gpsd/drivers/driver_oncore.c

/*
 * 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

#include <stdbool.h>
#include <stdio.h>
#include "../include/gpsd.h"

#if defined(ONCORE_ENABLE) && defined(BINARY_ENABLE)
#include "../include/bits.h"
#include "../include/timespec.h"

static char enableEa[] = { 'E', 'a', 1 };
static char enableBb[] = { 'B', 'b', 1 };
static char getfirmware[] = { 'C', 'j' };
/*static char enableEn[] =
    { 'E', 'n', 1, 0, 100, 100, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };*/
/*static char enableAt2[]       = { 'A', 't', 2, };*/
static unsigned char pollAs[] =
    { 'A', 's', 0x7f, 0xff, 0xff, 0xff, 0x7f, 0xff, 0xff, 0xff, 0x7f, 0xff,
    0xff, 0xff, 0xff
};
static unsigned char pollAt[] = { 'A', 't', 0xff };
static unsigned char pollAw[] = { 'A', 'w', 0xff };
static unsigned char pollAy[] = { 'A', 'y', 0xff, 0xff, 0xff, 0xff };
static unsigned char pollBo[] = { 'B', 'o', 0x01 };
static unsigned char pollEn[] = {
    'E', 'n', 0xff, 0xff, 0xff, 0xff, 0xff,
    0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
};


/*
 * These routines are specific to this driver
 */

static gps_mask_t oncore_parse_input(struct gps_device_t *);
static gps_mask_t oncore_dispatch(struct gps_device_t *, unsigned char *,
                                  size_t);
static gps_mask_t oncore_msg_navsol(struct gps_device_t *, unsigned char *,
                                    size_t);
static gps_mask_t oncore_msg_utc_offset(struct gps_device_t *,
                                        unsigned char *, size_t);
static gps_mask_t oncore_msg_pos_hold_mode(struct gps_device_t *,
                                           unsigned char *, size_t);
static gps_mask_t oncore_msg_pps_offset(struct gps_device_t *, unsigned char *,
                                        size_t);
static gps_mask_t oncore_msg_svinfo(struct gps_device_t *, unsigned char *,
                                    size_t);
static gps_mask_t oncore_msg_time_mode(struct gps_device_t *, unsigned char *,
                                       size_t);
static gps_mask_t oncore_msg_time_raim(struct gps_device_t *, unsigned char *,
                                       size_t);
static gps_mask_t oncore_msg_firmware(struct gps_device_t *, unsigned char *,
                                      size_t);

/*
 * These methods may be called elsewhere in gpsd
 */
static ssize_t oncore_control_send(struct gps_device_t *, char *, size_t);
static void oncore_event_hook(struct gps_device_t *, event_t);

/*
 * Decode the navigation solution message
 *
 * @@Ea - Position/Status/Data Message

@@EamdyyhmsffffaaaaoooohhhhmmmmvvhhddtntimsdimsdimsdimsdimsdimsdimsdimsdsC
<CR><LF>

