-There is now only one clock domain crossing involved with the reg files/ All clock domain crossings use the same 104 bit wide async fifo! If it's broken we are screwed, if it works we are perfect!
-Configuration can be done from host through txwr/txrd path of any register
-The RX IO pins can only access the RX side of the design
-Access without symmetry was awkward, now we can reach regs from TX or RX side
-Removes a special path for mailbox (came for free)
-At the same time reduced clock complexity (one clock for system!!)
-Moved mailbox to top level
-Changed main clock to "sys_clk" for all
