Initial Commit

1 files changed, 835 insertions, 0 deletions

diff --git a/libloragw/src/loragw_gps.c b/libloragw/src/loragw_gps.c
new file mode 100644
index 0000000..c0e0ded
--- /dev/null
+++ b/libloragw/src/loragw_gps.c
@@ -0,0 +1,835 @@
+/*
+ / _____)             _              | |
+( (____  _____ ____ _| |_ _____  ____| |__
+ \____ \| ___ |    (_   _) ___ |/ ___)  _ \
+ _____) ) ____| | | || |_| ____( (___| | | |
+(______/|_____)_|_|_| \__)_____)\____)_| |_|
+  (C)2013 Semtech-Cycleo
+
+Description:
+    Library of functions to manage a GNSS module (typically GPS) for accurate
+    timestamping of packets and synchronisation of gateways.
+    A limited set of module brands/models are supported.
+
+License: Revised BSD License, see LICENSE.TXT file include in the project
+Maintainer: Michael Coracin
+*/
+
+
+/* -------------------------------------------------------------------------- */
+/* --- DEPENDANCIES --------------------------------------------------------- */
+
+#define _GNU_SOURCE     /* needed for qsort_r to be defined */
+#include <stdint.h>     /* C99 types */
+#include <stdbool.h>    /* bool type */
+#include <stdio.h>      /* printf fprintf */
+#include <string.h>     /* memcpy */
+
+#include <time.h>       /* struct timespec */
+#include <fcntl.h>      /* open */
+#include <termios.h>    /* tcflush */
+#include <math.h>       /* modf */
+
+#include <stdlib.h>
+
+#include "loragw_gps.h"
+
+/* -------------------------------------------------------------------------- */
+/* --- PRIVATE MACROS ------------------------------------------------------- */
+
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
+#if DEBUG_GPS == 1
+    #define DEBUG_MSG(args...)  fprintf(stderr, args)
+    #define DEBUG_ARRAY(a,b,c)  for(a=0;a<b;++a) fprintf(stderr,"%x.",c[a]);fprintf(stderr,"end\n")
+    #define CHECK_NULL(a)       if(a==NULL){fprintf(stderr,"%s:%d: ERROR: NULL POINTER AS ARGUMENT\n", __FUNCTION__, __LINE__);return LGW_GPS_ERROR;}
+#else
+    #define DEBUG_MSG(args...)
+    #define DEBUG_ARRAY(a,b,c)  for(a=0;a!=0;){}
+    #define CHECK_NULL(a)       if(a==NULL){return LGW_GPS_ERROR;}
+#endif
+#define TRACE()         fprintf(stderr, "@ %s %d\n", __FUNCTION__, __LINE__);
+
+/* -------------------------------------------------------------------------- */
+/* --- PRIVATE CONSTANTS ---------------------------------------------------- */
+
+#define TS_CPS              1E6 /* count-per-second of the timestamp counter */
+#define PLUS_10PPM          1.00001
+#define MINUS_10PPM         0.99999
+#define DEFAULT_BAUDRATE    B9600
+
+#define UBX_MSG_NAVTIMEGPS_LEN  16
+
+/* -------------------------------------------------------------------------- */
+/* --- PRIVATE VARIABLES ---------------------------------------------------- */
+
+
+/* result of the NMEA parsing */
+static short gps_yea = 0; /* year (2 or 4 digits) */
+static short gps_mon = 0; /* month (1-12) */
+static short gps_day = 0; /* day of the month (1-31) */
+static short gps_hou = 0; /* hours (0-23) */
+static short gps_min = 0; /* minutes (0-59) */
+static short gps_sec = 0; /* seconds (0-60)(60 is for leap second) */
+static float gps_fra = 0.0; /* fractions of seconds (<1) */
+static bool gps_time_ok = false;
+static int16_t gps_week = 0; /* GPS week number of the navigation epoch */
+static uint32_t gps_iTOW = 0; /* GPS time of week in milliseconds */
+static int32_t gps_fTOW = 0; /* Fractional part of iTOW (+/-500000) in nanosec */
+
+static short gps_dla = 0; /* degrees of latitude */
+static double gps_mla = 0.0; /* minutes of latitude */
+static char gps_ola = 0; /* orientation (N-S) of latitude */
+static short gps_dlo = 0; /* degrees of longitude */
+static double gps_mlo = 0.0; /* minutes of longitude */
+static char gps_olo = 0; /* orientation (E-W) of longitude */
+static short gps_alt = 0; /* altitude */
+static bool gps_pos_ok = false;
+
+static char gps_mod = 'N'; /* GPS mode (N no fix, A autonomous, D differential) */
+static short gps_sat = 0; /* number of satellites used for fix */
+
+static struct termios ttyopt_restore;
+
+/* -------------------------------------------------------------------------- */
+/* --- PRIVATE FUNCTIONS DECLARATION ---------------------------------------- */
+
+static int nmea_checksum(const char *nmea_string, int buff_size, char *checksum);
+
+static char nibble_to_hexchar(uint8_t a);
+
+static bool validate_nmea_checksum(const char *serial_buff, int buff_size);
+
+static bool match_label(const char *s, char *label, int size, char wildcard);
+
+static int str_chop(char *s, int buff_size, char separator, int *idx_ary, int max_idx);
+
+/* -------------------------------------------------------------------------- */
+/* --- PRIVATE FUNCTIONS DEFINITION ----------------------------------------- */
+
+/*
+Calculate the checksum for a NMEA string
+Skip the first '$' if necessary and calculate checksum until '*' character is
+reached (or buff_size exceeded).
