[ECOS] network buffer alignment

[Lars Poeschel <larsi at wh2 dot tu-dresden dot de>]

Hello!

I am writing an ethernet driver for coldfire architecture and I am  
using redboot for simple ping tests.
I had the problem of strange ethernet destination addresses on the  
wire for outgoing packets. This was because the controller requires  
the buffers for transmitting to be 4 byte aligned and the buffer in  
question did not has this alignment. The buffer in question is in  
redboot/current/src/net/enet.c in function __enet_send, the eth_hdr  
stack variable. I now wonder if my ethernet controller is the only one  
with this 4 byte aligning requirement or if other architectures had  
luck in gcc aligning this buffer at a 4 byte boundary by random ?
I could make it work by forcing gcc with __attribute__((aligned(4)))  
to the right alignment. This would make a little change in the redboot  
sources neccessary, but I am not sure if this applies for all the  
other architectures out there. If this were not the case, my only  
other solution is: In the driver right before sending the packet I  
would check for the right buffer alignment and if it is not correct, I  
would have to allocate memory with the alignment in place and copy the  
wrong buffer there. This would be a really ugly solution.

What are your opinions ?

Thanks,

Lars

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