2525
2626/*------------------------------------------------------------------
2727 *
28- * Name: dtime_now
28+ * Name: dtime_realtime
2929 *
30- * Purpose: Return current time as double precision.
30+ * Purpose: Return current wall clock time as double precision.
3131 *
3232 * Input: none
3333 *
4040 * part of a second, and having extra calculations everywhere,
4141 * simply use double precision floating point to make usage
4242 * easier.
43- *
43+ *
44+ * NOTE: This is not a good way to calculate elapsed time because
45+ * it can jump forward or backware via NTP or other manual setting.
46+ *
47+ * Use the monotonic version for measuring elapsed time.
48+ *
49+ * History: Originally I called this dtime_now. We ran into issues where
50+ * we really cared about elapsed time, rather than wall clock time.
51+ * The wall clock time could be wrong at start up time if there
52+ * is no realtime clock or Internet access. It can then jump
53+ * when GPS time or Internet access becomes available.
54+ * All instances of dtime_now should be replaced by dtime_realtime
55+ * if we want wall clock time, or dtime_monotonic if it is to be
56+ * used for measuring elapsed time, such as between becons.
57+ *
4458 *---------------------------------------------------------------*/
4559
60+ double dtime_realtime (void )
61+ {
62+ double result ;
63+
64+ #if __WIN32__
65+ /* 64 bit integer is number of 100 nanosecond intervals from Jan 1, 1601. */
66+
67+ FILETIME ft ;
68+
69+ GetSystemTimeAsFileTime (& ft );
70+
71+ result = ((( (double )ft .dwHighDateTime * (256. * 256. * 256. * 256. ) +
72+ (double )ft .dwLowDateTime ) / 10000000. ) - 11644473600. );
73+ #else
74+ /* tv_sec is seconds from Jan 1, 1970. */
75+
76+ struct timespec ts ;
77+
78+ #ifdef __APPLE__
79+
80+ // Why didn't I use clock_gettime?
81+ // Not available before Max OSX 10.12? https://github.com/gambit/gambit/issues/293
82+
83+ struct timeval tp ;
84+ gettimeofday (& tp , NULL );
85+ ts .tv_nsec = tp .tv_usec * 1000 ;
86+ ts .tv_sec = tp .tv_sec ;
87+ #else
88+ clock_gettime (CLOCK_REALTIME , & ts );
89+ #endif
90+
91+ result = ((double )(ts .tv_sec ) + (double )(ts .tv_nsec ) * 0.000000001 );
92+
93+ #endif
94+
95+ #if DEBUG
96+ text_color_set (DW_COLOR_DEBUG );
97+ dw_printf ("dtime_realtime() returns %.3f\n" , result );
98+ #endif
99+
100+ return (result );
101+ }
102+
46103
47- double dtime_now (void )
104+ /*------------------------------------------------------------------
105+ *
106+ * Name: dtime_monotonic
107+ *
108+ * Purpose: Return montonically increasing time, which is not influenced
109+ * by the wall clock changing. e.g. leap seconds, NTP adjustments.
110+ *
111+ * Input: none
112+ *
113+ * Returns: Time as double precision, so we can get resolution
114+ * finer than one second.
115+ *
116+ * Description: Use this when calculating elapsed time.
117+ *
118+ *---------------------------------------------------------------*/
119+
120+ double dtime_monotonic (void )
48121{
49122 double result ;
50123
51124#if __WIN32__
125+
126+ // FIXME:
127+ // This is still returning wall clock time.
128+ // https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-gettickcount64
129+ // GetTickCount64 would be ideal but it requires Vista or Server 2008.
130+ // As far as I know, the current version of direwolf still works on XP.
131+ //
132+ // As a work-around, GetTickCount could be used if we add extra code to deal
133+ // with the wrap around after about 49.7 days.
134+ // Resolution is only about 10 or 16 milliseconds. Is that good enough?
135+
52136 /* 64 bit integer is number of 100 nanosecond intervals from Jan 1, 1601. */
53137
54138 FILETIME ft ;
@@ -63,12 +147,22 @@ double dtime_now (void)
63147 struct timespec ts ;
64148
65149#ifdef __APPLE__
150+
151+ // FIXME: Does MacOS have a monotonically increasing time?
152+ // https://stackoverflow.com/questions/41509505/clock-gettime-on-macos
153+
66154 struct timeval tp ;
67155 gettimeofday (& tp , NULL );
68156 ts .tv_nsec = tp .tv_usec * 1000 ;
69157 ts .tv_sec = tp .tv_sec ;
70158#else
71- clock_gettime (CLOCK_REALTIME , & ts );
159+
160+ // This is the only case handled properly.
161+ // Probably the only one that matters.
162+ // It is common to have a Raspberry Pi, without Internet,
163+ // starting up direwolf before GPS/NTP adjusts the time.
164+
165+ clock_gettime (CLOCK_MONOTONIC , & ts );
72166#endif
73167
74168 result = ((double )(ts .tv_sec ) + (double )(ts .tv_nsec ) * 0.000000001 );
@@ -84,6 +178,7 @@ double dtime_now (void)
84178}
85179
86180
181+
87182/*------------------------------------------------------------------
88183 *
89184 * Name: timestamp_now
@@ -104,7 +199,7 @@ double dtime_now (void)
104199
105200void timestamp_now (char * result , int result_size , int show_ms )
106201{
107- double now = dtime_now ();
202+ double now = dtime_realtime ();
108203 time_t t = (int )now ;
109204 struct tm tm ;
110205
@@ -150,7 +245,7 @@ void timestamp_now (char *result, int result_size, int show_ms)
150245
151246void timestamp_user_format (char * result , int result_size , char * user_format )
152247{
153- double now = dtime_now ();
248+ double now = dtime_realtime ();
154249 time_t t = (int )now ;
155250 struct tm tm ;
156251
@@ -191,7 +286,7 @@ void timestamp_user_format (char *result, int result_size, char *user_format)
191286
192287void timestamp_filename (char * result , int result_size )
193288{
194- double now = dtime_now ();
289+ double now = dtime_realtime ();
195290 time_t t = (int )now ;
196291 struct tm tm ;
197292
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