Looking for small form factor with HDLC

[Kenneth Porter]

I'm attempting to create a middleware system that talks to one of my 
vendor's motion control products. My vendor has an FPGA capable of perhaps 
10 megabit performance, and RS485 full-duplex tranceivers. I want to be 
able to send commands and receive events and bulk data efficiently. I'll 
also add electrical isolation, possibly with suitable 485 transceivers.

I'm thinking that HDLC is a natural fit for the bit-level protocol, so I'm 
looking for an SBC and Linux OS with natural HDLC support. Ideally the SBC 
would fit in a 3"x3"x1" volume, and include Ethernet. It will go on a 
backplane along with the motion control box.

The Freescale chips look like many have the hardware to do HDLC, so I'm 
wondering what's available for boards and drivers.