Re: [lwip-users] Problem with CS8900 driver

[address@hidden]

Bernhard 'Gustl' Bauer wrote:
> Hi,
>
> I'm using LWIP 1.3.0 with the modified CS8900 driver coming with contrib.
>    
First of all, I think the one in CVS might be outdated since it is not 
maintained any more (which is why it has been moved to the 'old' 
subdirectory). Please have a look at the driver linked on 
http://lwip.wikia.com/wiki/Available_device_drivers (submitted by an 
lwIP user), as that might be better.
> The transfer from CS8900 to RAM buffer is done by DMA and works fine so
> far. Then cs8900_input() does a pbuf_alloc() and copies 1 packet from
> DMA buffer to pbuf.
>
> But what if pbuf_alloc() fails? If I drop this packet I might get
> problems with HTTP handshake. If I try again next time cs8900_service()
> is called I will run into the same problem. Neither cs8900_input() nor
> cs8900if_input() does anything without pbuf. There must be a pbuf_free
> before a pbuf_alloc is successful.
>
> How do I do this the right way?
>    
If you are running out of pbufs, the packet will be dropped. Since HTTP 
uses TCP, it will eventually be retransmitted. If, at that point, you 
are still out of pbufs, chances are that you configured the number of 
pbufs too low.

Generally, PBUF_POOL pbufs shall only be used for RX while TX uses _REF, 
_ROM or _RAM pbufs. Incoming pbufs are only buffer a) by your 
application or b) by the TCP_QUEUE_OOSEQ code.

If you disable TCP_QUEUE_OOSEQ, the only reason pbuf_alloc(PBUF_POOL) 
fails in the driver is that packets are coming in faster than your 
device can handle them.

Simon