综述
本文通过在GNU Radio 中编写一个block的例子，系统介绍创建一个block的过程。该 block 的功能是可以在GRC中通过滑块(WX GUI Slider)来实时改变信号源(Signal Source)的相位偏移。
步骤详解
1. 使用 gr_modtool 工具创建 block 的框架，GNU Radio 会自动帮我们创建所需要的文件及文件夹。
$ gr_modtool newmod myblk
Creating out-of-tree module in ./gr-myblk... Done.
Use 'gr_modtool add' to add a new block to this currently empty module.
$ cd gr-myblk
/gr-myblk$ ls
apps cmake CMakeLists.txt docs examples grc include lib python swig
2. 使用Git版本控制(可选)
在gr-myblock文件夹下执行以下命令，创建一个Git仓库，可用于版本控制。git常用命令速查点这里。
/gr-myblk$ git init
3. 添加block
执行以下命令添加block。参数类型为double，因为我们要传递的角度是0~360度double类型，不填默认没有参数，但后期可以自己添加。根据是否需要Python或者C++测试代码选择Y或者n，如果不填默认为Y。
/gr-myblk$ gr_modtool add -t sync phase_offset
GNU Radio module name identified: myblk
Language: C++
Block/code identifier: phase_offset
Enter valid argument list, including default arguments: double angle
Add Python QA code? [Y/n] n
Add C++ QA code? [Y/n] n
Adding file 'lib/phase_offset_impl.h'...
Adding file 'lib/phase_offset_impl.cc'...
Adding file 'include/myblk/phase_offset.h'...
Editing swig/myblk_swig.i...
Adding file 'grc/myblk_phase_offset.xml'...
Editing grc/CMakeLists.txt...
4. 编辑代码
从上一条命令的输出可以看出，gr_modtood已经为我们自动创建了4个文件，分别是:
- lib/phase_offset_impl.h
- lib/phase_offset_impl.cc
- include/myblk/phase_offset.h
- grc/myblk_phase_offset.xml
分别修改这4个文件如下：
/* -*- c++ -*- */
/*
* Copyright 2016 <+YOU OR YOUR COMPANY+>.
*
* This is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this software; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/ #ifdef HAVE_CONFIG_H
#include "config.h"
#endif #include <gnuradio/io_signature.h>
#include "phase_offset_impl.h" namespace gr {
namespace myblk { phase_offset::sptr
phase_offset::make(double angle)
{
return gnuradio::get_initial_sptr
(new phase_offset_impl(angle));
} /*
* The private constructor
*/
phase_offset_impl::phase_offset_impl(double angle)
: gr::sync_block("phase_offset",
gr::io_signature::make(, , sizeof(gr_complex)),
gr::io_signature::make(, , sizeof(gr_complex)))
, d_offset_angle(angle)
{} /*
* Our virtual destructor.
*/
phase_offset_impl::~phase_offset_impl()
{
} int
phase_offset_impl::work(int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
const gr_complex *in = (const gr_complex *) input_items[];
gr_complex *out = (gr_complex *) output_items[]; double rad = d_offset_angle/*PI;//将角度变成弧度
// Do <+signal processing+>
for (int i = ; i < noutput_items; ++i)
{
out[i] = in[i] * gr_complex(cos(rad), sin(rad));
} std::cout << "d_offset_angle = " << d_offset_angle << std::endl; // Tell runtime system how many output items we produced.
return noutput_items;
} } /* namespace myblk */
} /* namespace gr */
phase_offset_impl.cc
/* -*- c++ -*- */
/*
* Copyright 2016 <+YOU OR YOUR COMPANY+>.
*
* This is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this software; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/ #ifndef INCLUDED_MYBLK_PHASE_OFFSET_IMPL_H
#define INCLUDED_MYBLK_PHASE_OFFSET_IMPL_H #include <myblk/phase_offset.h> namespace gr {
namespace myblk { class phase_offset_impl : public phase_offset
{
private:
double d_offset_angle; public:
phase_offset_impl(double angle);
~phase_offset_impl(); void set_angle_offset(double angle)
{
d_offset_angle = angle;
} // Where all the action really happens
int work(int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items);
}; } // namespace myblk
} // namespace gr #endif /* INCLUDED_MYBLK_PHASE_OFFSET_IMPL_H */
phase_offset_impl.h
/* -*- c++ -*- */
/*
* Copyright 2016 <+YOU OR YOUR COMPANY+>.
*
* This is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3, or (at your option)
* any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this software; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/ #ifndef INCLUDED_MYBLK_PHASE_OFFSET_H
#define INCLUDED_MYBLK_PHASE_OFFSET_H #include <myblk/api.h>
#include <gnuradio/sync_block.h> #define PI 3.14159265358979323846 namespace gr {
namespace myblk { /*!
* \brief <+description of block+>
* \ingroup myblk
*
*/
class MYBLK_API phase_offset : virtual public gr::sync_block
{
public:
typedef boost::shared_ptr<phase_offset> sptr; /*!
* \brief Return a shared_ptr to a new instance of myblk::phase_offset.
*
* To avoid accidental use of raw pointers, myblk::phase_offset's
* constructor is in a private implementation
* class. myblk::phase_offset::make is the public interface for
* creating new instances.
*/
static sptr make(double angle);
virtual void set_angle_offset(double angle) = ;
}; } // namespace myblk
} // namespace gr #endif /* INCLUDED_MYBLK_PHASE_OFFSET_H */
phase_offset.h
<block>
<name>Phase offset</name>
<key>myblk_phase_offset</key>
<category>MYBLK</category>
<import>import myblk</import>
<make>myblk.phase_offset($angle)</make>
<callback>set_angle_offset($angle)</callback>
<param>
<name>Angle</name>
<key>angle</key>
<value>0</value>
<type>real</type>
</param>
<sink>
<name>in</name>
<type>complex</type>
</sink>
<source>
<name>out</name>
<type>complex</type>
</source>
</block>
myblk_phase_offset.xml
5. 编译
依次执行下面的命令完成编译工作
/gr-myblk$ mkdir build
/gr-myblk$ cd build
/gr-myblk/build$ cmake ../
/gr-myblk/build$ make
/gr-myblk/build$ sudo make install
/gr-myblk/build$ sudo ldconfig
注意：如果出现类似错误提示 AttributeError: 'module' object has no attribute 'xxxx'， 运行 sudo ldconfig 即可解决.
6. 在GRC中测试验证
流图与运行结果如下：
注意事项
一般我们在block设置的参数，只有在C++类的构造函数中初始化一次赋值。也就是说我们设置的参数只能在程序运行的一开始将参数传递到C++中。但是如果要想像上面的 block 那样在程序运行过程中实时改变参数的值，就需要在xml文件中调用 <callback>...</callback> 关键字，调用C++的成员函数，修改成员变量的值。如本程序中xml中的语句： <callback>set_angle_offset($angle)</callback>
对应C++中函数如下：
void set_angle_offset(double angle)
{
d_offset_angle = angle;
}
除此之外，还要注意参数类型匹配。WX GUI Slider传递的参数类型为real，因此angle的数据类型也应该为real，如果设置为int则会报错，grc不会像C++一样支持数据类型隐式转换，因此要注意类型匹配。
Slider中输入的是角度，C++运算时需要将角度转化成弧度来计算。