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Re: [lwip-users] Interniche and lwIP

From: Timmy Brolin
Subject: Re: [lwip-users] Interniche and lwIP
Date: Thu, 09 Jul 2009 19:36:27 +0200
User-agent: Thunderbird (Windows/20090605)

> But the problems/disadvantages with Interniche:
> 6  They support scatter-gather DMA in hardware but their driver doesn't take
> advantage of it.
Unless things have changed recently in Interniche land, this is also the
main reason why Interniche uses much more RAM than lwIP.
A full 1518 Byte buffer has to be allocated for every incoming packet,
unless you want to do one extra copy and reallocation operation in the
Ethernet driver.

Just this week I found bugs in Interniche IP fragmentation routines as
well as in the handling of IP options.
> The good parts:
> 2. The scatter-gather DMA is nice if utilized.
Most processors with integrated 100Mbit MAC supports scatter-gather.
Not really a noteworthy feature unless it supports some more advanced
features such as automatic TCP/IP header length detection so that the
scatter transfer can separate the TCP/IP or UDP/IP header from the
payload, even when the headers may have varying lengths due to header
options and vlan tags.
If combined with a finely grained MMU, such a feature would allow true
zero copy without the hazzle of having to handle pbuf chains in the
application layer.

/Timmy Brolin

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