gpsd/packet.c

/****************************************************************************

NAME:
   packet.c -- a packet-sniffing engine for reading from GPS devices

DESCRIPTION:

Initial conditions of the problem:

1. We have a file descriptor open for (possibly non-blocking) read. The device
   on the other end is sending packets at us.

2. It may require more than one read to gather a packet.  Reads may span packet
   boundaries.

3. There may be leading garbage before the first packet.  After the first
   start-of-packet, the input should be well-formed.

The problem: how do we recognize which kind of packet we're getting?

No need to handle Garmin USB binary, we know that type by the fact we're
connected to the Garmin kernel driver.  But we need to be able to tell the
others apart and distinguish them from baud barf.

PERMISSIONS
   This file is Copyright 2010 by the GPSD project
   SPDX-License-Identifier: BSD-2-clause

***************************************************************************/

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

#include <arpa/inet.h>          /* for htons() */
#include <ctype.h>
#include <errno.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>           // for struct timeval
#include <sys/types.h>
#include <unistd.h>

#include "bits.h"
#include "driver_greis.h"
#include "gpsd.h"
#include "crc24q.h"
#include "strfuncs.h"

/*
 * The packet-recognition state machine.  This takes an incoming byte stream
 * and tries to segment it into packets.  There are four types of packets:
 *
 * 1) Comments. These begin with # and end with \r\n.
 *
 * 2) NMEA lines.  These begin with $, and with \r\n, and have a checksum.
 *
 * 3) Checksummed binary packets.  These begin with some fixed leader
 *    character(s), have a length embedded in them, and end with a
 *    checksum (and possibly some fixed trailing bytes).
 *
 * 4) ISGPS packets. The input may be a bitstream containing IS-GPS-200
 *    packets.  Each includes a fixed leader byte, a length, and check bits.
 *    In this case, it is not guaranteed that packet starts begin on byte
 *    boundaries; the recognizer has to run a separate state machine against
 *    each byte just to achieve synchronization lock with the bitstream.
 *
 * 5) Un-checksummed binary packets.  Like case 3, but without
 *    a checksum it's much easier to get a false match from garbage.
 *    The packet recognizer gives checksummed types higher priority.
 *
 * Adding support for a new GPS protocol typically reqires adding state
 * transitions to support whatever binary packet structure it has.  The
 * goal is for the lexer to be able to cope with arbitrarily mixed packet
 * types on the input stream.  This is a requirement because (1) sometimes
 * gpsd wants to switch a device that supports both NMEA and a binary
 * packet protocol to the latter for more detailed reporting, and (b) in
 * the presence of device hotplugging, the type of GPS report coming
 * in is subject to change at any time.
 *
 * Caller should consume a packet when it sees one of the *_RECOGNIZED
 * states.  It's good practice to follow the _RECOGNIZED transition
 * with one that recognizes a leader of the same packet type rather
 * than dropping back to ground state -- this for example will prevent
 * the state machine from hopping between recognizing TSIP and
 * EverMore packets that both start with a DLE.
 *
 * Error handling is brutally simple; any time we see an unexpected
 * character, go to GROUND_STATE and reset the machine (except that a
 * $ in an NMEA payload only resets back to NMEA_DOLLAR state).  Because
 * another good packet will usually be along in less than a second
 * repeating the same data, Boyer-Moore-like attempts to do parallel
 * recognition beyond the headers would make no sense in this
 * application, they'd just add complexity.
 *
 * The NMEA portion of the state machine allows the following talker IDs:
 *      $BD -- Beidou
 *      $EC -- Electronic Chart Display & Information System (ECDIS)
 *      $GA -- Galileo
 *      $GB -- Beidou
 *      $GL -- GLONASS, according to IEIC 61162-1
 *      $GN -- Mixed GPS and GLONASS data, according to IEIC 61162-1
 *      $GP -- Global Positioning System.
 *      $HC -- Heading/compass (Airmar PB200).
 *      $II -- Integrated Instrumentation (Raytheon's SeaTalk system).
 *      $IN -- Integrated Navigation (Garmin uses this).
 *      $P  -- Vendor-specific sentence
 *      $QZ -- QZSS GPS augmentation system
 *      $SD -- Depth Sounder
 *      $ST -- $STI, Skytraq Debug Output
 *      $TI -- Turn indicator (Airmar PB200).
 *      $WI -- Weather instrument (Airmar PB200, Radio Ocean ROWIND,
 *                                 Vaisala WXT520).
 *      $YX -- Transducer (used by some Airmar equipment including PB100)
 *
 *      !AB -- NMEA 4.0 Base AIS station
 *      !AD -- MMEA 4.0 Dependent AIS Base Station
 *      !AI -- Mobile AIS station
 *      !AN -- NMEA 4.0 Aid to Navigation AIS station
 *      !AR -- NMEA 4.0 AIS Receiving Station
 *      !AX -- NMEA 4.0 Repeater AIS station
 *      !AS -- NMEA 4.0 Limited Base Station
 *      !AT -- NMEA 4.0 AIS Transmitting Station
 *      !BS -- Base AIS station (deprecated in NMEA 4.0)
 *      !SA -- NMEA 4.0 Physical Shore AIS Station
 */

enum
{
#include "packet_states.h"
};

static char *state_table[] = {
#include "packet_names.h"
};

#define SOH     (unsigned char)0x01
#define DLE     (unsigned char)0x10
#define STX     (unsigned char)0x02
#define ETX     (unsigned char)0x03

#if defined(TSIP_ENABLE)
/* Maximum length a TSIP packet can be */
#define TSIP_MAX_PACKET 255
#endif

#ifdef ONCORE_ENABLE
static size_t oncore_payload_cksum_length(unsigned char id1, unsigned char id2)
{
    size_t l;

    /* For the packet sniffer to not terminate the message due to
     * payload data looking like a trailer, the known payload lengths
     * including the checksum are given.  Return -1 for unknown IDs.
     */

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

    /* *INDENT-OFF* */
    switch (ONCTYPE(id1,id2)) {
    case ONCTYPE('A','b'): l = 10; break; /* GMT offset */
    case ONCTYPE('A','w'): l =  8; break; /* time mode */
    case ONCTYPE('A','c'): l = 11; break; /* date */
    case ONCTYPE('A','a'): l = 10; break; /* time of day */
    case ONCTYPE('A','d'): l = 11; break; /* latitude */
    case ONCTYPE('A','e'): l = 11; break; /* longitude */
    case ONCTYPE('A','f'): l = 15; break; /* height */
    case ONCTYPE('E','a'): l = 76; break; /* position/status/data */
    case ONCTYPE('A','g'): l =  8; break; /* satellite mask angle */
    case ONCTYPE('B','b'): l = 92; break; /* visible satellites status */
    case ONCTYPE('B','j'): l =  8; break; /* leap seconds pending */
    case ONCTYPE('A','q'): l =  8; break; /* atmospheric correction mode */
    case ONCTYPE('A','p'): l = 25; break; /* set user datum / select datum */
    /* Command "Ao" gives "Ap" response   (select datum) */
    case ONCTYPE('C','h'): l =  9; break; /* almanac input ("Cb" response) */
    case ONCTYPE('C','b'): l = 33; break; /* almanac output ("Be" response) */
    case ONCTYPE('S','z'): l =  8; break; /* system power-on failure */
    case ONCTYPE('C','j'): l = 294; break; /* receiver ID */
    case ONCTYPE('F','a'): l =  9; break; /* self-test */
    case ONCTYPE('C','f'): l =  7; break; /* set-to-defaults */
    case ONCTYPE('E','q'): l = 96; break; /* ASCII position */
    case ONCTYPE('A','u'): l = 12; break; /* altitude hold height */
    case ONCTYPE('A','v'): l =  8; break; /* altitude hold mode */
    case ONCTYPE('A','N'): l =  8; break; /* velocity filter */
    case ONCTYPE('A','O'): l =  8; break; /* RTCM report mode */
    case ONCTYPE('C','c'): l = 80; break; /* ephemeris data input ("Bf") */
    case ONCTYPE('C','k'): l =  7; break; /* pseudorng correction inp. ("Ce")*/
    /* Command "Ci" (switch to NMEA, GT versions only) has no response */
    case ONCTYPE('B','o'): l =  8; break; /* UTC offset status */
    case ONCTYPE('A','z'): l = 11; break; /* 1PPS cable delay */
    case ONCTYPE('A','y'): l = 11; break; /* 1PPS offset */
    case ONCTYPE('A','P'): l =  8; break; /* pulse mode */
    case ONCTYPE('A','s'): l = 20; break; /* position-hold position */
    case ONCTYPE('A','t'): l =  8; break; /* position-hold mode */
    case ONCTYPE('E','n'): l = 69; break; /* time RAIM setup and status */
    default:
        return 0;
    }
    /* *INDENT-ON* */

    return l - 6;               /* Subtract header and trailer. */
}
#endif /* ONCORE_ENABLE */

#ifdef GREIS_ENABLE

static unsigned long greis_hex2bin(char c)
/* Convert hex char to binary form. Requires that c be a hex char. */
{
    if ((c >= 'a') && (c <= 'f'))
        c = c + 10 - 'a';
    else if ((c >= 'A') && (c <= 'F'))
        c = c + 10 - 'A';
    else if ((c >= '0') && (c <= '9'))
        c -= '0';

    return c;
}

#endif /* GREIS_ENABLE */

/* push back the last character grabbed, setting a specified state */
static bool character_pushback(struct gps_lexer_t *lexer, unsigned int newstate)
{
    --lexer->inbufptr;
    --lexer->char_counter;
    lexer->state = newstate;
    if (lexer->errout.debug >= LOG_RAW + 2)
    {
        unsigned char c = *lexer->inbufptr;
        GPSD_LOG(LOG_RAW + 2, &lexer->errout,
                 "%08ld: character '%c' [%02x]  pushed back, state set to %s\n",
                 lexer->char_counter,
                 (isprint((int)c) ? c : '.'), c,
                 state_table[lexer->state]);
    }

    return false;
}

/* shift the input buffer to discard one character and reread data */
static void character_discard(struct gps_lexer_t *lexer)
{
    memmove(lexer->inbuffer, lexer->inbuffer + 1, (size_t)-- lexer->inbuflen);
    lexer->inbufptr = lexer->inbuffer;
    if (lexer->errout.debug >= LOG_RAW + 1) {
        char scratchbuf[MAX_PACKET_LENGTH*4+1];
        GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                 "Character discarded, buffer %zu chars = %s\n",
                 lexer->inbuflen,
                 gpsd_packetdump(scratchbuf, sizeof(scratchbuf),
                                    (char *)lexer->inbuffer, lexer->inbuflen));
    }
}

