// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// dump1090.c: main program & miscellany
//
// Copyright (c) 2014-2016 Oliver Jowett <oliver@mutability.co.uk>
//
// This file is free software: you may copy, redistribute and/or modify it  
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your  
// option) any later version.  
//
// This file 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 program.  If not, see <http://www.gnu.org/licenses/>.

// This file incorporates work covered by the following copyright and  
// permission notice:
//
//   Copyright (C) 2012 by Salvatore Sanfilippo <antirez@gmail.com>
//
//   All rights reserved.
//
//   Redistribution and use in source and binary forms, with or without
//   modification, are permitted provided that the following conditions are
//   met:
//
//    *  Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//
//    *  Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
//   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
//   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
//   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
//   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
//   HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
//   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
//   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
//   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
//   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
//   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
//   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include "dump1090.h"

#include <rtl-sdr.h>

#include <stdarg.h>

static int verbose_device_search(char *s);

//
// ============================= Utility functions ==========================
//

static void log_with_timestamp(const char *format, ...) __attribute__((format (printf, 1, 2) ));

static void log_with_timestamp(const char *format, ...)
{
    char timebuf[128];
    char msg[1024];
    time_t now;
    struct tm local;
    va_list ap;

    now = time(NULL);
    localtime_r(&now, &local);
    strftime(timebuf, 128, "%c %Z", &local);
    timebuf[127] = 0;

    va_start(ap, format);
    vsnprintf(msg, 1024, format, ap);
    va_end(ap);
    msg[1023] = 0;

    fprintf(stderr, "%s  %s\n", timebuf, msg);
}

static void sigintHandler(int dummy) {
    MODES_NOTUSED(dummy);
    signal(SIGINT, SIG_DFL);  // reset signal handler - bit extra safety
    Modes.exit = 1;           // Signal to threads that we are done
    log_with_timestamp("Caught SIGINT, shutting down..\n");
}

static void sigtermHandler(int dummy) {
    MODES_NOTUSED(dummy);
    signal(SIGTERM, SIG_DFL); // reset signal handler - bit extra safety
    Modes.exit = 1;           // Signal to threads that we are done
    log_with_timestamp("Caught SIGTERM, shutting down..\n");
}
//
// =============================== Terminal handling ========================
//
#ifndef _WIN32
// Get the number of rows after the terminal changes size.
int getTermRows() { 
    struct winsize w; 
    ioctl(STDOUT_FILENO, TIOCGWINSZ, &w); 
    return (w.ws_row); 
} 

// Handle resizing terminal
void sigWinchCallback() {
    signal(SIGWINCH, SIG_IGN);
    Modes.interactive_rows = getTermRows();
    interactiveShowData();
    signal(SIGWINCH, sigWinchCallback); 
}
#else 
int getTermRows() { return MODES_INTERACTIVE_ROWS;}
#endif

static void start_cpu_timing(struct timespec *start_time)
{
    clock_gettime(CLOCK_THREAD_CPUTIME_ID, start_time);
}

static void end_cpu_timing(const struct timespec *start_time, struct timespec *add_to)
{
    struct timespec end_time;
    clock_gettime(CLOCK_THREAD_CPUTIME_ID, &end_time);

    add_to->tv_sec += (end_time.tv_sec - start_time->tv_sec - 1);
    add_to->tv_nsec += (1000000000L + end_time.tv_nsec - start_time->tv_nsec);
    add_to->tv_sec += add_to->tv_nsec / 1000000000L;
    add_to->tv_nsec = add_to->tv_nsec % 1000000000L;
}

//
// =============================== Initialization ===========================
//
void modesInitConfig(void) {

    // Default everything to zero/NULL
    memset(&Modes, 0, sizeof(Modes));

    // Now initialise things that should not be 0/NULL to their defaults
    Modes.rtl_gain                = MODES_RTL_MAX_GAIN;
#ifdef HAVE_AIRSPY
    Modes.mixer_gain              = AIRSPY_MIXER_GAIN;
    Modes.lna_gain                = AIRSPY_LNA_GAIN;
    Modes.vga_gain                = AIRSPY_VGA_GAIN;
#endif
    Modes.freq                    = MODES_DEFAULT_FREQ;
    Modes.ppm_error               = MODES_DEFAULT_PPM;
    Modes.check_crc               = 1;
    Modes.net_heartbeat_interval  = MODES_NET_HEARTBEAT_INTERVAL;
    Modes.net_input_raw_ports     = strdup("30001");
    Modes.net_output_raw_ports    = strdup("30002");
    Modes.net_output_sbs_ports    = strdup("30003");
    Modes.net_input_beast_ports   = strdup("30004,30104");
    Modes.net_output_beast_ports  = strdup("30005");
#ifdef ENABLE_WEBSERVER
    Modes.net_http_ports          = strdup("8080");
#endif
    Modes.interactive_rows        = getTermRows();
    Modes.interactive_display_ttl = MODES_INTERACTIVE_DISPLAY_TTL;
    Modes.html_dir                = HTMLPATH;
    Modes.json_interval           = 1000;
    Modes.json_location_accuracy  = 1;
    Modes.maxRange                = 1852 * 300; // 300NM default max range
#ifdef _WIN32
    Modes.isSocket                = 1;
#endif
}
//
//=========================================================================
//
void modesInit(void) {
    int i, q;

    pthread_mutex_init(&Modes.data_mutex,NULL);
    pthread_cond_init(&Modes.data_cond,NULL);

    Modes.sample_rate = 2400000.0;

    // Allocate the various buffers used by Modes
    if (Modes.prefer_airspy) {  // airspy
        Modes.sdr_buf_size = MODES_ASPY_BUF_SIZE;
        Modes.mag_buf_samples = MODES_ASPY_MAG_BUF_SAMPLES;
        Modes.mag_buf_num = MODES_ASPY_MAG_BUFFERS;
    } else {  // rtlsdr or file
        Modes.sdr_buf_size = MODES_RTL_BUF_SIZE;
        Modes.mag_buf_samples = MODES_RTL_MAG_BUF_SAMPLES;
        Modes.mag_buf_num = MODES_RTL_MAG_BUFFERS;
    }

    Modes.mag_buffers = malloc(sizeof(struct mag_buf) * Modes.mag_buf_num);
    memset(Modes.mag_buffers, 0, sizeof(struct mag_buf) * Modes.mag_buf_num);

    Modes.trailing_samples = (unsigned int)((MODES_PREAMBLE_US + MODES_LONG_MSG_BITS + 16) * 1e-6 * Modes.sample_rate);

    if ( ((Modes.maglut     = (uint16_t *) malloc(sizeof(uint16_t) * 256 * 256) ) == NULL) ||
         ((Modes.log10lut   = (uint16_t *) malloc(sizeof(uint16_t) * 256 * 256) ) == NULL) )
    {
        fprintf(stderr, "Out of memory allocating data buffer.\n");
        exit(1);
    }

    for (i = 0; i < Modes.mag_buf_num; ++i) {
        if ( (Modes.mag_buffers[i].data = calloc(Modes.mag_buf_samples+Modes.trailing_samples, sizeof(uint16_t))) == NULL ) {
            fprintf(stderr, "Out of memory allocating magnitude buffer.\n");
            exit(1);
        }

        Modes.mag_buffers[i].length = 0;
        Modes.mag_buffers[i].dropped = 0;
        Modes.mag_buffers[i].sampleTimestamp = 0;
    }

    // Validate the users Lat/Lon home location inputs
    if ( (Modes.fUserLat >   90.0)  // Latitude must be -90 to +90
      || (Modes.fUserLat <  -90.0)  // and 
      || (Modes.fUserLon >  360.0)  // Longitude must be -180 to +360
      || (Modes.fUserLon < -180.0) ) {
        Modes.fUserLat = Modes.fUserLon = 0.0;
    } else if (Modes.fUserLon > 180.0) { // If Longitude is +180 to +360, make it -180 to 0
        Modes.fUserLon -= 360.0;
    }
    // If both Lat and Lon are 0.0 then the users location is either invalid/not-set, or (s)he's in the 
    // Atlantic ocean off the west coast of Africa. This is unlikely to be correct. 
    // Set the user LatLon valid flag only if either Lat or Lon are non zero. Note the Greenwich meridian 
    // is at 0.0 Lon,so we must check for either fLat or fLon being non zero not both. 
    // Testing the flag at runtime will be much quicker than ((fLon != 0.0) || (fLat != 0.0))
    Modes.bUserFlags &= ~MODES_USER_LATLON_VALID;
    if ((Modes.fUserLat != 0.0) || (Modes.fUserLon != 0.0)) {
        Modes.bUserFlags |= MODES_USER_LATLON_VALID;
    }