 *
 *      Date
 *       m         - month                       1 .. 12
 *       d         - day                         1 .. 31
 *       yy        - year                        1980 .. 2079
 *
 *      Time
 *       h         - hours                       0 .. 23
 *       m         - minutes                     0 .. 59
 *       s         - seconds                     0 .. 60
 *       ffff      - fractional second           0 .. 999,999,999
 *                 (0.0 .. 0.999999999)
 *
 *      Position
 *       aaaa      - latitude in mas             -324,000,000 .. 324,000,000
 *                 (-90 degrees .. 90 degrees)
 *
 *       oooo      - longitude in mas            -648,000,000 .. 648,000,000
 *                 (-180 degrees .. 180 degrees)
 *
 *       hhhh       - ellipsoid height in cm     -100,000 .. 1,800,000
 *                 (-1000.00 .. 18,000.00m)*
 *
 *       mmmm  - not used                        0
 *
 *      Velocity
 *       vv        - velocity in cm/s            0 .. 51,400 (0..514.00 m/s)*
 *       hh        - heading                     0 .. 3599 (0.0..359.9 degrees)
 *
 *                 (true north res 0.1 degrees)
 *
 *      Geometry
 *       dd        - current DOP (0.1 res)       0 .. 999 (0.0 to 99.9 DOP)
 *             (0 = not computable, position-hold, or    position propagate)
 *
 *       t         - DOP TYPE
 *                   0   PDOP (3D)/antenna ok
 *                   1   PDOP (3D)/antenna OK
 *                   64  PDOP (3D)/antenna shorted
 *                   65  PDOP (3D)/antenna shorted
 *                   128 PDOP (3D)/antenna open
 *                   129 PDOP (3D)/antenna open
 *                   192 PDOP (3D)/antenna shorted
 *                   193 PDOP (3D)/antenna shorted
 *
 *      Satellite visibility and tracking status
 *       n         - num of visible sats         0 .. 12
 *       t         - num of satellites tracked   0 .. 8
 *
 *      For each of eight receiver channels
 *       i         - sat ID                      0 .. 37
 *       m         - channel tracking mode       0 .. 8
 *                 0 = code search    5 = message sync detect
 *                 1 = code acquire   6 = satellite time avail.
 *                 2 = AGC set        7 = ephemeris acquire
 *                 3 = prep acquire   8 = avail for position
 *                 4 = bit sync detect
 *
 *       s         - carrier to noise density ratio
 *                 (C/No)                        0 .. 255 db-Hz
 *
 *       d         - channel status flag
 *                 Each bit represents one of the following:
 *                 (msb)   Bit 7: using for position fix
 *                         Bit 6: satellite momentum alert flag
 *                         Bit 5: satellite anti-spoof flag set
 *                         Bit 4: satellite reported unhealthy
 *                         Bit 3: satellite reported inaccurate
 *                         (> 16m)
 *                         Bit 2: spare
 *                         Bit 1: spare
 *                 (lsb)   Bit 0: parity error
 *
 *      End of channel dependent data
 *       s         - receiver status flag
 *
 *                 Each bit represents one of the following:
 *                 (msb)   Bit 7: position propagate mode
 *                         Bit 6: poor geometry (DOP > 12)
 *                         Bit 5: 3D fix
 *                         Bit 4: 2D fix
 *                         Bit 3: acquiring satellites/position hold
 *                         Bit 2: spare
 *                         Bit 1: insufficient visible satellites
 *                         (< 3)
 *                 (lsb)   Bit 0: bad almanac
 *
 *       C  - checksum
 *       Message length: 76 bytes
 *
 */
static gps_mask_t
oncore_msg_navsol(struct gps_device_t *session, unsigned char *buf,
                  size_t data_len)
{
    gps_mask_t mask;
    unsigned char flags;
    double lat, lon, alt;
    float speed, track, dop;
    unsigned int i, j, st, nsv;
    int Bbused;
    struct tm unpacked_date;
    char ts_buf[TIMESPEC_LEN];

    if (data_len != 76)
        return 0;

    mask = ONLINE_SET;
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore NAVSOL - navigation data\n");

    flags = (unsigned char)getub(buf, 72);

    if (flags & 0x20) {
        session->newdata.status = STATUS_GPS;
        session->newdata.mode = MODE_3D;
    } else if (flags & 0x10) {
        session->newdata.status = STATUS_GPS;
        session->newdata.mode = MODE_2D;
    } else if ((flags & 0x08) &&
               session->driver.oncore.pos_hold_mode ==
               ONCORE_POS_HOLD_MODE_ON) {
        /* To be a good time solution for a fixed surveyed position,
         * the poshold/acquiring flag (0x08) must be accompanied by
         * the device being in position hold-mode.  The device is
         * also reporting acquiring (0x08) when it has no fix.
         * Therefore the pos_hold_mode check above.
         */
        session->newdata.status = STATUS_TIME;
        session->newdata.mode = MODE_3D;
    } else {
        GPSD_LOG(LOG_WARN, &session->context->errout,
                 "oncore NAVSOL no fix - flags 0x%02x\n", flags);
        session->newdata.mode = MODE_NO_FIX;
        session->newdata.status = STATUS_UNK;
    }
    mask |= MODE_SET | STATUS_SET;

