gpsd/drivers/driver_garmin.c

/*
 * This file contains two drivers for Garmin receivers and some code
 * shared by both drivers.
 *
 * One driver "garmin_usb_binary" handles the Garmin binary packet
 * format supported by the USB Garmins tested with the Garmin 18 and
 * other models.  (There is also "garmin_usb_binary_old".)  These are ONLY
 * for USB devices reporting as: 091e:0003.
 *
 * The other driver "garmin_ser_binary" is for Garmin receivers via a
 * serial port, whether or not one uses a USB/serial adaptor or a real
 * serial port.  These receivers provide adequate NMEA support, so it
 * often makes sense to just put them into NMEA mode.
 *
 * On Linux, USB Garmins (091e:0003) need the Linux garmin_gps driver and
 * will not function without it.  On other operating systems, it is clear
 * garmin_usb_binary_old does not work since it requires the Linux
 * garmin_gps module.
 *
 * This code has been tested and at least at one time is known to work on
 * big- and little-endian CPUs and 32 and 64 bit cpu modes.
 *
 *
 * Documentation for the Garmin protocols can be found via
 *   http://www.garmin.com/support/commProtocol.html
 * The file IOSDK.zip contains IntfSpec.pdf, which describes the
 * protocol in terms of Application, Link, and Physical.  This
 * identical file is also available at:
 *   http://www.garmin.com/support/pdf/iop_spec.pdf
 * An older version of iop_spec.pdf that describes only Serial Binary
 * is available at:
 *   http://vancouver-webpages.com/pub/peter/iop_spec.pdf
 * Information about the GPS 18
 *   http://www.garmin.com/manuals/425_TechnicalSpecification.pdf
 *
 * There is one physical link protocol for serial which uses DLE/ETX
 * framing.  There is another physical protocol for USB which relies
 * on the packetization intrinsic to USB bulk pipes.
 *
 * There are several link protocols; all devices implement L000.
 * There are then product-specific protocols; most devices implement
 * L001.  Link protocols are the same and carried over either Physical
 * protocol.
 *
 * Application protocols are named A000 and then with different
 * 3-digit numbers.  They are carried over Link protocols.
 *
 * Thus, much of the higher-level code dealing the data formats is
 * shared between USB Binary and Serial Binary.
 *
 * This code is partly from the Garmin IOSDK and partly from the
 * sample code in the Linux garmin_gps driver.
 *
 * bad code by: Gary E. Miller <gem@rellim.com>
 *
 * -D 3 = packet trace
 * -D 4 = packet details
 * -D 5 = more packet details
 * -D 6 = very excessive details
 *
 * limitations:
 *
 * do not have from garmin:
 *      pdop
 *      hdop
 *      vdop
 *      magnetic variation
 *
 * known bugs:
 *      hangs in the fread loop instead of keeping state and returning.
 *
 * This file is Copyright 2010 by the GPSD project
 * SPDX-License-Identifier: BSD-2-clause
 */

#include "../include/gpsd_config.h"  /* must be before all includes */

#ifdef GARMIN_ENABLE

#include <errno.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#if defined(HAVE_LIBUSB)
#include <libusb.h>
#endif

#include "../include/gpsd.h"
#include "../include/bits.h"
#include "../include/timespec.h"

#define GPSD_LE16TOH(x) getles16((char *)(&(x)), 0)
#define GPSD_LE32TOH(x) getles32((char *)(&(x)), 0)
#define GPSD_LEF32(x) getlef32((const char *)(&(x)), 0)
#define GPSD_LED64(x) getled64((const char *)(&(x)), 0)

#define USE_RMD 0

/* Used in Serial Physical Layer */
#define ETX 0x03
#define ACK 0x06
#define DLE 0x10
#define NAK 0x15

#define GARMIN_LAYERID_TRANSPORT (uint8_t)  0
#define GARMIN_LAYERID_APPL      (uint32_t) 20
// Linux Garmin USB driver layer-id to use for some control mechanisms
#define GARMIN_LAYERID_PRIVATE  0x01106E4B

// packet ids used in private layer
#define PRIV_PKTID_SET_DEBUG    1
#define PRIV_PKTID_SET_MODE     2
#define PRIV_PKTID_INFO_REQ     3
#define PRIV_PKTID_INFO_RESP    4
#define PRIV_PKTID_RESET_REQ    5
#define PRIV_PKTID_SET_DEF_MODE 6

#define MODE_NATIVE       0
#define MODE_GARMIN_SERIAL   1

#define GARMIN_PKTID_TRANSPORT_START_SESSION_REQ 5
#define GARMIN_PKTID_TRANSPORT_START_SESSION_RESP 6

#define GARMIN_PKTID_PROTOCOL_ARRAY     253
#define GARMIN_PKTID_PRODUCT_RQST       254
#define GARMIN_PKTID_PRODUCT_DATA       255
/* 0x29 ')' */
#define GARMIN_PKTID_RMD41_DATA  41
/* 0x33 '3' */
#define GARMIN_PKTID_PVT_DATA      51
/* 0x33 '4' */
#define GARMIN_PKTID_RMD_DATA      52
/* 0x72 'r' */
#define GARMIN_PKTID_SAT_DATA      114

#define GARMIN_PKTID_L001_XFER_CMPLT     12
#define GARMIN_PKTID_L001_COMMAND_DATA   10
#define GARMIN_PKTID_L001_DATE_TIME_DATA 14
#define GARMIN_PKTID_L001_RECORDS       27
#define GARMIN_PKTID_L001_WPT_DATA       35

#define CMND_ABORT                       0
#define CMND_START_PVT_DATA              49
#define CMND_STOP_PVT_DATA               50
#define CMND_START_RM_DATA               110

#define MAX_BUFFER_SIZE 4096

#define GARMIN_CHANNELS 12

// something magic about 64, garmin driver will not return more than
// 64 at a time.  If you read less than 64 bytes the next read will
// just get the last of the 64 byte buffer.
#define ASYNC_DATA_SIZE 64


