[lwip-users] Task priorities in TCP/IP Stack

[Christian Steffen]

Hello,

I use the lwIP/FreeRtos at the Atmel AVR32UC3. The current lwIP Version 
I use is 1.3.2.

Until now I had big problems with the stack and the priorities. At our 
system running three tasks, the TCP/IP task, the ETHINT task and the 
TCPECHO task. The FreeRtos is running in preemtive mode and the tcp/ip 
and ethint tasks are at the same priorities.

Now I see, that the ETHINT task don't use messages to commit the 
received frames to the TCP/IP task. It calls ethernet_input() directly. 
This depends, that two tasks work with the stack and the data structures 
are not ever constistent (read-modify-write). I receive a lot of 
assertions.

Is there a reason, why this is so implemented and not with messages?

At the moment I see three options to solve this problem.

1. Use messages to mbox in ethernetif() (I think this is a clean an safe 
alternative)
2. Use kooperative rtos. (this is no opinion for my application)
3. Run the ETHINT task with lower priority than the TCP/IP task. (this 
is not safe when an application with higher priority than tcp/ip task 
sends a message)

Best regards

Christian Steffen
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