Increase time accuracy

[WhymustIhaveaname]

• increase time accuracy to not above 100ms
  • complete decimal part of NTP
  • use high-freq polling
  • add _current_epoc_dec and get_millis() so that ms can be known
• rewrite update()
  • solved overflow problem
  • change update()'s return type to byte in order to carry more info
  • add a not-request-too-fast feature by adding _last_fail in update()

I also add a demo program. I set an NTP Server in my LAN. In this network condition, the time error can be reduced to no more than plus-minus 10ms.

[fededim]

Any plan to fix and merge this PR soon ?

[fededim]

The build fails for these 2 errors:

/home/travis/build/arduino-libraries/NTPClient/examples/ntp_demo.ino: In function 'void connect_wifi(char*, char*)':
ntp_demo:28:25: error: 'class WiFiClass' has no member named 'channel'
     Serial.println(WiFi.channel());
                         ^
ntp_demo:30:25: error: 'class WiFiClass' has no member named 'getAutoReconnect'
     Serial.println(WiFi.getAutoReconnect());

Unluckily the functions channel and getAutoReconnect exist in WiFi, so it's strange that gives such errors. @Testato can you do a check and let us know ?

[WhymustIhaveaname]

I have tested these codes on my esp32. It works very well. It has run for half a month without a bug or crash.

These prints are not important. They are just showing what information one can get from WiFi.

[fededim]

According to log the build is done with platform esp8266, which is a little bit different from esp32. I hope that all Arduino library functions are present in every supported platform.

[wujiang]

Any plans to get this merged?

[CLAassistant]

All committers have signed the CLA.