Re: [lwip-devel] Problem with custom buffers when MEM_ALIGNMENT=4 and ETH_PAD_SIZE=2

[Mason]

Simon Goldschmidt wrote:

> Mason <address@hidden> wrote:
> 
>> --- pbuf.c.orig 2011-08-24 11:02:34.484375000 +0200
>> +++ pbuf.c      2011-10-25 16:03:44.015625000 +0200
>> @@ -376,7 +376,7 @@
>>
>>    p->pbuf.next = NULL;
>>    if (payload_mem != NULL) {
>> -    p->pbuf.payload = LWIP_MEM_ALIGN((void *)((u8_t *)payload_mem + 
>> offset));
>> +    p->pbuf.payload = (u8_t *)payload_mem + offset;
>>    } else {
>>      p->pbuf.payload = NULL;
>>    }
> 
> I've recently changed that in git to:
> 
>   p->pbuf.payload = (u8_t *)payload_mem + LWIP_MEM_ALIGN_SIZE(offset);
> 
> Does that work for you?

I'm using PBUF_RAW, so offset=0, so your modification and mine are equivalent.

I think there might be another problem when pbuf_layer = PBUF_LINK

Assume payload = 0x82751742, thus the IP header is at 0x82751742 + 0xd = 
0x82751750
but the actual code will set payload to payload_mem + 16

But maybe we wouldn't use the PBUF_LINK layer in such a case?

>> Probably not appropriate, but again, I'm not sure what MEM_ALIGNMENT
>> really means.
> 
> Your MEM_ALIGNMENT is correct: it's used for accessing U32 variables,
> not for cache aligment.

Thanks for clearing this up.

-- 
Regards.