+Checksum must point to a 2-byte (or more) char array.
+Return position of the checksum in the string
+*/
+static int nmea_checksum(const char *nmea_string, int buff_size, char *checksum) {
+    int i = 0;
+    uint8_t check_num = 0;
+
+    /* check input parameters */
+    if ((nmea_string == NULL) ||  (checksum == NULL) || (buff_size <= 1)) {
+        DEBUG_MSG("Invalid parameters for nmea_checksum\n");
+        return -1;
+    }
+
+    /* skip the first '$' if necessary */
+    if (nmea_string[i] == '$') {
+        i += 1;
+    }
+
+    /* xor until '*' or max length is reached */
+    while (nmea_string[i] != '*') {
+        check_num ^= nmea_string[i];
+        i += 1;
+        if (i >= buff_size) {
+            DEBUG_MSG("Maximum length reached for nmea_checksum\n");
+            return -1;
+        }
+    }
+
+    /* Convert checksum value to 2 hexadecimal characters */
+    checksum[0] = nibble_to_hexchar(check_num / 16); /* upper nibble */
+    checksum[1] = nibble_to_hexchar(check_num % 16); /* lower nibble */
+
+    return i + 1;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+static char nibble_to_hexchar(uint8_t a) {
+    if (a < 10) {
+        return '0' + a;
+    } else if (a < 16) {
+        return 'A' + (a-10);
+    } else {
+        return '?';
+    }
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+/*
+Calculate the checksum of a NMEA frame and compare it to the checksum that is
+present at the end of it.
+Return true if it matches
+*/
+static bool validate_nmea_checksum(const char *serial_buff, int buff_size) {
+    int checksum_index;
+    char checksum[2]; /* 2 characters to calculate NMEA checksum */
+
+    checksum_index = nmea_checksum(serial_buff, buff_size, checksum);
+
+    /* could we calculate a verification checksum ? */
+    if (checksum_index < 0) {
+        DEBUG_MSG("ERROR: IMPOSSIBLE TO PARSE NMEA SENTENCE\n");
+        return false;
+    }
+
+    /* check if there are enough char in the serial buffer to read checksum */
+    if (checksum_index >= (buff_size - 2)) {
+        DEBUG_MSG("ERROR: IMPOSSIBLE TO READ NMEA SENTENCE CHECKSUM\n");
+        return false;
+    }
+
+    /* check the checksum per se */
+    if ((serial_buff[checksum_index] == checksum[0]) && (serial_buff[checksum_index+1] == checksum[1])) {
+        return true;
+    } else {
+        DEBUG_MSG("ERROR: NMEA CHECKSUM %c%c DOESN'T MATCH VERIFICATION CHECKSUM %c%c\n", serial_buff[checksum_index], serial_buff[checksum_index+1], checksum[0], checksum[1]);
+        return false;
+    }
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+/*
+Return true if the "label" string (can contain wildcard characters) matches
+the begining of the "s" string
+*/
+static bool match_label(const char *s, char *label, int size, char wildcard) {
+    int i;
+
+    for (i=0; i < size; i++) {
+        if (label[i] == wildcard) continue;
+        if (label[i] != s[i]) return false;
+    }
+    return true;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+/*
+Chop a string into smaller strings
+Replace every separator in the input character buffer by a null character so
+that all s[index] are valid strings.
+Populate an array of integer 'idx_ary' representing indexes of token in the
+string.
+buff_size and max_idx are there to prevent segfaults.
+Return the number of token found (number of idx_ary filled).
