1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| Next Payload  |C|  RESERVED   |         Payload Length        |
+---------------+---------------+-------------------------------+
|  Protocol ID  |   SPI Size    |      Notify Message Type      |
+---------------+---------------+-------------------------------+