Protocol
========

<Type>	<Seq>	<MaxSeq>

   0	0	X	Ping (no further payload)

   1	0	0	Pong (maybe return version string in the future)

   2	0	0	Reset (64 bytes reset secret)

   4	0	N	Unlock secret (64 bytes payload)
   4	1..N-1	N	Firmware binary (64 bytes payload)
   4	N	N	First half of hash

   5	n	N	Firmware ACK

   6	0..N-1	N+3	Image binary (64 bytes payload)
   6	N	N+3	Salt A
   6	N+1	N+3	Salt B
   6	N+2	N+3	Hash A
   6	N+3	N+3	Hash B

   7	n	0	Image ACK

   8	0	4	Parameter block (64 bytes payload)
   8	1	4	Salt A
   8	2	4	Salt B
   8	3	4	Hash A
   8	4	4	Hash B

   9	n	0	Parameter ACK

Unlock, firmware, image, and parameter packets all have a fixed-size
64 bytes payload. Pings and acknowledgements have no payload. Pongs
may have a variable-size payload.

Even numbered packet types correspond to packets sent from the remote
controller to the device. Odd numbered packet types correspond to
responses. The device never initiates communication.