#pragma pack(1)
// This is the data format of the satellite data from the garmin USB
typedef struct __attribute__((__packed__))
{
    uint8_t svid;
    uint16_t snr;               // 0 - 0xffff
    uint8_t elev;
    uint16_t azmth;
    uint8_t status;             // bit 0, has ephemeris, 1, has diff correction
    // bit 2 used in solution
    // bit 3??
} cpo_sat_data;

/* Garmin D800_Pvt_Datetype_Type */
/* packet type:  GARMIN_PKTID_PVT_DATA   52 */
/* This is the data format of the position data from the garmin USB */
typedef struct __attribute__((__packed__))
{
    float alt;                  /* altitude above WGS 84 (meters) */
    float epe;                  /* estimated position error, 2 sigma (meters) */
    float eph;                  /* epe, but horizontal only (meters) */
    float epv;                  /* epe but vertical only (meters ) */
    int16_t fix;                /* 0 - failed integrity check
                                 * 1 - invalid or unavailable fix
                                 * 2 - 2D
                                 * 3 - 3D
                                 * 4 - 2D Diff
                                 * 5 - 3D Diff
                                 */
    double gps_tow;             /* gps time of week (seconds) */
    double lat;                 /* ->latitude (radians) */
    double lon;                 /* ->longitude (radians) */
    float lon_vel;              /* velocity east (meters/second) */
    float lat_vel;              /* velocity north (meters/second) */
    float alt_vel;              /* velocity up (meters/sec) */
    // Garmin GPS25 uses pkt_id 0x28 and does not output the
    // next 3 items
    float msl_hght;             /* height of WGS 84 above MSL (meters) */
    int16_t leap_sec;           /* diff between GPS and UTC (seconds) */
    int32_t grmn_days;          /* days from UTC December 31st, 1989 to the
                                 * beginning of the current week */
} cpo_pvt_data;

typedef struct __attribute__((__packed__))
{
    uint32_t cycles;
    double pr;                  // pseudorange in meters
    uint16_t phase;
    int8_t slp_dtct;
    uint8_t snr_dbhz;
    uint8_t svid;
    int8_t valid;
} cpo_rcv_sv_data;

/* packet type:  GARMIN_PKTID_RMD_DATA   53 */
/* seems identical to the packet id 0x29 from the Garmin GPS 25 */
typedef struct __attribute__((__packed__))
{
    double rcvr_tow;
    int16_t rcvr_wn;
    cpo_rcv_sv_data sv[GARMIN_CHANNELS];
} cpo_rcv_data;

// This is the packet format to/from the Garmin USB
typedef struct __attribute__((__packed__))
{
    uint8_t mPacketType;
    uint8_t mReserved1;
    uint16_t mReserved2;
    uint16_t mPacketId;
    uint16_t mReserved3;
    uint32_t mDataSize;
    union
    {
        //int8_t chars[MAX_BUFFER_SIZE];
        // cppcheck-suppress unusedStructMember
        uint8_t uchars[MAX_BUFFER_SIZE];
        cpo_pvt_data pvt;
        cpo_sat_data sats;
    } mData;
} Packet_t;

// useful funcs to read/write ints
//  floats and doubles are Intel (little-endian) order only...
static inline void set_int16(uint8_t * buf, uint32_t value)
{
    buf[0] = (uint8_t) (0x0FF & value);
    buf[1] = (uint8_t) (0x0FF & (value >> 8));
}

static inline void set_int32(uint8_t * buf, uint32_t value)
{
    buf[0] = (uint8_t) (0x0FF & value);
    buf[1] = (uint8_t) (0x0FF & (value >> 8));
    buf[2] = (uint8_t) (0x0FF & (value >> 16));
    buf[3] = (uint8_t) (0x0FF & (value >> 24));
}

static inline uint16_t get_uint16(const uint8_t * buf)
{
    return (uint16_t) (0xFF & buf[0])
        | ((uint16_t) (0xFF & buf[1]) << 8);
}

#if defined(HAVE_LIBUSB) && defined(__linux__)
static inline uint32_t get_int32(const uint8_t * buf)
{
    return (uint32_t) (0xFF & buf[0])
        | ((uint32_t) (0xFF & buf[1]) << 8)
        | ((uint32_t) (0xFF & buf[2]) << 16)
        | ((uint32_t) (0xFF & buf[3]) << 24);
}
#endif /* HAVE_LIBUSB */

// convert radians to degrees
static inline double radtodeg(double rad)
{
    return (double)(rad * RAD_2_DEG);
}

static gps_mask_t PrintSERPacket(struct gps_device_t *session,
                                 unsigned char pkt_id, int pkt_len,
                                 unsigned char *buf);
#if defined(HAVE_LIBUSB) && defined(__linux__)
static gps_mask_t PrintUSBPacket(struct gps_device_t *session,
                                 Packet_t * pkt);
#endif /* HAVE_LIBUSB */

gps_mask_t PrintSERPacket(struct gps_device_t *session, unsigned char pkt_id,
                          int pkt_len, unsigned char *buf)
{

    gps_mask_t mask = ONLINE_SET;
    int i = 0, j = 0;
    uint16_t prod_id = 0;
    uint16_t ver = 0;
    int maj_ver;
    int min_ver;
    time_t time_l = 0;
    char msg_buf[512] = "";
    char *msg = NULL;
    cpo_sat_data *sats = NULL;
    cpo_pvt_data *pvt = NULL;
    cpo_rcv_data *rmd = NULL;
    double gps_tow = 0;

