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Re: [lwip-devel] again... Zero Copy Ethernet interface

From: Mike Kleshov
Subject: Re: [lwip-devel] again... Zero Copy Ethernet interface
Date: Tue, 23 Dec 2008 19:43:37 +0300

> As I was advised on this list last year, zero copy with DMA is possible and
> not difficult (for incoming packets) by allocating pbufs and pointing the
> DMA controller at the pbuf payload (you may have to play with alignment of
> this pointer depending on the architecture).  When a packet arrives,
> allocate a new pbuf, set the DMA controller to this new packet and return
> the pbuf that the DMA controller just filed to the caller of
> low_level_input.

I agree. That's exactly the way I did it and seemed quite natural.

> first, it could be necessary the possibility to allocate pbuf memory in
> particula memory region: my micro, for example, has emac dma which works on
> a fixed RAM region.

This is easily solved with a minor modification to lwip source code:
use your compiler/linker to locate the pbuf memory pool in that
specific region of memory. Since this is highly
compiler/linker-specific, I can't see how lwip could solve this for

- mike

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