On Fri, Sep 15, 2000 at 02:09:44PM -0700, Jun Sun wrote:
> I was trying to run some PCI ether drivers and always got bus error, at
> least when I use ipconfig bootp code.
> However, the problem seems to be generic.
> Ethernet device writes a whole packet in the memory. Driver and network
> stack code often directly dereference a pointer in to the packet.
> However, the ether header is 14 byte long. If you align packet from the
> beginning, then IP header will be off-aligned.
> Any suggestions?
The strategy is to get the alignment right for the IP header, that is
to make the received packet start on a address with bit 1 set.
> If this is a valid problem, I think the long term solution should be in
> network code, which should not assume they can dereference on an
> unaligned address.
It tries to avoid unaligned accesses - if necessary even at the price of
wasting some memory.
> For short-term solutions, we can have trap handler that supports the
> unaligned read/write. Does anybody know if there is such a trap handler
> for MIPS?
It's right there in your kernel ...
You _really_ _really_ want to avoid relying on the unaligned trap handler.
Performancewise that's equivalent to a swapping on a floppy disk on the
Mars over NFS via avian carriers ...
However unaligned accesses will result in an address error exception not
bus error therefore I suspect you've got another problem.