    GPSD_LOG(LOG_DATA, &session->context->errout,
             "Garmin: PrintSERPacket(, %#02x, %#02x, )\n", pkt_id, pkt_len);

    session->cycle_end_reliable = true;

    switch (pkt_id) {
    case ACK:
        GPSD_LOG(LOG_PROG, &session->context->errout, "Garmin: ACK\n");
        break;
    case NAK:
        GPSD_LOG(LOG_PROG, &session->context->errout, "Garmin: NAK\n");
        break;
    case GARMIN_PKTID_L001_COMMAND_DATA:
        prod_id = get_uint16((uint8_t *) buf);
        switch (prod_id) {
        case CMND_ABORT:
            msg = "Abort current xfer";
            break;
        case CMND_START_PVT_DATA:
            msg = "Start Xmit PVT data";
            break;
        case CMND_STOP_PVT_DATA:
            msg = "Stop Xmit PVT data";
            break;
        case CMND_START_RM_DATA:
            msg = "Start RMD data";
            break;
        default:
            (void)snprintf(msg_buf, sizeof(msg_buf), "Unknown: %u",
                           (unsigned int)prod_id);
            msg = msg_buf;
            break;
        }
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Appl, Command Data: %s\n", msg);
        break;
    case GARMIN_PKTID_PRODUCT_RQST:
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Appl, Product Data req\n");
        break;
    case GARMIN_PKTID_PRODUCT_DATA:
        prod_id = get_uint16((uint8_t *) buf);
        ver = get_uint16((uint8_t *) & buf[2]);
        maj_ver = (int)(ver / 100);
        min_ver = (int)(ver - (maj_ver * 100));
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Appl, Product Data, sz: %d\n",
                 pkt_len);
        (void)snprintf(session->subtype, sizeof(session->subtype),
                       "%d: %d.%02d", (int)prod_id, maj_ver, min_ver);
        GPSD_LOG(LOG_INF, &session->context->errout,
                 "Garmin: Product ID: %d, SoftVer: %d.%02d\n",
                 prod_id, maj_ver, min_ver);
        GPSD_LOG(LOG_INF, &session->context->errout,
                 "Garmin: Product Desc: %s\n", &buf[4]);
        mask |= DEVICEID_SET;
        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "Garmin: PRODUCT_DATA: subtype=%s\n",
                 session->subtype);
        break;
    case GARMIN_PKTID_PVT_DATA:
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: PVT Data (51) Sz: %d\n", pkt_len);

        pvt = (cpo_pvt_data *) buf;

        session->context->leap_seconds = (int)GPSD_LE16TOH(pvt->leap_sec);
        session->context->valid = LEAP_SECOND_VALID;

        // 631065600, unix seconds for 31 Dec 1989 Zulu
        time_l = (time_t) (631065600 + (GPSD_LE32TOH(pvt->grmn_days) * 86400));
        // TODO, convert grmn_days to context->gps_week
        time_l -= session->context->leap_seconds;

        // gps_tow is always like x.999 or x.998 just round it to nearest sec
        // FIXME! this will break 5Hz garmins...
        gps_tow = GPSD_LED64(pvt->gps_tow);
        time_l += (time_t)round(gps_tow);

        /* sanity check unix time against leap second.
         * Leap second 18 at 1 Jan 2017: 1483228800 */
        if (17 < session->context->leap_seconds &&
            1483228800L > time_l) {
            time_l += 619315200;               // fast forward 1024 weeks
        }

        DTOTS(&session->context->gps_tow, gps_tow);
        session->newdata.time.tv_sec = time_l;
        session->newdata.time.tv_nsec = 0;
        // (long long) for 32-bit systems
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: time_l: %lld\n", (long long)time_l);

        session->newdata.latitude = radtodeg(GPSD_LED64(pvt->lat));
        session->newdata.longitude = radtodeg(GPSD_LED64(pvt->lon));
        // altitude is WGS84
        session->newdata.altHAE = GPSD_LEF32(pvt->alt);

        // geoid separation from WGS 84
        // gpsd sign is opposite of garmin sign
        session->newdata.geoid_sep = -GPSD_LEF32(pvt->msl_hght);

        /* Estimated position error in meters.  Confidence (sigma) not
         * specified by Garmin.
         * We follow the advice at <http://gpsinformation.net/main/errors.htm>.
         * Since GPS data is not gaussian, this is marginal advice...
         * If this assumption changes here, it should also change in
         * nmea_parse.c where we analyze PGRME.
         */
        session->newdata.sep = GPSD_LEF32(pvt->epe) *
                                   (GPSD_CONFIDENCE / CEP50_SIGMA);
        /* eph, horizaontal error, 2 sigma */
        session->newdata.eph = GPSD_LEF32(pvt->eph) *
                                   (GPSD_CONFIDENCE / CEP50_SIGMA);
        /* eph, horizaontal error, 2 sigma */
        session->newdata.epv = GPSD_LEF32(pvt->epv) *
                                   (GPSD_CONFIDENCE / CEP50_SIGMA);

        /* meters/sec */
        session->newdata.NED.velN = GPSD_LEF32(pvt->lat_vel);
        session->newdata.NED.velE = GPSD_LEF32(pvt->lon_vel);
        session->newdata.NED.velD = -GPSD_LEF32(pvt->alt_vel);

        switch (GPSD_LE16TOH(pvt->fix)) {
        case 0:
        case 1:
        default:
            // no fix
            session->newdata.status = STATUS_UNK;
            session->newdata.mode = MODE_NO_FIX;
            break;
        case 2:
            // 2D fix
            session->newdata.status = STATUS_GPS;
            session->newdata.mode = MODE_2D;
            break;
        case 3:
            // 3D fix
            session->newdata.status = STATUS_GPS;
            session->newdata.mode = MODE_3D;
            break;
        case 4:
            // 2D Differential fix
            session->newdata.status = STATUS_DGPS;
            session->newdata.mode = MODE_2D;
            break;
        case 5:
            // 3D differential fix
            session->newdata.status = STATUS_DGPS;
            session->newdata.mode = MODE_3D;
            break;
        }

        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Appl, mode %d, status %d\n",
                 session->newdata.mode, session->newdata.status);

        /* save some expensive calculations if not needed */
        if (session->context->errout.debug >= LOG_INF) {

            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin: UTC Time: %lld\n",
                     (long long)session->newdata.time.tv_sec);
            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin: Geoid Separation (MSL-WGS84): from garmin %lf, "
                     "calculated %lf\n",
                     session->newdata.geoid_sep,
                     wgs84_separation(session->newdata.latitude,
                                         session->newdata.longitude));

