v1.2.0v1.2.0

- Added feature: new GPS module in the library for synchronization
- Removed feature: no more missed deadline detection in TX because of incompatibility with GPS
- Added documentation for GPS and legal notice
- Added flags in Makefiles for easier cross-compilation

2 files changed, 606 insertions, 19 deletions

diff --git a/libloragw/src/loragw_gps.c b/libloragw/src/loragw_gps.c
new file mode 100644
index 0000000..84db3b8
--- /dev/null
+++ b/libloragw/src/loragw_gps.c
@@ -0,0 +1,573 @@
+/*
+ / _____)             _              | |
+( (____  _____ ____ _| |_ _____  ____| |__
+ \____ \| ___ |    (_   _) ___ |/ ___)  _ \
+ _____) ) ____| | | || |_| ____( (___| | | |
+(______/|_____)_|_|_| \__)_____)\____)_| |_|
+    ©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: Sylvain Miermont
+*/
+
+
+/* -------------------------------------------------------------------------- */
+/* --- DEPENDANCIES --------------------------------------------------------- */
+
+/* fix an issue between POSIX and C99 */
+#if __STDC_VERSION__ >= 199901L
+	#define _XOPEN_SOURCE 600
+#else
+	#define _XOPEN_SOURCE 500
+#endif
+
+#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> // DEBUG
+
+#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
+
+/* -------------------------------------------------------------------------- */
+/* --- 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
+
+/* -------------------------------------------------------------------------- */
+/* --- 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 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 */
+
+/* -------------------------------------------------------------------------- */
+/* --- PRIVATE FUNCTIONS DECLARATION ---------------------------------------- */
+
+int nmea_checksum(char *nmea_string, int buff_size, char *checksum);
+
+char nibble_to_hexchar(uint8_t a);
+
+bool validate_nmea_checksum(char *serial_buff, int buff_size);
+
+bool match_label(char *s, char *label, int size, char wildcard);
+
+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 '$' if necessary and calculate checksum until '*' character is
+reached (or buff_size exceeded).
+Checksum must point to a 2-byte (or more) char array.
+Return position of the checksum in the string
+*/
+int nmea_checksum(char *nmea_string, int buff_size, char *checksum) {
+	int i = 0;
+	uint8_t check_num = 0;
+	
+	/* check input parameters */
+	if ((nmea_string == NULL) ||  (checksum == NULL) || (buff_size <= 1)) {
+		DEBUG_MSG("Invalid parameters for nmea_checksum\n");
+		return -1;
+	}
+	
+	/* skip the first '$' 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;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+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
+*/
+bool validate_nmea_checksum(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
+*/
+bool match_label(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_familly, 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 */
+	
+	/* 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_familly != NULL) {
+		DEBUG_MSG("WARNING: gps_familly parameter ignored for now\n"); // TODO
+	}
+	
+	/* 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;
+	}
+	
+	/* update baudrates */
+	cfsetispeed(&ttyopt, DEFAULT_BAUDRATE);
+	cfsetospeed(&ttyopt, DEFAULT_BAUDRATE);
+	
+	/* update terminal parameters */
+	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 */
+	ttyopt.c_iflag |= IGNPAR; /* ignore bytes with parity errors */
+	ttyopt.c_iflag |= ICRNL; /* map CR to NL */
+	ttyopt.c_iflag |= IGNCR; /* Ignore carriage return on input */
+	ttyopt.c_lflag |= ICANON; /* enable canonical input */
+	
+	/* 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);
+	
+	/* initialize global variables */
+	gps_time_ok = false;
+	gps_pos_ok = false;
+	gps_mod = 'N';
+	
+	return LGW_GPS_SUCCESS;
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+enum gps_msg lgw_parse_nmea(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 */
+	
+	/* check input parameters */
+	if (serial_buff == NULL) {
+		return UNKNOWN;
+	}
+	
+	/* display received serial data and checksum */
+	DEBUG_MSG("Note: parsing NMEA frame> %s", serial_buff);
+	
