Re: [lwip-users] Ethernet Driver development guidelines.

[Piero 74]

Bill,

i could have some problems:

- my emac dma works only in a dedicated 16kB ram, so, pbufs poll must be allocated in this memory area. 
I should want only PBUF_POOL allocated in this memory, but PBUF_POOL is a part of memp vars (i.e. memp_memory, memp_sizes....), so i cannot split pbufs in different memory area.

i'm thinking that something is possible using custom pools... but i have no idea how i can use them to solve my problem.

Anyway, my driver (which uses copy operation) works well... it will be an improvement for the future

2008/3/18, Bill Auerbach <address@hidden>:

This was the point I missed, at first, in that discussion.  You don't need to worry about when the pbuf is freed.  Simply replace the filled one with an empty one (allocate a new one) and when lwIP is done with the original one, it will free it, placing it in the pool for a future allocation in your packet receiver.

 

---

From: lwip-users-bounces+bauerbach=address@hidden [mailto:address@hidden] On Behalf Of Piero 74
Sent: Tuesday, March 18, 2008 10:55 AM
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Ethernet Driver development guidelines.

 

Very interesting discussion (http://lists.gnu.org/archive/html/lwip-users/2007-12/msg00071.html) !!!

Now i have not enough free time for rewrite driver, and i developed my driver for nxp 236x microcontroller (which has emac controller with dma) using copy from emac memory and pbuf in pool.
It can manage packet using fragments with size less of MTU, so, i use emac memory in optimizing way.
But it could be very usefull to avoid copy operation in low level.
I see a problem:
My dma controller uses two index cycling on buffers (producerIndex and ConsumerIndex)...
I should know when lwip free pbufs, and after move consumer index.
But LWIP doesn't inform low level about free operation in pbuf!! How driver can be informed about this??

I think this thread could became a meeting point for discussion about driver development and lwip changes for particular customization of memory management....
bye,
Piero

2008/3/18, Bill Auerbach <address@hidden>:

> -----Original Message-----
> From: lwip-users-bounces+bauerbach=address@hidden
> [mailto:address@hidden] On Behalf
> Of Stephane Lesage
> Sent: Tuesday, March 18, 2008 7:57 AM
> To: Mailing list for lwIP users
> Subject: [lwip-users] Ethernet Driver development guidelines.
>

<snip>

> 3- Packet Buffers...
>
> As everyone, I would like to achieve an ideal zero-copy mechanism...
>
> a. DMA-TX: I can eventually manage chained-pbufs with multiple DMA
> descriptors... The condition is that intermediary pbufs are always full
> and multiple of 4 bytes. Is that possible ?
> (I don't know if TCP merges packets before the Naggle algorithm delay is
> expired)
>
> b. DMA-RX: I need a full 1514 bytes buffer for reception.
>  From what I read, it's not a good idea to have a big size for PBUF_POOL.
> So I should not directly use pools.
> An idea would be a static array of DMA buffers.
> Then 1 bad solution is PBUF_REF, because no way to know when it's
> released...
> Another solution is to allocate a pbuf from the pool in my RX thread and
> copy from the pre-allocated buffer. But I want to avoid the copy.
>
> So the only way would be to malloc() PBUF_RAM buffers... A set of
> initial buffers + create a new one and insert it in my DMA list each
> time a packet is received.
> Are people doing this ?


I don't know Blackfin, but if it has buffer descriptors like the PowerPC,
then this thread answered the question for me for no-copy buffers that the
Ethernet controller can DMA into.  Works great for me on a PPC.

http://lists.gnu.org/archive/html/lwip-users/2007-12/msg00071.html


Bill




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