            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin: Alt: %.3f, sep: %.3f, eph: %.3f, Epv: %.3f, "
                     "Fix: %d, Gps_tow: %f, Lat: %.3f, Lon: %.3f, "
                     "velN: %.3f, velE: %.3f, velD: %.3f, geoidsep: %.3f, "
                     "Leap: %d, GarminDays: %d\n",
                     session->newdata.altHAE,
                     session->newdata.sep,
                     session->newdata.eph,
                     session->newdata.epv,
                     GPSD_LE16TOH(pvt->fix),
                     gps_tow,
                     session->newdata.latitude,
                     session->newdata.longitude,
                     session->newdata.NED.velN,
                     session->newdata.NED.velE,
                     session->newdata.NED.velD,
                     session->newdata.geoid_sep,
                     session->context->leap_seconds,
                     GPSD_LE32TOH(pvt->grmn_days));
        }

        if (session->newdata.mode > MODE_NO_FIX) {
            /* data only valid with a fix */
            mask |=
                TIME_SET | LATLON_SET | ALTITUDE_SET | STATUS_SET | MODE_SET |
                HERR_SET | PERR_IS | CLEAR_IS | REPORT_IS | VNED_SET;
            /*
             * Garmin documentation says we should wait until four good fixes
             * have been seen before trying to use the device for precision
             * time service.
             */
            if (session->fixcnt > 3)
                mask |= NTPTIME_IS;
        }
        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "Garmin: PVT_DATA: time=%lld, lat=%.2f lon=%.2f "
                 "eph=%.2f sep=%.2f epv=%.2f  mode=%d status=%d\n",
                 (long long)session->newdata.time.tv_sec,
                 session->newdata.latitude,
                 session->newdata.longitude,
                 session->newdata.eph,
                 session->newdata.sep,
                 session->newdata.epv,
                 session->newdata.mode,
                 session->newdata.status);
        break;
    case GARMIN_PKTID_RMD_DATA:
    case GARMIN_PKTID_RMD41_DATA:
        rmd = (cpo_rcv_data *) buf;
        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "Garmin: PVT RMD Data Sz: %d\n", pkt_len);
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: PVT RMD rcvr_tow: %f, rcvr_wn: %d\n",
                 GPSD_LED64(rmd->rcvr_tow), GPSD_LE16TOH(rmd->rcvr_wn));
        for (i = 0; i < GARMIN_CHANNELS; i++) {
            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin: PVT RMD Sat: %3u, cycles: %9u, pr: %16.6f, "
                     "phase: %7.3f, slp_dtct: %3s, snr: %3u, Valid: %3s\n",
                     (int)rmd->sv[i].svid + 1,
                     GPSD_LE32TOH(rmd->sv[i].cycles),
                     GPSD_LED64(rmd->sv[i].pr),
                     (GPSD_LE16TOH(rmd->sv[i].phase) * 360.0) / 2048.0,
                     rmd->sv[i].slp_dtct != 0 ? "Yes" : "No",
                     rmd->sv[i].snr_dbhz,
                     rmd->sv[i].valid != 0 ? "Yes" : "No");
        }
        break;

    case GARMIN_PKTID_SAT_DATA:
        // record ID 0x72 (114)
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: SAT Data Sz: %d\n", pkt_len);
        sats = (cpo_sat_data *) buf;

        session->gpsdata.satellites_used = 0;
        gpsd_zero_satellites(&session->gpsdata);
        for (i = 0, j = 0; i < GARMIN_CHANNELS; i++, sats++) {
            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin: Sat %2d, snr: %5u, elev: %2d, Azmth: %3d, "
                     "Stat: x%x\n",
                     sats->svid, GPSD_LE16TOH(sats->snr), sats->elev,
                     GPSD_LE16TOH(sats->azmth),
                     sats->status);

            if (255 == (int)sats->svid) {
                // Garmin uses 255 for empty
                // gpsd uses 0 for empty
                continue;
            }

            if ((int)sats->svid <= 32) {
                /* GPS 1-32 */
                session->gpsdata.skyview[j].PRN = (short)sats->svid;
                session->gpsdata.skyview[j].svid = (short)sats->svid;
                session->gpsdata.skyview[j].gnssid = GNSSID_GPS;
            } else {
                /* SBAS 33-64 */
                session->gpsdata.skyview[j].PRN = (short)sats->svid;
                session->gpsdata.skyview[j].svid = (short)sats->svid + 87;
                session->gpsdata.skyview[j].gnssid = GNSSID_SBAS;
            }
            session->gpsdata.skyview[j].azimuth =
                (short)GPSD_LE16TOH(sats->azmth);
            session->gpsdata.skyview[j].elevation = (short)sats->elev;
            if (0xffff == sats->snr) {
                session->gpsdata.skyview[j].ss = NAN;
            } else {
                // Garmin does not document this.  snr is in dB*100
                // Known, but not seen satellites have a dB value of -1*100
                session->gpsdata.skyview[j].ss =
                    (float)(GPSD_LE16TOH(sats->snr) / 100.0);
            }
            // FIX-ME: Garmin documents this, but Daniel Dorau
            // <daniel.dorau@gmx.de> says the behavior on his GPSMap60CSX
            // doesn't match it.
            if ((uint8_t) 0 != (sats->status & 4)) {
                // used in solution?
                session->gpsdata.skyview[j].used = true;
                session->gpsdata.satellites_used++;
            }
            session->gpsdata.satellites_visible++;
            j++;

        }
        session->gpsdata.skyview_time.tv_sec = 0;
        session->gpsdata.skyview_time.tv_nsec = 0;
        mask |= USED_IS | SATELLITE_SET;
        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "Garmin: SAT_DATA: visible=%d used=%d\n",
                 session->gpsdata.satellites_visible,
                 session->gpsdata.satellites_used);
        break;
    case GARMIN_PKTID_PROTOCOL_ARRAY:
        // Pid_Protocol_Array, ID 253
        // this packet is never requested, it just comes, in some case
        // after a GARMIN_PKTID_PRODUCT_RQST
        GPSD_LOG(LOG_INF, &session->context->errout,
                 "Garmin: Appl, Product Capability, sz: %d\n",
                 pkt_len);
        for (i = 0; i < pkt_len; i += 3) {
            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin:   %c%03d\n",
                     buf[i],    get_uint16((uint8_t *) & buf[i + 1]));
        }
        break;
    default:
        GPSD_LOG(LOG_WARN, &session->context->errout,
                 "Garmin: Unknown packet id: %#02x, Sz: %#02x\n",
                 pkt_id, pkt_len);
        break;
    }
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "Garmin: PrintSERPacket(, %#02x, %#02x, ) mask=(%s)\n",
             pkt_id, pkt_len, gps_maskdump(mask));
    return mask;
}