+*/
+int str_chop(char *s, int buff_size, char separator, int *idx_ary, int max_idx) {
+    int i = 0; /* index in the string */
+    int j = 0; /* index in the result array */
+
+    if ((s == NULL) || (buff_size < 0) || (separator == 0) || (idx_ary == NULL) || (max_idx < 0)) {
+        /* unsafe to do anything */
+        return -1;
+    }
+    if ((buff_size == 0) || (max_idx == 0)) {
+        /* nothing to do */
+        return 0;
+    }
+    s[buff_size - 1] = 0; /* add string terminator at the end of the buffer, just to be sure */
+    idx_ary[j] = 0;
+    j += 1;
+    /* loop until string terminator is reached */
+    while (s[i] != 0) {
+        if (s[i] == separator) {
+            s[i] = 0; /* replace separator by string terminator */
+            if (j >= max_idx) { /* no more room in the index array */
+                return j;
+            }
+            idx_ary[j] = i+1; /* next token start after replaced separator */
+            ++j;
+        }
+        ++i;
+    }
+    return j;
+}
+
+/* -------------------------------------------------------------------------- */
+/* --- PUBLIC FUNCTIONS DEFINITION ------------------------------------------ */
+
+int lgw_gps_enable(char *tty_path, char *gps_family, speed_t target_brate, int *fd_ptr) {
+    int i;
+    struct termios ttyopt; /* serial port options */
+    int gps_tty_dev; /* file descriptor to the serial port of the GNSS module */
+    uint8_t ubx_cmd_timegps[UBX_MSG_NAVTIMEGPS_LEN] = {
+                    0xB5, 0x62, /* UBX Sync Chars */
+                    0x06, 0x01, /* CFG-MSG Class/ID */
+                    0x08, 0x00, /* Payload length */
+                    0x01, 0x20, 0x00, 0x01, 0x01, 0x00, 0x00, 0x00, /* Enable NAV-TIMEGPS output on serial */
+                    0x32, 0x94 }; /* Checksum */
+    ssize_t num_written;
+
+    /* check input parameters */
+    CHECK_NULL(tty_path);
+    CHECK_NULL(fd_ptr);
+
+    /* open TTY device */
+    gps_tty_dev = open(tty_path, O_RDWR | O_NOCTTY);
+    if (gps_tty_dev <= 0) {
+        DEBUG_MSG("ERROR: TTY PORT FAIL TO OPEN, CHECK PATH AND ACCESS RIGHTS\n");
+        return LGW_GPS_ERROR;
+    }
+    *fd_ptr = gps_tty_dev;
+
+    /* manage the different GPS modules families */
+    if (gps_family == NULL) {
+        DEBUG_MSG("WARNING: this version of GPS module may not be supported\n");
+    } else if (strncmp(gps_family, "ubx7", 4) != 0) {
+        /* The current implementation relies on proprietary messages from U-Blox */
+        /* GPS modules (UBX, NAV-TIMEGPS...) and has only be tested with a u-blox 7. */
+        /* Those messages allow to get NATIVE GPS time (no leap seconds) required */
+        /* for class-B handling and GPS synchronization */
+        /* see lgw_parse_ubx() function for details */
+        DEBUG_MSG("WARNING: this version of GPS module may not be supported\n");
+    }
+
+    /* manage the target bitrate */
+    if (target_brate != 0) {
+        DEBUG_MSG("WARNING: target_brate parameter ignored for now\n"); // TODO
+    }
+
+    /* get actual serial port configuration */
+    i = tcgetattr(gps_tty_dev, &ttyopt);
+    if (i != 0) {
+        DEBUG_MSG("ERROR: IMPOSSIBLE TO GET TTY PORT CONFIGURATION\n");
+        return LGW_GPS_ERROR;
+    }
+
+    /* Save current serial port configuration for restoring later */
+    memcpy(&ttyopt_restore, &ttyopt, sizeof ttyopt);
+
+    /* update baudrates */
+    cfsetispeed(&ttyopt, DEFAULT_BAUDRATE);
+    cfsetospeed(&ttyopt, DEFAULT_BAUDRATE);
+
+    /* update terminal parameters */
+    /* The following configuration should allow to:
+            - Get ASCII NMEA messages
+            - Get UBX binary messages
+            - Send UBX binary commands
+        Note: as binary data have to be read/written, we need to disable
+              various character processing to avoid loosing data */
+    /* Control Modes */
+    ttyopt.c_cflag |= CLOCAL;  /* local connection, no modem control */
+    ttyopt.c_cflag |= CREAD;   /* enable receiving characters */
+    ttyopt.c_cflag |= CS8;     /* 8 bit frames */
+    ttyopt.c_cflag &= ~PARENB; /* no parity */
+    ttyopt.c_cflag &= ~CSTOPB; /* one stop bit */
+    /* Input Modes */
+    ttyopt.c_iflag |= IGNPAR;  /* ignore bytes with parity errors */