/* get 0-origin big-endian words relative to start of packet buffer
 * used for Zodiac */
#define getzuword(i) (unsigned)(lexer->inbuffer[2*(i)] | \
                                (lexer->inbuffer[2*(i)+1] << 8))
#define getzword(i) (short)(lexer->inbuffer[2*(i)] | \
                           (lexer->inbuffer[2*(i)+1] << 8))

static bool nextstate(struct gps_lexer_t *lexer, unsigned char c)
{
    static int n = 0;
#ifdef RTCM104V2_ENABLE
    enum isgpsstat_t isgpsstat;
#endif /* RTCM104V2_ENABLE */
#ifdef SUPERSTAR2_ENABLE
    static unsigned char ctmp;
#endif /* SUPERSTAR2_ENABLE */
    n++;
    switch (lexer->state) {
    case GROUND_STATE:
        n = 0;
#ifdef STASH_ENABLE
        lexer->stashbuflen = 0;
#endif
        if (c == '#') {
            lexer->state = COMMENT_BODY;
            break;
        }
#ifdef NMEA0183_ENABLE
        if (c == '$') {
            lexer->state = NMEA_DOLLAR;
            break;
        }
        if (c == '!') {
            lexer->state = NMEA_BANG;
            break;
        }
#endif /* NMEA0183_ENABLE */
#if defined(TNT_ENABLE) || defined(GARMINTXT_ENABLE) || defined(ONCORE_ENABLE)
        if (c == '@') {
#ifdef RTCM104V2_ENABLE
            if (rtcm2_decode(lexer, c) == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = AT1_LEADER;
            break;
        }
#endif
#if defined(SIRF_ENABLE) || defined(SKYTRAQ_ENABLE)
        if (c == 0xa0) {
            lexer->state = SIRF_LEADER_1;
            break;
        }
#endif /* SIRF_ENABLE || SKYTRAQ_ENABLE */
#ifdef SUPERSTAR2_ENABLE
        if (c == SOH) {
            lexer->state = SUPERSTAR2_LEADER;
            break;
        }
#endif /* SUPERSTAR2_ENABLE */
#if defined(TSIP_ENABLE) || defined(EVERMORE_ENABLE) || defined(GARMIN_ENABLE)
        if (c == DLE) {
            lexer->state = DLE_LEADER;
            break;
        }
#endif /* TSIP_ENABLE || EVERMORE_ENABLE || GARMIN_ENABLE */
#ifdef TRIPMATE_ENABLE
        if (c == 'A') {
#ifdef RTCM104V2_ENABLE
            if (rtcm2_decode(lexer, c) == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = ASTRAL_1;
            break;
        }
#endif /* TRIPMATE_ENABLE */
#ifdef EARTHMATE_ENABLE
        if (c == 'E') {
#ifdef RTCM104V2_ENABLE
            if (rtcm2_decode(lexer, c) == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = EARTHA_1;
            break;
        }
#endif /* EARTHMATE_ENABLE */
#ifdef ZODIAC_ENABLE
        if (c == 0xff) {
            lexer->state = ZODIAC_LEADER_1;
            break;
        }
#endif /* ZODIAC_ENABLE */
#ifdef UBLOX_ENABLE
        if (c == 0xb5) {
            lexer->state = UBX_LEADER_1;
            break;
        }
#endif /* UBLOX_ENABLE */
#ifdef ITRAX_ENABLE
        if (c == '<') {
            lexer->state = ITALK_LEADER_1;
            break;
        }
#endif /* ITRAX_ENABLE */
#ifdef NAVCOM_ENABLE
        if (c == 0x02) {
            lexer->state = NAVCOM_LEADER_1;
            break;
        }
#endif /* NAVCOM_ENABLE */
#ifdef GEOSTAR_ENABLE
        if (c == 'P') {
            lexer->state = GEOSTAR_LEADER_1;
            break;
        }
#endif /* GEOSTAR_ENABLE */
#ifdef GREIS_ENABLE
        if (c == 'R') {
            lexer->state = GREIS_REPLY_1;
            break;
        }
        /* Not the only possibility, but it is a distinctive cycle starter. */
        if (c == '~') {
            lexer->state = GREIS_ID_1;
            break;
        }
#endif /* GREIS_ENABLE */
#ifdef RTCM104V2_ENABLE
        if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
            lexer->state = RTCM2_SYNC_STATE;
            break;
        } else if (isgpsstat == ISGPS_MESSAGE) {
            lexer->state = RTCM2_RECOGNIZED;
            break;
        }
#endif /* RTCM104V2_ENABLE */
#ifdef RTCM104V3_ENABLE
        if (c == 0xD3) {
            lexer->state = RTCM3_LEADER_1;
            break;
        }
#endif /* RTCM104V3_ENABLE */
#ifdef PASSTHROUGH_ENABLE
        if (c == '{')
            return character_pushback(lexer, JSON_LEADER);
#endif /* PASSTHROUGH_ENABLE */
        break;
    case COMMENT_BODY:
        if (c == '\n')
            lexer->state = COMMENT_RECOGNIZED;
        else if (!isprint(c))
            return character_pushback(lexer, GROUND_STATE);
        break;
#ifdef NMEA0183_ENABLE
    case NMEA_DOLLAR:
        if (c == 'G')
            lexer->state = NMEA_PUB_LEAD;
        else if (c == 'P')      /* vendor sentence */
            lexer->state = NMEA_VENDOR_LEAD;
        else if (c == 'I')      /* Seatalk */
            lexer->state = SEATALK_LEAD_1;
        else if (c == 'W')      /* Weather instrument */
            lexer->state = WEATHER_LEAD_1;
        else if (c == 'H')      /* Heading/compass */
            lexer->state = HEADCOMP_LEAD_1;
        else if (c == 'T')      /* Turn indicator */
            lexer->state = TURN_LEAD_1;
        else if (c == 'A')      /* SiRF Ack */
            lexer->state = SIRF_ACK_LEAD_1;
        else if (c == 'E')      /* ECDIS */
            lexer->state = ECDIS_LEAD_1;
        else if (c == 'S')
            lexer->state = SOUNDER_LEAD_1;
        else if (c == 'Y')
            lexer->state = TRANSDUCER_LEAD_1;
        else if (c == 'B')
            lexer->state = BEIDOU_LEAD_1;
        else if (c == 'Q') {
            lexer->state = QZSS_LEAD_1;
#ifdef OCEANSERVER_ENABLE
        } else if (c == 'C') {
            // is this ever used?
            lexer->state = NMEA_LEADER_END;
        } else if (c == 'O') {
            // for $OHPR
            lexer->state = NMEA_LEADER_END;
#endif /* OCEANSERVER_ENABLE */
        } else {
            (void) character_pushback(lexer, GROUND_STATE);
        }
        break;
    case NMEA_PUB_LEAD:
        /*
         * $GP == GPS, $GL = GLONASS only, $GN = mixed GPS and GLONASS,
         * according to NMEA (IEIC 61162-1) DRAFT 02/06/2009.
         * We have a log from China with a Beidou device using $GB
         * rather than $BD.
         */
        if (c == 'B' || c == 'P' || c == 'N' || c == 'L' || c == 'A')
            lexer->state = NMEA_LEADER_END;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case NMEA_VENDOR_LEAD:
        if (c == 'A')
            lexer->state = NMEA_PASHR_A;
        else if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    /*
     * Without the following six states, DLE in a $PASHR can fool the
     * sniffer into thinking it sees a TSIP packet.  Hilarity ensues.
     */
    case NMEA_PASHR_A:
        if (c == 'S')
            lexer->state = NMEA_PASHR_S;
        else if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case NMEA_PASHR_S:
        if (c == 'H')
            lexer->state = NMEA_PASHR_H;
        else if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case NMEA_PASHR_H:
        if (c == 'R')
            lexer->state = NMEA_BINARY_BODY;
        else if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case NMEA_BINARY_BODY:
        if (c == '\r')
            lexer->state = NMEA_BINARY_CR;
        break;
    case NMEA_BINARY_CR:
        if (c == '\n')
            lexer->state = NMEA_BINARY_NL;
        else
            lexer->state = NMEA_BINARY_BODY;
        break;
    case NMEA_BINARY_NL:
        if (c == '$')
            (void) character_pushback(lexer, NMEA_RECOGNIZED);
        else
            lexer->state = NMEA_BINARY_BODY;
        break;
    case NMEA_BANG:
        if (c == 'A')
            lexer->state = AIS_LEAD_1;
        else if (c == 'B')
            lexer->state = AIS_LEAD_ALT1;
        else if (c == 'S')
            lexer->state = AIS_LEAD_ALT3;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case AIS_LEAD_1:
        if (strchr("BDINRSTX", c) != NULL)
            lexer->state = AIS_LEAD_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case AIS_LEAD_2:
        if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case AIS_LEAD_ALT1:
        if (c == 'S')
            lexer->state = AIS_LEAD_ALT2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case AIS_LEAD_ALT2:
        if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case AIS_LEAD_ALT3:
        if (c == 'A')
            lexer->state = AIS_LEAD_ALT4;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case AIS_LEAD_ALT4:
        if (isalpha(c))
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#if defined(TNT_ENABLE) || defined(GARMINTXT_ENABLE) || defined(ONCORE_ENABLE)
    case AT1_LEADER:
        switch (c) {
#ifdef ONCORE_ENABLE
        case '@':
            lexer->state = ONCORE_AT2;
            break;
#endif /* ONCORE_ENABLE */
#ifdef TNT_ENABLE
        case '*':
            /*
             * TNT has similar structure to NMEA packet, '*' before
             * optional checksum ends the packet. Since '*' cannot be
             * received from GARMIN working in TEXT mode, use this
             * difference to tell that this is not GARMIN TEXT packet,
             * could be TNT.
             */
            lexer->state = NMEA_LEADER_END;
            break;
#endif /* TNT_ENABLE */
#if defined(GARMINTXT_ENABLE)
        case '\r':
            /* stay in this state, next character should be '\n' */
            /* in the theory we can stop search here and don't wait for '\n' */
            lexer->state = AT1_LEADER;
            break;
        case '\n':
            /* end of packet found */
            lexer->state = GTXT_RECOGNIZED;
            break;
#endif /* GARMINTXT_ENABLE */
        default:
            if (!isprint(c))
                return character_pushback(lexer, GROUND_STATE);
        }
        break;
#endif // TNT_ENABLE || GARMINTXT_ENABLE || ONCORE_ENABLE
    case NMEA_LEADER_END:
        if (c == '\r')
            lexer->state = NMEA_CR;
        else if (c == '\n')
            /* not strictly correct, but helps for interpreting logfiles */
            lexer->state = NMEA_RECOGNIZED;
        else if (c == '$') {
#ifdef STASH_ENABLE
            (void) character_pushback(lexer, STASH_RECOGNIZED);
#else
            (void) character_pushback(lexer, GROUND_STATE);
#endif
        } else if (!isprint(c))
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case NMEA_CR:
        if (c == '\n')
            lexer->state = NMEA_RECOGNIZED;
        /*
         * There's a GPS called a Jackson Labs Firefly-1a that emits \r\r\n
         * at the end of each sentence.  Don't be confused by this.
         */
        else if (c == '\r')
            lexer->state = NMEA_CR;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case NMEA_RECOGNIZED:
        if (c == '#')
            lexer->state = COMMENT_BODY;
        else if (c == '$')
            lexer->state = NMEA_DOLLAR;
        else if (c == '!')
            lexer->state = NMEA_BANG;
#ifdef UBLOX_ENABLE
        else if (c == 0xb5)  // LEA-5H can/ will output NMEA/UBX back to back
            lexer->state = UBX_LEADER_1;
#endif
#ifdef PASSTHROUGH_ENABLE
        else if (c == '{')
            return character_pushback(lexer, JSON_LEADER);
#endif /* PASSTHROUGH_ENABLE */
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SEATALK_LEAD_1:
        if (c == 'I' || c == 'N')       /* II or IN are accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case WEATHER_LEAD_1:
        if (c == 'I')           /* Weather instrument leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case HEADCOMP_LEAD_1:
        if (c == 'C')           /* Heading/compass leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case TURN_LEAD_1:
        if (c == 'I')           /* Turn indicator leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ECDIS_LEAD_1:
        if (c == 'C')           /* ECDIS leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SOUNDER_LEAD_1:
        if (c == 'D')           /* Depth-sounder leader accepted */
            lexer->state = NMEA_LEADER_END;
#ifdef SKYTRAQ_ENABLE
        else if (c == 'T')              /* $ST leader accepted, to $STI */
            lexer->state = NMEA_LEADER_END;
#endif /* SKYTRAQ_ENABLE */
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case TRANSDUCER_LEAD_1:
        if (c == 'X')           /* Transducer leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case BEIDOU_LEAD_1:
        if (c == 'D')           /* Beidou leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case QZSS_LEAD_1:
        if (c == 'Z')           /* QZSS leader accepted */
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#ifdef TRIPMATE_ENABLE
    case ASTRAL_1:
        if (c == 'S') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = ASTRAL_2;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case ASTRAL_2:
        if (c == 'T') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = ASTRAL_3;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case ASTRAL_3:
        if (c == 'R') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = ASTRAL_5;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case ASTRAL_4:
        if (c == 'A') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = ASTRAL_2;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case ASTRAL_5:
        if (c == 'L') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = NMEA_RECOGNIZED;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
#endif /* TRIPMATE_ENABLE */
#ifdef EARTHMATE_ENABLE
    case EARTHA_1:
        if (c == 'A') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = EARTHA_2;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case EARTHA_2:
        if (c == 'R') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = EARTHA_3;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case EARTHA_3:
        if (c == 'T') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = EARTHA_4;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case EARTHA_4:
        if (c == 'H') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = EARTHA_5;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case EARTHA_5:
        if (c == 'A') {
#ifdef RTCM104V2_ENABLE
            if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_SYNC) {
                lexer->state = RTCM2_SYNC_STATE;
                break;
            } else if (isgpsstat == ISGPS_MESSAGE) {
                lexer->state = RTCM2_RECOGNIZED;
                break;
            }
#endif /* RTCM104V2_ENABLE */
            lexer->state = NMEA_RECOGNIZED;
        } else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
#endif /* EARTHMATE_ENABLE */
    case SIRF_ACK_LEAD_1:
        if (c == 'c')
            lexer->state = SIRF_ACK_LEAD_2;
        else if (c == 'I')
            lexer->state = AIS_LEAD_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SIRF_ACK_LEAD_2:
        if (c == 'k')
            lexer->state = NMEA_LEADER_END;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* NMEA0183_ENABLE */
#if defined(SIRF_ENABLE) || defined(SKYTRAQ_ENABLE)
    case SIRF_LEADER_1:
# ifdef SIRF_ENABLE
        /* SIRF leads with 0xA0,0xA2 */
        if (c == 0xa2)
            lexer->state = SIRF_LEADER_2;
        else
# endif /* SIRF_ENABLE */
# ifdef SKYTRAQ_ENABLE
        /* Skytraq leads with 0xA0,0xA1 */
        if (c == 0xa1)
            lexer->state = SKY_LEADER_2;
        else
# endif /* SKYTRAQ_ENABLE */
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* SIRF_ENABLE || SKYTRAQ_ENABLE */
#ifdef SIRF_ENABLE
    case SIRF_LEADER_2:
        lexer->length = (size_t) (c << 8);
        lexer->state = SIRF_LENGTH_1;
        break;
    case SIRF_LENGTH_1:
        lexer->length += c + 2;
        if (lexer->length <= MAX_PACKET_LENGTH)
            lexer->state = SIRF_PAYLOAD;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SIRF_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = SIRF_DELIVERED;
        break;
    case SIRF_DELIVERED:
        if (c == 0xb0)
            lexer->state = SIRF_TRAILER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SIRF_TRAILER_1:
        if (c == 0xb3)
            lexer->state = SIRF_RECOGNIZED;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SIRF_RECOGNIZED:
        if (c == 0xa0)
            lexer->state = SIRF_LEADER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* SIRF_ENABLE */
#ifdef SKYTRAQ_ENABLE
    case SKY_LEADER_2:
        /* MSB of length is first */
        lexer->length = (size_t) (c << 8);
        lexer->state = SKY_LENGTH_1;
        break;
    case SKY_LENGTH_1:
        /* Skytraq length can be any 16 bit number, except 0 */
        lexer->length += c;
        if ( 0 == lexer->length )
            return character_pushback(lexer, GROUND_STATE);
        if (lexer->length > MAX_PACKET_LENGTH)
            return character_pushback(lexer, GROUND_STATE);
        lexer->state = SKY_PAYLOAD;
        break;
    case SKY_PAYLOAD:
        if ( 00 == --lexer->length)
            lexer->state = SKY_DELIVERED;
        break;
    case SKY_DELIVERED:
        if ( lexer->errout.debug >= LOG_RAW + 1) {
            char scratchbuf[MAX_PACKET_LENGTH*4+1];
            GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                     "Skytraq = %s\n",
                     gpsd_packetdump(scratchbuf,  sizeof(scratchbuf),
                         (char *)lexer->inbuffer,
                         lexer->inbufptr - (unsigned char *)lexer->inbuffer));
        }
        {
            unsigned char csum = 0;
