esp-idf/examples/06_sntp

Example: using LwIP SNTP module and time functions

This example demonstrates the use of LwIP SNTP module to obtain time from Internet servers. See the README.md file in the upper level 'examples' directory for more information about examples.

Obtaining time using LwIP SNTP module

When this example boots first time after ESP32 is reset, it connects to WiFi and obtains time using SNTP. See initialize_sntp function for details.

Timekeeping

Once time is synchronized, ESP32 will perform timekeeping using built-in timers.

• RTC clock is used to maintain accurate time when chip is in deep sleep mode

• FRC1 timer is used to provide time at microsecond accuracy when ESP32 is running.

Timekeeping using RTC timer is demonstrated in this example by going into deep sleep mode. After wake up, ESP32 will print current time without connecting to WiFi.

To use this functionality, make sure "Timers used for gettimeofday function" option in "ESP32-specific config" menu of menuconfig is set to "RTC and FRC1" or "RTC".

Working with time

To get current time, gettimeofday function may be used. Additionally the following standard C library functions can be used to obtain time and manipulate it:

gettimeofday
time
asctime
clock
ctime
difftime
gmtime
localtime
mktime
strftime

To set time, settimeofday POSIX function can be used. It is used internally in LwIP SNTP library to set current time when response from NTP server is received.

Timezones

To set local timezone, use setenv and tzset POSIX functions. First, call setenv to set TZ environment variable to the correct value depending on device location. Format of the time string is described in libc documentation. Next, call tzset to update C library runtime data for the new time zone. Once these steps are done, localtime function will return correct local time, taking time zone offset and daylight saving time into account.