    // Limit the maximum requested raw output size to less than one Ethernet Block 
    if (Modes.net_output_flush_size > (MODES_OUT_FLUSH_SIZE))
      {Modes.net_output_flush_size = MODES_OUT_FLUSH_SIZE;}
    if (Modes.net_output_flush_interval > (MODES_OUT_FLUSH_INTERVAL))
      {Modes.net_output_flush_interval = MODES_OUT_FLUSH_INTERVAL;}
    if (Modes.net_sndbuf_size > (MODES_NET_SNDBUF_MAX))
      {Modes.net_sndbuf_size = MODES_NET_SNDBUF_MAX;}

    // compute UC8 magnitude lookup table
    for (i = 0; i <= 255; i++) {
        for (q = 0; q <= 255; q++) {
            float fI, fQ, magsq;

            fI = (float)((i - 127.5) / 127.5);
            fQ = (float)((q - 127.5) / 127.5);
            magsq = fI * fI + fQ * fQ;
            if (magsq > 1)
                magsq = 1;

            Modes.maglut[le16toh((i*256)+q)] = (uint16_t) round(sqrtf(magsq) * 65535.0);
        }
    }

    // Prepare the log10 lookup table: 100log10(x)
    Modes.log10lut[0] = 0; // poorly defined..
    for (i = 1; i <= 65535; i++) {
        Modes.log10lut[i] = (uint16_t) round(100.0 * log10(i));
    }

    // Prepare error correction tables
    modesChecksumInit(Modes.nfix_crc);
    icaoFilterInit();

    if (Modes.show_only)
        icaoFilterAdd(Modes.show_only);

    // Prepare sample conversion
    if (!Modes.net_only) {
        if (Modes.filename == NULL) // using a real RTLSDR, use UC8 input always
            Modes.input_format = INPUT_UC8;

        Modes.converter_function = init_converter(Modes.input_format,
                                                  Modes.sample_rate,
                                                  Modes.dc_filter,
                                                  &Modes.converter_state);
        if (!Modes.converter_function) {
            fprintf(stderr, "Can't initialize sample converter, giving up.\n");
            exit(1);
        }
    }
}

static void convert_samples(void *iq,
                            uint16_t *mag,
                            unsigned nsamples,
                            double *power)
{
    Modes.converter_function(iq, mag, nsamples, Modes.converter_state, power);
}

//
// =============================== RTLSDR handling ==========================
//
int modesInitRTLSDR(void) {
    int j;
    int device_count, dev_index = 0;
    char vendor[256], product[256], serial[256];

    if (Modes.dev_name) {
        if ((dev_index = verbose_device_search(Modes.dev_name)) < 0)
            return -1;
    }

    device_count = rtlsdr_get_device_count();
    if (!device_count) {
        fprintf(stderr, "No supported RTLSDR devices found.\n");
        return -1;
    }

    fprintf(stderr, "Found %d device(s):\n", device_count);
    for (j = 0; j < device_count; j++) {
        if (rtlsdr_get_device_usb_strings(j, vendor, product, serial) != 0) {
            fprintf(stderr, "%d: unable to read device details\n", j);
        } else {
            fprintf(stderr, "%d: %s, %s, SN: %s %s\n", j, vendor, product, serial,
                    (j == dev_index) ? "(currently selected)" : "");
        }
    }

    if (rtlsdr_open(&Modes.dev, dev_index) < 0) {
        fprintf(stderr, "Error opening the RTLSDR device: %s\n",
            strerror(errno));
        return -1;
    }

    // Set gain, frequency, sample rate, and reset the device
    rtlsdr_set_tuner_gain_mode(Modes.dev,
        (Modes.rtl_gain == MODES_AUTO_GAIN) ? 0 : 1);
    if (Modes.rtl_gain != MODES_AUTO_GAIN) {
        int *gains;
        int numgains;

        numgains = rtlsdr_get_tuner_gains(Modes.dev, NULL);
        if (numgains <= 0) {
            fprintf(stderr, "Error getting tuner gains\n");
            return -1;
        }

        gains = malloc(numgains * sizeof(int));
        if (rtlsdr_get_tuner_gains(Modes.dev, gains) != numgains) {
            fprintf(stderr, "Error getting tuner gains\n");
            free(gains);
            return -1;
        }

        if (Modes.rtl_gain == MODES_RTL_MAX_GAIN) {
            int highest = -1;
            int i;

            for (i = 0; i < numgains; ++i) {
                if (gains[i] > highest)
                    highest = gains[i];
            }

            Modes.rtl_gain = highest;
            fprintf(stderr, "Max available gain is: %.2f dB\n", Modes.rtl_gain / 10.0);
        } else {
            int closest = -1;
            int i;

            for (i = 0; i < numgains; ++i) {
                if (closest == -1 || abs(gains[i] - Modes.rtl_gain) < abs(closest - Modes.rtl_gain))
                    closest = gains[i];
            }

            if (closest != Modes.rtl_gain) {
                Modes.rtl_gain = closest;
                fprintf(stderr, "Closest available gain: %.2f dB\n", Modes.rtl_gain / 10.0);
            }
        }

        free(gains);

        fprintf(stderr, "Setting gain to: %.2f dB\n", Modes.rtl_gain / 10.0);
        if (rtlsdr_set_tuner_gain(Modes.dev, Modes.rtl_gain) < 0) {
            fprintf(stderr, "Error setting tuner gains\n");
            return -1;
        }
    } else {
        fprintf(stderr, "Using automatic gain control.\n");
    }
    rtlsdr_set_freq_correction(Modes.dev, Modes.ppm_error);
    if (Modes.enable_agc) rtlsdr_set_agc_mode(Modes.dev, 1);
    rtlsdr_set_center_freq(Modes.dev, Modes.freq);
    rtlsdr_set_sample_rate(Modes.dev, (unsigned)Modes.sample_rate);

    rtlsdr_reset_buffer(Modes.dev);
    fprintf(stderr, "Gain reported by device: %.2f dB\n",
        rtlsdr_get_tuner_gain(Modes.dev) / 10.0);

#ifdef HAVE_RTL_BIAST
    if (Modes.enable_rtlsdr_biast) {
        rtlsdr_set_bias_tee(Modes.dev, 1);
    } else {
        rtlsdr_set_bias_tee(Modes.dev, 0);
    }
#endif

	Modes.rtl_enabled = 1;

    return 0;
}

#ifdef HAVE_AIRSPY
//
// =============================== Airspy handling ========================== 
//
int modesInitAirspy(void) {
    #define AIRSPY_STATUS(status, message) \
        if (status != 0) { \
        fprintf(stderr, "%s\n", message); \
        goto errClose; \
        } \

    int status;
    uint32_t count;
    uint32_t *samplerates;
    soxr_error_t sox_err = NULL;
    soxr_io_spec_t ios = soxr_io_spec(SOXR_INT16_I, SOXR_INT16_I);
    soxr_quality_spec_t qts = soxr_quality_spec(SOXR_MQ, 0);
    soxr_runtime_spec_t rts = soxr_runtime_spec(2);

    Modes.airspy_scratch = calloc(2 * Modes.sdr_buf_size, sizeof(int16_t));
    Modes.airspy_bytes = malloc(2 * Modes.sdr_buf_size);
    if ((Modes.airspy_bytes == NULL) || (Modes.airspy_scratch == NULL)) {
        fprintf(stderr, "airspy buffer allocation failed\n");
        return -1;
    }

    if (Modes.serial_number) {
        status = airspy_open_sn(&Modes.airspy, Modes.serial_number);
        AIRSPY_STATUS(status, "airspy_open_sn failed");
    } else {
        status = airspy_open(&Modes.airspy);
        AIRSPY_STATUS(status, "No Airspy compatible devices found");
    }

    fprintf(stderr, "Configuring Airspy Device...\n");

    status = airspy_get_samplerates(Modes.airspy, &count, 0);
    AIRSPY_STATUS(status, "airspy_get_samplerates failed");
    samplerates = (uint32_t *)malloc(count * sizeof(uint32_t));
    airspy_get_samplerates(Modes.airspy, samplerates, count);
    // set the samplerate to the highest value available
    status = airspy_set_samplerate(Modes.airspy, samplerates[0]);
    AIRSPY_STATUS(status, "airspy_set_samplerate failed");
    // Configure the resampler using the airspy sample rate and the sample rate the demodulator expects
    Modes.resampler = soxr_create(samplerates[0], Modes.sample_rate, 2, &sox_err, &ios, &qts, &rts);
    if (sox_err) {
        fprintf(stderr, "soxr_create error: %s; %s\n", soxr_strerror(sox_err), strerror(errno));
        return -1;
    }
    free(samplerates);