    /* Unless we have seen non-zero utc offset data, the time is GPS time
     * and not UTC time.  Even if time mode (Aw) message already says UTC.
     * Do not use the time.
     */
    if (LEAP_SECOND_VALID == (session->context->valid & LEAP_SECOND_VALID)) {
        unsigned int nsec;
        unpacked_date.tm_mon = (int)getub(buf, 4) - 1;
        unpacked_date.tm_mday = (int)getub(buf, 5);
        unpacked_date.tm_year = (int)getbeu16(buf, 6) - 1900;
        unpacked_date.tm_hour = (int)getub(buf, 8);
        unpacked_date.tm_min = (int)getub(buf, 9);
        unpacked_date.tm_sec = (int)getub(buf, 10);
        unpacked_date.tm_isdst = 0;
        unpacked_date.tm_wday = unpacked_date.tm_yday = 0;
        nsec = (unsigned int) getbeu32(buf, 11);

        session->newdata.time.tv_sec = mkgmtime(&unpacked_date);
        session->newdata.time.tv_nsec = nsec;
        mask |= TIME_SET;
        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "oncore NAVSOL - time: %04d-%02d-%02d %02d:%02d:%02d.%09d\n",
                 unpacked_date.tm_year + 1900, unpacked_date.tm_mon + 1,
                 unpacked_date.tm_mday, unpacked_date.tm_hour,
                 unpacked_date.tm_min, unpacked_date.tm_sec, nsec);
    }

    lat = getbes32(buf, 15) / 3600000.0;
    lon = getbes32(buf, 19) / 3600000.0;
    alt = getbes32(buf, 23) / 100.0;
    speed = getbeu16(buf, 31) / 100.0f;
    track = getbeu16(buf, 33) / 10.0f;
    dop = getbeu16(buf, 35) / 10.0f;

    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore NAVSOL - %lf %lf %.2lfm | %.2fm/s %.1fdeg dop=%.1f\n",
             lat, lon, alt, speed, track,
             (float)dop);

    if (MODE_2D <= session->newdata.mode) {
        session->newdata.latitude = lat;
        session->newdata.longitude = lon;
        session->newdata.speed = speed;
        session->newdata.track = track;
        mask |= LATLON_SET | SPEED_SET | TRACK_SET;
    }
    if (MODE_3D <= session->newdata.mode) {
        session->newdata.altHAE = alt;  /* is WGS84 */
        mask |= ALTITUDE_SET;
    }

    gpsd_zero_satellites(&session->gpsdata);
    /* Merge the satellite information from the Bb message. */
    Bbused = 0;
    nsv = 0;
    for (i = st = 0; i < 8; i++) {
        int sv, mode, sn, status;
        unsigned int off;

        off = 40 + 4 * i;
        sv = (int)getub(buf, off);
        mode = (int)getub(buf, off + 1);
        sn = (int)getub(buf, off + 2);
        status = (int)getub(buf, off + 3);

        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "%2d %2d %2d %3d %02x\n", i, sv, mode, sn, status);

        if (sn) {
            session->gpsdata.skyview[st].PRN = (short)sv;
            session->gpsdata.skyview[st].ss = (double)sn;
            for (j = 0; (int)j < session->driver.oncore.visible; j++)
                if (session->driver.oncore.PRN[j] == sv) {
                    session->gpsdata.skyview[st].elevation =
                        (double)session->driver.oncore.elevation[j];
                    session->gpsdata.skyview[st].azimuth =
                        (double)session->driver.oncore.azimuth[j];
                    Bbused |= 1 << j;
                    break;
                }
            /* bit 7 of the status word: sat used for position */
            session->gpsdata.skyview[st].used = false;
            if (status & 0x80) {
                session->gpsdata.skyview[st].used = true;
                nsv++;
            }
            /* bit 2 of the status word: using for time solution */
            if (status & 0x02)
                mask |= NTPTIME_IS | GOODTIME_IS;
            /*
             * The GOODTIME_IS mask bit exists distinctly from TIME_SET exactly
             * so an OnCore running in time-service mode (and other GPS clocks)
             * can signal that it's returning time even though no position fixes
             * have been available.
             */
            st++;
        }
    }
    for (j = 0; (int)j < session->driver.oncore.visible; j++)
        if (!(Bbused & (1 << j))) {
            session->gpsdata.skyview[st].PRN =
                (short)session->driver.oncore.PRN[j];
            session->gpsdata.skyview[st].elevation =
                (double)session->driver.oncore.elevation[j];
            session->gpsdata.skyview[st].azimuth =
                (double)session->driver.oncore.azimuth[j];
            st++;
        }
    session->gpsdata.skyview_time = session->newdata.time;
    session->gpsdata.satellites_used = (int)nsv;
    session->gpsdata.satellites_visible = (int)st;

