Add support for UK daylight savings time (GMT/BST)

Doesn't fully handle date changes at the end of a month, but good enough
for the clock functionality currently in use.

diff --git a/clock.c b/clock.c
index e8df6699ba50d133818dfb128a16aac09733ffe4..a0333fd8faff5f95ec07e5affdb01ca23b618b9d 100644 (file)
--- a/clock.c
+++ b/clock.c
@@ -55,6 +55,7 @@ static os_timer_t ntp_timeout;
 
 static ip_addr_t ntp_server_ip;
 
+/* See RFC5905 7.3 */
 typedef struct {
        uint8 options;
        uint8 stratum;
@@ -93,6 +94,45 @@ bool ICACHE_FLASH_ATTR is_leap(uint32_t year)
        return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
 }
 
+bool ICACHE_FLASH_ATTR is_dst(struct tm *time)
+{
+       int lastsun = time->tm_mday - time->tm_wday;
+
+       if (time->tm_mon < 2 || time->tm_mon > 9)
+               return false;
+       if (time->tm_mon > 2 && time->tm_mon < 9)
+               return true;
+
+       /*
+        * Starts last Sunday in March, ends last Sunday in October, which must
+        * be at least the 25th of the month. So must be past that in March, or
+        * before that in October, to be in DST.
+        */
+       if (time->tm_mon == 2)
+               return (lastsun >= 25);
+       if (time->tm_mon == 9)
+               return (lastsun < 25);
+
+       return false;
+}
+
+/*
+ * Takes time, a Unix time (seconds since 1st Jan 1970) and breaks it down to:
+ *
+ * Time:
+ *   tm_sec    0-59
+ *   tm_min    0-59
+ *   tm_hour   0-23
+ *
+ * Date:
+ *   tm_year
+ *   tm_mon    0-11
+ *   tm_mday   1-31
+ *
+ *   tm_yday
+ *   tm_wday   Sunday = 0, Saturday = 6
+ *
+ */
 void ICACHE_FLASH_ATTR breakdown_time(uint32_t time, struct tm *result)
 {
        uint32_t era, doe, yoe, mp;
@@ -119,13 +159,27 @@ void ICACHE_FLASH_ATTR breakdown_time(uint32_t time, struct tm *result)
        mp = (5 * result->tm_yday + 2) / 153;
        result->tm_mday = result->tm_yday - (153 * mp + 2) / 5 + 1;
        result->tm_mon = mp + (mp < 10 ? 2 : -10);
-       if (result->tm_mon <=2)
+       if (result->tm_mon <= 2)
                result->tm_year++;
 
        /* result->tm_yday is March 1st indexed at this point; fix up */
        result->tm_yday += 28 + 31;
        if (is_leap(result->tm_year))
                result->tm_yday++;
+
+       result->tm_isdst = is_dst(result);
+       if (result->tm_isdst)
+               result->tm_hour++;
+       if (result->tm_hour > 23) {
+               /*
+                * We can ignore fixing up the date at the end of month etc.
+                * because all we're actually displaying is the time.
+                */
+               result->tm_hour = 0;
+               result->tm_wday++;
+               result->tm_mday++;
+               result->tm_yday++;
+       }
 }
 
 static void ICACHE_FLASH_ATTR ntp_udp_timeout(void *arg)
@@ -160,7 +214,7 @@ static void ICACHE_FLASH_ATTR ntp_udp_recv(void *arg, char *pdata,
        ntp = (ntp_t *) pdata;
        timestamp = ntp->trans_time[0] << 24 | ntp->trans_time[1] << 16 |
                ntp->trans_time[2] << 8 | ntp->trans_time[3];
-       // Convert to Unix time ms
+       // NTP 0 is 1st Jan 1900; convert to Unix time 0 of 1st Jan 1970
        timestamp -= 2208988800ULL;
 
        // Store the time