#if defined(HAVE_LIBUSB) && defined(__linux__)
static gps_mask_t PrintUSBPacket(struct gps_device_t *session, Packet_t * pkt)
/* For debugging, decodes and prints some known packets */
{
    gps_mask_t mask = 0;
    int maj_ver;
    int min_ver;
    uint32_t mode = 0;
    uint16_t prod_id = 0;
    uint32_t veri = 0;
    uint32_t serial;
    uint32_t mDataSize = get_int32((uint8_t *) & pkt->mDataSize);
    uint8_t *buffer = (uint8_t *) pkt;

    GPSD_LOG(LOG_PROG, &session->context->errout, "Garmin: PrintUSBPacket()\n");
    if (DLE == pkt->mPacketType) {
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: really a SER packet!\n");
        return PrintSERPacket(session,
                              (unsigned char)buffer[1],
                              (int)buffer[2], (unsigned char *)(buffer + 3));
    }

    if (4096 < mDataSize) {
        GPSD_LOG(LOG_WARN, &session->context->errout,
                 "Garmin: bogus packet, size too large=%d\n",
                 mDataSize);
        return 0;
    }

    switch (pkt->mPacketType) {
    case GARMIN_LAYERID_TRANSPORT:
        /* Garmin USB layer specific */
        switch (pkt->mPacketId) {
        case GARMIN_PKTID_TRANSPORT_START_SESSION_REQ:
            // Pid_Start_Session, ID 5
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Transport, Start Session req\n");
            break;
        case GARMIN_PKTID_TRANSPORT_START_SESSION_RESP:
            // Pid_Session_Started, ID 6
            mode = get_int32(&pkt->mData.uchars[0]);
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Transport, Start Session resp, unit: 0x%x\n",
                     mode);
            break;
        default:
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Transport, Packet: Type %d %d %d, ID: %d,"
                     "Sz: %d\n",
                     pkt->mPacketType, pkt->mReserved1, pkt->mReserved2,
                     pkt->mPacketId, mDataSize);
            break;
        }
        break;
    case GARMIN_LAYERID_APPL:
        /* raw data transport, shared with Garmin Serial Driver */

        mask = PrintSERPacket(session,
                              (unsigned char)pkt->mPacketId,
                              (int)mDataSize,
                              (unsigned char *)pkt->mData.uchars);
        break;
    case 75:
        // private, garmin USB kernel driver specific
        switch (pkt->mPacketId) {
        case PRIV_PKTID_SET_MODE:
            prod_id = get_uint16(&pkt->mData.uchars[0]);
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Private, Set Mode: %d\n", prod_id);
            break;
        case PRIV_PKTID_INFO_REQ:
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Private, ID: Info Req\n");
            break;
        case PRIV_PKTID_INFO_RESP:
            veri = get_int32(pkt->mData.uchars);
            maj_ver = (int)(veri >> 16);
            min_ver = (int)(veri & 0xffff);
            mode = get_int32(&pkt->mData.uchars[4]);
            serial = get_int32(&pkt->mData.uchars[8]);
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Private, ID: Info Resp\n");
            GPSD_LOG(LOG_INF, &session->context->errout,
                     "Garmin: USB Driver found, Version %d.%d, Mode: %d, GPS Serial# %u\n",
                     maj_ver, min_ver, mode, serial);
            break;
        default:
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: Private, Packet: ID: %d, Sz: %d\n",
                     pkt->mPacketId, mDataSize);
            break;
        }
        break;
    default:
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Packet: Type %d %d %d, ID: %d, Sz: %d\n",
                 pkt->mPacketType, pkt->mReserved1, pkt->mReserved2,
                 pkt->mPacketId, mDataSize);
        break;
    }

    return mask;
}

#endif /* HAVE_LIBUSB */


#if defined(HAVE_LIBUSB) && defined(__linux__)
/* build and send a packet w/ USB protocol */
static void Build_Send_USB_Packet(struct gps_device_t *session,
                                  uint32_t layer_id, uint32_t pkt_id,
                                  uint32_t length, uint32_t data)
{
    uint8_t *buffer = (uint8_t *) session->driver.garmin.Buffer;
    Packet_t *thePacket = (Packet_t *) buffer;
    ssize_t theBytesReturned = 0;
    ssize_t theBytesToWrite = 12 + (ssize_t) length;

    set_int32(buffer, layer_id);
    set_int32(buffer + 4, pkt_id);
    set_int32(buffer + 8, length);
    if (2 == length) {
        set_int16(buffer + 12, data);
    } else if (4 == length) {
        set_int32(buffer + 12, data);
    }
    (void)PrintUSBPacket(session, thePacket);

    theBytesReturned = gpsd_write(session, (const char *)thePacket,
                                  (size_t) theBytesToWrite);
    GPSD_LOG(LOG_PROG, &session->context->errout,
             "Garmin: SendPacket(), wrote %zd bytes\n",
             theBytesReturned);

    // Garmin says:
    // If the packet size was an exact multiple of the USB packet
    // size, we must make a final write call with no data

    // as a practical matter no known packets are 64 bytes long so
    // this is untested

    // So here goes just in case
    if (0 == (theBytesToWrite % ASYNC_DATA_SIZE)) {
        char *n = "";
        (void)gpsd_write(session, n, 0);
    }
}
#endif /* HAVE_LIBUSB && __linux__ */

