Re: [lwip-users] Help with LwIP Modem

[Sylvain Rochet]

Hi,

On Fri, Jul 08, 2016 at 10:14:32AM +0200, Simon Goldschmidt wrote:
> Sylvain Rochet wrote:
> > You can't call tcpip_input() from an interrupt, this is a blocking
> > message passing, it can block.
> 
> It's not: tcpip_input/tcpip_inpkt calls sys_mbox_trypost(), which does 
> not have to be blocking but should return != ERR_OK if the queue is 
> full (drop input packets).

> However, this is a port function, so the port may well not support 
> doing this from interrupt if it's written in a wrong way.

Wrong way is a bit hard, the problem here is that some OS have two 
differents API, one which must be called from interrupt context, and one 
from threads. This is the case at least for FreeRTOS:

xQueueSend vs xQueueSendFromISR
xSemaphoreGive vs xSemaphoreGiveFromISR
...

lwIP sys port is not designed to deal with interrupt context vs thread 
context, the necessary data bit about this condition is lost in the 
port, so calling xQueueSend from interrupt instead of xQueueSendFromISR 
can block, so tcpip_input() called from interrupt is actually a blocking 
function.

Sylvain

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