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[lwip-users] Pbuf pool size and network interface

From: Enrico Murador - Research & Development - CET
Subject: [lwip-users] Pbuf pool size and network interface
Date: Thu, 23 Jun 2011 17:08:40 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv: Gecko/20110616 Thunderbird/3.1.11

Hi all,

I'm using the callback API's of LWIP, with a network interface based on the Coldfire MCF5223x driver.
The Coldfire interface is DMA based, and the driver pre-allocates a number of pbufs from the pool that will be "filled" by DMA.
the maximum number of buffers that my interface can allocate is 4 (of PBUF_POOL_BUFSIZE maximum size), as the original driver.
By watching the Lwip code (only of callback ApI's), my network interface is the only place where PBUF_POOL type buffer allocation is used
(excluding SLIP interface, that I don't use).

Therefore, might be correct to define PBUF_POOL_SIZE not more than the maximum number of netif's available buffers (4 in my example)?

Supposing I have a 500 bytes TCP_WND size, and my server application allows 10 simultaneous TCP connections;
do I need at least (10 * 500) bytes of total pbuf pool space (available to the network interface) to be sure to avoid "TCP deadlocks"?

Thank you for your patience

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