interprocessor communication

[jerry at evasefor.com]

Good afternoon list,
I have a single board computer with 2 cpu each running their own freebsd
kernel:

PHY--CPU1-----------logic---------CPU2---PHY
            mii bus         mii bus

Packets should flow from cpu1 to cpu2.
after I'm done processing a packet on CPU1 how can I address it
to CPU2?
Is there a kernel level interface to the MII bus I could
use for this (i.e read/write)?
Or any other idea, like shared memory, anything that you think could
work? 
Should this be implemented in the ethernet driver?

FYI, we can't use SMP.

Thanks a lot.
Jerry