+    ttyopt.c_iflag &= ~ICRNL;  /* do not map CR to NL on input*/
+    ttyopt.c_iflag &= ~IGNCR;  /* do not ignore carriage return on input */
+    ttyopt.c_iflag &= ~IXON;   /* disable Start/Stop output control */
+    ttyopt.c_iflag &= ~IXOFF;  /* do not send Start/Stop characters */
+    /* Output Modes */
+    ttyopt.c_oflag = 0;        /* disable everything on output as we only write binary */
+    /* Local Modes */
+    ttyopt.c_lflag &= ~ICANON; /* disable canonical input - cannot use with binary input */
+    ttyopt.c_lflag &= ~ISIG;   /* disable check for INTR, QUIT, SUSP special characters */
+    ttyopt.c_lflag &= ~IEXTEN; /* disable any special control character */
+    ttyopt.c_lflag &= ~ECHO;   /* do not echo back every character typed */
+    ttyopt.c_lflag &= ~ECHOE;  /* does not erase the last character in current line */
+    ttyopt.c_lflag &= ~ECHOK;  /* do not echo NL after KILL character */
+
+    /* settings for non-canonical mode
+       read will block for until the lesser of VMIN or requested chars have been received */
+    ttyopt.c_cc[VMIN]  = LGW_GPS_MIN_MSG_SIZE;
+    ttyopt.c_cc[VTIME] = 0;
+
+    /* set new serial ports parameters */
+    i = tcsetattr(gps_tty_dev, TCSANOW, &ttyopt);
+    if (i != 0){
+        DEBUG_MSG("ERROR: IMPOSSIBLE TO UPDATE TTY PORT CONFIGURATION\n");
+        return LGW_GPS_ERROR;
+    }
+    tcflush(gps_tty_dev, TCIOFLUSH);
+
+    /* Send UBX CFG NAV-TIMEGPS message to tell GPS module to output native GPS time */
+    /* This is a binary message, serial port has to be properly configured to handle this */
+    num_written = write (gps_tty_dev, ubx_cmd_timegps, UBX_MSG_NAVTIMEGPS_LEN);
+    if (num_written != UBX_MSG_NAVTIMEGPS_LEN) {
+        DEBUG_MSG("ERROR: Failed to write on serial port (written=%d)\n", (int) num_written);
+    }
+
+    /* get timezone info */
+    tzset();
+
+    /* initialize global variables */
+    gps_time_ok = false;
+    gps_pos_ok = false;
+    gps_mod = 'N';
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_gps_disable(int fd) {
+    int i;
+
+    /* restore serial ports parameters */
+    i = tcsetattr(fd, TCSANOW, &ttyopt_restore);
+    if (i != 0){
+        DEBUG_MSG("ERROR: IMPOSSIBLE TO RESTORE TTY PORT CONFIGURATION\n");
+        return LGW_GPS_ERROR;
+    }
+    tcflush(fd, TCIOFLUSH);
+
+    i = close(fd);
+    if (i <= 0) {
+        DEBUG_MSG("ERROR: TTY PORT FAIL TO CLOSE\n");
+        return LGW_GPS_ERROR;
+    }
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+enum gps_msg lgw_parse_ubx(const char *serial_buff, size_t buff_size, size_t *msg_size) {
+    bool valid = 0;    /* iTOW, fTOW and week validity */
+    unsigned int payload_length;
+    uint8_t ck_a, ck_b;
+    uint8_t ck_a_rcv, ck_b_rcv;
+    unsigned int i;
+
+    *msg_size = 0; /* ensure msg_size alway receives a value */
+
+    /* check input parameters */
+    if (serial_buff == NULL) {
+        return IGNORED;
+    }
+    if (buff_size < 8) {
+        DEBUG_MSG("ERROR: TOO SHORT TO BE A VALID UBX MESSAGE\n");
+        return IGNORED;
+    }
+
+    /* display received serial data and checksum */
+    DEBUG_MSG("Note: parsing UBX frame> ");
+    for (i=0; i<buff_size; i++) {
+        DEBUG_MSG("%02x ", serial_buff[i]);
+    }
+    DEBUG_MSG("\n");
+
+    /* Check for UBX sync chars 0xB5 0x62 */
+    if ((serial_buff[0] == (char)0xB5) && (serial_buff[1] == (char)0x62)) {
+
+        /* Get payload length to compute message size */
+        payload_length  = (uint8_t)serial_buff[4];
+        payload_length |= (uint8_t)serial_buff[5] << 8;
+        *msg_size = 6 + payload_length + 2; /* header + payload + checksum */
+
+        /* check for complete message in buffer */
+        if(*msg_size <= buff_size) {
+            /* Validate checksum of message */
+            ck_a_rcv = serial_buff[*msg_size-2]; /* received checksum */
+            ck_b_rcv = serial_buff[*msg_size-1]; /* received checksum */
+            /* Use 8-bit Fletcher Algorithm to compute checksum of actual payload */
+            ck_a = 0; ck_b = 0;
+            for (i=0; i<(4 + payload_length); i++) {
+                ck_a = ck_a + serial_buff[i+2];
+                ck_b = ck_b + ck_a;
+            }
+
+            /* Compare checksums and parse if OK */
