RE: [lwip-users] Installed the new version, since all the changesand turned on the ASSERT debug

[Joolz [RSD]]

-----Original Message-----
From: Kieran Mansley [mailto:address@hidden 
Sent: 20 March 2007 13:18
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Installed the new version, since all the
changesand turned on the ASSERT debug

On Tue, 2007-03-20 at 11:22 +0000, Joolz [RSD] wrote:
> My code now stops with the following message.
> 
> Asserion p->flags==PBUF_FLAG_RAM || p->flags==PBUF_FLAG_POOL failed at

> line 487 in lwip2/src/core/pbuf.c
> 
> Now in my code what I do is the following
> 
> ...
> Struct pbuf *data;
> Unsigned char *tempBuffer;
> 
>       data = pbuf_alloc( PBUF_RAW, PAYLOAD_SIZE, PBUF_ROM);
>       tempBuffer = pvMalloc( PAYLOAD_SIZE); // Allocate my buffer from
my 
> memory
> 
> Now further in the code I need to fill a buffer from a circular buffer

> and if the data does not wrap around I do the following
> 
>       data->payload = currentBufferAddress;
>       udp_send( outUdp, data);
> 
> If the buffer will wrap around I copy the two parts into the temp 
> buffer allocated at the start
>       memcpy( tempBuffer, curren....
>       memcpy( tempBuffer+whatsLeft, ....
>       data->payload = tempBuffer;
>       udp_send( outUdp, data);

As an aside you could avoid this copy by just calling udp_send twice,
once for each fragment. 

> So what is the best way because I don't want to copy the data when I 
> do not need to.

>>The problem is that lwIP needs to stick a UDP and IP header on the
front of the pbuf payload, and for a ROM type of pbuf it can't do this,
as it has no 
>>knowledge of what is in memory before the pointer provided.  In your
case for example, there is a good chance that it would overwrite another
packet if it 
>>tried to use that space.

>>If you could arrange for there to be space in front of each fragment
you pass to udp_send() to store the pbuf structure, ethernet, IP and UDP
headers, then 
>>you could create your own PBUF_RAM pbuf rather than allocate a
PBUF_ROM pbuf and set the payload as you do above.  Then it should all
work fine.  
>>However, if you're transferring from a circular buffer then you'll
have a problem doing that I think, and so you're probably going to have
to take the hit of a 
>>copy.
>>
>>Kieran

I tried the 2 * udp_sends and some receiver boxes don't like it, they
seem to need the the buffer being sent at the correct size (7*188).

So I can build a buffer and copy the from the circular buffer every
time, ive got no dma so it would be a software copy. SLOW

My circular buffer is 512K so if I can do it the same way I would only
have to copy 1 out of every 400 buffers, that's a large saving in
cycles.

The box is a DTT to IP convertor and its possible that this box will be
transmitting a full TS which could be upto 5M (30Mbs) per second.

So can anybody come up with any way of getting around this, my processor
is 130Mhz and around 100Mips so any help would be most helpfull.

Joolz