UHD C/C++ 编程实例 USRP发送、接收数据

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1. UHD库函数简介

1.1 发送函数

新建一个usrp设备
std::string args = " "; args指定USRP地址，配置USRP参数等
uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(args);

设置时钟源和时钟频率
std::string ref = "internal"; // internal, external, MIMO.
usrp->set_clock_source(ref);
double rate = 40e6;
usrp->set_master_clock_rate(rate);

usrp->get_clock_source() //获取当前的时钟源
usrp->get_clock_sources() //获取所有可用的时钟源
usrp->get_master_clock_rate(); //获取时钟频率

设置采样率
double samp_rate = 20e6;
usrp->set_tx_rate(samp_rate);

usrp->get_tx_rate() //获取当前的采样率
usrp->get_tx_rates() //获取采样率的采样范围

设置发射中心频点
double freq = 2.412e9;
usrp->set_tx_freq(freq);

usrp->get_fe_tx_freq_range();
usrp->get_tx_freq();
usrp->get_tx__freq_range();

设置发射增益
double tx_gain = 60;
usrp->set_tx_gain(tx_gain);

设置发射天线
默认情况下无需设置发射天线，如需指定特定发射天线时设置。
usrp->set_tx_antenna(0);
usrp->get_tx_antenna();
usrp->get_tx_antennas();

创建发送流
新建发送流参数
std::string cpu_format = "fc32";
目前cpu_format支持的类型有：fc64 - complex fc32 - complex sc16 - complex sc8 - complex
std::string wire_format = "sc16";
目前wire_format支持的类型有：sc16 - Q16 I16 sc8 - Q8_1 I8_1 Q8_0 I8_0

uhd::stream_args_t stream_args(cpu_format, wire_format);
uhd::tx_streamer::sptr tx_stream = usrp->get_tx_stream(stream_args);

中频数据管理
uhd::tx_metada_t md; //结构体描述接收到的中频信号
md.start_of_burst = false; // 设置为真的时候发送第一个数据包
md.end_of_burst = false; // 设置为真的时候发送最后一个数据包
md.has_time_spec = false; // 设置为false时立即发送，设置为真的时候在特定时间发送

1.2 接收函数

创建一个usrp
std::string args = " ";
uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(args);

设置时钟源和时钟频率
std::string ref = "internal"; //internal, external and MIMO
usrp->set_clock_source(ref);

double clock_rate = 40e6;
usrp->set_master_clock_rate(clock_rate);

设置采样率
double rate = 20e6;
usrp->set_rx_rate(rate);

设置中心频率
double freq = 2.412e9;
usrp->set_rx_freq(freq);

设置增益
double rx_gain = 50;
usrp->set_rx_gain(rx_gain);

创建接收流
std::string cpu_format = "fc32";
std::string wire_format = "sc16";
uhd::stream_args_t stream_args(cpu_format, wire_format);
uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);

设置接收模式
uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);

//UHD_STREAM_MODE_START_CONTINUOUS=97, //UHD_STREAM_MODE_STOP_CONTINUOUS=111, //UHD_STREAM_MODE_NUM_SAMPS_AND_DONE=100, //UHD_STREAM_MODE_NUM_SAMPS_AND_MORE=109

stream_cmd.num_samps = 1000; // 接收采样点数
stream_cmd.stream_now = true; //现在开始接收
rx_stream->issue_stream_cmd(stream_cmd); //配置rx_stream参数

2. USRP发送数据

　　代码实现USRP发送二进制文件802.11a_BUPT41.seg内的数据。里面的数据为float complex类型，复数的实部和虚部交替存储。即如下图所示。用户可以把要发送的数据生成对应的二进制文件，也可以直接写成数组放在代码中。注意：float类型数据的单位1就是 “1”。

源码

#include <uhd/usrp/multi_usrp.hpp>#include <signal.h>#define SAMPLE_PER_BUFF 2000int stop_signal_called = 0;void sig_int_handle(int){    stop_signal_called = 1;    printf("stop tx.........\n");    exit(0);}int main(){    std::string addr_args = " ";    uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(addr_args);    printf("Create a usrp......\n");    // set the ref and clock rate    std::string ref = "internal";    usrp->set_clock_source(ref);    float clock_rate = 40e6;    usrp->set_master_clock_rate(clock_rate);    printf("set the  clock rate %0.2f \n", usrp->get_master_clock_rate() );    // set the sample rate    float samp_rate = 20e6;    usrp->set_tx_rate(samp_rate);    printf("set the tx sample rate to %0.2f \n", usrp->get_tx_rate());    // set the center frequency    float center_freq = 2.412e9;    usrp->set_tx_freq(center_freq);    printf("set the tx center freq to %0.2f \n", usrp->get_tx_freq());    // set the rf gain    float tx_gain = 90;    usrp->set_tx_gain(tx_gain);    printf("set the tx gain to %0.2f \n", usrp->get_tx_gain());    // create a tx stream    std::string cpu_format = "fc32";    std::string wire_format = "sc16";    uhd::stream_args_t stream_args(cpu_format, wire_format);    uhd::tx_streamer::sptr tx_stream = usrp->get_tx_stream(stream_args);    uhd::tx_metadata_t md;    // catch the INT signal    signal(SIGINT, sig_int_handle);    float read_buff[SAMPLE_PER_BUFF * 2] = {0};    while(!stop_signal_called)    {        FILE *fp = fopen("802.11a_BUPT41.seg", "rb");        md.start_of_burst = false;        md.end_of_burst = false;        while( (!md.end_of_burst) && (!stop_signal_called) )        {            int read_length = 0;            if( (read_length = fread(read_buff, sizeof(uint32_t), SAMPLE_PER_BUFF * 2, fp) ) == (SAMPLE_PER_BUFF * 2) )            {                //int index;                //for(index = 0; index < SAMPLE_PER_BUFF * 2; index++)                //    printf("%0.2f ", read_buff[index]);                //puts("");                //md.start_of_burst = true;                tx_stream->send(read_buff, SAMPLE_PER_BUFF, md);                //md.start_of_burst = false;                //sleep(1);            }            else if(read_length >= 0)            {                md.end_of_burst = true;            }        }        fclose(fp);    }    return 0;}