/* build and send a packet in serial protocol */
/* layer_id unused */
// FIX-ME: This should go through the common message buffer someday
static void Build_Send_SER_Packet(struct gps_device_t *session,
                                  uint32_t layer_id UNUSED, uint32_t pkt_id,
                                  uint32_t length, uint32_t data)
{
    uint8_t *buffer = (uint8_t *) session->driver.garmin.Buffer;
    uint8_t *buffer0 = buffer;
    Packet_t *thePacket = (Packet_t *) buffer;
    ssize_t theBytesReturned = 0;
    ssize_t theBytesToWrite = 6 + (ssize_t) length;
    uint8_t chksum = 0;

    *buffer++ = (uint8_t) DLE;
    *buffer++ = (uint8_t) pkt_id;
    chksum = pkt_id;
    *buffer++ = (uint8_t) length;
    chksum += length;
    /* ??? What is this doing? */
    if (2 == length) {
        /* careful!  no DLE stuffing here! */
        set_int16(buffer, data);
        chksum += buffer[0];
        chksum += buffer[1];
    } else if (4 == length) {
        /* careful!  no DLE stuffing here! */
        set_int32(buffer, data);
        chksum += buffer[0];
        chksum += buffer[1];
        chksum += buffer[2];
        chksum += buffer[3];
    }
    /* ??? How is data copied to the buffer? */
    buffer += length;

    // Add checksum
    *buffer++ = -chksum;
    if (DLE == -chksum) {
        /* stuff another DLE */
        *buffer++ = (uint8_t) DLE;
        theBytesToWrite++;
    }
    // Add DLE, ETX
    *buffer++ = (uint8_t) DLE;
    /* we used to say n++ here, but scan-build complains */
    *buffer = (uint8_t) ETX;

    (void)PrintSERPacket(session,
                         (unsigned char)buffer0[1],
                         (int)buffer0[2], (unsigned char *)(buffer0 + 3));

    theBytesReturned = gpsd_write(session, (const char *)thePacket,
                                  (size_t) theBytesToWrite);
    GPSD_LOG(LOG_PROG, &session->context->errout,
             "Garmin: SendPacket(), wrote %zd bytes\n",
             theBytesReturned);

}

#if defined(HAVE_LIBUSB) && defined(__linux__)
/*
 * is_usb_device() - is a specified device USB matching given vendor/product?
 *
 * BUG: Doesn't actually match against path yet. Must finish this function
 * by querying /sys/dev/char, either directly or using libudev. Greg KH
 * assures this is possible, though he is vague about how.
 *
 * libudev: http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/
 */
static bool is_usb_device(const char *path UNUSED, int vendor, int product,
                          struct gpsd_errout_t *errout)
{
    // discover devices
    libusb_device **list;
    ssize_t cnt;
    ssize_t i = 0;
    bool found = false;

    GPSD_LOG(LOG_INF, errout, "attempting USB device enumeration.\n");
    (void)libusb_init(NULL);

    if ((cnt = libusb_get_device_list(NULL, &list)) < 0) {
        GPSD_LOG(LOG_ERROR, errout, "USB device list call failed.\n");
        libusb_exit(NULL);
        return false;
    }

    for (i = 0; i < cnt; i++) {
        struct libusb_device_descriptor desc;
        libusb_device *dev = list[i];

        int r = libusb_get_device_descriptor(dev, &desc);
        if (r < 0) {
            GPSD_LOG(LOG_ERROR, errout,
                     "USB descriptor fetch failed on device %zd.\n", i);
            continue;
        }

        /* we can extract device descriptor data */
        GPSD_LOG(LOG_INF, errout,
                 "%04x:%04x (bus %d, device %d)\n",
                 desc.idVendor, desc.idProduct,
                 libusb_get_bus_number(dev),
                 libusb_get_device_address(dev));

        /* we match if vendor and product ID are right */
        if (desc.idVendor == (uint16_t)vendor && desc.idProduct == (uint16_t)product) {
            found = true;
            break;
        }
    }

    GPSD_LOG(LOG_INF, errout,
             "vendor/product match with %04x:%04x %sfound\n",
             vendor, product, found ? "" : "not ");
    libusb_free_device_list(list, 1);
    libusb_exit(NULL);
    return found;
}

#endif /* HAVE_LIBUSB */

/*
 * garmin_usb_detect() - detect a Garmin USB device connected to session fd.
 *
 * This is ONLY for USB devices reporting as: 091e:0003.
 *
 * This driver ONLY works in Linux and ONLY when the garmin_gps kernel
 * module is installed.
 *
 * This is only necessary because under Linux Garmin USB devices need a
 * kernel module rather than being normal USB-serial devices.
 *
 * The actual wire protocol from the Garmin device is very strange. There
 * are no delimiters.  End of packet is signaled by a zero-length read
 * on the USB device, and start of packet is the next read.  You can't just
 * ignore the zero reads and pass the data through - you'd never be able
 * to tell where the packet boundaries are.
 *
 * The garmin_usb module's job is to grab the packet and frame it in
 * DLEs (with DLE stuffing).  This makes the USB packets look as
 * though they came from a regular Garmin *serial* device, which is how
 * most of the processing for both types can be unified here.
 *
 * return 1 is device found
 * return 0 if not
 */
static bool garmin_usb_detect(struct gps_device_t *session UNUSED)
{
#if defined(__linux__)
    /*
     * Only perform this check if we're looking at a USB-serial
     * device.  This prevents drivers for attached serial GPSes
     * fronm being rudely elbowed aside by this one if they happen
     * to be trying to coexist with the Garmin.
     */
    if (SOURCE_USB != session->sourcetype) {
        return false;
    }

#ifdef HAVE_LIBUSB
    if (!is_usb_device(session->gpsdata.dev.path, 0x091e, 0x0003,
            &session->context->errout))
        return false;

    if (!gpsd_set_raw(session)) {
        GPSD_LOG(LOG_ERROR, &session->context->errout,
                 "Garmin: garmin_usb_detect: error changing port "
                 "attributes: %s\n",
                 strerror(errno));
        return false;
    }

    if (sizeof(session->driver.garmin.Buffer) < sizeof(Packet_t)) {
        /* dunno how this happens, but it does on some compilers */
        GPSD_LOG(LOG_ERROR, &session->context->errout,
                 "Garmin: garmin_usb_detect: Compile error, garmin.Buffer too small.\n");
        return false;
    }