    status = airspy_set_sample_type(Modes.airspy, AIRSPY_SAMPLE_INT16_IQ);
    AIRSPY_STATUS(status, "airspy_set_sample_type failed");

    status = airspy_set_freq(Modes.airspy, Modes.freq);
    AIRSPY_STATUS(status, "airspy_set_freq failed");

    if (Modes.enable_linearity) {
        status = airspy_set_linearity_gain(Modes.airspy, Modes.linearity_gain);
        AIRSPY_STATUS(status, "airspy_set_linearity_gain failed");
        fprintf(stderr, "Linearity Mode Gain: %i, ", Modes.linearity_gain);
    } else if (Modes.enable_sensitivity) {
        status = airspy_set_sensitivity_gain(Modes.airspy, Modes.sensitivity_gain);
        AIRSPY_STATUS(status, "airspy_set_sensitivity_gain failed");
        fprintf(stderr, "Sensitivity Mode Gain: %i, ", Modes.sensitivity_gain);
    } else {
        if (Modes.enable_mixer_agc) {
            status = airspy_set_mixer_agc(Modes.airspy, 1);
            AIRSPY_STATUS(status, "airspy_set_mixer_agc failed");
            fprintf(stderr, "MIXER Gain: AGC, ");
        } else {
            status = airspy_set_mixer_gain(Modes.airspy, Modes.mixer_gain);
            AIRSPY_STATUS(status, "airspy_set_mixer_gain failed");
            fprintf(stderr, "MIXER Gain: %i, ", Modes.mixer_gain);
        }

        if (Modes.enable_lna_agc) {
            status = airspy_set_lna_agc(Modes.airspy, 1);
            AIRSPY_STATUS(status, "airspy_set_lna_agc failed");
            fprintf(stderr, "LNA Gain: AGC, ");
        } else {
            status = airspy_set_lna_gain(Modes.airspy, Modes.lna_gain);
            AIRSPY_STATUS(status, "airspy_set_lna_gain failed");
            fprintf(stderr, "LNA Gain: %i, ", Modes.lna_gain);
        }

        status = airspy_set_vga_gain(Modes.airspy, Modes.vga_gain);
        AIRSPY_STATUS(status, "airspy_set_vga_gain failed");
        fprintf(stderr, "VGA Gain: %i, ", Modes.vga_gain);
    }

    if (Modes.enable_airspy_biast) {
        status = airspy_set_rf_bias(Modes.airspy, 1);
        AIRSPY_STATUS(status, "airspy_set_rf_bias (on) failed");
        fprintf(stderr, "Bias-t: ON\n");
    } else {
        status = airspy_set_rf_bias(Modes.airspy, 0);
        AIRSPY_STATUS(status, "airspy_set_rf_bias (off) failed");
        fprintf(stderr, "Bias-t: OFF\n");
    }

    fprintf(stderr, "Airspy successfully initialized\n");

    Modes.airspy_enabled = 1;

    return 0;

errClose:
    if (Modes.airspy) {
        if (airspy_is_streaming(Modes.airspy) == AIRSPY_TRUE)
            airspy_stop_rx(Modes.airspy);
        airspy_close(Modes.airspy);
        Modes.airspy = NULL;
    }

    if (Modes.airspy_scratch)
        free(Modes.airspy_scratch);

    if (Modes.airspy_bytes)
        free(Modes.airspy_bytes);

    if (Modes.resampler)
        soxr_delete(Modes.resampler);

    return -1;
}
#endif

//
//=========================================================================
//
// We use a thread reading data in background, while the main thread
// handles decoding and visualization of data to the user.
//
// The reading thread calls the RTLSDR API to read data asynchronously, and
// uses a callback to populate the data buffer.
//
// A Mutex is used to avoid races with the decoding thread.
//

static struct timespec reader_thread_start;

void rtlsdrCallback(unsigned char *buf, uint32_t len, void *ctx) {
    struct mag_buf *outbuf;
    struct mag_buf *lastbuf;
    uint32_t slen;
    unsigned next_free_buffer;
    unsigned free_bufs;
    unsigned block_duration;

    static int was_odd = 0; // paranoia!!
    static int dropping = 0;

    MODES_NOTUSED(ctx);

    // Lock the data buffer variables before accessing them
    pthread_mutex_lock(&Modes.data_mutex);
    if (Modes.exit) {
        rtlsdr_cancel_async(Modes.dev); // ask our caller to exit
    }

    next_free_buffer = (Modes.first_free_buffer + 1) % Modes.mag_buf_num;
    outbuf = &Modes.mag_buffers[Modes.first_free_buffer];
    lastbuf = &Modes.mag_buffers[(Modes.first_free_buffer + Modes.mag_buf_num - 1) % Modes.mag_buf_num];
    free_bufs = (Modes.first_filled_buffer - next_free_buffer + Modes.mag_buf_num) % Modes.mag_buf_num;

    // Paranoia! Unlikely, but let's go for belt and suspenders here

    if (len != Modes.sdr_buf_size) {
       fprintf(stderr, "weirdness: sdr gave us a block with an unusual size (got %u bytes, expected %u bytes)\n",
            (unsigned)len, (unsigned)Modes.sdr_buf_size);

        if (len > Modes.sdr_buf_size) {
            // wat?! Discard the start.
            unsigned discard = (len - Modes.sdr_buf_size + 1) / 2;
            outbuf->dropped += discard;
            buf += discard*2;
            len -= discard*2;
        }
    }

    if (was_odd) {
        // Drop a sample so we are in sync with I/Q samples again (hopefully)
        ++buf;
        --len;
        ++outbuf->dropped;
    }

    was_odd = (len & 1);
    slen = len/2;

    if (free_bufs == 0 || (dropping && free_bufs < (unsigned)Modes.mag_buf_num/2)) {
        // FIFO is full. Drop this block.
        dropping = 1;
        outbuf->dropped += slen;
        pthread_mutex_unlock(&Modes.data_mutex);
        return;
    }

    dropping = 0;
    pthread_mutex_unlock(&Modes.data_mutex);

    // Compute the sample timestamp and system timestamp for the start of the block
    outbuf->sampleTimestamp = (uint64_t)(lastbuf->sampleTimestamp + 12e6 * (lastbuf->length + outbuf->dropped) / Modes.sample_rate);
    block_duration = (unsigned int)(1e9 * slen / Modes.sample_rate);

    // Get the approx system time for the start of this block
    clock_gettime(CLOCK_REALTIME, &outbuf->sysTimestamp);

    outbuf->sysTimestamp.tv_nsec -= block_duration;
    normalize_timespec(&outbuf->sysTimestamp);

    // Copy trailing data from last block (or reset if not valid)
    if (outbuf->dropped == 0 && lastbuf->length >= Modes.trailing_samples) {
        memcpy(outbuf->data, lastbuf->data + lastbuf->length - Modes.trailing_samples, Modes.trailing_samples * sizeof(uint16_t));
    } else {
        memset(outbuf->data, 0, Modes.trailing_samples * sizeof(uint16_t));
    }

    // Convert the new data
    outbuf->length = slen;
    convert_samples(buf, &outbuf->data[Modes.trailing_samples], slen, &outbuf->total_power);

    // Push the new data to the demodulation thread
    pthread_mutex_lock(&Modes.data_mutex);

    Modes.mag_buffers[next_free_buffer].dropped = 0;
    Modes.mag_buffers[next_free_buffer].length = 0;  // just in case
    Modes.first_free_buffer = next_free_buffer;

    // accumulate CPU while holding the mutex, and restart measurement
    end_cpu_timing(&reader_thread_start, &Modes.reader_cpu_accumulator);
    start_cpu_timing(&reader_thread_start);

    pthread_cond_signal(&Modes.data_cond);
    pthread_mutex_unlock(&Modes.data_mutex);
}

#ifdef HAVE_AIRSPY
int airspyCallback(airspy_transfer *transfer) {
	int16_t *inptr = (int16_t *)transfer->samples;
	int16_t *outptr = (int16_t *)Modes.airspy_scratch;
	size_t i_len = transfer->sample_count;
	size_t i, i_done, o_done;
    struct mag_buf *outbuf;
    struct mag_buf *lastbuf;
    uint32_t slen;
    unsigned next_free_buffer;
    unsigned free_bufs;
    unsigned block_duration;
    static int dropping = 0;

    if (Modes.exit) {
        airspy_stop_rx(Modes.airspy);  // ask our caller to stop
        return (0);
    }