+	/* 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 (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: $GPRMC,,V,,,,,,,,,,N*00
+		*/
+		if (!validate_nmea_checksum(serial_buff, buff_size)) {
+			DEBUG_MSG("Warning: invalid RMC sentence (bad checksum)\n");
+			return INVALID;
+		}
+		nb_fields = str_chop(serial_buff, buff_size, ',', str_index, ARRAY_SIZE(str_index));
+		if (nb_fields != 13) {
+			DEBUG_MSG("Warning: invalid RMC sentence (number of fields)\n");
+			return INVALID;
+		}
+		/* parse GPS status */
+		gps_mod = *(serial_buff + str_index[12]); /* get first character, no need to bother with sscanf */
+		if ((gps_mod != 'N') && (gps_mod != 'A') && (gps_mod != 'D')) {
+			gps_mod = 'N';
+		}
+		/* parse complete time */
+		i = sscanf(serial_buff + str_index[1], "%2hd%2hd%2hd%4f", &gps_hou, &gps_min, &gps_sec, &gps_fra);
+		j = sscanf(serial_buff + str_index[9], "%2hd%2hd%2hd", &gps_day, &gps_mon, &gps_yea);
+		if ((i == 4) && (j == 3)) {
+			if ((gps_mod == 'A') || (gps_mod == 'D')) {
+				gps_time_ok = true;
+				DEBUG_MSG("Note: Valid RMC sentence, GPS locked, date: 20%02d-%02d-%02dT%02d:%02d:%06.3fZ\n", gps_yea, gps_mon, gps_day, gps_hou, gps_min, gps_fra + (float)gps_sec);
+			} else {
+				gps_time_ok = false;
+				DEBUG_MSG("Note: Valid RMC sentence, no satellite fix, estimated date: 20%02d-%02d-%02dT%02d:%02d:%06.3fZ\n", gps_yea, gps_mon, gps_day, gps_hou, gps_min, gps_fra + (float)gps_sec);
+			}
+		} else {
+			/* could not get a valid hour AND date */
+			gps_time_ok = false;
+			DEBUG_MSG("Note: Valid RMC sentence, mode %c, no date\n", gps_mod);
+		}
+		return NMEA_RMC;
+	} else if (match_label(serial_buff, "$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
+		*/
+		if (!validate_nmea_checksum(serial_buff, buff_size)) {
+			DEBUG_MSG("Warning: invalid GGA sentence (bad checksum)\n");
+			return INVALID;
+		}
+		nb_fields = str_chop(serial_buff, buff_size, ',', str_index, ARRAY_SIZE(str_index));
+		if (nb_fields != 15) {
+			DEBUG_MSG("Warning: invalid GGA sentence (number of fields)\n");
+			return INVALID;
+		}
+		/* parse number of satellites used for fix */
+		sscanf(serial_buff + str_index[7], "%hd", &gps_sat);
+		/* parse 3D coordinates */
+		i = sscanf(serial_buff + str_index[2], "%2hd%10lf", &gps_dla, &gps_mla);
+		gps_ola = *(serial_buff + str_index[3]);
+		j = sscanf(serial_buff + str_index[4], "%3hd%10lf", &gps_dlo, &gps_mlo);
+		gps_olo = *(serial_buff + str_index[5]);
+		k = sscanf(serial_buff + 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 INVALID;
+	}
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
+int lgw_gps_get(struct timespec *utc, struct coord_s *loc, struct coord_s *err) {
+	struct tm x;
+	time_t y;
+	
+	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);
+		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 (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) {
+	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 = (count_us - ref->count_us) / TS_CPS; /* uncorrected by xtal_err */
+	utc_diff = (utc.tv_sec - (ref->utc).tv_sec) + 1E-9 * (utc.tv_nsec - (ref->utc).tv_nsec);
+	if (utc_diff == 0.0) { // prevent divide by zero
+		DEBUG_MSG("ERROR: ATTEMPT TO DIVIDE BY ZERO\n");
+		return LGW_GPS_ERROR;
+	}
+	
+	/* detect aberrant points by measuring if slope limits are exceeded */
+	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;
+	}
+	
+	/* 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 = utc;
+		ref->xtal_err = (0.9 * ref->xtal_err) + (0.1 *  slope); /* 10% smoothing factor */
+		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 = utc;
+		/* 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;
+}
+
+/* --- EOF ------------------------------------------------------------------ */
diff --git a/libloragw/src/loragw_hal.c b/libloragw/src/loragw_hal.c
index c2329fc..4319d5e 100644
--- a/libloragw/src/loragw_hal.c
+++ b/libloragw/src/loragw_hal.c
@@ -296,7 +296,7 @@ int setup_sx1257(uint8_t rf_chain, uint32_t freq_hz) {
 		DEBUG_MSG("ERROR: INVALID RF_CHAIN\n");
 		return -1;
 	}
-		
+	
 	sx125x_write(rf_chain, 0x10, SX125x_TX_DAC_CLK_SEL + 2); /* Enable 'clock out' for both radios */
 	sx125x_write(rf_chain, 0x26, 0X2D); /* Disable gm of oscillator block */
 	
