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ppsthread.c
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/*
* ppsthread.c - manage PPS watcher threads
*
* To enable KPPS, this file needs to be compiled with -DHAVE_SYS_TIMEPPS_H
*
* If you are not good at threads do not touch this file!
* For example: errno is thread safe; strerror() is not.
*
* It helps to know that there are two PPS measurement methods in
* play. One is defined by RFC2783 and typically implemented in the
* kernel. It is available on FreeBSD, Linux, and NetBSD. In gpsd it
* is referred to as KPPS. KPPS is accessed on Linux via /dev/ppsN
* devices. On BSD it is accessed via the same device as the serial
* port. This mechanism is preferred as it should provide the smallest
* latency and jitter from control line transition to timestamp.
*
* The other mechanism is user-space PPS, which uses the (not
* standardized) TIOCMIWAIT ioctl to wait for PPS transitions on
* serial port control lines. It is implemented on Linux and OpenBSD.
*
* On Linux, RFC2783 PPS requires root permissions for initialization;
* user-space PPS does not. User-space PPS loses some functionality
* when not initialized as root. In gpsd, user-space PPS is referred
* to as "plain PPS".
*
* On {Free,Net}BSD, RFC2783 PPS should only require access to the
* serial port, but details have not yet been tested and documented
* here.
*
* Note that for easy debugging all logging from this file is prefixed
* with PPS or KPPS.
*
* To use the thread manager, you need to first fill in the
* devicefd, devicename, and the four hook function members in the thread
* context structure. The void *context member is available for your hook
* functions to use; the thread-monitor code doesn't touch it.
*
* After this setup, you can call pps_thread_activate() and the
* thread will launch. It is OK to do this before the device is open,
* the thread will wait on that.
*
* WARNING! Loss of precision
* UNIX time to nanoSec precision is 62 significant bits
* UNIX time to nanoSec precision after 2038 is 63 bits
* a double is only 53 significant bits.
*
* You cannot do PPS math with doubles
*
* This file is Copyright (c) 2013 by the GPSD project. BSD terms
* apply: see the file COPYING in the distribution root for details.
*/
#include <string.h>
#include <stdio.h>
#include <stdbool.h>
#include <limits.h>
#include <errno.h>
#include <math.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <unistd.h>
#include <pthread.h> /* pacifies OpenBSD's compiler */
/* use RFC 2783 PPS API */
/* this needs linux >= 2.6.34 and
* CONFIG_PPS=y
* CONFIG_PPS_DEBUG=y [optional to kernel log pulses]
* CONFIG_PPS_CLIENT_LDISC=y
*
* Also beware that setting
* CONFIG_PPS_CLIENT_KTIMER=y
* adds a fake software-generated PPS intended for testing. This
* doesn't even run at exactly 1Hz, so any attempt to use it for
* real timing is disastrous. Hence we try to avoid it.
*/
#define FAKE_PPS_NAME "ktimer"
#if defined(HAVE_SYS_TIMEPPS_H)
// include unistd.h here as it is missing on older pps-tools releases.
// 'close' is not defined otherwise.
#include <unistd.h>
#include <sys/timepps.h>
#endif
#include "timespec.h"
#include "ppsthread.h"
#include "os_compat.h"
/*
* Tell GCC that we want thread-safe behavior with _REENTRANT;
* in particular, errno must be thread-local.
* Tell POSIX-conforming implementations with _POSIX_THREAD_SAFE_FUNCTIONS.
* See http://www.unix.org/whitepapers/reentrant.html
*/
#ifndef _REENTRANT
#define _REENTRANT
#endif
#ifndef _POSIX_THREAD_SAFE_FUNCTIONS
#define _POSIX_THREAD_SAFE_FUNCTIONS
#endif
/*
* Warning: This is a potential portability problem.
* It's needed so that TIOCMIWAIT will be defined and the plain PPS
* code will work, but it's not a SuS/POSIX standard header. We're
* going to include it unconditionally here because we expect both
* Linux and BSD to have it and we want compilation to break with
* an audible snapping sound if it's not present.