    // Lock the data buffer variables before accessing them
    pthread_mutex_lock(&Modes.data_mutex);

    next_free_buffer = (Modes.first_free_buffer + 1) % Modes.mag_buf_num;
    outbuf = &Modes.mag_buffers[Modes.first_free_buffer];
    lastbuf = &Modes.mag_buffers[(Modes.first_free_buffer + Modes.mag_buf_num - 1) % Modes.mag_buf_num];
    free_bufs = (Modes.first_filled_buffer - next_free_buffer + Modes.mag_buf_num) % Modes.mag_buf_num;

    // Give the demodulater function what it expects
    soxr_process(Modes.resampler, inptr, i_len, &i_done, outptr, MODES_ASPY_BUF_SIZE, &o_done);
    for (i = 0; i < o_done; i++)
        Modes.airspy_bytes[i] = (int8_t)(outptr[i] >> 4) + 127;

    // The resampler often produces an odd sample count, no real value in tracking how often
    if (o_done & 1)
        o_done -= 1;

    slen = o_done;

    if (free_bufs == 0 || (dropping && free_bufs < (unsigned)Modes.mag_buf_num / 2)) {
        // FIFO is full. Drop this block.
        dropping = 1;
        outbuf->dropped += slen;
        pthread_mutex_unlock(&Modes.data_mutex);
        return 0;
    }

    dropping = 0;
    pthread_mutex_unlock(&Modes.data_mutex);

    // Compute the sample timestamp and system timestamp for the start of the block
    outbuf->sampleTimestamp = (uint64_t)(lastbuf->sampleTimestamp + 12e6 * (lastbuf->length + outbuf->dropped) / Modes.sample_rate);
    block_duration = (unsigned int)(1e9 * slen / Modes.sample_rate);

    // Get the approx system time for the start of this block
    clock_gettime(CLOCK_REALTIME, &outbuf->sysTimestamp);

    outbuf->sysTimestamp.tv_nsec -= block_duration;
    normalize_timespec(&outbuf->sysTimestamp);

    // Copy trailing data from last block (or reset if not valid)
    if (outbuf->dropped == 0 && lastbuf->length >= Modes.trailing_samples) {
        memcpy(outbuf->data, lastbuf->data + lastbuf->length - Modes.trailing_samples, Modes.trailing_samples * sizeof(uint16_t));
    } else {
        memset(outbuf->data, 0, Modes.trailing_samples * sizeof(uint16_t));
    }

    // Convert the new data
    outbuf->length = slen;
    convert_samples(Modes.airspy_bytes, &outbuf->data[Modes.trailing_samples], slen, &outbuf->total_power);

    // Push the new data to the demodulation thread
    pthread_mutex_lock(&Modes.data_mutex);

    Modes.mag_buffers[next_free_buffer].dropped = 0;
    Modes.mag_buffers[next_free_buffer].length = 0;  // just in case
    Modes.first_free_buffer = next_free_buffer;

    // accumulate CPU while holding the mutex, and restart measurement
    end_cpu_timing(&reader_thread_start, &Modes.reader_cpu_accumulator);
    start_cpu_timing(&reader_thread_start);

    pthread_cond_signal(&Modes.data_cond);
    pthread_mutex_unlock(&Modes.data_mutex);

	return (0);
}
#endif

//
//=========================================================================
//
// This is used when --ifile is specified in order to read data from file
// instead of using an RTLSDR device
//
void readDataFromFile(void) {
    int eof = 0;
    struct timespec next_buffer_delivery;
    void *readbuf;
    int bytes_per_sample = 0;

    switch (Modes.input_format) {
    case INPUT_UC8:
        bytes_per_sample = 2;
        break;
    case INPUT_SC16:
    case INPUT_SC16Q11:
        bytes_per_sample = 4;
        break;
    }

    if (!(readbuf = malloc(Modes.mag_buf_samples * bytes_per_sample))) {
        fprintf(stderr, "failed to allocate read buffer\n");
        exit(1);
    }

    clock_gettime(CLOCK_MONOTONIC, &next_buffer_delivery);

    pthread_mutex_lock(&Modes.data_mutex);
    while (!Modes.exit && !eof) {
        ssize_t nread, toread;
        void *r;
        struct mag_buf *outbuf, *lastbuf;
        unsigned next_free_buffer;
        unsigned slen;

        next_free_buffer = (Modes.first_free_buffer + 1) % Modes.mag_buf_num;
        if (next_free_buffer == Modes.first_filled_buffer) {
            // no space for output yet
            pthread_cond_wait(&Modes.data_cond, &Modes.data_mutex);
            continue;
        }

        outbuf = &Modes.mag_buffers[Modes.first_free_buffer];
        lastbuf = &Modes.mag_buffers[(Modes.first_free_buffer + Modes.mag_buf_num - 1) % Modes.mag_buf_num];
        pthread_mutex_unlock(&Modes.data_mutex);

        // Compute the sample timestamp and system timestamp for the start of the block
        outbuf->sampleTimestamp = (uint64_t)(lastbuf->sampleTimestamp + 12e6 * lastbuf->length / Modes.sample_rate);

        // Copy trailing data from last block (or reset if not valid)
        if (lastbuf->length >= Modes.trailing_samples) {
            memcpy(outbuf->data, lastbuf->data + lastbuf->length - Modes.trailing_samples, Modes.trailing_samples * sizeof(uint16_t));
        } else {
            memset(outbuf->data, 0, Modes.trailing_samples * sizeof(uint16_t));
        }

        // Get the system time for the start of this block
        clock_gettime(CLOCK_REALTIME, &outbuf->sysTimestamp);

        toread = Modes.mag_buf_samples * bytes_per_sample;
        r = readbuf;
        while (toread) {
            nread = read(Modes.fd, r, toread);
            if (nread <= 0) {
                // Done.
                eof = 1;
                break;
            }
#ifndef _WIN32
            r += nread;
#else
            (char *)r += nread;
#endif
            toread -= nread;
        }

        slen = outbuf->length = Modes.mag_buf_samples - toread / bytes_per_sample;

        // Convert the new data
        convert_samples(readbuf, &outbuf->data[Modes.trailing_samples], slen, &outbuf->total_power);

        if (Modes.throttle) {
            // Wait until we are allowed to release this buffer to the main thread
            while (clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &next_buffer_delivery, NULL) == EINTR)
                ;

            // compute the time we can deliver the next buffer.
            next_buffer_delivery.tv_nsec += (long)(outbuf->length * 1e9 / Modes.sample_rate);
            normalize_timespec(&next_buffer_delivery);
        }

        // Push the new data to the main thread
        pthread_mutex_lock(&Modes.data_mutex);
        Modes.first_free_buffer = next_free_buffer;
        // accumulate CPU while holding the mutex, and restart measurement
        end_cpu_timing(&reader_thread_start, &Modes.reader_cpu_accumulator);
        start_cpu_timing(&reader_thread_start);
        pthread_cond_signal(&Modes.data_cond);
    }

    free(readbuf);

    // Wait for the main thread to consume all data
    while (!Modes.exit && Modes.first_filled_buffer != Modes.first_free_buffer)
        pthread_cond_wait(&Modes.data_cond, &Modes.data_mutex);

    pthread_mutex_unlock(&Modes.data_mutex);
}
//
//=========================================================================
//
// We read data using a thread, so the main thread only handles decoding
// without caring about data acquisition
//

void *readerThreadEntryPoint(void *arg) {
    MODES_NOTUSED(arg);

    start_cpu_timing(&reader_thread_start); // we accumulate in rtlsdrCallback() or readDataFromFile()

    if (Modes.filename == NULL) {
        while (!Modes.exit) {
            if (Modes.rtl_enabled) {  // rtlsdr
                rtlsdr_read_async(Modes.dev, rtlsdrCallback, NULL,
                    MODES_RTL_BUFFERS,
                    Modes.sdr_buf_size);

                if (!Modes.exit) {
                    log_with_timestamp("Warning: lost the connection to the RTLSDR device.");
#ifdef HAVE_RTL_BIAST
                    if (Modes.enable_rtlsdr_biast) {
                        rtlsdr_close_bt(Modes.dev);
                    } else {
                        rtlsdr_close(Modes.dev);
                    }
#else
                    rtlsdr_close(Modes.dev);
#endif
                    Modes.dev = NULL;

                    do {
                        sleep(5);
                        log_with_timestamp("Trying to reconnect to the RTLSDR device..");
                    } while (!Modes.exit && modesInitRTLSDR() < 0);
                }
            }
#ifdef HAVE_AIRSPY
            else if (Modes.airspy_enabled) {  // airspy
                airspy_start_rx(Modes.airspy, airspyCallback, NULL);

                while ((airspy_is_streaming(Modes.airspy) == AIRSPY_TRUE) && (!Modes.exit)) {
                    usleep(1000);  // 1 ms
                }

                if (!Modes.exit) {
                    log_with_timestamp("Warning: lost the connection to the Airspy device.");
                    airspy_stop_rx(Modes.airspy);
                    airspy_close(Modes.airspy);
                    Modes.airspy = NULL;

                    do {
                        sleep(2);
                        log_with_timestamp("Trying to reconnect to the Airspy device..");
                    } while (!Modes.exit && modesInitAirspy() < 0);
                }
            }
#endif
        }

        if (Modes.dev != NULL) {
#ifdef HAVE_RTL_BIAST
            if (Modes.enable_rtlsdr_biast) {
                rtlsdr_close_bt(Modes.dev);
            } else {
                rtlsdr_close(Modes.dev);
            }
#else
            rtlsdr_close(Modes.dev);
#endif
            Modes.dev = NULL;
        }
#ifdef HAVE_AIRSPY
        else if (Modes.airspy != NULL) {
            if (airspy_is_streaming(Modes.airspy) == AIRSPY_TRUE)
                airspy_stop_rx(Modes.airspy);
            airspy_close(Modes.airspy);
            soxr_delete(Modes.resampler);
            Modes.airspy = NULL;
        }
#endif
    } else {   // file
        readDataFromFile();
    }