            for (n = 4;
                 (unsigned char *)(lexer->inbuffer + n) < lexer->inbufptr - 1;
                 n++)
                csum ^= lexer->inbuffer[n];
            if (csum != c) {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "Skytraq bad checksum 0x%hhx, expecting 0x%x\n",
                         csum, c);
                lexer->state = GROUND_STATE;
                break;
            }
        }
        lexer->state = SKY_CSUM;
        break;
    case SKY_CSUM:
        if ( 0x0d != c)
            return character_pushback(lexer, GROUND_STATE);
        lexer->state = SKY_TRAILER_1;
        break;
    case SKY_TRAILER_1:
        if ( 0x0a != c)
            return character_pushback(lexer, GROUND_STATE);
        lexer->state = SKY_RECOGNIZED;
        break;
    case SKY_RECOGNIZED:
        if ( 0xa0 != c)
            return character_pushback(lexer, GROUND_STATE);
        lexer->state = SIRF_LEADER_1;
        break;
#endif /* SKYTRAQ */
#ifdef SUPERSTAR2_ENABLE
    case SUPERSTAR2_LEADER:
        ctmp = c;
        lexer->state = SUPERSTAR2_ID1;
        break;
    case SUPERSTAR2_ID1:
        if ((ctmp ^ 0xff) == c)
            lexer->state = SUPERSTAR2_ID2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case SUPERSTAR2_ID2:
        lexer->length = (size_t) c;  // how many data bytes follow this byte
        if (lexer->length)
            lexer->state = SUPERSTAR2_PAYLOAD;
        else
            lexer->state = SUPERSTAR2_CKSUM1;   /* no data, jump to checksum */
        break;
    case SUPERSTAR2_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = SUPERSTAR2_CKSUM1;
        break;
    case SUPERSTAR2_CKSUM1:
        lexer->state = SUPERSTAR2_CKSUM2;
        break;
    case SUPERSTAR2_CKSUM2:
        lexer->state = SUPERSTAR2_RECOGNIZED;
        break;
    case SUPERSTAR2_RECOGNIZED:
        if (c == SOH)
            lexer->state = SUPERSTAR2_LEADER;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* SUPERSTAR2_ENABLE */
#ifdef ONCORE_ENABLE
    case ONCORE_AT2:
        if (isupper(c)) {
            lexer->length = (size_t) c;
            lexer->state = ONCORE_ID1;
        } else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ONCORE_ID1:
        if (isalpha(c)) {
            lexer->length =
                oncore_payload_cksum_length((unsigned char)lexer->length, c);
            if (lexer->length != 0) {
                lexer->state = ONCORE_PAYLOAD;
                break;
            }
        } else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ONCORE_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = ONCORE_CHECKSUM;
        break;
    case ONCORE_CHECKSUM:
        if (c != '\r')
            return character_pushback(lexer, GROUND_STATE);
        else
            lexer->state = ONCORE_CR;
        break;
    case ONCORE_CR:
        if (c == '\n')
            lexer->state = ONCORE_RECOGNIZED;
        else
            lexer->state = ONCORE_PAYLOAD;
        break;
    case ONCORE_RECOGNIZED:
        if (c == '@')
            lexer->state = AT1_LEADER;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* ONCORE_ENABLE */
#if defined(TSIP_ENABLE) || defined(EVERMORE_ENABLE) || defined(GARMIN_ENABLE)
    case DLE_LEADER:
#ifdef EVERMORE_ENABLE
        if (c == STX) {
            lexer->state = EVERMORE_LEADER_2;
            break;
        }
#endif /* EVERMORE_ENABLE */
#if defined(TSIP_ENABLE) || defined(GARMIN_ENABLE) || defined(NAVCOM_ENABLE)
        /* garmin is special case of TSIP */
        /* check last because there's no checksum */
#if defined(TSIP_ENABLE)
        if (c >= 0x13) {
            lexer->length = TSIP_MAX_PACKET;
            lexer->state = TSIP_PAYLOAD;
            break;
        }
#endif /* TSIP_ENABLE */
        if (c == DLE) {
            lexer->state = GROUND_STATE;
            break;
        }
        /* give up */
        lexer->state = GROUND_STATE;
        break;
#endif /* TSIP_ENABLE */
#ifdef NAVCOM_ENABLE
    case NAVCOM_LEADER_1:
        if (c == 0x99)
            lexer->state = NAVCOM_LEADER_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case NAVCOM_LEADER_2:
        if (c == 0x66)
            lexer->state = NAVCOM_LEADER_3;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case NAVCOM_LEADER_3:
        lexer->state = NAVCOM_ID;
        break;
    case NAVCOM_ID:
        lexer->length = (size_t) c - 4;
        lexer->state = NAVCOM_LENGTH_1;
        break;
    case NAVCOM_LENGTH_1:
        lexer->length += (c << 8);
        lexer->state = NAVCOM_LENGTH_2;
        break;
    case NAVCOM_LENGTH_2:
        if (--lexer->length == 0)
            lexer->state = NAVCOM_PAYLOAD;
        break;
    case NAVCOM_PAYLOAD:
    {
        unsigned char csum = lexer->inbuffer[3];
        for (n = 4;
             (unsigned char *)(lexer->inbuffer + n) < lexer->inbufptr - 1;
             n++)
            csum ^= lexer->inbuffer[n];
        if (csum != c) {
            GPSD_LOG(LOG_IO, &lexer->errout,
                     "Navcom packet type 0x%hhx bad checksum 0x%hhx, "
                     "expecting 0x%x\n",
                     lexer->inbuffer[3], csum, c);
            lexer->state = GROUND_STATE;
            break;
        }
    }
        lexer->state = NAVCOM_CSUM;
        break;
    case NAVCOM_CSUM:
        if (c == 0x03)
            lexer->state = NAVCOM_RECOGNIZED;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case NAVCOM_RECOGNIZED:
        if (c == 0x02)
            lexer->state = NAVCOM_LEADER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* NAVCOM_ENABLE */
#endif /* TSIP_ENABLE || EVERMORE_ENABLE || GARMIN_ENABLE */
#ifdef RTCM104V3_ENABLE
    case RTCM3_LEADER_1:
        /* high 6 bits must be zero, low 2 bits are MSB of a 10-bit length */
        if ((c & 0xFC) == 0) {
            lexer->length = (size_t) (c << 8);
            lexer->state = RTCM3_LEADER_2;
        } else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case RTCM3_LEADER_2:
        /* third byte is the low 8 bits of the RTCM3 packet length */
        lexer->length |= c;
        lexer->length += 3;     /* to get the three checksum bytes */
        lexer->state = RTCM3_PAYLOAD;
        break;
    case RTCM3_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = RTCM3_RECOGNIZED;
        break;
#endif /* RTCM104V3_ENABLE */
#ifdef ZODIAC_ENABLE
    case ZODIAC_EXPECTED:
    case ZODIAC_RECOGNIZED:
        if (c == 0xff)
            lexer->state = ZODIAC_LEADER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ZODIAC_LEADER_1:
        if (c == 0x81)
            lexer->state = ZODIAC_LEADER_2;
        else
            (void) character_pushback(lexer, GROUND_STATE);
        break;
    case ZODIAC_LEADER_2:
        lexer->state = ZODIAC_ID_1;
        break;
    case ZODIAC_ID_1:
        lexer->state = ZODIAC_ID_2;
        break;
    case ZODIAC_ID_2:
        lexer->length = (size_t) c;
        lexer->state = ZODIAC_LENGTH_1;
        break;
    case ZODIAC_LENGTH_1:
        lexer->length += (c << 8);
        lexer->state = ZODIAC_LENGTH_2;
        break;
    case ZODIAC_LENGTH_2:
        lexer->state = ZODIAC_FLAGS_1;
        break;
    case ZODIAC_FLAGS_1:
        lexer->state = ZODIAC_FLAGS_2;
        break;
    case ZODIAC_FLAGS_2:
        lexer->state = ZODIAC_HSUM_1;
        break;
    case ZODIAC_HSUM_1:
    {
        short sum = getzword(0) + getzword(1) + getzword(2) + getzword(3);
        sum *= -1;
        if (sum != getzword(4)) {
            GPSD_LOG(LOG_IO, &lexer->errout,
                     "Zodiac Header checksum 0x%x expecting 0x%x\n",
                     sum, getzword(4));
            lexer->state = GROUND_STATE;
            break;
        }
    }
        GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                 "Zodiac header id=%u len=%u flags=%x\n",
                 getzuword(1), getzuword(2), getzuword(3));
        if (lexer->length == 0) {
            lexer->state = ZODIAC_RECOGNIZED;
            break;
        }
        lexer->length *= 2;     /* word count to byte count */
        lexer->length += 2;     /* checksum */
        /* 10 bytes is the length of the Zodiac header */
        if (lexer->length <= MAX_PACKET_LENGTH - 10)
            lexer->state = ZODIAC_PAYLOAD;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ZODIAC_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = ZODIAC_RECOGNIZED;
        break;
#endif /* ZODIAC_ENABLE */
#ifdef UBLOX_ENABLE
    case UBX_LEADER_1:
        if (c == 0x62)
            lexer->state = UBX_LEADER_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case UBX_LEADER_2:
        lexer->state = UBX_CLASS_ID;
        break;
    case UBX_CLASS_ID:
        lexer->state = UBX_MESSAGE_ID;
        break;
    case UBX_MESSAGE_ID:
        lexer->length = (size_t) c;
        lexer->state = UBX_LENGTH_1;
        break;
    case UBX_LENGTH_1:
        lexer->length += (c << 8);
        if (lexer->length <= MAX_PACKET_LENGTH)
            lexer->state = UBX_LENGTH_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case UBX_LENGTH_2:
        lexer->state = UBX_PAYLOAD;
        break;
    case UBX_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = UBX_CHECKSUM_A;
        /* else stay in payload state */
        break;
    case UBX_CHECKSUM_A:
        lexer->state = UBX_RECOGNIZED;
        break;
    case UBX_RECOGNIZED:
        if (c == 0xb5)
            lexer->state = UBX_LEADER_1;
#ifdef NMEA0183_ENABLE
        else if (c == '$')  // LEA-5H can/will output NMEA/UBX back to back
            lexer->state = NMEA_DOLLAR;
#endif /* NMEA0183_ENABLE */
#ifdef PASSTHROUGH_ENABLE
        else if (c == '{')
            return character_pushback(lexer, JSON_LEADER);
#endif /* PASSTHROUGH_ENABLE */
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* UBLOX_ENABLE */
#ifdef EVERMORE_ENABLE
    case EVERMORE_LEADER_1:
        if (c == STX)
            lexer->state = EVERMORE_LEADER_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case EVERMORE_LEADER_2:
        lexer->length = (size_t) c;
        if (c == DLE)
            lexer->state = EVERMORE_PAYLOAD_DLE;
        else
            lexer->state = EVERMORE_PAYLOAD;
        break;
    case EVERMORE_PAYLOAD:
        if (c == DLE)
            lexer->state = EVERMORE_PAYLOAD_DLE;
        else if (--lexer->length == 0)
            return character_pushback(lexer, GROUND_STATE);
        break;
    case EVERMORE_PAYLOAD_DLE:
        switch (c) {
        case DLE:
            lexer->state = EVERMORE_PAYLOAD;
            break;
        case ETX:
            lexer->state = EVERMORE_RECOGNIZED;
            break;
        default:
            lexer->state = GROUND_STATE;
        }
        break;
    case EVERMORE_RECOGNIZED:
        if (c == DLE)
            lexer->state = EVERMORE_LEADER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* EVERMORE_ENABLE */
#ifdef ITRAX_ENABLE
    case ITALK_LEADER_1:
        if (c == '!')
            lexer->state = ITALK_LEADER_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ITALK_LEADER_2:
        lexer->length = (size_t) (lexer->inbuffer[6] & 0xff);
        lexer->state = ITALK_LENGTH;
        break;
    case ITALK_LENGTH:
        lexer->length += 1;     /* fix number of words in payload */
        lexer->length *= 2;     /* convert to number of bytes */
        lexer->length += 3;     /* add trailer length */
        lexer->state = ITALK_PAYLOAD;
        break;
    case ITALK_PAYLOAD:
        /* lookahead for "<!" because sometimes packets are short but valid */
        if ((c == '>') && (lexer->inbufptr[0] == '<') &&
            (lexer->inbufptr[1] == '!')) {
            lexer->state = ITALK_RECOGNIZED;
            GPSD_LOG(LOG_IO, &lexer->errout,
                     "ITALK: trying to process runt packet\n");
            break;
        } else if (--lexer->length == 0)
            lexer->state = ITALK_DELIVERED;
        break;
    case ITALK_DELIVERED:
        if (c == '>')
            lexer->state = ITALK_RECOGNIZED;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case ITALK_RECOGNIZED:
        if (c == '<')
            lexer->state = ITALK_LEADER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* ITRAX_ENABLE */
#ifdef GEOSTAR_ENABLE
    case GEOSTAR_LEADER_1:
        if (c == 'S')
            lexer->state = GEOSTAR_LEADER_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case GEOSTAR_LEADER_2:
        if (c == 'G')
            lexer->state = GEOSTAR_LEADER_3;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case GEOSTAR_LEADER_3:
        if (c == 'G')
            lexer->state = GEOSTAR_LEADER_4;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case GEOSTAR_LEADER_4:
        lexer->state = GEOSTAR_MESSAGE_ID_1;
        break;
    case GEOSTAR_MESSAGE_ID_1:
        lexer->state = GEOSTAR_MESSAGE_ID_2;
        break;
    case GEOSTAR_MESSAGE_ID_2:
        lexer->length = (size_t)(c * 4);
        lexer->state = GEOSTAR_LENGTH_1;
        break;
    case GEOSTAR_LENGTH_1:
        lexer->length += (c << 8) * 4;
        if (lexer->length <= MAX_PACKET_LENGTH)
            lexer->state = GEOSTAR_LENGTH_2;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case GEOSTAR_LENGTH_2:
        lexer->state = GEOSTAR_PAYLOAD;
        break;
    case GEOSTAR_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = GEOSTAR_CHECKSUM_A;
        /* else stay in payload state */
        break;
    case GEOSTAR_CHECKSUM_A:
        lexer->state = GEOSTAR_CHECKSUM_B;
        break;
    case GEOSTAR_CHECKSUM_B:
        lexer->state = GEOSTAR_CHECKSUM_C;
        break;
    case GEOSTAR_CHECKSUM_C:
        lexer->state = GEOSTAR_RECOGNIZED;
        break;
    case GEOSTAR_RECOGNIZED:
        if (c == 'P')
            lexer->state = GEOSTAR_LEADER_1;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* GEOSTAR_ENABLE */
#ifdef GREIS_ENABLE
    case GREIS_EXPECTED:
    case GREIS_RECOGNIZED:
        if (!isascii(c)) {
            return character_pushback(lexer, GROUND_STATE);
        } else if (c == '#') {
            /* Probably a comment used by the testsuite */
            lexer->state = COMMENT_BODY;
        } else if (c == '\r' || c == '\n') {
            /* Arbitrary CR/LF allowed here, so continue to expect GREIS */
            lexer->state = GREIS_EXPECTED;
            character_discard(lexer);
        } else {
            lexer->state = GREIS_ID_1;
        }
        break;
    case GREIS_REPLY_1:
        if (c != 'E')
            return character_pushback(lexer, GROUND_STATE);
        lexer->state = GREIS_REPLY_2;
        break;
    case GREIS_ID_1:
        if (!isascii(c))
            return character_pushback(lexer, GROUND_STATE);
        lexer->state = GREIS_ID_2;
        break;
    case GREIS_REPLY_2:
    case GREIS_ID_2:
        if (!isxdigit(c))
            return character_pushback(lexer, GROUND_STATE);
        lexer->length = greis_hex2bin(c) << 8;
        lexer->state = GREIS_LENGTH_1;
        break;
    case GREIS_LENGTH_1:
        if (!isxdigit(c))
            return character_pushback(lexer, GROUND_STATE);
        lexer->length += greis_hex2bin(c) << 4;
        lexer->state = GREIS_LENGTH_2;
        break;
    case GREIS_LENGTH_2:
        if (!isxdigit(c))
            return character_pushback(lexer, GROUND_STATE);
        lexer->length += greis_hex2bin(c);
        lexer->state = GREIS_PAYLOAD;
        break;
    case GREIS_PAYLOAD:
        if (--lexer->length == 0)
            lexer->state = GREIS_RECOGNIZED;
        /* else stay in payload state */
        break;
#endif /* GREIS_ENABLE */
#ifdef TSIP_ENABLE
    case TSIP_LEADER:
        /* unused case */
        if (c >= 0x13) {
            lexer->length = TSIP_MAX_PACKET;
            lexer->state = TSIP_PAYLOAD;
        } else
            return character_pushback(lexer, GROUND_STATE);
        break;
    case TSIP_PAYLOAD:
        if (c == DLE)
            lexer->state = TSIP_DLE;
        if ( 0 == --lexer->length ) {
            /* uh, oh, packet too long, probably was never TSIP */
            /* note lexer->length is unsigned */
            lexer->state = GROUND_STATE;
        }
        break;
    case TSIP_DLE:
        switch (c) {
        case ETX:
            lexer->state = TSIP_RECOGNIZED;
            break;
        case DLE:
            lexer->length = TSIP_MAX_PACKET;
            lexer->state = TSIP_PAYLOAD;
            break;
        default:
            lexer->state = GROUND_STATE;
            break;
        }
        break;
    case TSIP_RECOGNIZED:
        if (c == DLE)
            /*
             * Don't go to TSIP_LEADER state -- TSIP packets aren't
             * checksummed, so false positives are easy.  We might be
             * looking at another DLE-stuffed protocol like EverMore
             * or Garmin streaming binary.
             */
            lexer->state = DLE_LEADER;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* TSIP_ENABLE */
#ifdef RTCM104V2_ENABLE
    case RTCM2_SYNC_STATE:
    case RTCM2_SKIP_STATE:
        if ((isgpsstat = rtcm2_decode(lexer, c)) == ISGPS_MESSAGE) {
            lexer->state = RTCM2_RECOGNIZED;
            break;
        } else if (isgpsstat == ISGPS_NO_SYNC)
            lexer->state = GROUND_STATE;
        break;

