Re: [lwip-users] ERR_MEM after write [LwIP 1.4]

[Sergio R. Caprile]

> Does anyone have any ideas?

Yes!

You said '1.4', is there another number after that ? You should move to 
at least 1.4.1 if somehow you can't go 2.0 (unless you are on a ESP8266...)

Don't attach screen captures, do attach capture files. For instance, I 
can't see the frame numbers in your snapshot, nor if there is an invalid 
checksum.

As you know, TCP needs the other end to ACK before it can send more. 
Those unsent frames are there in your memory waiting to be ACKed. You 
shouldn't be sending at will but after you know for sure what you've 
sent has been ACKed. You do this by registering a tcp_sent() callback.
50ms seems a long time, but it depends on what your port does. What do 
you have below lwIP ? Is it an OS ? Is it bare metal ?
Are you calling sys_check_timeouts() ?
You must call lwIP low-level functions from within the same context, all 
from ints or all from main, no mix. Are you ?

Your driver needs to behave in order for the pbufs to be properly freed. 
Does it ?

Have you tried running a working example to see if your port + driver 
works OK ?

Have you tried enabling statistics ?