@@ -669,7 +669,9 @@ int lgw_start(void) {
 	
 	/* configure Lora 'multi' demodulators aka. Lora 'sensor' channels (IF0-3) */
 	j = 0;
-	for(i=0;i<=7;++i) j += (if_rf_chain[i] == 1 ? 1 << i : 0); /* transform bool array into binary word */
+	for(i=0; i<=7; ++i) {
+		j += (if_rf_chain[i] == 1 ? 1 << i : 0); /* transform bool array into binary word */
+	}
 	lgw_reg_w(LGW_RADIO_SELECT, j); /* IF mapping to radio A/B (per bit, 0=A, 1=B) */
 	
 	lgw_reg_w(LGW_IF_FREQ_0, IF_HZ_TO_REG(if_freq[0])); /* default -384 */
@@ -694,7 +696,9 @@ int lgw_start(void) {
 			case BW_125KHZ: lgw_reg_w(LGW_MBWSSF_MODEM_BW,0); break;
 			case BW_250KHZ: lgw_reg_w(LGW_MBWSSF_MODEM_BW,1); break;
 			case BW_500KHZ: lgw_reg_w(LGW_MBWSSF_MODEM_BW,2); break;
-			default: DEBUG_PRINTF("ERROR: UNEXPECTED VALUE %d IN SWITCH STATEMENT\n", lora_rx_bw); return LGW_HAL_ERROR;
+			default:
+				DEBUG_PRINTF("ERROR: UNEXPECTED VALUE %d IN SWITCH STATEMENT\n", lora_rx_bw);
+				return LGW_HAL_ERROR;
 		}
 		switch(lora_rx_sf) {
 			case DR_LORA_SF7: lgw_reg_w(LGW_MBWSSF_RATE_SF,7); break;
@@ -703,7 +707,9 @@ int lgw_start(void) {
 			case DR_LORA_SF10: lgw_reg_w(LGW_MBWSSF_RATE_SF,10); break;
 			case DR_LORA_SF11: lgw_reg_w(LGW_MBWSSF_RATE_SF,11); break;
 			case DR_LORA_SF12: lgw_reg_w(LGW_MBWSSF_RATE_SF,12); break;
-			default: DEBUG_PRINTF("ERROR: UNEXPECTED VALUE %d IN SWITCH STATEMENT\n", lora_rx_sf); return LGW_HAL_ERROR;
+			default:
+				DEBUG_PRINTF("ERROR: UNEXPECTED VALUE %d IN SWITCH STATEMENT\n", lora_rx_sf);
+				return LGW_HAL_ERROR;
 		}
 		lgw_reg_w(LGW_MBWSSF_PPM_OFFSET, lora_rx_ppm_offset); /* default 0 */
 		lgw_reg_w(LGW_MBWSSF_MODEM_ENABLE, 1); /* default 0 */
@@ -730,6 +736,9 @@ int lgw_start(void) {
 	lgw_reg_w(LGW_MCU_RST_0, 0);
 	lgw_reg_w(LGW_MCU_RST_1, 0);
 	
+	/* enable GPS event capture */
+	lgw_reg_w(LGW_GPS_EN,1);
+	
 	/* enable LEDs */
 	lgw_reg_w(LGW_GPIO_MODE,31);
 	// lgw_reg_w(LGW_GPIO_SELECT_OUTPUT,0); /* default 0 */
@@ -786,7 +795,6 @@ int lgw_receive(uint8_t max_pkt, struct lgw_pkt_rx_s *pkt_data) {
 		
