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[lwip-devel] [task #7896] Support zero-copy drivers

From: Mike Kleshov
Subject: [lwip-devel] [task #7896] Support zero-copy drivers
Date: Sat, 22 May 2010 08:59:30 +0000
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/ Safari/532.5

Follow-up Comment #2, task #7896 (project lwip):

I am wondering how zero-copy transmission could be implemented with Coldfire
v2 Ethernet controller. The limitations of its DMA is that transmit buffers
must be 32-bit aligned and each buffer's size must be a multiple of 16 bytes.
The latter limitation is strange since in the very same microcontroller manual
they suggest to allocate one buffer for IP header, another for TCP header and
so on, but those headers' sizes are not multiples of 16 bytes...
Anyway, with those limitations I cannot see how zero-copy transmission could
work without imposing severe restrictions on how the application supplies data
to lwip. Basically, it would not be practical.
Am I right in this?


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