Add update_wday() and calculate day of week by using UBX-NAV-TIMEUTC

firmware/gps.c

@@ -544,6 +544,7 @@ static void make_packet(packet_t *packet){
               gps_utc.tm_hour = buf.utc.hour;         // Hours   [0-23]
               gps_utc.tm_min  = buf.utc.min;          // Minutes [0-59]
               gps_utc.tm_sec  = buf.utc.sec;          // Seconds [0-60]
+              update_wday(&gps_utc);
               gps_utc_valid = TRUE;
             }else if((ubx_state.packet_type == AID_EPH) && (buf.svid <= UBX_GPS_MAX_ID)){
               u32 mask = 1;

firmware/util.c

@@ -199,3 +199,14 @@ long str2num(char *s, char **endptr){
   if(endptr){*endptr = s;}
   return res;
 }
+
+void update_wday(struct tm *t){
+  // Recalculate weekday
+  // @see https://en.wikipedia.org/wiki/Determination_of_the_day_of_the_week#Sakamoto's_methods
+  // modified base date from 1753/1/1(1=Monday) -> 1980/1/1(2=Tuesday)
+  // valid from 1980/1/1 to 2099/12/31
+  u8 y = t->tm_year - 76; // y > 1980
+  static const u8 tbl[] = {5, 1, 0, 3, 5, 1, 3, 6, 2, 4, 0, 2};
+  if(t->tm_mon < 2){y -= 1;}
+  t->tm_wday = ((y + y/4 + tbl[t->tm_mon] + (u8)t->tm_mday) % 7);
+}

firmware/util.h

@@ -34,6 +34,7 @@
 
 #include "main.h"
 #include "type.h"
+#include <time.h>
 
 void wait_8n6clk(unsigned char i);
 void _wait_us(unsigned int count);
@@ -82,6 +83,7 @@ u16 swap_u16(u16 w);
 
 u16 crc16(u8 *buf, u8 size, u16 crc);
 long str2num(char *str, char **endptr);
+void update_wday(struct tm *t);
 
 #endif /* __UTIL_H__ */