    // FIXME!!! needs to use libusb totally and move garmin_gps aside */
    // set Mode 1, mode 0 is broken somewhere past 2.6.14
    // but how?
    GPSD_LOG(LOG_PROG, &session->context->errout,
             "Garmin: Set garmin_gps driver mode = 0\n");
    Build_Send_USB_Packet(session, GARMIN_LAYERID_PRIVATE,
                          PRIV_PKTID_SET_MODE, 4, MODE_GARMIN_SERIAL);
    // expect no return packet !?

    return true;
#endif /* HAVE_LIBUSB */
#endif /* __linux__ */
    return false;
}

static void garmin_event_hook(struct gps_device_t *session, event_t event)
{
    if (session->context->readonly ||
        session->context->passive) {
        return;
    }
    /*
     * FIX-ME: It might not be necessary to call this on reactivate.
     * Experiment to see if the holds its settings through a close.
     */
    if (event == event_identified || event == event_reactivate) {
        // Tell the device to send product data
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Get Product Data\n");
        Build_Send_SER_Packet(session, GARMIN_LAYERID_APPL,
                              GARMIN_PKTID_PRODUCT_RQST, 0, 0);

        // turn on PVT data 49
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Set to send reports every 1 second\n");

        Build_Send_SER_Packet(session, GARMIN_LAYERID_APPL,
                              GARMIN_PKTID_L001_COMMAND_DATA, 2,
                              CMND_START_PVT_DATA);

#if USE_RMD
        // turn on RMD data 110
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: Set to send Raw sat data\n");
        Build_Send_SER_Packet(session, GARMIN_LAYERID_APPL,
                              GARMIN_PKTID_L001_COMMAND_DATA, 2,
                              CMND_START_RM_DATA);
#endif
    }
    if (event == event_deactivate)
        /* FIX-ME: is any action needed, or is closing the port sufficient? */
        GPSD_LOG(LOG_PROG, &session->context->errout,
                 "Garmin: garmin_close()\n");
}

#define Send_ACK()    Build_Send_SER_Packet(session, 0, ACK, 0, 0)
#define Send_NAK()    Build_Send_SER_Packet(session, 0, NAK, 0, 0)

gps_mask_t garmin_ser_parse(struct gps_device_t *session)
{
    unsigned char *buf = session->lexer.outbuffer;
    size_t len = session->lexer.outbuflen;
    unsigned char data_buf[MAX_BUFFER_SIZE];
    unsigned char c;
    int i = 0;
    size_t n = 0;
    int data_index = 0;
    int got_dle = 0;
    unsigned char pkt_id = 0;
    unsigned char pkt_len = 0;
    unsigned char chksum = 0;
    gps_mask_t mask = 0;
    struct timespec delay;

    GPSD_LOG(LOG_RAW, &session->context->errout,
             "Garmin: garmin_ser_parse()\n");
    if (6 > len) {
        /* WTF? */
        /* minimum packet; <DLE> [pkt id] [length=0] [chksum] <DLE> <STX> */
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: serial too short: %zd\n", len);
        return 0;
    }
    /* debug */
    for (i = 0; i < (int)len; i++) {
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: Char: %#02x\n", buf[i]);
    }

    if ('\x10' != buf[0]) {
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: buf[0] not DLE\n");
        return 0;
    }
    n = 1;
    pkt_id = buf[n++];
    chksum = pkt_id;
    if ('\x10' == pkt_id) {
        if ('\x10' != buf[n++]) {
            Send_NAK();
            GPSD_LOG(LOG_RAW, &session->context->errout,
                     "Garmin: Bad pkt_id %#02x\n", pkt_id);
            return 0;
        }
    }

    pkt_len = buf[n++];
    chksum += pkt_len;
    if ('\x10' == pkt_len) {
        if ('\x10' != buf[n++]) {
            GPSD_LOG(LOG_RAW, &session->context->errout,
                     "Garmin: Bad pkt_len %#02x\n", pkt_len);
            Send_NAK();
            return 0;
        }
    }
    data_index = 0;
    for (i = 0; i < 256; i++) {

        if ((int)pkt_len == data_index) {
            // got it all
            break;
        }
        if (len < n + i) {
            GPSD_LOG(LOG_RAW, &session->context->errout,
                     "Garmin: Packet too short %zd < %zd\n",
                     len, n + i);
            Send_NAK();
            return 0;
        }
        c = buf[n + i];
        if (got_dle) {
            got_dle = 0;
            if ('\x10' != c) {
                Send_NAK();
                GPSD_LOG(LOG_RAW, &session->context->errout,
                         "Garmin: Bad DLE %#02x\n", c);
                return 0;
            }
        } else {
            chksum += c;
            data_buf[data_index++] = c;
            if ('\x10' == c) {
                got_dle = 1;
            }
        }
    }
    /* get checksum */
    if (len < n + i) {
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: No checksum, Packet too short %zd < %zd\n", len,
                 n + i);
        return 0;
    }
    c = buf[n + i++];
    chksum += c;
    /* get final DLE */
    if (len < n + i) {
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: No final DLE, Packet too short %zd < %zd\n", len,
                 n + i);
        return 0;
    }
    c = buf[n + i++];
    if ('\x10' != c) {
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: Final DLE not DLE\n");
        return 0;
    }
    /* get final ETX */
    if (len < n + i) {
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: No final ETX, Packet too short %zd < %zd\n", len,
                 n + i);
        return 0;
    }
    /* we used to say n++ here, but scan-build complains */
    c = buf[n + i];
    if ('\x03' != c) {
        Send_NAK();
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: Final ETX not ETX\n");
        return 0;
    }

    /* debug */
    for (i = 0; i < data_index; i++) {
        GPSD_LOG(LOG_RAW, &session->context->errout,
                 "Garmin: Char: %#02x\n", data_buf[i]);
    }