    // Wake the main thread (if it's still waiting)
    pthread_mutex_lock(&Modes.data_mutex);
    Modes.exit = 1; // just in case
    pthread_cond_signal(&Modes.data_cond);
    pthread_mutex_unlock(&Modes.data_mutex);

#ifndef _WIN32
    pthread_exit(NULL);
#else
    return NULL;
#endif
}
//
// ============================== Snip mode =================================
//
// Get raw IQ samples and filter everything is < than the specified level
// for more than 256 samples in order to reduce example file size
//
void snipMode(int level) {
    int i, q;
    uint64_t c = 0;

    while ((i = getchar()) != EOF && (q = getchar()) != EOF) {
        if (abs(i-127) < level && abs(q-127) < level) {
            c++;
            if (c > MODES_PREAMBLE_SIZE) continue;
        } else {
            c = 0;
        }
        putchar(i);
        putchar(q);
    }
}
//
// ================================ Main ====================================
//
void showHelp(void) {
    printf(
"-----------------------------------------------------------------------------\n"
"| dump1090 ModeS Receiver     %45s |\n"
"-----------------------------------------------------------------------------\n"
"Input to use (you must specify one):\n"
"--rtlsdr                 use RTLSDR device\n"
#ifdef HAVE_AIRSPY
"--airspy                 use Airspy device\n"
#endif
"--ifile <filename>       Read data from File (use '-' for stdin)\n"
"--net-only               Enable just networking, no SDR device or file used\n"
"RTL-SDR specific options:\n"
"    --device-index <index>   Select SDR device (default: 0)\n"
"    --rtl-gain <db>          Set gain (default: max gain. Use -10 for auto-gain)\n"
"    --enable-agc             Enable the Automatic Gain Control (default: off)\n"
"    --ppm <error>            Set receiver error in parts per million (default 0)\n"
#ifdef HAVE_RTL_BIAST
"    --enable-rtlsdr-biast    Set bias tee supply on (default off)\n"
#endif
#ifdef HAVE_AIRSPY
"AIRSPY specific options:\n"
"    --serial-number <0x...>  Serial number (in hex) of Airspy to open (optional)\n"
"    --linearity-gain <n>     Set linearity simplified gain, 0-21\n"
"    --sensitivity-gain <n>   Set sensitivity simplified gain, 0-21\n"
"    --mixer-gain <n>         Set MIXER gain (0-15, default 8)\n"
"    --vga-gain <n>           Set VGA gain (0-15, default 5)\n"
"    --lna-gain <n>           Set LNA gain (0-14, default 13)\n"
"    --enable-lna-agc         Enable LNA AGC (default off)\n"
"    --enable-mixer-agc       Enable MIXER AGC (default off)\n"
"    --enable-airspy-biast    Set bias tee supply on (default off)\n"
#endif
"FILE specific options:\n"
"    --iformat <format>       Sample format for input file: UC8 (default), SC16, or SC16Q11\n"
"    --throttle               When reading from a file, play back in realtime, not at max speed\n"
"Common options:\n"
"--freq <hz>              Set frequency (default: 1090 Mhz)\n"
"--interactive            Interactive mode refreshing data on screen (implies --throttle when using --file)\n"
"--interactive-rows <num> Max number of rows in interactive mode (default: 22)\n"
"--interactive-ttl <sec>  Remove from list if idle for <sec> (default: 60)\n"
"--interactive-rtl1090    Display flight table in RTL1090 format\n"
"--raw                    Show only messages hex values\n"
"--net                    Enable networking\n"
"--modeac                 Enable decoding of SSR Modes 3/A & 3/C\n"
"--net-bind-address <ip>  IP address to bind to (default: Any; Use 127.0.0.1 for private)\n"
#ifdef ENABLE_WEBSERVER
"--net-http-port <ports>  HTTP server ports (default: 8080)\n"
#endif
"--net-ri-port <ports>    TCP raw input listen ports  (default: 30001)\n"
"--net-ro-port <ports>    TCP raw output listen ports (default: 30002)\n"
"--net-sbs-port <ports>   TCP BaseStation output listen ports (default: 30003)\n"
"--net-bi-port <ports>    TCP Beast input listen ports  (default: 30004,30104)\n"
"--net-bo-port <ports>    TCP Beast output listen ports (default: 30005)\n"
"--net-ro-size <size>     TCP output minimum size (default: 0)\n"
"--net-ro-interval <rate> TCP output memory flush rate in seconds (default: 0)\n"
"--net-heartbeat <rate>   TCP heartbeat rate in seconds (default: 60 sec; 0 to disable)\n"
"--net-buffer <n>         TCP buffer size 64Kb * (2^n) (default: n=0, 64Kb)\n"
"--net-verbatim           Do not apply CRC corrections to messages we forward; send unchanged\n"
"--forward-mlat           Allow forwarding of received mlat results to output ports\n"
"--lat <latitude>         Reference/receiver latitude for surface posn (opt)\n"
"--lon <longitude>        Reference/receiver longitude for surface posn (opt)\n"
"--max-range <distance>   Absolute maximum range for position decoding (in nm, default: 300)\n"
"--fix                    Enable single-bits error correction using CRC\n"
"--no-fix                 Disable single-bits error correction using CRC\n"
"--no-crc-check           Disable messages with broken CRC (discouraged)\n"
#ifdef ALLOW_AGGRESSIVE
"--aggressive             More CPU for more messages (two bits fixes, ...)\n"
#endif
"--mlat                   Display raw messages in Beast ascii mode\n"
"--stats                  Print statistics at exit\n"
"--stats-range            Collect/show range histogram\n"
"--stats-every <seconds>  Show and reset stats every <seconds> seconds\n"
"--onlyaddr               Show only ICAO addresses (testing purposes)\n"
"--metric                 Use metric units (meters, km/h, ...)\n"
"--gnss                   Show altitudes as HAE/GNSS (with H suffix) when available\n"
"--snip <level>           Strip IQ file removing samples < level\n"
"--debug <flags>          Debug mode (verbose), see README for details\n"
"--quiet                  Disable output to stdout. Use for daemon applications\n"
"--show-only <addr>       Show only messages from the given ICAO on stdout\n"
"--html-dir <dir>         Use <dir> as base directory for the internal HTTP server. Defaults to " HTMLPATH "\n"
"--write-json <dir>       Periodically write json output to <dir> (for serving by a separate webserver)\n"
"--write-json-every <t>   Write json output every t seconds (default 1)\n"
"--json-location-accuracy <n>  Accuracy of receiver location in json metadata: 0=no location, 1=approximate, 2=exact\n"
"--dcfilter               Apply a 1Hz DC filter to input data (requires lots more CPU)\n"
"--help                   Show this help\n"
"\n"
"Debug mode flags: d = Log frames decoded with errors\n"
"                  D = Log frames decoded with zero errors\n"
"                  c = Log frames with bad CRC\n"
"                  C = Log frames with good CRC\n"
"                  p = Log frames with bad preamble\n"
"                  n = Log network debugging info\n"
"                  j = Log frames to frames.js, loadable by debug.html\n",
MODES_DUMP1090_VARIANT " " MODES_DUMP1090_VERSION
    );
}

static void display_total_stats(void)
{
    struct stats added;
    add_stats(&Modes.stats_alltime, &Modes.stats_current, &added);
    display_stats(&added);
}