    mask |= SATELLITE_SET | USED_IS;

    /* Some messages can only be polled.  As they are not so
     * important, would be enough to poll e.g. one message per cycle.
     */
    (void)oncore_control_send(session, (char *)pollAs, sizeof(pollAs));
    (void)oncore_control_send(session, (char *)pollAt, sizeof(pollAt));
    (void)oncore_control_send(session, (char *)pollAw, sizeof(pollAw));
    (void)oncore_control_send(session, (char *)pollAy, sizeof(pollAy));
    (void)oncore_control_send(session, (char *)pollBo, sizeof(pollBo));
    (void)oncore_control_send(session, (char *)pollEn, sizeof(pollEn));

    GPSD_LOG(LOG_DATA, &session->context->errout,
             "NAVSOL: time=%s lat=%.2f lon=%.2f altMSL=%.2f speed=%.2f "
             "track=%.2f mode=%d status=%d visible=%d used=%d\n",
             timespec_str(&session->newdata.time, ts_buf, sizeof(ts_buf)),
             session->newdata.latitude,
             session->newdata.longitude, session->newdata.altHAE,
             session->newdata.speed, session->newdata.track,
             session->newdata.mode, session->newdata.status,
             session->gpsdata.satellites_used,
             session->gpsdata.satellites_visible);
    return mask;
}

/**
 * GPS Leap Seconds = UTC offset
 */
static gps_mask_t
oncore_msg_utc_offset(struct gps_device_t *session, unsigned char *buf,
                      size_t data_len)
{
    int utc_offset;

    if (data_len != 8)
        return 0;

    utc_offset = (int)getub(buf, 4);
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore UTCTIME - leap seconds: %d\n", utc_offset);
    if (utc_offset == 0)
        return 0;               /* that part of almanac not received yet */

    session->context->leap_seconds = utc_offset;
    session->context->valid |= LEAP_SECOND_VALID;
    return 0;                   /* no flag for leap seconds update */
}

/**
 * Pos hold mode
 *
 * @@AtmC<CR><LF>
 *
 *       m         - mode, 0=off, 1=on, 2=surveying
 */
static gps_mask_t
oncore_msg_pos_hold_mode(struct gps_device_t *session, unsigned char *buf,
                         size_t data_len)
{
    int pos_hold_mode;

    if (data_len != 8)
        return 0;

    pos_hold_mode = (int)getub(buf, 4);
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore pos hold mode: %d\n", pos_hold_mode);

    /* Add 1 to distinguish an unknown (not set) value from mode off. */
    session->driver.oncore.pos_hold_mode = pos_hold_mode + 1;
    return 0;
}

/**
 * PPS offset
 */
static gps_mask_t
oncore_msg_pps_offset(struct gps_device_t *session, unsigned char *buf,
                      size_t data_len)
{
    int pps_offset_ns;

    if (data_len != 11)
        return 0;

    pps_offset_ns = (int)getbes32(buf, 4);
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore PPS offset: %d\n", pps_offset_ns);

    session->driver.oncore.pps_offset_ns = pps_offset_ns;
    return 0;
}

/**
 * GPS Satellite Info
 */
static gps_mask_t
oncore_msg_svinfo(struct gps_device_t *session, unsigned char *buf,
                  size_t data_len)
{
    unsigned int i, nchan;

    if (data_len != 92)
        return 0;