    GPSD_LOG(LOG_DATA, &session->context->errout,
             "Garmin: garmin_ser_parse() Type: %#02x, Len: %#02x, chksum: %#02x\n",
             pkt_id, pkt_len, chksum);
    mask = PrintSERPacket(session, pkt_id, pkt_len, data_buf);

    // sending ACK too soon might hang the session
    // so send ACK last, after a pause
    /* wait 300 uSec */
    delay.tv_sec = 0;
    delay.tv_nsec = 300000L;
    nanosleep(&delay, NULL);

    Send_ACK();
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "Garmin: garmin_ser_parse( )\n");
    return mask;
}


static void settle(void)
{
    struct timespec delay, rem;
    memset(&delay, 0, sizeof(delay));
    delay.tv_sec = 0;
    delay.tv_nsec = 333000000L;
    nanosleep(&delay, &rem);
}

static void garmin_switcher(struct gps_device_t *session, int mode)
{
    if (mode == MODE_NMEA) {
        const unsigned  char switcher[] =
            { 0x10, 0x0A, 0x02, 0x26, 0x00, 0xCE, 0x10, 0x03 };
        // Note hard-coded string length in the next line...
        ssize_t status = gpsd_write(session, (char *)switcher,
                                    sizeof(switcher));
        if (status == (ssize_t)sizeof(switcher)) {
            GPSD_LOG(LOG_PROG, &session->context->errout,
                     "Garmin: => GPS: turn off binary %02x %02x %02x... \n",
                     switcher[0], switcher[1], switcher[2]);
        } else {
            GPSD_LOG(LOG_ERROR, &session->context->errout,
                     "Garmin: => GPS: FAILED\n");
        }
        settle();               // wait 333mS, essential!

        /* once a sec, no binary, no averaging, NMEA 2.3, WAAS */
        (void)nmea_send(session, "$PGRMC1,1,1");
        //(void)nmea_send(fd, "$PGRMC1,1,1,1,,,,2,W,N");
        (void)nmea_send(session, "$PGRMI,,,,,,,R");
        settle();               // wait 333mS, essential!
    } else {
        (void)nmea_send(session, "$PGRMC1,1,2,1,,,,2,W,N");
        (void)nmea_send(session, "$PGRMI,,,,,,,R");
        settle();               // wait 333mS, essential!
    }
}

static ssize_t garmin_control_send(struct gps_device_t *session,
                                   char *buf, size_t buflen)
/* not used by the daemon, it's for gpsctl and friends */
{
    session->msgbuflen = buflen;
    (void)memcpy(session->msgbuf, buf, buflen);
    return gpsd_write(session, session->msgbuf, session->msgbuflen);
}

static double garmin_time_offset(struct gps_device_t *session)
{
    if (SOURCE_USB == session->sourcetype) {
        return 0.035;           /* Garmin USB, expect +/- 40mS jitter */
    }
    /* only two sentences ships time */
    /* but the PVT data is always first */
    switch (session->gpsdata.dev.baudrate) {
    case 4800:
        return 0.430;           /* TBD */
    case 9600:
        return 0.430;           /* tested 12Arp10 */
    case 19200:
        return 0.430;           /* TBD */
    case 38400:
        return 0.430;           /* TBD */
    }
    return 0.430;               /* WTF?  WAG */
}

/* this is everything we export */

/* *INDENT-OFF* */
const struct gps_type_t driver_garmin_usb_binary =
{
    .type_name      = "Garmin USB binary",  // full name of type
    .packet_type    = GARMIN_PACKET,        // associated lexer packet type
    .flags          = DRIVER_STICKY,        // remember this
    .trigger        = NULL,                 // no trigger, it has a probe
    .channels       = GARMIN_CHANNELS,      // consumer-grade GPS
    .probe_detect   = garmin_usb_detect,    // how to detect at startup time
    .get_packet     = generic_get,          // how to grab a packet
    .parse_packet   = garmin_ser_parse,     // parse message packets
    .rtcm_writer    = NULL,                 // don't send DGPS corrections
    .init_query     = NULL,                 // non-perturbing initial query
    .event_hook     = garmin_event_hook,    // lifetime ebent handler
    .speed_switcher = NULL,                 // no speed switcher
    .mode_switcher  = NULL,                 // Garmin USB Binary has no NMEA
    .rate_switcher  = NULL,                 // no sample-rate switcher
    .min_cycle.tv_sec  = 0,
    .min_cycle.tv_nsec = 10000000,          // 10Hz
    .control_send   = garmin_control_send,  // send raw bytes
    .time_offset     = garmin_time_offset,
};
/* *INDENT-ON* */

/* *INDENT-OFF* */
const struct gps_type_t driver_garmin_ser_binary =
{
    .type_name      = "Garmin Serial binary",  // full name of type
    .packet_type    = GARMIN_PACKET,           // associated lexer packet type
    .flags          = DRIVER_STICKY,           // remember this
    .trigger        = NULL,                    // no trigger, it has a probe
    .channels       = GARMIN_CHANNELS,         // consumer-grade GPS
    .probe_detect   = NULL,                    // how to detect at startup time
    .get_packet     = generic_get,             // how to grab a packet
    .parse_packet   = garmin_ser_parse,        // parse message packets
    .rtcm_writer    = NULL,                    // don't send DGPS corrections
    .init_query     = NULL,                    // non-perturbing initial query
    /* The Garmin Gek0 301 needs to be kicked to start sending binary.
     * like the Garmin USB. */
    .event_hook     = garmin_event_hook,       // lifetime event handler
    .speed_switcher = NULL,                    // no speed switcher
    .mode_switcher  = garmin_switcher,         // how to change modes
    .rate_switcher  = NULL,                    // no sample-rate switcher
    .min_cycle.tv_sec  = 0,
    .min_cycle.tv_nsec = 10000000,             // 10Hz
    .control_send   = garmin_control_send,     // send raw bytes
    .time_offset     = garmin_time_offset,
};
/* *INDENT-ON* */

#endif /* GARMIN_ENABLE */

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