//
//=========================================================================
//
// This function is called a few times every second by main in order to
// perform tasks we need to do continuously, like accepting new clients
// from the net, refreshing the screen in interactive mode, and so forth
//
void backgroundTasks(void) {
    static uint64_t next_stats_display;
    static uint64_t next_stats_update;
    static uint64_t next_json, next_history;

    uint64_t now = mstime();

    icaoFilterExpire();
    trackPeriodicUpdate();

    if (Modes.net) {
	modesNetPeriodicWork();
    }    


    // Refresh screen when in interactive mode
    if (Modes.interactive) {
        interactiveShowData();
    }

    // always update end time so it is current when requests arrive
    Modes.stats_current.end = now;

    if (now >= next_stats_update) {
        int i;

        if (next_stats_update == 0) {
            next_stats_update = now + 60000;
        } else {
            Modes.stats_latest_1min = (Modes.stats_latest_1min + 1) % 15;
            Modes.stats_1min[Modes.stats_latest_1min] = Modes.stats_current;
            
            add_stats(&Modes.stats_current, &Modes.stats_alltime, &Modes.stats_alltime);
            add_stats(&Modes.stats_current, &Modes.stats_periodic, &Modes.stats_periodic);
            
            reset_stats(&Modes.stats_5min);
            for (i = 0; i < 5; ++i)
                add_stats(&Modes.stats_1min[(Modes.stats_latest_1min - i + 15) % 15], &Modes.stats_5min, &Modes.stats_5min);
            
            reset_stats(&Modes.stats_15min);
            for (i = 0; i < 15; ++i)
                add_stats(&Modes.stats_1min[i], &Modes.stats_15min, &Modes.stats_15min);
            
            reset_stats(&Modes.stats_current);
            Modes.stats_current.start = Modes.stats_current.end = now;
            
            if (Modes.json_dir)
                writeJsonToFile("stats.json", generateStatsJson);

            next_stats_update += 60000;
        }
    }

    if (Modes.stats && now >= next_stats_display) {
        if (next_stats_display == 0) {
            next_stats_display = now + Modes.stats;
        } else {
            add_stats(&Modes.stats_periodic, &Modes.stats_current, &Modes.stats_periodic);
            display_stats(&Modes.stats_periodic);
            reset_stats(&Modes.stats_periodic);

            next_stats_display += Modes.stats;
            if (next_stats_display <= now) {
                /* something has gone wrong, perhaps the system clock jumped */
                next_stats_display = now + Modes.stats;
            }
        }
    }

    if (Modes.json_dir && now >= next_json) {
        writeJsonToFile("aircraft.json", generateAircraftJson);
        next_json = now + Modes.json_interval;
    }

    if (now >= next_history) {
        int rewrite_receiver_json = (Modes.json_dir && Modes.json_aircraft_history[HISTORY_SIZE-1].content == NULL);

        free(Modes.json_aircraft_history[Modes.json_aircraft_history_next].content); // might be NULL, that's OK.
        Modes.json_aircraft_history[Modes.json_aircraft_history_next].content =
            generateAircraftJson("/data/aircraft.json", &Modes.json_aircraft_history[Modes.json_aircraft_history_next].clen);

        if (Modes.json_dir) {
            char filebuf[PATH_MAX];
            snprintf(filebuf, PATH_MAX, "history_%d.json", Modes.json_aircraft_history_next);
            writeJsonToFile(filebuf, generateHistoryJson);
        }

        Modes.json_aircraft_history_next = (Modes.json_aircraft_history_next+1) % HISTORY_SIZE;

        if (rewrite_receiver_json)
            writeJsonToFile("receiver.json", generateReceiverJson); // number of history entries changed

        next_history = now + HISTORY_INTERVAL;
    }
}

//
//=========================================================================
//
int verbose_device_search(char *s)
{
	int i, device_count, device, offset;
	char *s2;
	char vendor[256], product[256], serial[256];
	device_count = rtlsdr_get_device_count();
	if (!device_count) {
		fprintf(stderr, "No supported devices found.\n");
		return -1;
	}
	fprintf(stderr, "Found %d device(s):\n", device_count);
	for (i = 0; i < device_count; i++) {
            if (rtlsdr_get_device_usb_strings(i, vendor, product, serial) != 0) {
                fprintf(stderr, "  %d:  unable to read device details\n", i);
            } else {
                fprintf(stderr, "  %d:  %s, %s, SN: %s\n", i, vendor, product, serial);
            }
	}
	fprintf(stderr, "\n");
	/* does string look like raw id number */
	device = (int)strtol(s, &s2, 0);
	if (s2[0] == '\0' && device >= 0 && device < device_count) {
		fprintf(stderr, "Using device %d: %s\n",
			device, rtlsdr_get_device_name((uint32_t)device));
		return device;
	}
	/* does string exact match a serial */
	for (i = 0; i < device_count; i++) {
		rtlsdr_get_device_usb_strings(i, vendor, product, serial);
		if (strcmp(s, serial) != 0) {
			continue;}
		device = i;
		fprintf(stderr, "Using device %d: %s\n",
			device, rtlsdr_get_device_name((uint32_t)device));
		return device;
	}
	/* does string prefix match a serial */
	for (i = 0; i < device_count; i++) {
		rtlsdr_get_device_usb_strings(i, vendor, product, serial);
		if (strncmp(s, serial, strlen(s)) != 0) {
			continue;}
		device = i;
		fprintf(stderr, "Using device %d: %s\n",
			device, rtlsdr_get_device_name((uint32_t)device));
		return device;
	}
	/* does string suffix match a serial */
	for (i = 0; i < device_count; i++) {
		rtlsdr_get_device_usb_strings(i, vendor, product, serial);
		offset = strlen(serial) - strlen(s);
		if (offset < 0) {
			continue;}
		if (strncmp(s, serial+offset, strlen(s)) != 0) {
			continue;}
		device = i;
		fprintf(stderr, "Using device %d: %s\n",
			device, rtlsdr_get_device_name((uint32_t)device));
		return device;
	}
	fprintf(stderr, "No matching devices found.\n");
	return -1;
}

int parse_u64(char* s, uint64_t* const value) {
    char* s_end;
    uint64_t u64_value;

    s_end = s;
    u64_value = strtoull(s, &s_end, 0);
    if ((s != s_end) && (*s_end == 0)) {
        *value = u64_value;
        return true;
    } else {
        return false;
    }
}

//
//=========================================================================
//
int main(int argc, char **argv) {
    int j;

    // Set sane defaults
    modesInitConfig();

    // signal handlers:
    signal(SIGINT, sigintHandler);
    signal(SIGTERM, sigtermHandler);

    // Parse the command line options
    for (j = 1; j < argc; j++) {
        int more = j+1 < argc; // There are more arguments

