DST presets for EU and USA, new tz_dst_country config

iNavFlight · digitalentity · May 20, 2018 · Apr 19, 2018 · Apr 19, 2018 · Apr 19, 2018
commit d861ee805c4a22c0a429bc9962f796615e25a84e
diff --git a/docs/Cli.md b/docs/Cli.md
@@ -411,6 +411,7 @@ Re-apply any new defaults as desired.
 |  airspeed_adc_channel        |  -  | ADC channel to use for analog pitot tube (airspeed) sensor. If board doesn't have a dedicated connector for analog airspeed sensor will default to 0 |
 |  tz_offset  | 0 | Time zone offset from UTC, in minutes. This is applied to the GPS time for logging and time-stamping of Blackbox logs |
 |  tz_automatic_dst  | OFF | Automatically add Daylight Saving Time to the GPS time when needed or simply ignore it |
+|  tz_dst_country  | EU | Country to use for DST calculations, presets are given for either EU or USA. If you live outside this areas it is suggested to disable automatic handling of DST (`tz_automatic_dst` = OFF) and manage `tz_offset` by yourself |
 
 This Markdown table is made by MarkdwonTableMaker addon for google spreadsheet.
 Original Spreadsheet used to make this table can be found here https://docs.google.com/spreadsheets/d/1ubjYdMGmZ2aAMUNYkdfe3hhIF7wRfIjcuPOi_ysmp00/edit?usp=sharing
diff --git a/src/main/common/time.c b/src/main/common/time.c
@@ -33,7 +33,6 @@
 #include "drivers/time.h"
 
 #define UNIX_REFERENCE_YEAR 1970
-#define UNIX_REFERENCE_DOW 3
 #define MILLIS_PER_SECOND 1000
 
 // rtcTime_t when the system was started.
@@ -53,6 +52,7 @@ PG_REGISTER_WITH_RESET_TEMPLATE(timeConfig_t, timeConfig, PG_TIME_CONFIG, 1);
 PG_RESET_TEMPLATE(timeConfig_t, timeConfig,
     .tz_offset = 0,
     .tz_automatic_dst = false,
+    .tz_dst_country = DST_EU,
 );
 
 static rtcTime_t dateTimeToRtcTime(dateTime_t *dt)
@@ -122,15 +122,69 @@ static bool rtcIsDateTimeValid(dateTime_t *dateTime)
            (dateTime->millis <= 999);
 }
 
+static int lastSundayOfMonth(int currentYear, int wantedMonth) {
+    int days[] = {31,29,31,30,31,30,31,31,30,31,30,31};
+	int m, y = currentYear, w;
+    days[1] -= (y % 4) || (!(y % 100) && (y % 400));
+    w = y * 365 + (y - 1) / 4 - (y - 1) / 100 + (y - 1) / 400 + 6;
+
+	for(m = 0; m < 12; m++) {
+		w = (w + days[m]) % 7;
+        if (m == wantedMonth - 1) {
+            return days[m] + (w < 5 ? -2 : 5) - w;
+        }
+	}
+    return 0;
+}
+
+static int nthSundayOfMonth(int lastSunday, int nth) {
+    while (lastSunday > 7 * nth) {
+        lastSunday -= 7;
+    }
+    return lastSunday;
+}
+
 static bool isDST(rtcTime_t t) {
     dateTime_t dateTime;
     rtcTimeToDateTime(&dateTime, t);
-    if (dateTime.month < 3 || dateTime.month > 11) { return false; }
-    if (dateTime.month > 3 && dateTime.month < 11) { return true; }
-    uint8_t dow = (uint8_t) (((t / MILLIS_PER_SECOND) / 86400) + UNIX_REFERENCE_DOW) % 7;
-    int previousSunday = dateTime.day - dow;
-    if (dateTime.month == 3) { return previousSunday >= 8; }
-    return previousSunday <= 0;
+    int lastSunday;
+    switch (timeConfig()->tz_dst_country) {
+        case DST_USA: // begins at 2:00 a.m. on the second Sunday of March and ends at 2:00 a.m. on the first Sunday of November
+            if (dateTime.month < 3 || dateTime.month > 11) { return false; }
+            if (dateTime.month > 3 && dateTime.month < 11) { return true; }
+            lastSunday = lastSundayOfMonth(dateTime.year, dateTime.month);
+            if (dateTime.month == 3) {
+                int secondSunday = nthSundayOfMonth(lastSunday, 2);
+                if (dateTime.day == secondSunday) {
+                    return dateTime.hours >= 2;
+                }
+                return dateTime.day > secondSunday;
+            }
+            if (dateTime.month == 11) {
+                int firstSunday = nthSundayOfMonth(lastSunday, 1);
+                if (dateTime.day == firstSunday) {
+                    return dateTime.hours < 2;
+                }
+                return dateTime.day < firstSunday;
+            }
+            break;
+        case DST_EU: // begins at 1:00 a.m. on the last Sunday of March and ends at 1:00 a.m. on the last Sunday of October
+            if (dateTime.month < 3 || dateTime.month > 10) { return false; }
+            if (dateTime.month > 3 && dateTime.month < 10) { return true; }
+            lastSunday = lastSundayOfMonth(dateTime.year, dateTime.month);
+            if (dateTime.day < lastSunday) { return !(dateTime.month == 3); }
+            if (dateTime.day > lastSunday) { return !(dateTime.month == 3); }
+            if (dateTime.day == lastSunday) {
+                if (dateTime.month == 3) {
+                    return dateTime.hours >= 1;
+                }
+                if (dateTime.month == 10) {
+                    return dateTime.hours < 1;
+                }
+            }
+            break;
+    }
+    return false;
 }
 
 static void dateTimeWithOffset(dateTime_t *dateTimeOffset, dateTime_t *dateTimeInitial, int16_t minutes, bool automatic_dst)

diff --git a/src/main/common/time.h b/src/main/common/time.h
@@ -39,9 +39,15 @@ typedef uint32_t timeUs_t;
 
 static inline timeDelta_t cmpTimeUs(timeUs_t a, timeUs_t b) { return (timeDelta_t)(a - b); }
 
+typedef enum {
+    DST_EU,
+    DST_USA,
+} tz_dst_country_e;
+
 typedef struct timeConfig_s {
     int16_t tz_offset; // Offset from UTC in minutes, might be positive or negative
     bool tz_automatic_dst; // Automatically handle DST or ignore it
+    tz_dst_country_e tz_dst_country;
 } timeConfig_t;
 
 PG_DECLARE(timeConfig_t, timeConfig);

diff --git a/src/main/fc/settings.yaml b/src/main/fc/settings.yaml
@@ -90,6 +90,9 @@ tables:
   - name: smartport_fuel_unit
     values: ["PERCENT", "MAH", "MWH"]
     enum: smartportFuelUnit_e
+  - name: tz_dst_country
+    values: ["EU", "USA"]
+    enum: tz_dst_country_e
 
 groups:
   - name: PG_GYRO_CONFIG
@@ -1649,6 +1652,9 @@ groups:
         max: 1440
       - name: tz_automatic_dst
         type: bool
+      - name: tz_dst_country
+        table: tz_dst_country
+        type: uint8_t
 
   - name: PG_DISPLAY_CONFIG
     type: displayConfig_t