*/
#include <sys/ioctl.h>
#if defined(HAVE_SYS_TIMEPPS_H)
#include <glob.h>
#include <fcntl.h> /* needed for open() and friends */
#endif
#if defined(TIOCMIWAIT)
static int get_edge_tiocmiwait( volatile struct pps_thread_t *,
struct timespec *, int *,
volatile struct timedelta_t *);
#endif /* TIOCMIWAIT */
struct inner_context_t {
volatile struct pps_thread_t *pps_thread;
bool pps_canwait; /* can RFC2783 wait? */
#if defined(HAVE_SYS_TIMEPPS_H)
int pps_caps; /* RFC2783 getcaps() */
pps_handle_t kernelpps_handle;
#endif /* defined(HAVE_SYS_TIMEPPS_H) */
};
#if defined(HAVE_SYS_TIMEPPS_H)
static int get_edge_rfc2783(struct inner_context_t *,
struct timespec *,
int *,
struct timespec *,
int *,
volatile struct timedelta_t *);
#endif /* defined(HAVE_SYS_TIMEPPS_H) */
static pthread_mutex_t ppslast_mutex = PTHREAD_MUTEX_INITIALIZER;
static void thread_lock(volatile struct pps_thread_t *pps_thread)
{
int pthread_err = pthread_mutex_lock(&ppslast_mutex);
if ( 0 != pthread_err ) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_ERROR,
"PPS:%s pthread_mutex_lock() : %s\n",
pps_thread->devicename, errbuf);
}
}
static void thread_unlock(volatile struct pps_thread_t *pps_thread)
{
int pthread_err = pthread_mutex_unlock(&ppslast_mutex);
if ( 0 != pthread_err ) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_ERROR,
"TPPS:%s pthread_mutex_unlock() : %s\n",
pps_thread->devicename, errno, errbuf);
}
}
#if defined(HAVE_SYS_TIMEPPS_H)
#ifdef __linux__
/* Obtain contents of specified sysfs variable; null string if failure */
static void get_sysfs_var(const char *path, char *buf, size_t bufsize)
{
buf[0] = '\0';
int fd = open(path, O_RDONLY);
if ( 0 <= fd ) {
ssize_t r = read( fd, buf, bufsize -1);
if ( 0 < r ) {
buf[r - 1] = '\0'; /* remove trailing \x0a */
}
(void)close(fd);
}
}
/* Check to see whether the named PPS source is the fake one */
int pps_check_fake(const char *name) {
char path[PATH_MAX] = "";
char buf[32] = "";
snprintf(path, sizeof(path), "/sys/devices/virtual/pps/%s/name", name);
get_sysfs_var(path, buf, sizeof(buf));
return strcmp(buf, FAKE_PPS_NAME) == 0;
}
/* Get first "real" PPS device, skipping the fake, if any */
char *pps_get_first(void)
{
if (pps_check_fake("pps0"))
return "/dev/pps1";
return "/dev/pps0";
}
#endif /* __linux__ */
static int init_kernel_pps(struct inner_context_t *inner_context)
/* return handle for kernel pps, or -1; requires root privileges */
{
pps_params_t pp;
int ret;
#ifdef __linux__
/* These variables are only needed by Linux to find /dev/ppsN. */
int ldisc = 18; /* the PPS line discipline */
glob_t globbuf;
#endif
char path[PATH_MAX] = "";
volatile struct pps_thread_t *pps_thread = inner_context->pps_thread;
inner_context->kernelpps_handle = -1;
inner_context->pps_canwait = false;
/*
* This next code block abuses "ret" by storing the filedescriptor
* to use for RFC2783 calls.
*/
#ifndef __clang_analyzer__
ret = -1; /* this ret will not be unneeded when the 'else' part
* of the followinng ifdef becomes an #elif */
#endif /* __clang_analyzer__ */
#ifdef __linux__
/*
* Some Linuxes, like the RasPi's, have PPS devices preexisting.
* Other OS have no way to automatically determine the proper /dev/ppsX.
* Allow user to pass in an explicit PPS device path.
*
* (We use strncpy() here because this might be compiled where
* strlcpy() is not available.)
*/
if (strncmp(pps_thread->devicename, "/dev/pps", 8) == 0) {
if (pps_check_fake(pps_thread->devicename + 5))
pps_thread->log_hook(pps_thread, THREAD_WARN,
"KPPS:%s is fake PPS,"
" timing will be inaccurate\n",
pps_thread->devicename);
(void)strncpy(path, pps_thread->devicename, sizeof(path)-1);
}
else {
char pps_num = '\0'; /* /dev/pps[pps_num] is our device */
size_t i; /* to match type of globbuf.gl_pathc */
/*
* Otherwise one must make calls to associate a serial port with a
* /dev/ppsN device and then grovel in system data to determine
* the association.