    case RTCM2_RECOGNIZED:
        if (c == '#')
            /*
             * There's a remote possibility this could fire when # =
             * 0x23 is legitimate in-stream RTCM2 data.  No help for
             * it, the test framework needs this case so it can inject
             * # EOF and we'll miss a packet.
             */
            return character_pushback(lexer, GROUND_STATE);
        else if (rtcm2_decode(lexer, c) == ISGPS_SYNC) {
            lexer->state = RTCM2_SYNC_STATE;
            break;
        } else
            lexer->state = GROUND_STATE;
        break;
#endif /* RTCM104V2_ENABLE */
#ifdef PASSTHROUGH_ENABLE
    case JSON_LEADER:
        if (c == '{' || c == '[') {
            lexer->json_depth++;
        } else if (c == '}' || c == ']') {
            if (--lexer->json_depth == 0)
                lexer->state = JSON_RECOGNIZED;
        } else if (isspace(c) || c == ',')
            break;
        else if (c == '"') {
            lexer->state = JSON_STRINGLITERAL;
            lexer->json_after = JSON_END_ATTRIBUTE;
        } else {
            GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                     "%08ld: missing attribute start after header\n",
                     lexer->char_counter);
            lexer->state = GROUND_STATE;
        }
        break;
    case JSON_STRINGLITERAL:
        if (c == '\\')
            lexer->state = JSON_STRING_SOLIDUS;
        else if (c == '"')
            lexer->state = lexer->json_after;
        break;
    case JSON_STRING_SOLIDUS:
        lexer->state = JSON_STRINGLITERAL;
        break;
    case JSON_END_ATTRIBUTE:
        if (isspace(c))
            break;
        else if (c == ':')
            lexer->state = JSON_EXPECT_VALUE;
        else
            /* saw something other than value start after colon */
            return character_pushback(lexer, GROUND_STATE);
        break;
    case JSON_EXPECT_VALUE:
        if (isspace(c))
            break;
        else if (c == '"') {
            lexer->state = JSON_STRINGLITERAL;
            lexer->json_after = JSON_END_VALUE;
        } else if (c == '{' || c == '[') {
            return character_pushback(lexer, JSON_LEADER);
        } else if (strchr("-0123456789", c) != NULL) {
            lexer->state = JSON_NUMBER;
        } else if (c == 't' || c == 'f' || c == 'n')
            /*
             * This is a bit more permissive than strictly necessary, as
             * GPSD JSON does not include the null token.  Still, it's
             * futureproofing.
             */
            lexer->state = JSON_SPECIAL;
        else
            /* couldn't recognize start of value literal */
            return character_pushback(lexer, GROUND_STATE);
        break;
    case JSON_NUMBER:
        /*
         * Will recognize some ill-formed numeric literals.
         * Should be OK as we're already three stages deep inside
         * JSON recognition; odds that we'll actually see an
         * ill-formed literal are quite low. and the worst
         * possible result if it happens is our JSON parser will
         * quietly chuck out the object.
         */
        if (strchr("1234567890.eE+-", c) == NULL) {
            return character_pushback(lexer, JSON_END_VALUE);
        }
        break;
    case JSON_SPECIAL:
        if (strchr("truefalsnil", c) == NULL)
            return character_pushback(lexer, JSON_END_VALUE);
        break;
    case JSON_END_VALUE:
        if (isspace(c))
            break;
        else if (c == ',')
            lexer->state = JSON_LEADER;
        else if (c == '}' || c == ']')
            return character_pushback(lexer, JSON_LEADER);
        else
            /* trailing garbage after JSON value */
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* PASSTHROUGH_ENABLE */
#ifdef STASH_ENABLE
    case STASH_RECOGNIZED:
        if (c == '$')
            lexer->state = NMEA_DOLLAR;
        else
            return character_pushback(lexer, GROUND_STATE);
        break;
#endif /* STASH_ENABLE */
    }