    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore SVINFO - satellite data\n");
    nchan = (unsigned int)getub(buf, 4);
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore SVINFO - %d satellites:\n", nchan);
    // Then we clamp the value to not read outside the table.
    if (nchan > 12)
        nchan = 12;
    session->driver.oncore.visible = (int)nchan;
    for (i = 0; i < nchan; i++) {
        // get info for one channel/satellite
        unsigned int off = 5 + 7 * i;

        int sv = (int)getub(buf, off);
        int el = (int)getub(buf, off + 3);
        int az = (int)getbeu16(buf, off + 4);

        GPSD_LOG(LOG_DATA, &session->context->errout,
                 "%2d %2d %2d %3d\n", i, sv, el, az);

        // Store for use when Ea messages come.
        session->driver.oncore.PRN[i] = sv;
        session->driver.oncore.elevation[i] = (short)el;
        session->driver.oncore.azimuth[i] = (short)az;
    }

    return 0;
}

/**
 * GPS Time Mode
 *
 * @@AwmC<CR><LF>
 *
 *       m         - mode, 0=GPS, 1=UTC
 */
static gps_mask_t oncore_msg_time_mode(struct gps_device_t *session UNUSED,
                                       unsigned char *buf UNUSED,
                                       size_t data_len UNUSED)
{
    int time_mode;

    if (data_len != 8)
        return 0;

    time_mode = (int)getub(buf, 4);
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore time mode (0=GPS, 1=UTC): %d\n",time_mode);

    return 0;
}

/**
 * GPS Time RAIM
 */
static gps_mask_t oncore_msg_time_raim(struct gps_device_t *session UNUSED,
                                       unsigned char *buf UNUSED,
                                       size_t data_len UNUSED)
{
    int sawtooth_ns;

    if (data_len != 69)
        return 0;

    sawtooth_ns = (int)getub(buf, 25);
    GPSD_LOG(LOG_DATA, &session->context->errout,
             "oncore PPS sawtooth: %d\n",sawtooth_ns);

    // session->driver.oncore.traim_sawtooth_ns = sawtooth_ns;

    return 0;
}

/**
 * GPS Firmware
 */
static gps_mask_t oncore_msg_firmware(struct gps_device_t *session UNUSED,
                                      unsigned char *buf UNUSED,
                                      size_t data_len UNUSED)
{
    return 0;
}

#define ONCTYPE(id2,id3) ((((unsigned int)id2)<<8)|(id3))

/**
 * Parse the data from the device
 */
gps_mask_t oncore_dispatch(struct gps_device_t * session, unsigned char *buf,
                           size_t len)
{
    unsigned int type;

    if (0 == len) {
        return 0;
    }

    type = ONCTYPE(buf[2], buf[3]);

    // we may need to dump the raw packet
    GPSD_LOG(LOG_RAW, &session->context->errout,
             "raw Oncore packet type 0x%04x\n", type);

    session->cycle_end_reliable = true;

    switch (type) {
    case ONCTYPE('B', 'b'):
        return oncore_msg_svinfo(session, buf, len);
    case ONCTYPE('E', 'a'):
        return oncore_msg_navsol(session, buf, len) | (CLEAR_IS | REPORT_IS);
    case ONCTYPE('E', 'n'):
        return oncore_msg_time_raim(session, buf, len);
    case ONCTYPE('C', 'j'):
        return oncore_msg_firmware(session, buf, len);
    case ONCTYPE('B', 'o'):
        return oncore_msg_utc_offset(session, buf, len);
    case ONCTYPE('A', 's'):
        return 0;               /* position hold position */
    case ONCTYPE('A', 't'):
        return oncore_msg_pos_hold_mode(session, buf, len);
    case ONCTYPE('A', 'w'):
        return oncore_msg_time_mode(session, buf, len);
    case ONCTYPE('A', 'y'):
        return oncore_msg_pps_offset(session, buf, len);

    default:
        /* FIX-ME: This gets noisy in a hurry. Change once your driver works */
        GPSD_LOG(LOG_WARN, &session->context->errout,
                 "unknown packet id @@%c%c length %zd\n",
                 type >> 8, type & 0xff, len);
        return 0;
    }
}


