Drew:
You need to look around. There is at least one firewire controller that has a generic bus interface on it and has sufficient onboard buffering support (and I dont recall if that is on-board RAM or an interface to off-board SRAM chip) to assemble and disassemble packets at bus speed and yet permit the host processor to access the packets at it's speed.

One of the manufacturers of these 1394 controllers is Fujitsu. You can look at their MB86613/14/17 series controllers to see one of the type I am talking about. For example the MB86617B controller has dual onboard 4K byte buffers.

Michael Karas