Examples update, add a note for configTime() that only one ntp server…

… is supported by lwip (#5343)

lwip lib bundled with esp32 Arduino supports only one ntp server. Any additional servers set are just silently ignored.
This default is different from esp8266 Arduino core and very confusing. Most of the examples provided uses 3 different ntp servers for redundancy while only the first one is used actually.
Addressing issue #4964

cores/esp32/esp32-hal-time.c

@@ -44,6 +44,8 @@ static void setTimeZone(long offset, int daylight)
 /*
  * configTime
  * Source: https://github.com/esp8266/Arduino/blob/master/cores/esp8266/time.c
+ * Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+ *       see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
  * */
 void configTime(long gmtOffset_sec, int daylightOffset_sec, const char* server1, const char* server2, const char* server3)
 {
@@ -63,6 +65,8 @@ void configTime(long gmtOffset_sec, int daylightOffset_sec, const char* server1,
 /*
  * configTzTime
  * sntp setup using TZ environment variable
+ * Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+ *       see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
  * */
 void configTzTime(const char* tz, const char* server1, const char* server2, const char* server3)
 {

libraries/FFat/examples/FFat_time/FFat_time.ino

@@ -148,6 +148,10 @@ void setup(){
     Serial.println("IP address: ");
     Serial.println(WiFi.localIP());
     Serial.println("Contacting Time Server");
+    /*
+        Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+        see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
+     */
 	configTime(3600*timezone, daysavetime*3600, "time.nist.gov", "0.pool.ntp.org", "1.pool.ntp.org");
 	struct tm tmstruct ;
     delay(2000);

libraries/HTTPUpdate/examples/httpUpdateSecure/httpUpdateSecure.ino

@@ -17,6 +17,10 @@ WiFiMulti WiFiMulti;
 
 // Set time via NTP, as required for x.509 validation
 void setClock() {
+  /*
+    Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+    see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
+  */
   configTime(0, 0, "pool.ntp.org", "time.nist.gov");  // UTC
 
   Serial.print(F("Waiting for NTP time sync: "));

libraries/LittleFS/examples/LITTLEFS_time/LITTLEFS_time.ino

@@ -160,6 +160,10 @@ void setup(){
     Serial.println("IP address: ");
     Serial.println(WiFi.localIP());
     Serial.println("Contacting Time Server");
+    /*
+        Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+        see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
+     */
 	configTime(3600*timezone, daysavetime*3600, "time.nist.gov", "0.pool.ntp.org", "1.pool.ntp.org");
 	struct tm tmstruct ;
     delay(2000);

libraries/SD/examples/SD_time/SD_time.ino

@@ -164,6 +164,10 @@ void setup(){
     Serial.println("IP address: ");
     Serial.println(WiFi.localIP());
     Serial.println("Contacting Time Server");
+    /*
+        Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+        see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
+     */
 	configTime(3600*timezone, daysavetime*3600, "time.nist.gov", "0.pool.ntp.org", "1.pool.ntp.org");
 	struct tm tmstruct ;
     delay(2000);

libraries/SD_MMC/examples/SDMMC_time/SDMMC_time.ino

@@ -164,6 +164,10 @@ void setup(){
     Serial.println("IP address: ");
     Serial.println(WiFi.localIP());
     Serial.println("Contacting Time Server");
+    /*
+        Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+        see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
+     */
 	configTime(3600*timezone, daysavetime*3600, "time.nist.gov", "0.pool.ntp.org", "1.pool.ntp.org");
 	struct tm tmstruct ;
     delay(2000);

libraries/SPIFFS/examples/SPIFFS_time/SPIFFS_time.ino

@@ -148,6 +148,10 @@ void setup(){
     Serial.println("IP address: ");
     Serial.println(WiFi.localIP());
     Serial.println("Contacting Time Server");
+    /*
+        Note: Bundled Arduino lwip supports only ONE ntp server, 2nd and 3rd options are silently ignored
+        see CONFIG_LWIP_DHCP_MAX_NTP_SERVERS define in ./tools/sdk/esp32/sdkconfig
+     */
 	configTime(3600*timezone, daysavetime*3600, "time.nist.gov", "0.pool.ntp.org", "1.pool.ntp.org");
 	struct tm tmstruct ;
     delay(2000);