Generate a CW signal on a HackRF One with set frequency and gain settings

cwgen.cpp

#include <cstdio>
#include <cstring>
extern "C" {
#include <libhackrf/hackrf.h>
}
#include <pthread.h>
#include <unistd.h>
#include <complex>
#include <cstdint>
#include <numbers>
#include <signal.h>


const uint64_t SAMPLE_RATE = 2000000;

volatile int should_stop = 0;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;


int transfer_callback(hackrf_transfer *transfer) {
    int8_t *signed_buffer = (int8_t*)transfer->buffer;

    memset(signed_buffer, 127, transfer->buffer_length);
    transfer->valid_length = transfer->buffer_length;

    if (should_stop) {
        return 1;
    }
    return 0;
}

void flush_callback(void* transfer_ptr, int x) {
    pthread_mutex_lock(&mutex);
    pthread_cond_broadcast(&cond);
    pthread_mutex_unlock(&mutex);
}

uint32_t CURRENT_GAIN = 0;
uint32_t MAX_GAIN = 47;
uint64_t FREQ = 10000000;

int main(int nargs, char** args) {
    if (nargs != 3) {
        printf("Usage: \"%s <freq> <gain>\", where freq is in Hz and gain is 0-47.\nTransmits CW with maximum amplitude (I=Q=127) and amp off.\n", args[0]);
        return -1;
    }
    sscanf(args[1], "%ld", &FREQ);
    sscanf(args[2], "%d", &CURRENT_GAIN);
    if (CURRENT_GAIN > MAX_GAIN) {
        printf("Invalid gain setting: %d\n", CURRENT_GAIN);
        return -1;
    }
    printf("Freq: %.06lf MHz\n", (double)FREQ/1000000.0);
    printf("Gain: %d dB\n", CURRENT_GAIN);

    hackrf_init();
    hackrf_device *device = NULL;
    
    if (hackrf_open(&device)) {
        printf("Could not open any devices...\n");
        return -1;
    }

    hackrf_set_freq(device, FREQ);
    hackrf_set_sample_rate(device, SAMPLE_RATE);
    //hackrf_set_amp_enable(device, 1);
    hackrf_set_txvga_gain(device, CURRENT_GAIN);

    // hackrf_set_tx_underrun_limit(device, 100000);
    //hackrf_enable_tx_flush(device, flush_callback, NULL);
    hackrf_start_tx(device, transfer_callback, NULL);

    getchar();
    
    should_stop = 1;

    //pthread_mutex_lock(&mutex);
    //pthread_cond_wait(&cond, &mutex);

    hackrf_stop_tx(device);
    hackrf_close(device);
    hackrf_exit();
    return 0;
}