*/
/* Attach the line PPS discipline, so no need to ldattach */
/* This activates the magic /dev/pps0 device */
/* Note: this ioctl() requires root, and device is a tty */
if ( 0 > ioctl(pps_thread->devicefd, TIOCSETD, &ldisc)) {
char errbuf[BUFSIZ] = "unknown error";
strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s cannot set PPS line discipline %s\n",
pps_thread->devicename, errbuf);
return -1;
}
/* uh, oh, magic file names!, RFC2783 neglects to specify how
* to associate the serial device and pps device names */
/* need to look in /sys/devices/virtual/pps/pps?/path
* (/sys/class/pps/pps?/path is just a link to that)
* to find the /dev/pps? that matches our serial port.
* this code fails if there are more then 10 pps devices.
*
* yes, this could be done with libsysfs, but trying to keep
* the number of required libs small, and libsysfs would still
* be linux only */
memset( (void *)&globbuf, 0, sizeof(globbuf));
(void)glob("/sys/devices/virtual/pps/pps?/path", 0, NULL, &globbuf);
memset( (void *)&path, 0, sizeof(path));
for ( i = 0; i < globbuf.gl_pathc; i++ ) {
get_sysfs_var(globbuf.gl_pathv[i], path, sizeof(path));
pps_thread->log_hook(pps_thread, THREAD_PROG,
"KPPS:%s checking %s, %s\n",
pps_thread->devicename,
globbuf.gl_pathv[i], path);
if ( 0 == strncmp( path, pps_thread->devicename, sizeof(path))) {
/* this is the pps we are looking for */
/* FIXME, now build the proper pps device path */
pps_num = globbuf.gl_pathv[i][28];
break;
}
memset( (void *)&path, 0, sizeof(path));
}
/* done with blob, clear it */
globfree(&globbuf);
if ( 0 == (int)pps_num ) {
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s device not found.\n",
pps_thread->devicename);
return -1;
}
/* construct the magic device path */
(void)snprintf(path, sizeof(path), "/dev/pps%c", pps_num);
}
/* root privs are probably required for this device open
* do not bother to check uid, just go for the open() */
ret = open(path, O_RDWR);
if ( 0 > ret ) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s running as %d/%d, cannot open %s: %s\n",
pps_thread->devicename,
getuid(), geteuid(),
path, errbuf);
return -1;
}
#else /* not __linux__ */
/*
* On BSDs that support RFC2783, one uses the API calls on serial
* port file descriptor.
*
* FIXME! need more specific than 'not linux'
*/
(void)strlcpy(path, pps_thread->devicename, sizeof(path));
// cppcheck-suppress redundantAssignment
ret = pps_thread->devicefd;
#endif
/* assert(ret >= 0); */
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s RFC2783 path:%s, fd is %d\n",
pps_thread->devicename, path,
ret);
/* RFC 2783 implies the time_pps_setcap() needs priviledges *
* keep root a tad longer just in case */
if ( 0 > time_pps_create(ret, (pps_handle_t *)&inner_context->kernelpps_handle )) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s time_pps_create(%d) failed: %s\n",
pps_thread->devicename,
ret, errbuf);
return -1;
}
/* have kernel PPS handle */
/* get RFC2783 features supported */
inner_context->pps_caps = 0;
if ( 0 > time_pps_getcap(inner_context->kernelpps_handle,
&inner_context->pps_caps)) {
char errbuf[BUFSIZ] = "unknown error";
inner_context->pps_caps = 0;
(void)strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s time_pps_getcap() failed: %.100s\n",
pps_thread->devicename, errbuf);
return -1;
} else {
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s pps_caps 0x%02X\n",
pps_thread->devicename,
inner_context->pps_caps);
}
/* construct the setparms structure */
memset( (void *)&pp, 0, sizeof(pps_params_t));
pp.api_version = PPS_API_VERS_1; /* version 1 protocol */
if ( 0 == (PPS_TSFMT_TSPEC & inner_context->pps_caps ) ) {
/* PPS_TSFMT_TSPEC means return a timespec
* mandatory for driver to implement, require it */
pps_thread->log_hook(pps_thread, THREAD_WARN,
"KPPS:%s fail, missing mandatory PPS_TSFMT_TSPEC\n",
pps_thread->devicename);
return -1;
}
if ( 0 != (PPS_CANWAIT & inner_context->pps_caps ) ) {
/* we can wait! so no need for TIOCMIWAIT */
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s have PPS_CANWAIT\n",
pps_thread->devicename);
inner_context->pps_canwait = true;
}
pp.mode = PPS_TSFMT_TSPEC;
switch ( (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR) & inner_context->pps_caps ) {
case PPS_CAPTUREASSERT:
pps_thread->log_hook(pps_thread, THREAD_WARN,
"KPPS:%s missing PPS_CAPTURECLEAR, pulse may be offset\n",
pps_thread->devicename);
pp.mode |= PPS_CAPTUREASSERT;
break;
case PPS_CAPTURECLEAR:
pps_thread->log_hook(pps_thread, THREAD_WARN,
