SNTP issue when NTP server is temporarily unavailable

Question

Greetings, I have a small problem with SNTP and I could not find any trace of the source of that problem. I use W5500 with ATmega128p and I use the Windows time service as the NTP server to test my code. I have been able to initialize the SNTP and update time periodically from the local server with no problems as examples show. Now, I want to test a case as if the NTP server is unavailable temporarily. So, I stop the windows service to simulate this for a while, and when start it back W5500 can not communicate with the server even if it is available. If I reset the MCU , it reads NTP correctly, but when stop/restart the service it can not communicate with server again. By looking at Wireshark: When the NTP server is running, I see packets for NTP protocol (as expected) When the NTP server is stopped, I see captured packet for ICMP error -port unreachable (as expected) But when the NTP server is available again, the server does not receive any request from W5500 at all, despite the SNTP_run() is running and returns 0. If I reset the MCU and W5500 , SNTP works again as expected. It seems that there is variable updated when the server is unavailable but not updated back when the server is available. I tried to go through sntp.c for the past two days but frankly I was lost. Can any one assist in identifying the problem? Thank you

Eugeny · Answer

We need your code under consideration and link to libraries you use.

Eugeny · Answer

Ca mzedan: I use the original files in ioLibrary_Driver. Can you give a link to it? There may be a number of places for sources over the internet, point me to the ones you used.

mzedan · Answer

Well, I have downloaded them. I am attaching them here Drivers.zip (12.1 KB)

Eugeny · Answer

Thanks. The routine is very small and simple, instead of guessing what is wrong put diagnostic output after each command displaying the stage it is in (what command is going to be executed) and result of previous command. i am sure you will get what is wrong very quickly