    return true;        /* no pushback */
}

static void packet_accept(struct gps_lexer_t *lexer, int packet_type)
/* packet grab succeeded, move to output buffer */
{
    size_t packetlen = lexer->inbufptr - lexer->inbuffer;

    if (packetlen < sizeof(lexer->outbuffer)) {
        memcpy(lexer->outbuffer, lexer->inbuffer, packetlen);
        lexer->outbuflen = packetlen;
        lexer->outbuffer[packetlen] = '\0';
        lexer->type = packet_type;
        if (lexer->errout.debug >= LOG_RAW + 1) {
            char scratchbuf[MAX_PACKET_LENGTH*4+1];
            GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                     "Packet type %d accepted %zu = %s\n",
                     packet_type, packetlen,
                     gpsd_packetdump(scratchbuf,  sizeof(scratchbuf),
                                     (char *)lexer->outbuffer,
                                     lexer->outbuflen));
        }
    } else {
        GPSD_LOG(LOG_ERROR, &lexer->errout,
                 "Rejected too long packet type %d len %zu\n",
                 packet_type, packetlen);
    }
}

static void packet_discard(struct gps_lexer_t *lexer)
/* shift the input buffer to discard all data up to current input pointer */
{
    size_t discard = lexer->inbufptr - lexer->inbuffer;
    size_t remaining = lexer->inbuflen - discard;
    lexer->inbufptr = memmove(lexer->inbuffer, lexer->inbufptr, remaining);
    lexer->inbuflen = remaining;
    if (lexer->errout.debug >= LOG_RAW + 1) {
        char scratchbuf[MAX_PACKET_LENGTH*4+1];
        GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                 "Packet discard of %zu, chars remaining is %zu = %s\n",
                 discard, remaining,
                 gpsd_packetdump(scratchbuf, sizeof(scratchbuf),
                                    (char *)lexer->inbuffer, lexer->inbuflen));
    }
}

#ifdef STASH_ENABLE
static void packet_stash(struct gps_lexer_t *lexer)
/* stash the input buffer up to current input pointer */
{
    size_t stashlen = lexer->inbufptr - lexer->inbuffer;

    memcpy(lexer->stashbuffer, lexer->inbuffer, stashlen);
    lexer->stashbuflen = stashlen;
    if (lexer->errout.debug >= LOG_RAW+1) {
        char scratchbuf[MAX_PACKET_LENGTH*4+1];
        GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                 "Packet stash of %zu = %s\n",
                 stashlen,
                 gpsd_packetdump(scratchbuf, sizeof(scratchbuf),
                                 (char *)lexer->stashbuffer,
                                 lexer->stashbuflen));
    }
}

/* return stash to start of input buffer */
static void packet_unstash(struct gps_lexer_t *lexer)
{
    size_t available = sizeof(lexer->inbuffer) - lexer->inbuflen;
    size_t stashlen = lexer->stashbuflen;

    if (stashlen <= available) {
        memmove(lexer->inbuffer + stashlen, lexer->inbuffer, lexer->inbuflen);
        memcpy(lexer->inbuffer, lexer->stashbuffer, stashlen);
        lexer->inbuflen += stashlen;
        lexer->stashbuflen = 0;
        if (lexer->errout.debug >= LOG_RAW+1) {
            char scratchbuf[MAX_PACKET_LENGTH*4+1];
            GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                     "Packet unstash of %zu, reconstructed is %zu = %s\n",
                     stashlen, lexer->inbuflen,
                     gpsd_packetdump(scratchbuf, sizeof(scratchbuf),
                                     (char *)lexer->inbuffer, lexer->inbuflen));
        }
    } else {
        GPSD_LOG(LOG_ERROR, &lexer->errout,
                 "Rejected too long unstash of %zu\n", stashlen);
        lexer->stashbuflen = 0;
    }
}
#endif /* STASH_ENABLE */

/* entry points begin here */

void lexer_init(struct gps_lexer_t *lexer)
{
    lexer->char_counter = 0;
    lexer->retry_counter = 0;
#ifdef PASSTHROUGH_ENABLE
    lexer->json_depth = 0;
#endif /* PASSTHROUGH_ENABLE */
    lexer->start_time.tv_sec = 0;
    lexer->start_time.tv_nsec = 0;
    packet_reset(lexer);
    errout_reset(&lexer->errout);
}