"KPPS:%s missing PPS_CAPTUREASSERT, pulse may be offset\n",
pps_thread->devicename);
pp.mode |= PPS_CAPTURECLEAR;
break;
case PPS_CAPTUREASSERT | PPS_CAPTURECLEAR:
pp.mode |= PPS_CAPTUREASSERT | PPS_CAPTURECLEAR;
break;
default:
/* THREAD_ERR in the calling routine */
pps_thread->log_hook(pps_thread, THREAD_INF,
"KPPS:%s missing PPS_CAPTUREASSERT and CLEAR\n",
pps_thread->devicename);
return -1;
}
if ( 0 > time_pps_setparams(inner_context->kernelpps_handle, &pp)) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
pps_thread->log_hook(pps_thread, THREAD_ERROR,
"KPPS:%s time_pps_setparams(mode=0x%02X) failed: %s\n",
pps_thread->devicename, pp.mode,
errbuf);
(void)time_pps_destroy(inner_context->kernelpps_handle);
return -1;
}
return 0;
}
#endif /* defined(HAVE_SYS_TIMEPPS_H) */
#if defined(TIOCMIWAIT)
/* wait for, and get, an edge using TIOCMIWAIT
* return -1 for error
* 0 for OK
*/
static int get_edge_tiocmiwait( volatile struct pps_thread_t *thread_context,
struct timespec *clock_ts,
int *state,
volatile struct timedelta_t *last_fixtime)
{
char ts_str[TIMESPEC_LEN];
/* we are lucky to have TIOCMIWAIT, so wait for next edge */
#define PPS_LINE_TIOC (TIOCM_CD|TIOCM_RI|TIOCM_CTS|TIOCM_DSR)
/*
* DB9 DB25 Name Full name
* --- ---- ---- --------------------
* 3 2 TXD --> Transmit Data
* 2 3 RXD <-- Receive Data
* 7 4 RTS --> Request To Send
* 8 5 CTS <-- Clear To Send
* 6 6 DSR <-- Data Set Ready
* 4 20 DTR --> Data Terminal Ready
* 1 8 DCD <-- Data Carrier Detect
* 9 22 RI <-- Ring Indicator
* 5 7 GND Signal ground
*
* Wait for status change on any handshake line. Just one edge,
* we do not want to be spinning waiting for the trailing edge of
* a pulse. The only assumption here is that no GPS lights up more
* than one of these pins. By waiting on all of them we remove a
* configuration switch.
*
* Note that it only makes sense to wait on handshake lines
* activated from the receive side (DCE->DTE) here; in this
* context "DCE" is the GPS. {CD,RI,CTS,DSR} is the
* entire set of these.
*
*/
if (ioctl(thread_context->devicefd, TIOCMIWAIT, PPS_LINE_TIOC) != 0) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
thread_context->log_hook(thread_context, THREAD_WARN,
"TPPS:%s ioctl(TIOCMIWAIT) failed: %d %.40s\n",
thread_context->devicename, errno, errbuf);
return -1;;
}
/*
* Start of time critical section
* Only error reporting, not success reporting in critical section
*/
/* duplicate copy in get_edge_rfc2783 */
/* quick, grab a copy of last_fixtime before it changes */
thread_lock(thread_context);
*last_fixtime = thread_context->fix_in;
thread_unlock(thread_context);
/* end duplicate copy in get_edge_rfc2783 */
/* get the time after we just woke up */
if ( 0 > clock_gettime(CLOCK_REALTIME, clock_ts) ) {
/* uh, oh, can not get time! */
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
thread_context->log_hook(thread_context, THREAD_ERROR,
"TPPS:%s clock_gettime() failed: %.100s\n",
thread_context->devicename, errbuf);
return -1;;
}
/* got the edge, got the time just after the edge, now quickly
* get the edge state */
if (ioctl(thread_context->devicefd, (unsigned long)TIOCMGET, state) != 0) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
thread_context->log_hook(thread_context, THREAD_ERROR,
"TPPS:%s ioctl(TIOCMGET) failed: %.100s\n",
thread_context->devicename, errbuf);
return -1;
}
/* end of time critical section */
/* mask for monitored lines */
*state &= PPS_LINE_TIOC;
timespec_str( clock_ts, ts_str, sizeof(ts_str) );
thread_context->log_hook(thread_context, THREAD_PROG,
"TPPS:%s ioctl(TIOCMIWAIT) succeeded, time:%s, state: %d\n",
thread_context->devicename, ts_str, *state);
return 0;
}
#endif /* TIOCMIWAIT */
#if defined(HAVE_SYS_TIMEPPS_H)
/* wait for, and get, last two edges using RFC2783
* return -1 for error
* 0 for OK
* 1 no edge found, continue
*
* on a quad core 2.4GHz Xeon using KPPS timestamp instead of plain
* PPS timestamp removes about 20uS of latency, and about +/-5uS
* of jitter
*/
static int get_edge_rfc2783(struct inner_context_t *inner_context,
struct timespec *prev_clock_ts,
int *prev_edge,
struct timespec *clock_ts,
int *edge,
volatile struct timedelta_t *last_fixtime)
{
pps_info_t pi;
char ts_str1[TIMESPEC_LEN], ts_str2[TIMESPEC_LEN];
struct timespec kernelpps_tv;
volatile struct pps_thread_t *thread_context = inner_context->pps_thread;
if ( inner_context->pps_canwait ) {
/*
* RFC2783 specifies that a NULL timeval means to wait, if
* PPS_CANWAIT is available.
