VIA Operation

To transmit:
User malloc()s memory buffer 
Memory pinned to RAM through ioctl()
User constructs send descriptor 
User writes pointer to "Tx doorbell" (mapped from Myrinet SRAM)
Board DMAs data and transmits

To receive:
User malloc()s memory buffer
Memory pinned to RAM through ioctl()
User constructs free-buffer descriptor 
User writes pointer to "Rx doorbell"
Board obtains descriptor for later use

User polls descriptor, or gets a signal