/* grab a packet from the input buffer */
void packet_parse(struct gps_lexer_t *lexer)
{
    lexer->outbuflen = 0;
    while (packet_buffered_input(lexer) > 0) {
        unsigned char c = *lexer->inbufptr++;
        unsigned int oldstate = lexer->state;
        if (!nextstate(lexer, c))
            continue;
        GPSD_LOG(LOG_RAW + 2, &lexer->errout,
                 "%08ld: character '%c' [%02x], %s -> %s\n",
                 lexer->char_counter, (isprint(c) ? c : '.'), c,
                 state_table[oldstate], state_table[lexer->state]);
        lexer->char_counter++;

        if (lexer->state == GROUND_STATE) {
            character_discard(lexer);
        } else if (lexer->state == COMMENT_RECOGNIZED) {
            packet_accept(lexer, COMMENT_PACKET);
            packet_discard(lexer);
            lexer->state = GROUND_STATE;
            break;
        }
#ifdef NMEA0183_ENABLE
        else if (lexer->state == NMEA_RECOGNIZED) {
            /*
             * $PASHR packets have no checksum. Avoid the possibility
             * that random garbage might make it look like they do.
             */
            if (!str_starts_with((const char *)lexer->inbuffer, "$PASHR,")) {
                bool checksum_ok = true;
                char csum[3] = { '0', '0', '0' };
                char *end;
                /*
                 * Back up past any whitespace.  Need to do this because
                 * at least one GPS (the Firefly 1a) emits \r\r\n
                 */
                for (end = (char *)lexer->inbufptr - 1;
                     isspace((unsigned char) *end); end--)
                    continue;
                while (strchr("0123456789ABCDEF", *end))
                    --end;
                if (*end == '*') {
                    unsigned int n, crc = 0;
                    for (n = 1; (char *)lexer->inbuffer + n < end; n++)
                        crc ^= lexer->inbuffer[n];
                    (void)snprintf(csum, sizeof(csum), "%02X", crc);
                    checksum_ok = (csum[0] == toupper((unsigned char) end[1]) &&
                                   csum[1] == toupper((unsigned char) end[2]));
                }
                if (!checksum_ok) {
                    GPSD_LOG(LOG_WARN, &lexer->errout,
                             "bad checksum in NMEA packet; expected %s.\n",
                             csum);
                    packet_accept(lexer, BAD_PACKET);
                    lexer->state = GROUND_STATE;
                    packet_discard(lexer);
                    break;    /* exit case */
                }
            }
            /* checksum passed or not present */
#ifdef AIVDM_ENABLE
            /* !ABVDx  - NMEA 4.0 Base AIS station
             * !ADVDx  - MMEA 4.0 Dependent AIS Base Station
             * !AIVDx  - Mobile AIS station
             * !ANVDx  - NMEA 4.0 Aid to Navigation AIS station
             * !ARVDx  - NMEA 4.0 AIS Receiving Station
             * !ASVDx  - NMEA 4.0 Limited Base Station
             * !ATVDx  - NMEA 4.0 AIS Transmitting Station
             * !AXVDx  - NMEA 4.0 Repeater AIS station
             * !BSVDx  - Base AIS station (deprecated in NMEA 4.0)
             * !SAVDx  - NMEA 4.0 Physical Shore AIS Station
             *
             * where x is:
             *   M -- from other ships
             *   O -- from your own ship
             */
            /* make some simple char tests first to stop wasting cycles
             * on a lot of strncmp()s */
            if ('!' == lexer->inbuffer[0] &&
                'V' == lexer->inbuffer[3] &&
                'D' == lexer->inbuffer[4] &&
                ',' == lexer->inbuffer[6] &&
                (str_starts_with((char *)lexer->inbuffer, "!ABVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ABVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ADVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ADVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!AIVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!AIVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ANVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ANVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ARVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ARVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ASVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ASVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ATVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!ATVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!AXVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!AXVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!BSVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!BSVDO,") ||
                 str_starts_with((char *)lexer->inbuffer, "!SAVDM,") ||
                 str_starts_with((char *)lexer->inbuffer, "!SAVDO,"))) {
                packet_accept(lexer, AIVDM_PACKET);
            } else
#endif /* AIVDM_ENABLE */
                packet_accept(lexer, NMEA_PACKET);
            packet_discard(lexer);
#ifdef STASH_ENABLE
            if (lexer->stashbuflen)
                packet_unstash(lexer);
#endif /* STASH_ENABLE */
            break;
        }
#endif /* NMEA0183_ENABLE */
#ifdef SIRF_ENABLE
        else if (lexer->state == SIRF_RECOGNIZED) {
            unsigned char *trailer = lexer->inbufptr - 4;
            unsigned int checksum =
                (unsigned)((trailer[0] << 8) | trailer[1]);
            unsigned int n, crc = 0;
            for (n = 4; n < (unsigned)(trailer - lexer->inbuffer); n++)
                crc += (int)lexer->inbuffer[n];
            crc &= 0x7fff;
            if (checksum == crc)
                packet_accept(lexer, SIRF_PACKET);
            else {
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
            packet_discard(lexer);
            break;
        }
#endif /* SIRF_ENABLE */
#ifdef SKYTRAQ_ENABLE
        else if (lexer->state == SKY_RECOGNIZED) {
            packet_accept(lexer, SKY_PACKET);
            packet_discard(lexer);
            break;
        }
#endif /* SKYTRAQ_ENABLE */
#ifdef SUPERSTAR2_ENABLE
        else if (lexer->state == SUPERSTAR2_RECOGNIZED) {
            unsigned a = 0, b;
            size_t n;

            lexer->length = 4 + (size_t)lexer->inbuffer[3] + 2;
            if (261 < lexer->length) {
                // can't happen, pacify coverity by checking anyway.
                lexer->length = 261;
            }
            for (n = 0; n < lexer->length - 2; n++)
                a += (unsigned)lexer->inbuffer[n];
            b = (unsigned)getleu16(lexer->inbuffer, lexer->length - 2);
            GPSD_LOG(LOG_IO, &lexer->errout,
                     "SuperStarII pkt dump: type %u len %u\n",
                     lexer->inbuffer[1], (unsigned)lexer->length);
            if (a != b) {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "REJECT SuperStarII packet type 0x%02x"
                         "%zd bad checksum 0x%04x, expecting 0x%04x\n",
                         lexer->inbuffer[1], lexer->length, a, b);
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            } else {
                packet_accept(lexer, SUPERSTAR2_PACKET);
            }
            packet_discard(lexer);
            break;
        }
#endif /* SUPERSTAR2_ENABLE */
#ifdef ONCORE_ENABLE
        else if (lexer->state == ONCORE_RECOGNIZED) {
            char a, b;
            int i, len;

            len = lexer->inbufptr - lexer->inbuffer;
            a = (char)(lexer->inbuffer[len - 3]);
            b = '\0';
            for (i = 2; i < len - 3; i++)
                b ^= lexer->inbuffer[i];
            if (a == b) {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "Accept OnCore packet @@%c%c len %d\n",
                         lexer->inbuffer[2], lexer->inbuffer[3], len);
                packet_accept(lexer, ONCORE_PACKET);
            } else {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "REJECT OnCore packet @@%c%c len %d\n",
                         lexer->inbuffer[2], lexer->inbuffer[3], len);
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
            packet_discard(lexer);
            break;
        }
#endif /* ONCORE_ENABLE */
#if defined(TSIP_ENABLE) || defined(GARMIN_ENABLE)
        else if (lexer->state == TSIP_RECOGNIZED) {
            size_t packetlen = lexer->inbufptr - lexer->inbuffer;
#ifdef TSIP_ENABLE
            unsigned int pos, dlecnt;
            /* don't count stuffed DLEs in the length */
            dlecnt = 0;
            for (pos = 0; pos < (unsigned int)packetlen; pos++)
                if (lexer->inbuffer[pos] == DLE)
                    dlecnt++;
            if (dlecnt > 2) {
                dlecnt -= 2;
                dlecnt /= 2;
                GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                         "Unstuffed %d DLEs\n", dlecnt);
                packetlen -= dlecnt;
            }
#endif /* TSIP_ENABLE */
            if (packetlen < 5) {
                lexer->state = GROUND_STATE;
            } else {
                unsigned int pkt_id;
#ifdef GARMIN_ENABLE
                unsigned int len;
                size_t n;
                unsigned int ch, chksum;
                n = 0;
#ifdef TSIP_ENABLE
                /* shortcut garmin */
                if (TSIP_PACKET == lexer->type)
                    goto not_garmin;
#endif /* TSIP_ENABLE */
                if (lexer->inbuffer[n++] != DLE)
                    goto not_garmin;
                pkt_id = lexer->inbuffer[n++];  /* packet ID */
                len = lexer->inbuffer[n++];
                chksum = len + pkt_id;
                if (len == DLE) {
                    if (lexer->inbuffer[n++] != DLE)
                        goto not_garmin;
                }
                for (; len > 0; len--) {
                    chksum += lexer->inbuffer[n];
                    if (lexer->inbuffer[n++] == DLE) {
                        if (lexer->inbuffer[n++] != DLE)
                            goto not_garmin;
                    }
                }
                /* check sum byte */
                ch = lexer->inbuffer[n++];
                chksum += ch;
                if (ch == DLE) {
                    if (lexer->inbuffer[n++] != DLE)
                        goto not_garmin;
                }
                if (lexer->inbuffer[n++] != DLE)
                    goto not_garmin;
                /* we used to say n++ here, but scan-build complains */
                if (lexer->inbuffer[n] != ETX)
                    goto not_garmin;
                chksum &= 0xff;
                if (chksum) {
                    GPSD_LOG(LOG_IO, &lexer->errout,
                             "Garmin checksum failed: %02x!=0\n", chksum);
                    goto not_garmin;
                }
                packet_accept(lexer, GARMIN_PACKET);
                packet_discard(lexer);
                break;
              not_garmin:;
                GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                         "Not a Garmin packet\n");
#endif /* GARMIN_ENABLE */
#ifdef TSIP_ENABLE
                /* check for some common TSIP packet types:
                 * 0x13, TSIP Parsing Error Notification
                 * 0x1c, Hardware/Software Version Information
                 * 0x38, Request SV system data
                 * 0x40, Almanac
                 * 0x41, GPS time, data length 10
                 * 0x42, Single Precision Fix XYZ, data length 16
                 * 0x43, Velocity Fix XYZ, ECEF, data length 20
                 * 0x45, Software Version Information, data length 10
                 * 0x46, Health of Receiver, data length 2
                 * 0x47, Signal Level all Sats Tracked, data length 1+5*numSV
                 * 0x48, GPS System Messages, data length 22
                 * 0x49, Almanac Health Page, data length 32
                 * 0x4a, Single Precision Fix LLA, data length 20
                 * 0x4b, Machine Code Status, data length 3
                 * 0x4c, Operating Parameters Report, data length 17
                 * 0x4d, Oscillator Offset
                 * 0x4e, Response to set GPS time
                 * 0x54, One Satellite Bias, data length 12
                 * 0x55, I/O Options, data length 4
                 * 0x56, Velocity Fix ENU, data length 20
                 * 0x57, Last Computed Fix Report, data length 8
                 * 0x58, Satellite System Data
                 * 0x58-05, UTC
                 * 0x59, Satellite Health
                 * 0x5a, Raw Measurements
                 * 0x5b, Satellite Ephemeris Status, data length 16
                 * 0x5c, Satellite Tracking Status, data length 24
                 * 0x5d, Satellite Tracking Status (multi-gnss), data length 26
                 * 0x5e, Additional Fix Status Report
                 * 0x5f, Severe Failure Notification
                 * 0x5F-01-0B: Reset Error Codes
                 * 0x5F-02: Ascii text message
                 * 0x6c, Satellite Selection List, data length 18+numSV
                 * 0x6d, All-In-View Satellite Selection, data length 17+numSV
                 * 0x6f, Synced Measurement Packet
                 * 0x72, PV filter parameters
                 * 0x74, Altitude filter parameters
                 * 0x78, Max DGPS correction age
                 * 0x7b, NMEA message schedule
                 * 0x82, Differential Position Fix Mode, data length 1
                 * 0x83, Double Precision Fix XYZ, data length 36
                 * 0x84, Double Precision Fix LLA, data length 36
                 * 0x85, DGPS Correction status
                 * 0x8f, Superpackets
                 * 0x8f-01,
                 * 0x8f-02,
                 * 0x8f-03, port configuration
                 * 0x8f-14, datum
                 * 0x8f-15, datum
                 * 0x8f-17, Single Precision UTM
                 * 0x8f-18, Double Precision UTM
                 * 0x8f-20, LLA & ENU
                 * 0x8f-26, SEEPROM write status
                 * 0x8f-40, TAIP Configuration
                 * 0xbb, GPS Navigation Configuration
                 * 0xbc, Receiver Port Configuration
                 *
                 * <DLE>[pkt id] [data] <DLE><ETX>
                 *
                 * The best description is in [TSIP], the Trimble Standard
                 * Interface Protocol manual; unless otherwise specified
                 * that is where these type/length notifications are from.
                 *
                 * Note that not all Trimble chips conform perfectly to this
                 * specification, nor does it cover every packet type we
                 * may see on the wire.
                 */
                pkt_id = lexer->inbuffer[1];    /* packet ID */
                /* *INDENT-OFF* */
                if (!((0x13 == pkt_id) ||
                      (0x1c == pkt_id) ||
                      (0x38 == pkt_id) ||
                      ((0x41 <= pkt_id) && (0x4c >= pkt_id)) ||
                      ((0x54 <= pkt_id) && (0x57 >= pkt_id)) ||
                      ((0x5a <= pkt_id) && (0x5f >= pkt_id)) ||
                      (0x6c == pkt_id) ||
                      (0x6d == pkt_id) ||
                      ((0x82 <= pkt_id) && (0x84 >= pkt_id)) ||
                      (0x8f == pkt_id) ||
                      (0xbb == pkt_id) ||
                      (0xbc == pkt_id))) {
                    GPSD_LOG(LOG_IO, &lexer->errout,
                             "Packet ID 0x%02x out of range for TSIP\n",
                             pkt_id);
                    goto not_tsip;
                }
                /* *INDENT-ON* */
#define TSIP_ID_AND_LENGTH(id, len)     ((id == pkt_id) && \
                                         (len == packetlen-4))