*
* since we pps_canwait, we skipped the TIOMCIWAIT
*
* 3 second time out, some GPS output 0.5Hz and some RFC2783
* can only trigger on one edge
* a better and more complex solution would be to wait
* for 1/20 second and suffer the cycles
*/
kernelpps_tv.tv_sec = 3;
kernelpps_tv.tv_nsec = 0;
} else {
/*
* We use of a non-NULL zero timespec here,
* which means to return immediately with -1 (section
* 3.4.3). This is because we know we just got a pulse because
* TIOCMIWAIT just woke up.
* The timestamp has already been captured in the kernel, and we
* are merely fetching it here.
*/
memset( (void *)&kernelpps_tv, 0, sizeof(kernelpps_tv));
}
memset( (void *)&pi, 0, sizeof(pi)); /* paranoia */
if ( 0 > time_pps_fetch(inner_context->kernelpps_handle, PPS_TSFMT_TSPEC
, &pi, &kernelpps_tv)) {
char errbuf[BUFSIZ] = "unknown error";
(void)strerror_r(errno, errbuf, sizeof(errbuf));
if ( ETIMEDOUT == errno || EINTR == errno ) {
/* just a timeout */
thread_context->log_hook(thread_context, THREAD_INF,
"KPPS:%s kernel PPS timeout %s\n",
thread_context->devicename, errbuf);
return 1;
}
thread_context->log_hook(thread_context, THREAD_WARN,
"KPPS:%s kernel PPS failed %s\n",
thread_context->devicename, errbuf);
return 0;
}
if ( inner_context->pps_canwait ) {
/* get_edge_tiocmiwait() got this if !pps_canwait */
/* quick, grab a copy of last fixtime before it changes */
thread_lock(thread_context);
*last_fixtime = thread_context->fix_in;
thread_unlock(thread_context);
}
// find the last edge
if ( pi.assert_timestamp.tv_sec > pi.clear_timestamp.tv_sec ) {
/* assert 1 sec or more after than clear */
*edge = 1;
} else if ( pi.assert_timestamp.tv_sec < pi.clear_timestamp.tv_sec ) {
/* assert 1 sec or more before than clear */
*edge = 0;
} else if ( pi.assert_timestamp.tv_nsec > pi.clear_timestamp.tv_nsec ) {
/* assert less than 1 sec after clear */
*edge = 1;
} else {
/* assert less than 1 sec before clear */
*edge = 0;
}
if ( 1 == *edge ) {
/* assert after clear */
*prev_edge = 0;
if ( 0 == pi.clear_timestamp.tv_sec ) {
/* brain damaged pps-gpio sometimes never fills in clear
* so make it look like an invisible pulse
* if clear is the leading edge, then we are off by the
* pulse width */
*prev_clock_ts = pi.assert_timestamp;
} else {
*prev_clock_ts = pi.clear_timestamp;
}
*clock_ts = pi.assert_timestamp;
} else {
/* assert before clear */
*prev_edge = 1;
*prev_clock_ts = pi.assert_timestamp;
*clock_ts = pi.clear_timestamp;
}
/*
* pps_seq_t is uint32_t on NetBSD, so cast to
* unsigned long as a wider-or-equal type to
* accomodate Linux's type.