		if (!strcmp(argv[j], "--device-index") && more) {
			Modes.dev_name = strdup(argv[++j]);
        } else if (!strcmp(argv[j], "--rtlsdr")) {
            Modes.prefer_rtlsdr = 1;
        } else if (!strcmp(argv[j],"--rtl-gain") && more) {
            Modes.rtl_gain = (int) (atof(argv[++j])*10); // Gain is in tens of DBs
        } else if (!strcmp(argv[j], "--enable-agc")) {
            Modes.enable_agc = 1;
        } else if (!strcmp(argv[j], "--ppm") && more) {
            Modes.ppm_error = atoi(argv[++j]);
#ifdef HAVE_RTL_BIAST
        } else if (!strcmp(argv[j], "--enable-rtlsdr-biast")) {
            Modes.enable_rtlsdr_biast = 1;
#endif
#ifdef HAVE_AIRSPY
        } else if (!strcmp(argv[j], "--airspy")) {
            Modes.prefer_airspy = 1;
        } else if (!strcmp(argv[j], "--serial-number") && more) {
            if (!parse_u64(argv[++j], &Modes.serial_number))
                exit(1);
        } else if (!strcmp(argv[j], "--enable-airspy-biast")) {
            Modes.enable_airspy_biast = true;
        } else if (!strcmp(argv[j], "--linearity-gain") && more) {
            Modes.linearity_gain = atoi(argv[++j]);
            Modes.enable_linearity = true;
        } else if (!strcmp(argv[j], "--sensitivity-gain") && more) {
            Modes.sensitivity_gain = atoi(argv[++j]);
            Modes.enable_sensitivity = true;
        } else if (!strcmp(argv[j], "--mixer-gain") && more) {
            Modes.mixer_gain = atoi(argv[++j]);
        } else if (!strcmp(argv[j], "--lna-gain") && more) {
            Modes.lna_gain = atoi(argv[++j]);
        } else if (!strcmp(argv[j], "--vga-gain") && more) {
            Modes.vga_gain = atoi(argv[++j]);
        } else if (!strcmp(argv[j], "--enable-lna-agc")) {
            Modes.enable_lna_agc = true;
        } else if (!strcmp(argv[j], "--enable-mixer-agc")) {
            Modes.enable_mixer_agc = true;
#endif
        } else if (!strcmp(argv[j],"--freq") && more) {
            Modes.freq = (int) strtoll(argv[++j],NULL,10);
        } else if (!strcmp(argv[j],"--ifile") && more) {
            Modes.filename = strdup(argv[++j]);
            Modes.prefer_file = 1;
        } else if (!strcmp(argv[j],"--iformat") && more) {
            ++j;
            if (!strcasecmp(argv[j], "uc8")) {
                Modes.input_format = INPUT_UC8;
            } else if (!strcasecmp(argv[j], "sc16")) {
                Modes.input_format = INPUT_SC16;
            } else if (!strcasecmp(argv[j], "sc16q11")) {
                Modes.input_format = INPUT_SC16Q11;
            } else {
                fprintf(stderr, "Input format '%s' not understood (supported values: UC8, SC16, SC16Q11)\n",
                        argv[j]);
                exit(1);
            }
        } else if (!strcmp(argv[j],"--dcfilter")) {
            Modes.dc_filter = 1;
        } else if (!strcmp(argv[j],"--measure-noise")) {
            // Ignored
        } else if (!strcmp(argv[j],"--fix")) {
            Modes.nfix_crc = 1;
        } else if (!strcmp(argv[j],"--no-fix")) {
            Modes.nfix_crc = 0;
        } else if (!strcmp(argv[j],"--no-crc-check")) {
            Modes.check_crc = 0;
        } else if (!strcmp(argv[j],"--phase-enhance")) {
            // Ignored, always enabled
        } else if (!strcmp(argv[j],"--raw")) {
            Modes.raw = 1;
        } else if (!strcmp(argv[j],"--net")) {
            Modes.net = 1;
        } else if (!strcmp(argv[j],"--modeac")) {
            Modes.mode_ac = 1;
        } else if (!strcmp(argv[j],"--net-beast")) {
            fprintf(stderr, "--net-beast ignored, use --net-bo-port to control where Beast output is generated\n");
        } else if (!strcmp(argv[j],"--net-only")) {
            Modes.net = 1;
            Modes.net_only = 1;
       } else if (!strcmp(argv[j],"--net-heartbeat") && more) {
            Modes.net_heartbeat_interval = (uint64_t)(1000 * atof(argv[++j]));
       } else if (!strcmp(argv[j],"--net-ro-size") && more) {
            Modes.net_output_flush_size = atoi(argv[++j]);
        } else if (!strcmp(argv[j],"--net-ro-rate") && more) {
            Modes.net_output_flush_interval = 1000 * atoi(argv[++j]) / 15; // backwards compatibility
        } else if (!strcmp(argv[j],"--net-ro-interval") && more) {
            Modes.net_output_flush_interval = (uint64_t)(1000 * atof(argv[++j]));
        } else if (!strcmp(argv[j],"--net-ro-port") && more) {
            free(Modes.net_output_raw_ports);
            Modes.net_output_raw_ports = strdup(argv[++j]);
        } else if (!strcmp(argv[j],"--net-ri-port") && more) {
            free(Modes.net_input_raw_ports);
            Modes.net_input_raw_ports = strdup(argv[++j]);
        } else if (!strcmp(argv[j],"--net-bo-port") && more) {
            free(Modes.net_output_beast_ports);
            Modes.net_output_beast_ports = strdup(argv[++j]);
        } else if (!strcmp(argv[j],"--net-bi-port") && more) {
            free(Modes.net_input_beast_ports);
            Modes.net_input_beast_ports = strdup(argv[++j]);
        } else if (!strcmp(argv[j],"--net-bind-address") && more) {
            free(Modes.net_bind_address);
            Modes.net_bind_address = strdup(argv[++j]);
        } else if (!strcmp(argv[j],"--net-http-port") && more) {
#ifdef ENABLE_WEBSERVER
            free(Modes.net_http_ports);
            Modes.net_http_ports = strdup(argv[++j]);
#else
            if (strcmp(argv[++j], "0")) {
                fprintf(stderr, "warning: --net-http-port not supported in this build, option ignored.\n");
            }
#endif
        } else if (!strcmp(argv[j],"--net-sbs-port") && more) {
            free(Modes.net_output_sbs_ports);
            Modes.net_output_sbs_ports = strdup(argv[++j]);
        } else if (!strcmp(argv[j],"--net-buffer") && more) {
            Modes.net_sndbuf_size = atoi(argv[++j]);
        } else if (!strcmp(argv[j],"--net-verbatim")) {
            Modes.net_verbatim = 1;
        } else if (!strcmp(argv[j],"--forward-mlat")) {
            Modes.forward_mlat = 1;
        } else if (!strcmp(argv[j],"--onlyaddr")) {
            Modes.onlyaddr = 1;
        } else if (!strcmp(argv[j],"--metric")) {
            Modes.metric = 1;
        } else if (!strcmp(argv[j],"--hae") || !strcmp(argv[j],"--gnss")) {
            Modes.use_gnss = 1;
        } else if (!strcmp(argv[j],"--aggressive")) {
#ifdef ALLOW_AGGRESSIVE
            Modes.nfix_crc = MODES_MAX_BITERRORS;
#else
            fprintf(stderr, "warning: --aggressive not supported in this build, option ignored.\n");
#endif
        } else if (!strcmp(argv[j],"--interactive")) {
            Modes.interactive = Modes.throttle = 1;
        } else if (!strcmp(argv[j],"--throttle")) {
            Modes.throttle = 1;
        } else if (!strcmp(argv[j],"--interactive-rows") && more) {
            Modes.interactive_rows = atoi(argv[++j]);
        } else if (!strcmp(argv[j],"--interactive-ttl") && more) {
            Modes.interactive_display_ttl = (uint64_t)(1000 * atof(argv[++j]));
        } else if (!strcmp(argv[j],"--lat") && more) {
            Modes.fUserLat = atof(argv[++j]);
        } else if (!strcmp(argv[j],"--lon") && more) {
            Modes.fUserLon = atof(argv[++j]);
        } else if (!strcmp(argv[j],"--max-range") && more) {
            Modes.maxRange = atof(argv[++j]) * 1852.0; // convert to metres
        } else if (!strcmp(argv[j],"--debug") && more) {
            char *f = argv[++j];
            while(*f) {
                switch(*f) {
                case 'D': Modes.debug |= MODES_DEBUG_DEMOD; break;
                case 'd': Modes.debug |= MODES_DEBUG_DEMODERR; break;
                case 'C': Modes.debug |= MODES_DEBUG_GOODCRC; break;
                case 'c': Modes.debug |= MODES_DEBUG_BADCRC; break;
                case 'p': Modes.debug |= MODES_DEBUG_NOPREAMBLE; break;
                case 'n': Modes.debug |= MODES_DEBUG_NET; break;
                case 'j': Modes.debug |= MODES_DEBUG_JS; break;
                default:
                    fprintf(stderr, "Unknown debugging flag: %c\n", *f);
                    exit(1);
                    break;
                }
                f++;
            }
        } else if (!strcmp(argv[j],"--stats")) {
            if (!Modes.stats)
                Modes.stats = (uint64_t)1 << 60; // "never"
        } else if (!strcmp(argv[j],"--stats-range")) {
            Modes.stats_range_histo = 1;
        } else if (!strcmp(argv[j],"--stats-every") && more) {
            Modes.stats = (uint64_t)(1000 * atof(argv[++j]));
        } else if (!strcmp(argv[j],"--snip") && more) {
            snipMode(atoi(argv[++j]));
            exit(0);
        } else if (!strcmp(argv[j],"--help")) {
            showHelp();
            exit(0);
        } else if (!strcmp(argv[j],"--quiet")) {
            Modes.quiet = 1;
        } else if (!strcmp(argv[j],"--show-only") && more) {
            Modes.show_only = (uint32_t)strtoul(argv[++j], NULL, 16);
        } else if (!strcmp(argv[j],"--mlat")) {
            Modes.mlat = 1;
        } else if (!strcmp(argv[j],"--interactive-rtl1090")) {
            Modes.interactive = 1;
            Modes.interactive_rtl1090 = 1;
        } else if (!strcmp(argv[j],"--oversample")) {
            // Ignored
        } else if (!strcmp(argv[j], "--html-dir") && more) {
            Modes.html_dir = strdup(argv[++j]);
        } else if (!strcmp(argv[j], "--write-json") && more) {
            Modes.json_dir = strdup(argv[++j]);
        } else if (!strcmp(argv[j], "--write-json-every") && more) {
            Modes.json_interval = (uint64_t)(1000 * atof(argv[++j]));
            if (Modes.json_interval < 100) // 0.1s
                Modes.json_interval = 100;
        } else if (!strcmp(argv[j], "--json-location-accuracy") && more) {
            Modes.json_location_accuracy = atoi(argv[++j]);
        } else {
            fprintf(stderr,
                "\nUnknown or not enough arguments for option '%s'.\n\n",
                argv[j]);
            showHelp();
            exit(1);
        }
    }

    if ((Modes.prefer_airspy + Modes.prefer_rtlsdr + Modes.prefer_file + Modes.net_only) == 0) {
        fprintf(stderr,
            "\nError: you must specify either "
#ifdef HAVE_AIRSPY
            "--airspy, "
#endif
            "--rtlsdr, --ifile, or --net-only.\n\n");
        showHelp();
        exit(1);
    }

    if ((Modes.prefer_airspy + Modes.prefer_rtlsdr + Modes.prefer_file + Modes.net_only) > 1) {
        fprintf(stderr,
            "\nError: only one of "
#ifdef HAVE_AIRSPY
            "--airspy, "
#endif
            "--rtlsdr, --ifile, and --net-only may be specified.\n\n");
        showHelp();
        exit(1);
    }