                if ((0x13 == pkt_id) && (1 <= packetlen))
                    /* pass */ ;
                /*
                 * Not in [TSIP],  Accutime Gold only. Variable length.
                 */
                else if ((0x1c == pkt_id) && (11 <= packetlen))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x41, 10))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x42, 16))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x43, 20))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x45, 10))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x46, 2))
                    /* pass */ ;
                else if ((0x47 == pkt_id) && ((packetlen % 5) == 0))
                    /*
                     * 0x47 data length 1+5*numSV, packetlen is 5+5*numSV
                     * FIXME, should be a proper length calculation
                     */
                     /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x48, 22))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x49, 32))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x4a, 20))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x4b, 3))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x4c, 17))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x54, 12))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x55, 4))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x56, 20))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x57, 8))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x5a, 25))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x5b, 16))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x5c, 24))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x5d, 26))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x5e, 2))
                    /* pass */ ;
                /*
                 * Not in [TSIP]. the TSIP driver doesn't use type 0x5f.
                 * but we test for it so as to avoid setting packet not_tsip
                 */
                else if (TSIP_ID_AND_LENGTH(0x5f, 66))
                    /*
                     * 0x6c data length 18+numSV, total packetlen is 22+numSV
                     * numSV up to 224
                     */
                    /* pass */ ;
                else if ((0x6c == pkt_id)
                         && ((22 <= packetlen) && (246 >= packetlen)))
                    /*
                     * 0x6d data length 17+numSV, total packetlen is 21+numSV
                     * numSV up to 32
                     */
                    /* pass */ ;
                else if ((0x6d == pkt_id)
                         && ((21 <= packetlen) && (53 >= packetlen)))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x82, 1))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x83, 36))
                    /* pass */ ;
                else if (TSIP_ID_AND_LENGTH(0x84, 36))
                    /* pass */ ;
                /* super packets, variable length */
                else if (0x8f == pkt_id)
                    /* pass */ ;
                /*
                 * This is according to [TSIP].
                 */
                else if (TSIP_ID_AND_LENGTH(0xbb, 40))
                    /* pass */ ;
                /*
                 * The Accutime Gold ships a version of this packet with a
                 * 43-byte payload.  We only use the first 21 bytes, and
                 * parts after byte 27 are padding.
                 */
                else if (TSIP_ID_AND_LENGTH(0xbb, 43))
                    /* pass */ ;
                else {
                    /* pass */ ;
                    GPSD_LOG(LOG_IO, &lexer->errout,
                             "TSIP REJECT pkt_id = %#02x, packetlen= %zu\n",
                             pkt_id, packetlen);
                    goto not_tsip;
                }
#undef TSIP_ID_AND_LENGTH
                /* Debug */
                GPSD_LOG(LOG_RAW, &lexer->errout,
                         "TSIP pkt_id = %#02x, packetlen= %zu\n",
                         pkt_id, packetlen);
                packet_accept(lexer, TSIP_PACKET);
                packet_discard(lexer);
                break;
              not_tsip:
                GPSD_LOG(LOG_RAW + 1, &lexer->errout, "Not a TSIP packet\n");
                /*
                 * More attempts to recognize ambiguous TSIP-like
                 * packet types could go here.
                 */
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
                packet_discard(lexer);
                break;
#endif /* TSIP_ENABLE */
            }
        }
#endif /* TSIP_ENABLE || GARMIN_ENABLE */
#ifdef RTCM104V3_ENABLE
        else if (lexer->state == RTCM3_RECOGNIZED) {
            if (crc24q_check(lexer->inbuffer,
                             lexer->inbufptr - lexer->inbuffer)) {
                packet_accept(lexer, RTCM3_PACKET);
            } else {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "RTCM3 data checksum failure, "
                         "%0x against %02x %02x %02x\n",
                         crc24q_hash(lexer->inbuffer,
                                     lexer->inbufptr - lexer->inbuffer -
                                     3), lexer->inbufptr[-3],
                         lexer->inbufptr[-2], lexer->inbufptr[-1]);
                packet_accept(lexer, BAD_PACKET);
            }
            packet_discard(lexer);
            lexer->state = GROUND_STATE;
            break;
        }
#endif /* RTCM104V3_ENABLE */
#ifdef ZODIAC_ENABLE
        else if (lexer->state == ZODIAC_RECOGNIZED) {
            unsigned len, n;
            short sum;

            // be paranoid, look ahead for a good checksum
            len = getzuword(2);
            if (253 < len) {
                // pacify coverity, 253 seems to be max length
                len = 253;
            }
            for (n = sum = 0; n < len; n++)
                sum += getzword(5 + n);
            sum *= -1;
            if (len == 0 || sum == getzword(5 + len)) {
                packet_accept(lexer, ZODIAC_PACKET);
            } else {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "Zodiac data checksum 0x%x over length %u, "
                         "expecting 0x%x\n",
                         sum, len, getzword(5 + len));
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
            packet_discard(lexer);
            break;
        }
#endif /* ZODIAC_ENABLE */
#ifdef UBLOX_ENABLE
        else if (lexer->state == UBX_RECOGNIZED) {
            /* UBX use a TCP like checksum */
            int n, len;
            unsigned char ck_a = (unsigned char)0;
            unsigned char ck_b = (unsigned char)0;
            len = lexer->inbufptr - lexer->inbuffer;
            GPSD_LOG(LOG_IO, &lexer->errout, "UBX: len %d\n", len);
            for (n = 2; n < (len - 2); n++) {
                ck_a += lexer->inbuffer[n];
                ck_b += ck_a;
            }
            if (ck_a == lexer->inbuffer[len - 2] &&
                ck_b == lexer->inbuffer[len - 1])
                packet_accept(lexer, UBX_PACKET);
            else {
                GPSD_LOG(LOG_IO, &lexer->errout, 
                         "UBX checksum 0x%02hhx%02hhx over length %d,"
                         " expecting 0x%02hhx%02hhx (type 0x%02hhx%02hhx)\n",
                         ck_a,
                         ck_b,
                         len,
                         lexer->inbuffer[len - 2],
                         lexer->inbuffer[len - 1],
                         lexer->inbuffer[2], lexer->inbuffer[3]);
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
            packet_discard(lexer);
            break;
        }
#endif /* UBLOX_ENABLE */
#ifdef EVERMORE_ENABLE
        else if (lexer->state == EVERMORE_RECOGNIZED) {
            unsigned int n, crc, checksum, len;
            n = 0;
            if (lexer->inbuffer[n++] != DLE)
                goto not_evermore;
            if (lexer->inbuffer[n++] != STX)
                goto not_evermore;
            len = lexer->inbuffer[n++];
            if (len == DLE) {
                if (lexer->inbuffer[n++] != DLE)
                    goto not_evermore;
            }
            len -= 2;
            crc = 0;
            for (; len > 0; len--) {
                crc += lexer->inbuffer[n];
                if (lexer->inbuffer[n++] == DLE) {
                    if (lexer->inbuffer[n++] != DLE)
                        goto not_evermore;
                }
            }
            checksum = lexer->inbuffer[n++];
            if (checksum == DLE) {
                if (lexer->inbuffer[n++] != DLE)
                    goto not_evermore;
            }
            if (lexer->inbuffer[n++] != DLE)
                goto not_evermore;
            /* we used to say n++ here, but scan-build complains */
            if (lexer->inbuffer[n] != ETX)
                goto not_evermore;
            crc &= 0xff;
            if (crc != checksum) {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "EverMore checksum failed: %02x != %02x\n",
                         crc, checksum);
                goto not_evermore;
            }
            packet_accept(lexer, EVERMORE_PACKET);
            packet_discard(lexer);
            break;
          not_evermore:
            packet_accept(lexer, BAD_PACKET);
            lexer->state = GROUND_STATE;
            packet_discard(lexer);
            break;
        }
#endif /* EVERMORE_ENABLE */
/* XXX CSK */
#ifdef ITRAX_ENABLE
#define getib(j) ((uint8_t)lexer->inbuffer[(j)])
#define getiw(i) ((uint16_t)(((uint16_t)getib((i)+1) << 8) | \
                             (uint16_t)getib((i))))

        else if (lexer->state == ITALK_RECOGNIZED) {
            volatile uint16_t len, n, csum, xsum;