+            if ((ck_a == ck_a_rcv) && (ck_b == ck_b_rcv)) {
+                /* Check for Class 0x01 (NAV) and ID 0x20 (NAV-TIMEGPS) */
+                if ((serial_buff[2] == 0x01) && (serial_buff[3] == 0x20)) {
+                    /* Check validity of information */
+                    valid = serial_buff[17] & 0x3; /* towValid, weekValid */
+                    if (valid) {
+                        /* Parse buffer to extract GPS time */
+                        /* Warning: payload byte ordering is Little Endian */
+                        gps_iTOW =  (uint8_t)serial_buff[6];
+                        gps_iTOW |= (uint8_t)serial_buff[7] << 8;
+                        gps_iTOW |= (uint8_t)serial_buff[8] << 16;
+                        gps_iTOW |= (uint8_t)serial_buff[9] << 24; /* GPS time of week, in ms */
+
+                        gps_fTOW =  (uint8_t)serial_buff[10];
+                        gps_fTOW |= (uint8_t)serial_buff[11] << 8;
+                        gps_fTOW |= (uint8_t)serial_buff[12] << 16;
+                        gps_fTOW |= (uint8_t)serial_buff[13] << 24; /* Fractional part of iTOW, in ns */
+
+                        gps_week =  (uint8_t)serial_buff[14];
+                        gps_week |= (uint8_t)serial_buff[15] << 8; /* GPS week number */
+
+                        gps_time_ok = true;
+#if 0
+                        /* For debug */
+                        {
+                            short ubx_gps_hou = 0; /* hours (0-23) */
+                            short ubx_gps_min = 0; /* minutes (0-59) */
+                            short ubx_gps_sec = 0; /* seconds (0-59) */
+
+                            /* Format GPS time in hh:mm:ss based on iTOW */
+                            ubx_gps_sec = (gps_iTOW / 1000) % 60;
+                            ubx_gps_min = (gps_iTOW / 1000 / 60) % 60;
+                            ubx_gps_hou = (gps_iTOW / 1000 / 60 / 60) % 24;
+                            printf("  GPS time = %02d:%02d:%02d\n", ubx_gps_hou, ubx_gps_min, ubx_gps_sec);
+                        }
+#endif
+                    } else { /* valid */
+                        gps_time_ok = false;
+                    }
+
+                    return UBX_NAV_TIMEGPS;
+                } else if ((serial_buff[2] == 0x05) && (serial_buff[3] == 0x00)) {
+                    DEBUG_MSG("NOTE: UBX ACK-NAK received\n");
+                    return IGNORED;
+                } else if ((serial_buff[2] == 0x05) && (serial_buff[3] == 0x01)) {
+                    DEBUG_MSG("NOTE: UBX ACK-ACK received\n");
+                    return IGNORED;
+                } else { /* not a supported message */
+                    DEBUG_MSG("ERROR: UBX message is not supported (%02x %02x)\n", serial_buff[2], serial_buff[3]);
+                    return IGNORED;
+                }
+            } else { /* checksum failed */
+                DEBUG_MSG("ERROR: UBX message is corrupted, checksum failed\n");
+                return INVALID;
+            }
+        } else { /* message contains less bytes than indicated by header */
+            DEBUG_MSG("ERROR: UBX message incomplete\n");
+            return INCOMPLETE;
+        }
+    } else { /* Not a UBX message */
+        /* Ignore messages which are not UBX ones for now */
+        return IGNORED;
+    }
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+enum gps_msg lgw_parse_nmea(const char *serial_buff, int buff_size) {
+    int i, j, k;
+    int str_index[30]; /* string index from the string chopping */
+    int nb_fields; /* number of strings detected by string chopping */
+    char parser_buf[256]; /* parsing modifies buffer so need a local copy */
+
+    /* check input parameters */
+    if (serial_buff == NULL) {
+        return UNKNOWN;
+    }
+
+    if(buff_size > (int)(sizeof(parser_buf) - 1)) {
+        DEBUG_MSG("Note: input string to big for parsing\n");
+        return INVALID;
+    }
+
+    /* look for some NMEA sentences in particular */
+    if (buff_size < 8) {
+        DEBUG_MSG("ERROR: TOO SHORT TO BE A VALID NMEA SENTENCE\n");
+        return UNKNOWN;
+    } else if (!validate_nmea_checksum(serial_buff, buff_size)) {
+        DEBUG_MSG("Warning: invalid NMEA sentence (bad checksum)\n");
+        return INVALID;
+    } else if (match_label(serial_buff, "$G?RMC", 6, '?')) {