#ifdef HAVE_AIRSPY
    if (Modes.prefer_airspy) {
        if (Modes.enable_linearity && Modes.enable_sensitivity) {
            fprintf(stderr,
                "\nError: --linearity-gain and --sensitivity-gain cannot be used together.\n\n");
            showHelp();
            exit(1);
        }

        if ((Modes.enable_linearity || Modes.enable_sensitivity) && (Modes.enable_lna_agc || Modes.enable_mixer_agc)) {
            fprintf(stderr,
                "\nError: --linearity-gain/--sensitivity-gain cannot be used with --enable-lna-agc/--enable-mixer-agc.\n\n");
            showHelp();
            exit(1);
        }

        if (Modes.vga_gain > VGA_GAIN_MAX) {
            fprintf(stderr, "\nError: --vga_gain out of range.\n\n");
            showHelp();
            exit(1);
        }

        if (Modes.mixer_gain > MIXER_GAIN_MAX) {
            fprintf(stderr, "\nError: --mixer_gain out of range.\n\n");
            showHelp();
            exit(1);
        }

        if (Modes.lna_gain > LNA_GAIN_MAX) {
            fprintf(stderr, "\nError: --lna_gain out of range.\n\n");
            showHelp();
            exit(1);
        }

        if (Modes.linearity_gain > LINEARITY_GAIN_MAX) {
            fprintf(stderr, "\nError: --linearity_gain out of range.\n\n");
            showHelp();
            exit(1);
        }

        if (Modes.sensitivity_gain > SENSITIVITY_GAIN_MAX) {
            fprintf(stderr, "\nError: --sensitivity_gain out of range.\n\n");
            showHelp();
            exit(1);
        }
    }
#endif

#ifndef _WIN32
    // Setup for SIGWINCH for handling lines
    if (Modes.interactive) {signal(SIGWINCH, sigWinchCallback);}
#endif

    // Initialization
    log_with_timestamp("%s %s starting up.", MODES_DUMP1090_VARIANT, MODES_DUMP1090_VERSION);
    modesInit();

    if (Modes.net_only) {
        fprintf(stderr,"Net-only mode, no SDR device or file open.\n");
    } else if (Modes.filename == NULL) {
        if (Modes.prefer_rtlsdr == 1 && modesInitRTLSDR() < 0) {
            exit(1);
        }
#ifdef HAVE_AIRSPY        
        else if (Modes.prefer_airspy == 1 && modesInitAirspy() < 0) {
            exit(1);
        }
#endif
    } else {
        if (Modes.filename[0] == '-' && Modes.filename[1] == '\0') {
            Modes.fd = STDIN_FILENO;
        } else if ((Modes.fd = open(Modes.filename,
#ifndef _WIN32
                                    (O_RDONLY)
#else
                                    (O_RDONLY | O_BINARY)
#endif
                                    )) == -1) {
            perror("Opening data file");
            exit(1);
        }
    }
    if (Modes.net) modesInitNet();

    // init stats:
    Modes.stats_current.start = Modes.stats_current.end =
        Modes.stats_alltime.start = Modes.stats_alltime.end =
        Modes.stats_periodic.start = Modes.stats_periodic.end =
        Modes.stats_5min.start = Modes.stats_5min.end =
        Modes.stats_15min.start = Modes.stats_15min.end = mstime();

    for (j = 0; j < 15; ++j)
        Modes.stats_1min[j].start = Modes.stats_1min[j].end = Modes.stats_current.start;

    // write initial json files so they're not missing
    writeJsonToFile("receiver.json", generateReceiverJson);
    writeJsonToFile("stats.json", generateStatsJson);
    writeJsonToFile("aircraft.json", generateAircraftJson);

    // If the user specifies --net-only, just run in order to serve network
    // clients without reading data from the RTL device
    if (Modes.net_only) {
        while (!Modes.exit) {
            struct timespec start_time;

            start_cpu_timing(&start_time);
            backgroundTasks();
            end_cpu_timing(&start_time, &Modes.stats_current.background_cpu);

            usleep(100000);
        }
    } else {
        int watchdogCounter = 10; // about 1 second

        // Create the thread that will read the data from the device.
        pthread_mutex_lock(&Modes.data_mutex);
        pthread_create(&Modes.reader_thread, NULL, readerThreadEntryPoint, NULL);

        while (Modes.exit == 0) {
            struct timespec start_time;

            if (Modes.first_free_buffer == Modes.first_filled_buffer) {
                /* wait for more data.
                 * we should be getting data every 50-60ms. wait for max 100ms before we give up and do some background work.
                 * this is fairly aggressive as all our network I/O runs out of the background work!
                 */

                struct timespec ts;
                clock_gettime(CLOCK_REALTIME, &ts);
                ts.tv_nsec += 100000000;
                normalize_timespec(&ts);

                pthread_cond_timedwait(&Modes.data_cond, &Modes.data_mutex, &ts); // This unlocks Modes.data_mutex, and waits for Modes.data_cond
            }

            // Modes.data_mutex is locked, and possibly we have data.

            // copy out reader CPU time and reset it
            add_timespecs(&Modes.reader_cpu_accumulator, &Modes.stats_current.reader_cpu, &Modes.stats_current.reader_cpu);
            Modes.reader_cpu_accumulator.tv_sec = 0;
            Modes.reader_cpu_accumulator.tv_nsec = 0;

            if (Modes.first_free_buffer != Modes.first_filled_buffer) {
                // FIFO is not empty, process one buffer.

                struct mag_buf *buf;

                start_cpu_timing(&start_time);
                buf = &Modes.mag_buffers[Modes.first_filled_buffer];

                // Process data after releasing the lock, so that the capturing
                // thread can read data while we perform computationally expensive
                // stuff at the same time.
                pthread_mutex_unlock(&Modes.data_mutex);

                demodulate2400(buf);
                if (Modes.mode_ac) {
                    demodulate2400AC(buf);
                }

                Modes.stats_current.samples_processed += buf->length;
                Modes.stats_current.samples_dropped += buf->dropped;
                end_cpu_timing(&start_time, &Modes.stats_current.demod_cpu);

                // Mark the buffer we just processed as completed.
                pthread_mutex_lock(&Modes.data_mutex);
                Modes.first_filled_buffer = (Modes.first_filled_buffer + 1) % Modes.mag_buf_num;
                pthread_cond_signal(&Modes.data_cond);
                pthread_mutex_unlock(&Modes.data_mutex);
                watchdogCounter = 10;
            } else {
                // Nothing to process this time around.
                pthread_mutex_unlock(&Modes.data_mutex);
                if (--watchdogCounter <= 0) {
                    log_with_timestamp("No data received from the dongle for a long time, it may have wedged");
                    watchdogCounter = 600;
                }
            }

            start_cpu_timing(&start_time);
            backgroundTasks();
            end_cpu_timing(&start_time, &Modes.stats_current.background_cpu);

            pthread_mutex_lock(&Modes.data_mutex);
        }

        pthread_mutex_unlock(&Modes.data_mutex);

        log_with_timestamp("Waiting for receive thread termination");
        pthread_join(Modes.reader_thread,NULL);     // Wait on reader thread exit
        pthread_cond_destroy(&Modes.data_cond);     // Thread cleanup - only after the reader thread is dead!
        pthread_mutex_destroy(&Modes.data_mutex);
    }

    // If --stats were given, print statistics
    if (Modes.stats) {
        display_total_stats();
    }

    cleanup_converter(Modes.converter_state);
    log_with_timestamp("Normal exit.");

#ifndef _WIN32
    pthread_exit(0);
#else
    return (0);
#endif
}
//
//=========================================================================
//
