Ethernet.begin() does not return under certian circumstances

[pulli7]

In the past, with the Arduino-Ethernet-Shield, I used the following code to wait for ethernet connection to get available, so that I can have at least some limited functionality when ethernet is not available at this time, and automatically jump to full functionality as soon as link gets available.

void setup()
{
  if (Ethernet.begin(mac) == 0)
  {
    FallBackMode();
  } 
}

void FallBackMode()
{
  int Timestamp = millis();
  while(1)
  {
     if ( millis() - Timestamp > 300000)  //try reconnect every 5min
     {
       if (Ethernet.begin(mac, 30000) != 0)  //Problem here
       {                                   
         break;  //successfully connected
       }
       Timestamp = millis();
    }
    //call  "offline application"  here, which serves all functionality that does not need Ethernet
  }//ENDwhile
}

With the Nucleo 429ZI this does not work. As long as the cable is unplugged everthing is fine, but as soon as it is plugged in and ethernet gets available, the program gets locked inside the Ethernet.begin() function and never returns.

Am I misusing the function and it worked just coincidentally with the standard ethernet-shield, or is this a bug?
If this usage of the begin() function is not intended, is there another way to achieve that the board tries reconnecting itself?

Issue reproduced. This is under investigation.

[fpistm]

Hi all,
maybe the PR #5 fix this issue as the Ethernet scheduler is called by timer every 1ms?

[pulli7]

Gave it a quick try:

Looks like it changes the behavior in the way, that now calling Ethernet.begin() a second time, after the first try failed, always locks the program inside the function, no matter if ethernet is still unavailable or not.

@pulli7
Could you try the PR #5? It fixes your issue when several call of begin().

[pulli7]

Confirmed, issue is fixed.
Thank you again @fprwi6labs !

You're welcome @pulli7 .
@fpistm you can close all those issues.

[fpistm]

Thanks guy.

[bertoruiz]

I'm having the same problem with my Arduino UNO and ethernet shield. How exactly do I fix the problem when it hangs?

Examples of hanging:

• If I turn ON or reset the arduino and I am not connected via CAT5 to a good DHCP source.
• If arduino is working fine with IP and then if I pull the CAT5(do not reconnect it), but then reset the Arduino and then after it is fully restarted, I then insert the CAT5 from a good DHCP source.
• If the arduino is already running without it being connected to a good DHCP source, and I then I connect the arduino ethernet shield to a good DHCP source.

It works fine when:

• I am connected to a good DHCP source prior to turning ON arduino and get an IP right away.
• I am connected to a good DHCP source prior to RESETING arduino and get an IP right away.

[fpistm]

This library is designed for STM32 boards with native Ethernet.
You should submit your issue on https://github.com/adafruit/Ethernet2 or https://github.com/arduino/Arduino/tree/master/libraries/Ethernet depending of your shield.