6 years ago.

How stable is lwIP

Hi,

I have a webserver application that reveals the TCP/IP stack to be highly unreliable. I have spend, over a period of several months, numerous hours debugging my application software.

When I was left with just a few hears on my head, I hooked the mbed LPC1768 with a fixed IP up with a PC configured as a router (at 172.16.0.250) running Wireshark.

On an other device (in an class C private network at 192.168.1.3) running Google Chrome and Crontabs I refreshed a simple page every minute, requesting the page http://192.168.1.11/ ... (my router 's upstream address and the html page), the page forces the MBED to sync the RTC over NTP. It takes only an hour or two till the MBED freezes. I've included the Wireshark capture. /media/uploads/KKempeneers/mbed_spurious_retransmissions.pcapng

MBED application (at 172.16.0.100) eventually freezes up during an NTP request.

I'm actualy quite keen on getting problem solved, but unfortunately this problem raised beyond my technical capabilities.

Any input would be greatly appreciated,

KK

1 Answer

6 years ago.

I don't have enough experience myself with it to give you a useful answer regarding the stability. However in general with networking stuff, my experience is that it is too complicated: Programming an MCU to poll a sensor, and depending on the result do something, is something I would happily leave 10 years in the field without any worries about problems. Now getting any kind of internet stuff working for over an hour when stressing it is alot more questionable. Different wifi solutions I have used all had stability issues.

So in general: Make sure you have a watchdog timer running with proper seeding of the timer, so when it crashes it automatically reboots itself.

Accepted Answer

Thanks for the comment, your point of view is quite right. On the topic at hand. I've spend some more time debugging today. I was sure I wouldn't do so but what can one do on a rainy Sunday afternoon? I narrowed the problem down to the NTP Client software. The topic might therefor be more suitable for the forum see https://developer.mbed.org/forum/bugs-suggestions/topic/17133/.

posted by Koen Kempeneers 18 Oct 2015