*/
timespec_str( &pi.assert_timestamp, ts_str1, sizeof(ts_str1) );
timespec_str( &pi.clear_timestamp, ts_str2, sizeof(ts_str2) );
thread_context->log_hook(thread_context, THREAD_PROG,
"KPPS:%s assert %s, sequence: %lu, "
"clear %s, sequence: %lu - using: %.10s\n",
thread_context->devicename,
ts_str1,
(unsigned long) pi.assert_sequence,
ts_str2,
(unsigned long) pi.clear_sequence,
*edge ? "assert" : "clear");
return 0;
}
#endif /* defined(HAVE_SYS_TIMEPPS_H) */
/* gpsd_ppsmonitor()
*
* the core loop of the PPS thread.
* All else is initialization, cleanup or subroutine
*/
static void *gpsd_ppsmonitor(void *arg)
{
char ts_str1[TIMESPEC_LEN], ts_str2[TIMESPEC_LEN];
struct inner_context_t inner_context = *((struct inner_context_t *)arg);
volatile struct pps_thread_t *thread_context = inner_context.pps_thread;
/* the GPS time and system clock timme, to the nSec,
* when the last fix received
* using a double would cause loss of precision */
volatile struct timedelta_t last_fixtime = {{0, 0}, {0, 0}};
struct timespec clock_ts = {0, 0};
time_t last_second_used = 0;
long long cycle = 0, duration = 0;
/* state is the last state of the tty control signals */
int state = 0;
/* count of how many cycles unchanged data */
int unchanged = 0;
/* state_last is previous state */
int state_last = 0;
/* edge, used as index into pulse to find previous edges */
int edge = 0; /* 0 = clear edge, 1 = assert edge */
#if defined(TIOCMIWAIT)
int edge_tio = 0;
long long cycle_tio = 0;
long long duration_tio = 0;
int state_tio = 0;
int state_last_tio = 0;
struct timespec clock_ts_tio = {0, 0};
/* pulse stores the time of the last two edges */
struct timespec pulse_tio[2] = { {0, 0}, {0, 0} };
#endif /* TIOCMIWAIT */
#if defined(HAVE_SYS_TIMEPPS_H)
long long cycle_kpps = 0, duration_kpps = 0;
/* kpps_pulse stores the time of the last two edges */
struct timespec pulse_kpps[2] = { {0, 0}, {0, 0} };
#endif /* defined(HAVE_SYS_TIMEPPS_H) */
bool not_a_tty = false;
/* Acknowledge that we've grabbed the inner_context data */
((volatile struct inner_context_t *)arg)->pps_thread = NULL;
/* before the loop, figure out how we can detect edges:
* TIOMCIWAIT, which is linux specifix
* RFC2783, a.k.a kernel PPS (KPPS)
* or if KPPS is deficient a combination of the two */
if ( 0 > thread_context->devicefd
|| 0 == isatty(thread_context->devicefd) ) {
thread_context->log_hook(thread_context, THREAD_PROG,
"KPPS:%s gps_fd:%d not a tty, can not use TIOMCIWAIT\n",
thread_context->devicename,
thread_context->devicefd);
/* why do we care the device is a tty? so as not to ioctl(TIO..)
* /dev/pps0 is not a tty and we need to use it */
not_a_tty = true;
}
/* if no TIOCMIWAIT, we hope to have PPS_CANWAIT */
if ( not_a_tty && !inner_context.pps_canwait ) {
/* for now, no way to wait for an edge, in the future maybe figure out
* a sleep */
}
/*
* this is the main loop, exit and never any further PPS processing.
*
* Four stages to the loop,
* an unwanted condition at any point and the loop restarts
* an error condition and we exit for all time.
*
* Stage One: wait for the next edge.