/**********************************************************
 *
 * Externally called routines below here
 *
 **********************************************************/

/**
 * Write data to the device, doing any required padding or checksumming
 */
static ssize_t oncore_control_send(struct gps_device_t *session,
                                   char *msg, size_t msglen)
{
    size_t i;
    char checksum = 0;

    session->msgbuf[0] = '@';
    session->msgbuf[1] = '@';
    for (i = 0; i < msglen; i++) {
        checksum ^= session->msgbuf[i + 2] = msg[i];
    }
    session->msgbuf[msglen + 2] = checksum;
    session->msgbuf[msglen + 3] = '\r';
    session->msgbuf[msglen + 4] = '\n';
    session->msgbuflen = msglen + 5;

    GPSD_LOG(LOG_PROG, &session->context->errout,
             "writing oncore control type %c%c\n", msg[0], msg[1]);
    return gpsd_write(session, session->msgbuf, session->msgbuflen);
}


static void oncore_event_hook(struct gps_device_t *session, event_t event)
{
    if (session->context->readonly)
        return;

    /*
     * Some oncore VP variants that have not been used after long
     * power-down will be silent on startup.  Provoke
     * identification by requesting the firmware version.
     */
    if (event == event_wakeup)
        (void)oncore_control_send(session, getfirmware, sizeof(getfirmware));

    if (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) {
        (void)oncore_control_send(session, enableEa, sizeof(enableEa));
        (void)oncore_control_send(session, enableBb, sizeof(enableBb));
        /*(void)oncore_control_send(session, enableEn, sizeof(enableEn)); */
        /*(void)oncore_control_send(session,enableAt2,sizeof(enableAt2)); */
        /*(void)oncore_control_send(session,pollAs,sizeof(pollAs)); */
        (void)oncore_control_send(session, (char*)pollBo, sizeof(pollBo));
    }
}

static double oncore_time_offset(struct gps_device_t *session UNUSED)
{
    /*
     * Only one sentence (NAVSOL) ships time.  0.175 seems best at
     * 9600 for UT+, not sure what the fudge should be at other baud
     * rates or for other models.
     */
    return 0.175;
}

static gps_mask_t oncore_parse_input(struct gps_device_t *session)
{
    if (ONCORE_PACKET == session->lexer.type) {
        return oncore_dispatch(session, session->lexer.outbuffer,
                             session->lexer.outbuflen);
    }
    if (NMEA_PACKET == session->lexer.type) {
        return nmea_parse((char *)session->lexer.outbuffer, session);
    }
    return 0;
}

// This is everything we export
// *INDENT-OFF*
const struct gps_type_t driver_oncore = {

    .type_name        = "Motorola Oncore",      // Full name of type
    .packet_type      = ONCORE_PACKET,          // numeric packet type
    .flags            = DRIVER_STICKY,          // remember this
    .trigger          = NULL,                   // identifying response
    .channels         = 12,                     // device channel count
    .probe_detect     = NULL,                   // no probe
    .get_packet       = generic_get,            // packet getter
    .parse_packet     = oncore_parse_input,     // packet parser
    .rtcm_writer      = gpsd_write,             // device accepts RTCM
    .init_query       = NULL,                   // non-perturbing query
    .event_hook       = oncore_event_hook,      // lifetime event hook
    .speed_switcher   = NULL,                   // no speed setter
    .mode_switcher    = NULL,                   // no mode setter
    .rate_switcher    = NULL,                   // no speed setter
    .min_cycle.tv_sec  = 1,                     // 1Hz
    .min_cycle.tv_nsec = 0,
    // Control string sender - should provide checksum and headers/trailer
    .control_send   = oncore_control_send,      // to send control strings
    .time_offset = oncore_time_offset,          // NTP offset array
};
// *INDENT-ON*
#endif  // defined(ONCORE_ENABLE) && defined(BINARY_ENABLE)

// vim: set expandtab shiftwidth=4