 		/* how many packets are in the RX buffer ? Break if zero */
 		if (buff[0] == 0) {
-			DEBUG_MSG("Note: RX packet buffer empty, receive function returning nothing\n");
 			break; /* no more packets to fetch, exit out of FOR loop */
 		}
 		
@@ -949,8 +957,6 @@ int lgw_send(struct lgw_pkt_tx_s pkt_data) {
 	int transfer_size = 0; /* data to transfer from host to TX databuffer */
 	int payload_offset = 0; /* start of the payload content in the databuffer */
 	uint8_t power_nibble = 0; /* 4-bit value to set the firmware TX power */
-	uint32_t current_tstamp; /* current timestamp, to check for missed TX deadlines */
-	uint32_t deadline_tstamp; /* packet must be scheduled before that timestamp value is reached */
 	
 	/* check if the gateway is running */
 	if (lgw_is_started == false) {
@@ -1023,11 +1029,6 @@ int lgw_send(struct lgw_pkt_tx_s pkt_data) {
 	}
 	// TODO: implement LUT in the firmware and matched value in the HAL
 	
-	/* reset TX command flags */
-	lgw_reg_w(LGW_TX_TRIG_IMMEDIATE, 0);
-	lgw_reg_w(LGW_TX_TRIG_DELAYED, 0);
-	lgw_reg_w(LGW_TX_TRIG_GPS, 0);
-	
 	/* fixed metadata, useful payload and misc metadata compositing */
 	transfer_size = TX_METADATA_NB + pkt_data.size; /*  */
 	payload_offset = TX_METADATA_NB; /* start the payload just after the metadata */
@@ -1148,6 +1149,11 @@ int lgw_send(struct lgw_pkt_tx_s pkt_data) {
 	/* copy payload from user struct to buffer containing metadata */
 	memcpy((void *)(buff + payload_offset), (void *)(pkt_data.payload), pkt_data.size);
 	
+	/* reset TX command flags */
+	lgw_reg_w(LGW_TX_TRIG_IMMEDIATE, 0);
+	lgw_reg_w(LGW_TX_TRIG_DELAYED, 0);
+	lgw_reg_w(LGW_TX_TRIG_GPS, 0);
+	
 	/* put metadata + payload in the TX data buffer */
 	lgw_reg_w(LGW_TX_DATA_BUF_ADDR, 0);
 	lgw_reg_wb(LGW_TX_DATA_BUF_DATA, buff, transfer_size);
@@ -1161,13 +1167,6 @@ int lgw_send(struct lgw_pkt_tx_s pkt_data) {
 			
 		case TIMESTAMPED:
 			lgw_reg_w(LGW_TX_TRIG_DELAYED, 1);
-			lgw_reg_r(LGW_TIMESTAMP, (int32_t *)&current_tstamp); /* unusable value if GPS is enabled */
-			deadline_tstamp = pkt_data.count_us - TX_START_DELAY; /* time at which the controller with start TX sequence */
-			if ((deadline_tstamp - current_tstamp) > 0x7FFFFFFF) {
-				lgw_reg_w(LGW_TX_TRIG_DELAYED, 0); /* cancel TX if deadline was missed */
-				DEBUG_MSG("ERROR: MISSED TX DEADLINE\n");
-			    return LGW_HAL_ERROR; // should return a specific error message
-			}
 			break;
 			
 		case ON_GPS:
@@ -1216,6 +1215,21 @@ int lgw_status(uint8_t select, uint8_t *code) {
 
 /* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
 
+int lgw_get_trigcnt(uint32_t* trig_cnt_us) {
+	int i;
+	int32_t val;
+	
+	i = lgw_reg_r(LGW_TIMESTAMP, &val);
+	if (i == LGW_REG_SUCCESS) {
+		*trig_cnt_us = (uint32_t)val;
+		return LGW_HAL_SUCCESS;
+	} else {
+		return LGW_HAL_ERROR;
+	}
+}
+
+/* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ */
+
 const char* lgw_version_info() {
 	return lgw_version_string;
 }