So I made some small progress in debugging, at least something that are likely correlated with the hanging issue. Inspired by a work-around here: https://github.com/ntruchsess/arduino_uip/issues/167 I started checking the values of two registers on ENC28J60, specifically the ESTAT and EIR registers. These two contain certain bits (specifically buffer overflow flag ESTAT.BUFFER, and receive error flag EIR.RXERIF) that the work-around uses to flag a hanging state and reboot the microcontroller. But here are my findings: I put two OS 3.2 with ethernet modules on my network, they run exactly the same code:
– on the one that’s connected to my main router, these two bits are flagged shortly after the controller starts. No hanging yet, but assume that eventually that may happen.
– on the one that’s connected to my secondary router (as I described above, in order to isolate the OS from the rest of my main network), these two bits remain 0 since I started the experiment two days ago, and the OS has been running fine with no hanging since then.
I suspect that some device or maybe the main router itself is constantly sending broadcast messages of some sort which quickly led to an erroneous state. Of course this doesn’t mean that the controller will hang immediately, but if these bits are not cleared, they may lead to a hanging state eventually.
This should be fixable in software by modifying the UIPEthernet library. The reason is that I also tested the EtherCard library, which we’ve been using for a long time prior to UIPEthernet. When using EtherCard, these two bits remain 0 on both of the testing controllers. This seems a strong evidence that the two bits are related to the hanging issue.
So we will keep digging and maybe reach out to the author of UIPEthernet to see if he can help. The bottomline is that I don’t think there is anything fundamentally wrong with ENC28J60 at the hardware level — it’s a chip that has been around for a very long time. So I am pretty confident that the issue can be resolved by a firmware update.