* If we have KPPS
* If we have PPS_CANWAIT
* use KPPS and PPS_CANWAIT - this is the most accurate
* else
* use KPPS and TIOMCIWAIT together - this is pretty accurate
* else If we have TIOMCIWAIT
* use TIOMCIWAIT - this is the least accurate
* else
* give up
*
* Success is we have a good edge, otherwise loop some more
*
* On a successul stage one, we know this about the exact moment
* of current pulse:
* GPS (real) time
* system (clock) time
* edge type: Assert (rising) or Clear (falling)
*
* From the above 3 items, we can compute:
* cycle length - elapsed time from the previous edge of the same type
* pulse length (duration) - elapsed time from the previous edge
* (the previous edge would be the opposite type)
*
* Stage Two: Categorize the current edge
* Decide if we have 0.5Hz, 1Hz, 5 Hz cycle time
* knowing cycle time determine if we have the leading or trailing edge
* restart the loop if the edge looks dodgy
*
* Stage Three: Calculate
* Calculate the offset (difference) between the system time
* and the GPS time at the pulse moment
* restart the loop if the offset looks dodgy
*
* Stage Four: Tell ntpd, chronyd, or gpsmon what we learned
* a few more sanity checks
* call the report hook with our PPS report
*/
while (thread_context->report_hook != NULL) {
bool ok = false;
char *log = NULL;
char *edge_str = "";
if (++unchanged == 10) {
/* last ten edges no good, stop spinning, just wait 10 seconds */
unchanged = 0;
thread_context->log_hook(thread_context, THREAD_WARN,
"PPS:%s unchanged state, ppsmonitor sleeps 10\n",
thread_context->devicename);
(void)sleep(10);
}
/* Stage One; wait for the next edge */
#if defined(TIOCMIWAIT)
if ( !not_a_tty && !inner_context.pps_canwait ) {
int ret;
/* we are a tty, so can TIOCMIWAIT */
/* we have no PPS_CANWAIT, so must TIOCMIWAIT */
ret = get_edge_tiocmiwait( thread_context, &clock_ts_tio,
&state_tio, &last_fixtime );
if ( 0 != ret ) {
thread_context->log_hook(thread_context, THREAD_PROG,
"PPS:%s die: TIOCMIWAIT Error\n",
thread_context->devicename);
break;
}
edge_tio = (state_tio > state_last_tio) ? 1 : 0;
state_last_tio = state_tio;
/* three things now known about the current edge:
* clock_ts - time of the edge
* state - the serial line input states
* edge - rising edge (1), falling edge (0) or invisble edge (0)
*/
/* calculate cycle and duration from previous edges */
cycle_tio = timespec_diff_ns(clock_ts_tio, pulse_tio[edge_tio]);
cycle_tio /= 1000; /* nsec to usec */
duration_tio = timespec_diff_ns(clock_ts_tio,
pulse_tio[edge_tio ? 0 : 1])/1000;
/* save this edge so we know next cycle time */
pulse_tio[edge_tio] = clock_ts_tio;
/* use this data */
ok = true;
clock_ts = clock_ts_tio;
state = edge_tio;
edge = edge_tio;
edge_str = edge ? "Assert" : "Clear";
cycle = cycle_tio;
duration = duration_tio;
timespec_str( &clock_ts, ts_str1, sizeof(ts_str1) );
thread_context->log_hook(thread_context, THREAD_PROG,
"TPPS:%s %.10s, cycle: %lld, duration: %lld @ %s\n",
thread_context->devicename, edge_str, cycle, duration,
ts_str1);
}
#endif /* TIOCMIWAIT */
/* ok and log used by KPPS and TIOCMIWAIT */
log = NULL;
#if defined(HAVE_SYS_TIMEPPS_H)
if ( 0 <= inner_context.kernelpps_handle ) {
int ret;
int edge_kpps = 0; /* 0 = clear edge, 1 = assert edge */
/* time of the last edge */
struct timespec clock_ts_kpps = {0, 0};
/* time of the edge before the last edge */
struct timespec prev_clock_ts = {0, 0};
/* direction of next to last edge 1 = assert, 0 = clear */
int prev_edge = 0;
/* get last and previsou edges, in order
* optionally wait for goood data
*/
ret = get_edge_rfc2783(&inner_context,
&prev_clock_ts,
&prev_edge,
&clock_ts_kpps,
&edge_kpps,
&last_fixtime);
if ( -1 == ret ) {
/* error, so break */
thread_context->log_hook(thread_context, THREAD_ERROR,
"PPS:%s die: RFC2783 Error\n",
thread_context->devicename);
break;
}
if ( 1 == ret ) {
/* no edge found, so continue */
/* maybe use TIOCMIWAIT edge instead?? */
continue;
}
/* for now, as we have been doing all of gpsd 3.x, just
*use the last edge, not the previous edge */
/* compute time from previous saved similar edge */
cycle_kpps = timespec_diff_ns(clock_ts_kpps, pulse_kpps[edge_kpps]);