+        /*
+        NMEA sentence format: $xxRMC,time,status,lat,NS,long,EW,spd,cog,date,mv,mvEW,posMode*cs<CR><LF>
+        Valid fix: $GPRMC,083559.34,A,4717.11437,N,00833.91522,E,0.004,77.52,091202,,,A*00
+        No fix: $GPRMC,,V,,,,,,,,,,N*00
+        */
+        memcpy(parser_buf, serial_buff, buff_size);
+        parser_buf[buff_size] = '\0';
+        nb_fields = str_chop(parser_buf, buff_size, ',', str_index, ARRAY_SIZE(str_index));
+        if (nb_fields != 13) {
+            DEBUG_MSG("Warning: invalid RMC sentence (number of fields)\n");
+            return IGNORED;
+        }
+        /* parse GPS status */
+        gps_mod = *(parser_buf + str_index[12]); /* get first character, no need to bother with sscanf */
+        if ((gps_mod != 'N') && (gps_mod != 'A') && (gps_mod != 'D')) {
+            gps_mod = 'N';
+        }
+        /* parse complete time */
+        i = sscanf(parser_buf + str_index[1], "%2hd%2hd%2hd%4f", &gps_hou, &gps_min, &gps_sec, &gps_fra);
+        j = sscanf(parser_buf + str_index[9], "%2hd%2hd%2hd", &gps_day, &gps_mon, &gps_yea);
+        if ((i == 4) && (j == 3)) {
+            if ((gps_mod == 'A') || (gps_mod == 'D')) {
+                gps_time_ok = true;
+                DEBUG_MSG("Note: Valid RMC sentence, GPS locked, date: 20%02d-%02d-%02dT%02d:%02d:%06.3fZ\n", gps_yea, gps_mon, gps_day, gps_hou, gps_min, gps_fra + (float)gps_sec);
+            } else {
+                gps_time_ok = false;
+                DEBUG_MSG("Note: Valid RMC sentence, no satellite fix, estimated date: 20%02d-%02d-%02dT%02d:%02d:%06.3fZ\n", gps_yea, gps_mon, gps_day, gps_hou, gps_min, gps_fra + (float)gps_sec);
+            }
+        } else {
+            /* could not get a valid hour AND date */
+            gps_time_ok = false;
+            DEBUG_MSG("Note: Valid RMC sentence, mode %c, no date\n", gps_mod);
+        }
+        return NMEA_RMC;
+    } else if (match_label(serial_buff, "$G?GGA", 6, '?')) {
+        /*
+        NMEA sentence format: $xxGGA,time,lat,NS,long,EW,quality,numSV,HDOP,alt,M,sep,M,diffAge,diffStation*cs<CR><LF>
+        Valid fix: $GPGGA,092725.00,4717.11399,N,00833.91590,E,1,08,1.01,499.6,M,48.0,M,,*5B
+        */
+        memcpy(parser_buf, serial_buff, buff_size);
+        parser_buf[buff_size] = '\0';
+        nb_fields = str_chop(parser_buf, buff_size, ',', str_index, ARRAY_SIZE(str_index));
+        if (nb_fields != 15) {
+            DEBUG_MSG("Warning: invalid GGA sentence (number of fields)\n");
+            return IGNORED;
+        }
+        /* parse number of satellites used for fix */
+        sscanf(parser_buf + str_index[7], "%hd", &gps_sat);
+        /* parse 3D coordinates */
+        i = sscanf(parser_buf + str_index[2], "%2hd%10lf", &gps_dla, &gps_mla);
+        gps_ola = *(parser_buf + str_index[3]);
+        j = sscanf(parser_buf + str_index[4], "%3hd%10lf", &gps_dlo, &gps_mlo);
+        gps_olo = *(parser_buf + str_index[5]);
+        k = sscanf(parser_buf + str_index[9], "%hd", &gps_alt);
+        if ((i == 2) && (j == 2) && (k == 1) && ((gps_ola=='N')||(gps_ola=='S')) && ((gps_olo=='E')||(gps_olo=='W'))) {
+            gps_pos_ok = true;
+            DEBUG_MSG("Note: Valid GGA sentence, %d sat, lat %02ddeg %06.3fmin %c, lon %03ddeg%06.3fmin %c, alt %d\n", gps_sat, gps_dla, gps_mla, gps_ola, gps_dlo, gps_mlo, gps_olo, gps_alt);
+        } else {
+            /* could not get a valid latitude, longitude AND altitude */
+            gps_pos_ok = false;
+            DEBUG_MSG("Note: Valid GGA sentence, %d sat, no coordinates\n", gps_sat);
+        }
+        return NMEA_GGA;
+    } else {
+        DEBUG_MSG("Note: ignored NMEA sentence\n"); /* quite verbose */
+        return IGNORED;
+    }
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_gps_get(struct timespec *utc, struct timespec *gps_time, struct coord_s *loc, struct coord_s *err) {
+    struct tm x;
+    time_t y;
+    double intpart, fractpart;
+
+    if (utc != NULL) {
+        if (!gps_time_ok) {
+            DEBUG_MSG("ERROR: NO VALID TIME TO RETURN\n");
+            return LGW_GPS_ERROR;
+        }
+        memset(&x, 0, sizeof(x));
+        if (gps_yea < 100) { /* 2-digits year, 20xx */
+            x.tm_year = gps_yea + 100; /* 100 years offset to 1900 */
