_hook in the constructor and recompile. Load the code as -before and set a break point on gri_debugger_hook.</para> - -</sect2> - -<sect2 id="oprofile"> -<title>Performance Measurement with <application>oprofile</application></title> -<para>Oprofile is your friend. -See <ulink url="http://oprofile.sourceforge.net">http://oprofile.sourceforge.net</ulink>. -</para> -</sect2> - -</sect1><!-- end tips --> - -<sect1 id="futures"><title>Coming Attractions</title> -<para></para> - -<sect2 id="types"><title>Improved Type System</title> -<para></para> -</sect2> - -<sect2 id="hierarchy"><title>Hierarchical Blocks</title> -<para></para> -</sect2> - -</sect1><!-- end Coming Attractions --> - -</article> |