编译
g++ 编译时需要链接uhd库，系统需提前安装UHD驱动。具体过程参见之前博客。Ubuntu14.04 源码安装 UHD3.8.0
g++ tx.cpp -o tx -luhd

3. USRP接收数据

　　启动USRP，并使USRP一直接收数据。

源码

#include <uhd/usrp/multi_usrp.hpp>#include <csignal>#define SAMPLE_PER_BUFF 2000int stop_signal_called = false;void sig_int_handle(){    stop_signal_called = true;}int main(){    std::string addr_args = " ";    uhd::usrp::multi_usrp::sptr usrp = uhd::usrp::multi_usrp::make(addr_args);    // set the clock source and clock rate    std::string ref = "internal";    usrp->set_clock_source(ref);    float clock_rate = 40e6;    usrp->set_master_clock_rate(clock_rate);    printf("set the  clock rate %0.2f \n", usrp->get_master_clock_rate() );    // set the sample rate    float samp_rate = 20e6;    usrp->set_rx_rate(samp_rate);    printf("set the tx sample rate to %0.2f \n", usrp->get_rx_rate());    // set the center frequency    float center_freq = 2.412e9;    usrp->set_rx_freq(center_freq);    printf("set the tx center freq to %0.2f \n", usrp->get_rx_freq());    // set the rf gain    float rx_gain = 80;    usrp->set_rx_gain(rx_gain);    printf("set the tx gain to %0.2f \n", usrp->get_rx_gain());    std::string cpu_format = "fc32";    std::string wire_format = "sc16";    uhd::stream_args_t stream_args(cpu_format, wire_format);    uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);    uhd::rx_metadata_t md;    //uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_DONE);    uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);    stream_cmd.num_samps = SAMPLE_PER_BUFF;    stream_cmd.stream_now = true;    //stream_cmd.time_spec = uhd::time_spec_t();    stream_cmd.time_spec = usrp->get_time_now();    rx_stream->issue_stream_cmd(stream_cmd);    uint32_t buff[SAMPLE_PER_BUFF*2] = {0};    unsigned long long num_total_samps = 0;    while(!stop_signal_called)    {        //int num_rx_samps = rx_stream->recv(buff, SAMPLE_PER_BUFF, md);        memset(buff, 0, SAMPLE_PER_BUFF * sizeof(uint32_t));        int num_rx_samps = rx_stream->recv(buff, SAMPLE_PER_BUFF, md, 3.0, false);        if(md.error_code == uhd::rx_metadata_t::ERROR_CODE_TIMEOUT)        {            printf("Timeout while streaming......\n");            break;        }        if(md.error_code == uhd::rx_metadata_t::ERROR_CODE_OVERFLOW)        {            printf("Overflowing while stream......\n");            continue;        }        if(md.error_code != uhd::rx_metadata_t::ERROR_CODE_NONE)        {            //printf("Receive error: %s \n", md.strerror());            continue;        }    //printf("num_rx_samps = %d \n",num_rx_samps);        num_total_samps += num_rx_samps;    }    printf("num_total_samps = %d \n", num_total_samps);    stream_cmd.stream_mode = uhd::stream_cmd_t::STREAM_MODE_STOP_CONTINUOUS;    rx_stream->issue_stream_cmd(stream_cmd);    return 0;}

编译
g++ 编译时需要链接uhd库，系统需提前安装UHD驱动。具体过程参见之前博客。Ubuntu14.04 源码安装 UHD3.8.0
g++ rx.cpp -o rx -luhd

４. 结论

　　以上代码在Ubuntu上采用USRP B200测试通过。
　　掌握UHD库函数的使用、g++ 链接 UHD库等是基于USRP开发软件无线电项目的基础。之后，我们可以进一步设计发送程序和接收程序，用USRP搭建一套SDR 收发系统。