+        } else { /* 4-digits year, Gregorian calendar */
+            x.tm_year = gps_yea - 1900;
+        }
+        x.tm_mon = gps_mon - 1; /* tm_mon is [0,11], gps_mon is [1,12] */
+        x.tm_mday = gps_day;
+        x.tm_hour = gps_hou;
+        x.tm_min = gps_min;
+        x.tm_sec = gps_sec;
+        y = mktime(&x) - timezone; /* need to substract timezone bc mktime assumes time vector is local time */
+        if (y == (time_t)(-1)) {
+            DEBUG_MSG("ERROR: FAILED TO CONVERT BROKEN-DOWN TIME\n");
+            return LGW_GPS_ERROR;
+        }
+        utc->tv_sec = y;
+        utc->tv_nsec = (int32_t)(gps_fra * 1e9);
+    }
+    if (gps_time != NULL) {
+        if (!gps_time_ok) {
+            DEBUG_MSG("ERROR: NO VALID TIME TO RETURN\n");
+            return LGW_GPS_ERROR;
+        }
+        fractpart = modf(((double)gps_iTOW / 1E3) + ((double)gps_fTOW / 1E9), &intpart);
+        /* Number of seconds since beginning on current GPS week */
+        gps_time->tv_sec = (time_t)intpart;
+        /* Number of seconds since GPS epoch 06.Jan.1980 */
+        gps_time->tv_sec += (time_t)gps_week * 604800; /* day*hours*minutes*secondes: 7*24*60*60; */
+        /* Fractional part in nanoseconds */
+        gps_time->tv_nsec = (long)(fractpart * 1E9);
+    }
+    if (loc != NULL) {
+        if (!gps_pos_ok) {
+            DEBUG_MSG("ERROR: NO VALID POSITION TO RETURN\n");
+            return LGW_GPS_ERROR;
+        }
+        loc->lat = ((double)gps_dla + (gps_mla/60.0)) * ((gps_ola == 'N')?1.0:-1.0);
+        loc->lon = ((double)gps_dlo + (gps_mlo/60.0)) * ((gps_olo == 'E')?1.0:-1.0);
+        loc->alt = gps_alt;
+    }
+    if (err != NULL) {
+        DEBUG_MSG("Warning: localization error processing not implemented yet\n");
+        err->lat = 0.0;
+        err->lon = 0.0;
+        err->alt = 0;
+    }
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_gps_sync(struct tref *ref, uint32_t count_us, struct timespec utc, struct timespec gps_time) {
+    double cnt_diff; /* internal concentrator time difference (in seconds) */
+    double utc_diff; /* UTC time difference (in seconds) */
+    double slope; /* time slope between new reference and old reference (for sanity check) */
+
+    bool aber_n0; /* is the update value for synchronization aberrant or not ? */
+    static bool aber_min1 = false; /* keep track of whether value at sync N-1 was aberrant or not  */
+    static bool aber_min2 = false; /* keep track of whether value at sync N-2 was aberrant or not  */
+
+    CHECK_NULL(ref);
+
+    /* calculate the slope */
+
+    cnt_diff = (double)(count_us - ref->count_us) / (double)(TS_CPS); /* uncorrected by xtal_err */
+    utc_diff = (double)(utc.tv_sec - (ref->utc).tv_sec) + (1E-9 * (double)(utc.tv_nsec - (ref->utc).tv_nsec));
+
+    /* detect aberrant points by measuring if slope limits are exceeded */
+    if (utc_diff != 0) { // prevent divide by zero
+        slope = cnt_diff/utc_diff;
+        if ((slope > PLUS_10PPM) || (slope < MINUS_10PPM)) {
+            DEBUG_MSG("Warning: correction range exceeded\n");
+            aber_n0 = true;
+        } else {
+            aber_n0 = false;
+        }
+    } else {
+        DEBUG_MSG("Warning: aberrant UTC value for synchronization\n");
+        aber_n0 = true;
+    }
+
+    /* watch if the 3 latest sync point were aberrant or not */
+    if (aber_n0 == false) {
+        /* value no aberrant -> sync with smoothed slope */
+        ref->systime = time(NULL);
+        ref->count_us = count_us;
+        ref->utc.tv_sec = utc.tv_sec;
+        ref->utc.tv_nsec = utc.tv_nsec;
+        ref->gps.tv_sec = gps_time.tv_sec;
+        ref->gps.tv_nsec = gps_time.tv_nsec;
+        ref->xtal_err = slope;
+        aber_min2 = aber_min1;
+        aber_min1 = aber_n0;
+        return LGW_GPS_SUCCESS;
+    } else if (aber_n0 && aber_min1 && aber_min2) {
+        /* 3 successive aberrant values -> sync reset (keep xtal_err) */
+        ref->systime = time(NULL);
+        ref->count_us = count_us;
+        ref->utc.tv_sec = utc.tv_sec;
+        ref->utc.tv_nsec = utc.tv_nsec;
+        ref->gps.tv_sec = gps_time.tv_sec;
+        ref->gps.tv_nsec = gps_time.tv_nsec;
+        /* reset xtal_err only if the present value is out of range */
