BlinkenlightsProtocolEnglish

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Stream

The Blinkenlights protocol is used to transmit black/white Blinkenlights streams using UDP packets. Simply, a UDP packet is sent for every new frame (frames lasting more than one second are repeated every second):

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

It is also possible to send those packets over stream-like connections, like TCP or serial ports.

Dynamic Extension

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

Additional Information

A further extension allows to transmit information in addition to the stream packets or the request packets of the dynamic extension. Those information packets have the following structure:

+-----------------------+
| magic                 |
| 0xDE 0xAD   0xBE 0x23 |
+-----------------------+
| info                  |
| 0x45 0x4E   0x44 0x00 |
| 0x00 0x00   0x00 0x00 |
+-----------------------+

• magic: fixed value
• info: 0..8 ASCII characters, padded with 0x00 to 8 bytes in total
  • "END", S2R: the stream has ended
• abbreviations:
  • S2R: sender to receiver, packet is sent in same direction as stream frames
  • R2S: receiver to sender, packet is sent in same direction as stream requests