            /* number of words */
            len = (uint16_t) (lexer->inbuffer[6] & 0xff);

            /* expected checksum */
            xsum = getiw(7 + 2 * len);


            csum = 0;
            for (n = 0; n < len; n++) {
                volatile uint16_t tmpw = getiw(7 + 2 * n);
                volatile uint32_t tmpdw  = (csum + 1) * (tmpw + n);
                csum ^= (tmpdw & 0xffff) ^ ((tmpdw >> 16) & 0xffff);
            }
            if (len == 0 || csum == xsum)
                packet_accept(lexer, ITALK_PACKET);
            else {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "ITALK: checksum failed - "
                         "type 0x%02x expected 0x%04x got 0x%04x\n",
                         lexer->inbuffer[4], xsum, csum);
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
            packet_discard(lexer);
            break;
        }
#undef getiw
#undef getib
#endif /* ITRAX_ENABLE */
#ifdef NAVCOM_ENABLE
        else if (lexer->state == NAVCOM_RECOGNIZED) {
            /* By the time we got here we know checksum is OK */
            packet_accept(lexer, NAVCOM_PACKET);
            packet_discard(lexer);
            break;
        }
#endif /* NAVCOM_ENABLE */
#ifdef GEOSTAR_ENABLE
        else if (lexer->state == GEOSTAR_RECOGNIZED) {
            /* GeoStar uses a XOR 32bit checksum */
            int n, len;
            unsigned int cs = 0L;
            len = lexer->inbufptr - lexer->inbuffer;

            /* Calculate checksum */
            for (n = 0; n < len; n += 4) {
                cs ^= getleu32(lexer->inbuffer, n);
            }

            if (cs == 0)
                packet_accept(lexer, GEOSTAR_PACKET);
            else {
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "GeoStar checksum failed 0x%x over length %d\n",
                         cs, len);
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
            packet_discard(lexer);
            break;
        }
#endif /* GEOSTAR_ENABLE */
#ifdef GREIS_ENABLE
        else if (lexer->state == GREIS_RECOGNIZED) {
            int len = lexer->inbufptr - lexer->inbuffer;

            if (lexer->inbuffer[0] == 'R' && lexer->inbuffer[1] == 'E') {
                /* Replies don't have checksum */
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "Accept GREIS reply packet len %d\n", len);
                packet_accept(lexer, GREIS_PACKET);
            } else if (lexer->inbuffer[0] == 'E' && lexer->inbuffer[1] == 'R') {
                /* Error messages don't have checksum */
                GPSD_LOG(LOG_IO, &lexer->errout,
                         "Accept GREIS error packet len %d\n", len);
                packet_accept(lexer, GREIS_PACKET);
            } else {
                unsigned char expected_cs = lexer->inbuffer[len - 1];
                unsigned char cs = greis_checksum(lexer->inbuffer, len - 1);

                if (cs == expected_cs) {
                    GPSD_LOG(LOG_IO, &lexer->errout,
                             "Accept GREIS packet type '%c%c' len %d\n",
                             lexer->inbuffer[0], lexer->inbuffer[1], len);
                    packet_accept(lexer, GREIS_PACKET);
                } else {
                    /*
                     * Print hex instead of raw characters, since they might be
                     * unprintable. If \0, it will even mess up the log output.
                     */
                    GPSD_LOG(LOG_IO, &lexer->errout,
                             "REJECT GREIS len %d."
                             " Bad checksum %#02x, expecting %#02x."
                             " Packet type in hex: 0x%02x%02x",
                             len, cs, expected_cs, lexer->inbuffer[0],
                             lexer->inbuffer[1]);
                    packet_accept(lexer, BAD_PACKET);
                    /* got this far, fair to expect we will get more GREIS */
                    lexer->state = GREIS_EXPECTED;
                }
            }
            packet_discard(lexer);
            break;
        }
#endif /* GREIS_ENABLE */
#ifdef RTCM104V2_ENABLE
        else if (lexer->state == RTCM2_RECOGNIZED) {
            /*
             * RTCM packets don't have checksums.  The six bits of parity
             * per word and the preamble better be good enough.
             */
            packet_accept(lexer, RTCM2_PACKET);
            packet_discard(lexer);
            break;
        }
#endif /* RTCM104V2_ENABLE */
#ifdef GARMINTXT_ENABLE
        else if (lexer->state == GTXT_RECOGNIZED) {
            size_t packetlen = lexer->inbufptr - lexer->inbuffer;
            if (57 <= packetlen) {
                packet_accept(lexer, GARMINTXT_PACKET);
                packet_discard(lexer);
                lexer->state = GROUND_STATE;
                break;
            } else {
                packet_accept(lexer, BAD_PACKET);
                lexer->state = GROUND_STATE;
            }
        }
#endif
#ifdef PASSTHROUGH_ENABLE
        else if (lexer->state == JSON_RECOGNIZED) {
            size_t packetlen = lexer->inbufptr - lexer->inbuffer;
            if (packetlen >= 11)
                /* {"class": } */
                packet_accept(lexer, JSON_PACKET);
            else
                packet_accept(lexer, BAD_PACKET);
            packet_discard(lexer);
            lexer->state = GROUND_STATE;
            break;
        }
#endif /* PASSTHROUGH_ENABLE */
#ifdef STASH_ENABLE
        else if (lexer->state == STASH_RECOGNIZED) {
            packet_stash(lexer);
            packet_discard(lexer);
        }
#endif /* STASH_ENABLE */
    }                           /* while */
}

ssize_t packet_get(int fd, struct gps_lexer_t *lexer)
/* grab a packet; return -1=>I/O error, 0=>EOF, or a length */
{
    ssize_t recvd;

    errno = 0;
    /* O_NONBLOCK set, so this should not block.
     * Best not to block on an unresponsive GNSS receiver */
    recvd = read(fd, lexer->inbuffer + lexer->inbuflen,
                 sizeof(lexer->inbuffer) - (lexer->inbuflen));
    if (recvd == -1) {
        if ((errno == EAGAIN) || (errno == EINTR)) {
            GPSD_LOG(LOG_RAW + 2, &lexer->errout, "no bytes ready\n");
            recvd = 0;
            /* fall through, input buffer may be nonempty */
        } else {
            GPSD_LOG(LOG_RAW + 2, &lexer->errout,
                     "errno: %s\n", strerror(errno));
            return -1;
        }
    } else {
        if (lexer->errout.debug >= LOG_RAW + 1) {
            char scratchbuf[MAX_PACKET_LENGTH*4+1];
            GPSD_LOG(LOG_RAW + 1, &lexer->errout,
                     "Read %zd chars to buffer offset %zd (total %zd): %s\n",
                     recvd, lexer->inbuflen, lexer->inbuflen + recvd,
                     gpsd_packetdump(scratchbuf, sizeof(scratchbuf),
                                     (char *)lexer->inbufptr, (size_t) recvd));
        }
        lexer->inbuflen += recvd;
    }
    GPSD_LOG(LOG_SPIN, &lexer->errout,
             "packet_get() fd %d -> %zd (%d)\n",
             fd, recvd, errno);

    /*
     * Bail out, indicating no more input, only if we just received
     * nothing from the device and there is nothing waiting in the
     * packet input buffer.
     */
    if (recvd <= 0 && packet_buffered_input(lexer) <= 0)
        return recvd;

    /* Otherwise, consume from the packet input buffer */
    /* coverity[tainted_data] */
    packet_parse(lexer);

    /* if input buffer is full, discard */
    if (sizeof(lexer->inbuffer) == (lexer->inbuflen)) {
        /* coverity[tainted_data] */
        packet_discard(lexer);
        lexer->state = GROUND_STATE;
    }

    /*
     * If we gathered a packet, return its length; it will have been
     * consumed out of the input buffer and moved to the output
     * buffer.  We don't care whether the read() returned 0 or -1 and
     * gathered packet data was all buffered or whether it was partly
     * just physically read.
     *
     * Note: this choice greatly simplifies life for callers of
     * packet_get(), but means that they cannot tell when a nonzero
     * return means there was a successful physical read.  They will
     * thus credit a data source that drops out with being alive
     * slightly longer than it actually was.  This is unlikely to
     * matter as long as any policy timeouts are large compared to
     * the time required to consume the greatest possible amount
     * of buffered input, but if you hack this code you need to
     * be aware of the issue. It might also slightly affect
     * performance profiling.
     */
    if (lexer->outbuflen > 0)
        return (ssize_t) lexer->outbuflen;
    else
        /*
         * Otherwise recvd is the size of whatever packet fragment we got.
         * It can still be 0 or -1 at this point even if buffer data
         * was consumed.
         */
        return recvd;
}

void packet_reset(struct gps_lexer_t *lexer)
/* return the packet machine to the ground state */
{
    lexer->type = BAD_PACKET;
    lexer->state = GROUND_STATE;
    lexer->inbuflen = 0;
    lexer->inbufptr = lexer->inbuffer;
#ifdef BINARY_ENABLE
    isgps_init(lexer);
#endif /* BINARY_ENABLE */
#ifdef STASH_ENABLE
    lexer->stashbuflen = 0;
#endif /* STASH_ENABLE */
}


#ifdef __UNUSED__
/* push back the last packet grabbed */
void packet_pushback(struct gps_lexer_t *lexer)
{
    if (lexer->outbuflen + lexer->inbuflen < MAX_PACKET_LENGTH) {
        memmove(lexer->inbuffer + lexer->outbuflen,
                lexer->inbuffer, lexer->inbuflen);
        memmove(lexer->inbuffer, lexer->outbuffer, lexer->outbuflen);
        lexer->inbuflen += lexer->outbuflen;
        lexer->inbufptr += lexer->outbuflen;
        lexer->outbuflen = 0;
    }
}
#endif /* __UNUSED */

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