+        if ((ref->xtal_err > PLUS_10PPM) || (ref->xtal_err < MINUS_10PPM)) {
+            ref->xtal_err = 1.0;
+        }
+        DEBUG_MSG("Warning: 3 successive aberrant sync attempts, sync reset\n");
+        aber_min2 = aber_min1;
+        aber_min1 = aber_n0;
+        return LGW_GPS_SUCCESS;
+    } else {
+        /* only 1 or 2 successive aberrant values -> ignore and return an error */
+        aber_min2 = aber_min1;
+        aber_min1 = aber_n0;
+        return LGW_GPS_ERROR;
+    }
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_cnt2utc(struct tref ref, uint32_t count_us, struct timespec *utc) {
+    double delta_sec;
+    double intpart, fractpart;
+    long tmp;
+
+    CHECK_NULL(utc);
+    if ((ref.systime == 0) || (ref.xtal_err > PLUS_10PPM) || (ref.xtal_err < MINUS_10PPM)) {
+        DEBUG_MSG("ERROR: INVALID REFERENCE FOR CNT -> UTC CONVERSION\n");
+        return LGW_GPS_ERROR;
+    }
+
+    /* calculate delta in seconds between reference count_us and target count_us */
+    delta_sec = (double)(count_us - ref.count_us) / (TS_CPS * ref.xtal_err);
+
+    /* now add that delta to reference UTC time */
+    fractpart = modf (delta_sec , &intpart);
+    tmp = ref.utc.tv_nsec + (long)(fractpart * 1E9);
+    if (tmp < (long)1E9) { /* the nanosecond part doesn't overflow */
+        utc->tv_sec = ref.utc.tv_sec + (time_t)intpart;
+        utc->tv_nsec = tmp;
+    } else { /* must carry one second */
+        utc->tv_sec = ref.utc.tv_sec + (time_t)intpart + 1;
+        utc->tv_nsec = tmp - (long)1E9;
+    }
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_utc2cnt(struct tref ref, struct timespec utc, uint32_t *count_us) {
+    double delta_sec;
+
+    CHECK_NULL(count_us);
+    if ((ref.systime == 0) || (ref.xtal_err > PLUS_10PPM) || (ref.xtal_err < MINUS_10PPM)) {
+        DEBUG_MSG("ERROR: INVALID REFERENCE FOR UTC -> CNT CONVERSION\n");
+        return LGW_GPS_ERROR;
+    }
+
+    /* calculate delta in seconds between reference utc and target utc */
+    delta_sec = (double)(utc.tv_sec - ref.utc.tv_sec);
+    delta_sec += 1E-9 * (double)(utc.tv_nsec - ref.utc.tv_nsec);
+
+    /* now convert that to internal counter tics and add that to reference counter value */
+    *count_us = ref.count_us + (uint32_t)(delta_sec * TS_CPS * ref.xtal_err);
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_cnt2gps(struct tref ref, uint32_t count_us, struct timespec *gps_time) {
+    double delta_sec;
+    double intpart, fractpart;
+    long tmp;
+
+    CHECK_NULL(gps_time);
+    if ((ref.systime == 0) || (ref.xtal_err > PLUS_10PPM) || (ref.xtal_err < MINUS_10PPM)) {
+        DEBUG_MSG("ERROR: INVALID REFERENCE FOR CNT -> GPS CONVERSION\n");
+        return LGW_GPS_ERROR;
+    }
+
+    /* calculate delta in milliseconds between reference count_us and target count_us */
+    delta_sec = (double)(count_us - ref.count_us) / (TS_CPS * ref.xtal_err);
+
+    /* now add that delta to reference GPS time */
+    fractpart = modf (delta_sec , &intpart);
+    tmp = ref.gps.tv_nsec + (long)(fractpart * 1E9);
+    if (tmp < (long)1E9) { /* the nanosecond part doesn't overflow */
+        gps_time->tv_sec = ref.gps.tv_sec + (time_t)intpart;
+        gps_time->tv_nsec = tmp;
+    } else { /* must carry one second */
+        gps_time->tv_sec = ref.gps.tv_sec + (time_t)intpart + 1;
+        gps_time->tv_nsec = tmp - (long)1E9;
+    }
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_gps2cnt(struct tref ref, struct timespec gps_time, uint32_t *count_us) {
+    double delta_sec;
+
+    CHECK_NULL(count_us);
+    if ((ref.systime == 0) || (ref.xtal_err > PLUS_10PPM) || (ref.xtal_err < MINUS_10PPM)) {
+        DEBUG_MSG("ERROR: INVALID REFERENCE FOR GPS -> CNT CONVERSION\n");
+        return LGW_GPS_ERROR;
+    }
+
+    /* calculate delta in seconds between reference gps time and target gps time */
+    delta_sec = (double)(gps_time.tv_sec - ref.gps.tv_sec);
+    delta_sec += 1E-9 * (double)(gps_time.tv_nsec - ref.gps.tv_nsec);
+
+    /* now convert that to internal counter tics and add that to reference counter value */
+    *count_us = ref.count_us + (uint32_t)(delta_sec * TS_CPS * ref.xtal_err);
+
+    return LGW_GPS_SUCCESS;
+}
+
+/* --- EOF ------------------------------------------------------------------ */