Re: [lwip-users] Why does enabling Debug fix this tcp_sndbuf()

[address@hidden]

Am 24.03.2021 um 16:32 schrieb Osborne, David:
> Hi All,
>
>  
>
> I’m using LwIP + FreeRTOS + Sockets on STM32H7 with external SDRAM and
> FLASH (Ethernet buffers are internal).  It works well until the server
> has to send a very large message (> 18Kbytes).  One in five attempts
> ends in failure.  During the transmission tcp_sndbuf() (in api_msg.c)
> returns zero and the connection falls over.  From what I’ve read, a
> common cause is that it’s waiting for an outstanding ACK.  I’m no
> expert, but it looks like the ACK has been sent (see Wireshark attachment).
>
>  
>
> When I enable certain debug settings it works every time (don’t you hate
> that).

That's an indication that there's something wrong that's hidden by
either longer runtime (more debug code enabled) or by heavier cache
usage (more code/data in the caches).

In any case, I'd suggest thoroughly review the OS port and the netif
driver regarding caching issues and/or threading issues (where interrupt
vs. thread/main loop also counts in).

Regards,
Simon