cycle_kpps /= 1000;
/* compute time from previous saved dis-similar edge */
duration_kpps = timespec_diff_ns(clock_ts_kpps, prev_clock_ts)/1000;
/* save for later */
pulse_kpps[edge_kpps] = clock_ts_kpps;
pulse_kpps[edge_kpps ? 0 : 1] = prev_clock_ts;
/* sanity checks are later */
/* use this data */
state = edge_kpps;
edge = edge_kpps;
edge_str = edge ? "Assert" : "Clear";
clock_ts = clock_ts_kpps;
cycle = cycle_kpps;
duration = duration_kpps;
timespec_str( &clock_ts_kpps, ts_str1, sizeof(ts_str1) );
thread_context->log_hook(thread_context, THREAD_PROG,
"KPPS:%s %.10s cycle: %7lld, duration: %7lld @ %s\n",
thread_context->devicename,
edge_str,
cycle_kpps, duration_kpps, ts_str1);
}
#endif /* defined(HAVE_SYS_TIMEPPS_H) */
if ( not_a_tty && !inner_context.pps_canwait ) {
/* uh, oh, no TIOMCIWAIT, nor RFC2783, die */
thread_context->log_hook(thread_context, THREAD_WARN,
"PPS:%s die: no TIOMCIWAIT, nor RFC2783 CANWAIT\n",
thread_context->devicename);
break;
}
/*
* End of Stge One
* we now know this about the exact moment of current pulse:
* GPS (real) time
* system (clock) time
* edge type: Assert (rising) or Clear (falling)
*
* we have computed:
* cycle length
* pulse length (duration)
*/
/*
* Stage Two: Categorize the current edge
* Decide if we have 0.5Hz, 1Hz, 5 Hz cycle time
* determine if we have the leading or trailing edge
*/
/* FIXME! this block duplicates a lot of the next block
* of cycle detetion code */
if (state != state_last) {
thread_context->log_hook(thread_context, THREAD_RAW,
"PPS:%s %.10s pps-detect changed to %d\n",
thread_context->devicename, edge_str, state);
unchanged = 0;
} else if ( (180000 < cycle && 220000 > cycle) /* 5Hz */
|| (900000 < cycle && 1100000 > cycle) /* 1Hz */
|| (1800000 < cycle && 2200000 > cycle) ) { /* 0.5Hz */
/* some pulses may be so short that state never changes
* and some RFC2783 only can detect one edge */
duration = 0;
unchanged = 0;
thread_context->log_hook(thread_context, THREAD_RAW,
"PPS:%s %.10s pps-detect invisible pulse\n",
thread_context->devicename, edge_str);
}
/* else, unchannged state, and weird cycle time */
state_last = state;
timespec_str( &clock_ts, ts_str1, sizeof(ts_str1) );
thread_context->log_hook(thread_context, THREAD_PROG,
"PPS:%s %.10s cycle: %7lld, duration: %7lld @ %s\n",
thread_context->devicename,
edge_str,
cycle, duration, ts_str1);
if (unchanged) {
// strange, try again
continue;
}
/*
* The PPS pulse is normally a short pulse with a frequency of
* 1 Hz, and the UTC second is defined by the front edge. But we
* don't know the polarity of the pulse (different receivers
* emit different polarities). The duration variable is used to
* determine which way the pulse is going. When the duration
* is less than 1/2 the cycle we are on the trailing edge.
*
* Some GPSes instead output a square wave that is 0.5 Hz and each
* edge denotes the start of a second.
*
* Some GPSes, like the Globalsat MR-350P, output a 1uS pulse.
* The pulse is so short that TIOCMIWAIT sees a state change
* but by the time TIOCMGET is called the pulse is gone. gpsd
* calls that an invisible pulse.
*
* A few stupid GPSes, like the Furuno GPSClock, output a 1.0 Hz
* square wave where the leading edge is the start of a second
* gpsd can only guess the correct edge.
*
* 5Hz GPS (Garmin 18-5Hz) pulses at 5Hz. Set the pulse length to
* 40ms which gives a 160ms pulse before going high.
*
* You may think that PPS is very accurate, so the cycle time
* valid window should be very small. This is not the case,
* The Raspberry Pi clock is very coarse when it starts and/or chronyd
* may be doing a fast slew. chronyd by default will slew up
* to 8.334%! So the cycle time as measured by the system clock
* may be almost +/- 9%. Therefore, gpsd uses a 10% window.
* Don't worry, ntpd and chronyd will do further validation.
*/
log = "Unknown error";
if ( 0 > cycle ) {
log = "Rejecting negative cycle\n";
} else if (180000 > cycle) {
/* shorter than 200 milliSec - 10%
* too short to even be a 5Hz pulse */
log = "Too short for 5Hz\n";
} else if (201000 > cycle) {
/* longer than 200 milliSec - 10%
* shorter than 200 milliSec + 10%
* about 200 milliSec cycle */