BLP - Blinkenlights protocol

The Blinkenlights protocol is used to transmit black/white Blinkenlights streams using UDP packets. Simply, a UDP packet is sent for every new frame:

+-----------------------+
| magic                 |
| 0xDE 0xAD   0xBE 0xEF |
+-----------------------+
| frame number          |
| 0x00 0x00   0x00 0x00 |
+-----------+-----------+
| width     | height    |
| 0x00 0x12 | 0x00 0x08 |
+-----------+-----------+
| pixels                |
| 0x01 0x01   0x00 0x00 |
| 0x00 0x00   0x01 0x00 |
| ...                   |
| 0x00 0x00   0x00 0x00 |
+-----------------------+

• magic: fixed value
• frame number: number of the frame, incremented with every frame, use is optional
• width: the width of the image in pixels
• height: the height of the image in pixels
• pixels: the value of the width * height pixels
  • 0x00 for off, 0x01 for on, no other values allowed
  • from left to right, then from top to bottom (i.e. top left pixel first, pixel right to it next, ...)
• all values are in network byte order - big endian - highbyte first

The dynamic extension can be used to request a BLP stream dynamically. A request packet is sent periodically (e.g. every 10s) to the UDP port of the server. The server then replys with a BLP stream sent from this port to the source port of the request packet. After no request packet has been received for a longer time (e.g. 30s), the stream is no longer sent.

The format of the request packet is as follows:

+-----------------------+
| magic                 |
| 0xDE 0xAD   0xBE 0xCD |
+-----------------------+
| command               |
| 'R'  'E'    'F'  'R'  |
| 'E'  'S'    'H'       |
+-----------------------+

• magic: fixed value
• command: fixed value

It is also possible to tell the server that the stream is no longer needed. This happens by sending a close packet instead of a request packet:

+-----------------------+
| magic                 |
| 0xDE 0xAD   0xBE 0xCD |
+-----------------------+
| command               |
| 'C'  'L'    'O'  'S'  |
| 'E'                   |
+-----------------------+

• magic: fixed value
• command: fixed value

The UDP port should be configurable at server and client side. The standard port is UDP 2323.

-- StefanSchuermans - 06 Jun 2004