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Fadecandy: Open Pixel Control Protocol
======================================
The Fadecandy Server (`fcserver`) operates as a bridge between LED controllers attached over USB, and visual effects that communicate via a TCP socket.
The primary protocol supported by `fcserver` is [Open Pixel Control](http://openpixelcontrol.org), a super simple way to send RGB values over a socket. We support the standard Open Pixel Control commands, as well as some Fadecandy extensions.
Socket
------
Open Pixel Control uses a TCP socket, by default on port 7890. For the best performance, remember to set TCP_NODELAY socket option.
Command Format
--------------
All OPC commands follow the same general format. All multi-byte values in Open Pixel Control are in network byte order, high byte followed by low byte.
Channel | Command | Length (N) | Data
---------- | --------- | ---------- | --------------------------
1 byte | 1 byte | 2 bytes | N bytes of message data
Set Pixel Colors
----------------
Video data arrives in a **Set Pixel Colors** command:
Byte | **Set Pixel Colors** command
------ | --------------------------------
0 | Channel Number
1 | Command (0x01)
2 - 3 | Data length
4 | Pixel #0, Red
5 | Pixel #0, Green
6 | Pixel #0, Blue
7 | Pixel #1, Red
8 | Pixel #1, Green
9 | Pixel #1, Blue
… | …
As soon as a complete Set Pixel Colors command is received, a new frame of video will be broadcast simultaneously to all attached Fadecandy devices.
Set Global Color Correction
---------------------------
The color correction data (from the 'color' configuration key) can also be changed at runtime, by sending a new blob of JSON text in a Fadecandy-specific command. Fadecandy's 16-bit System ID for Open Pixel Control's System Exclusive (0xFF) command is **0x0001**.
Byte | **Set Global Color Correction** command
------ | ------------------------------------------
0 | Channel Number (0x00, reserved)
1 | Command (0xFF, System Exclusive)
2 - 3 | Data length (JSON Length + 4)
4 - 5 | System ID (0x0001, Fadecandy)
6 - 7 | SysEx ID (0x0001, Set Global Color Correction)
8 - … | JSON Text
Set Firmware Configuration
--------------------------
The firmware supports some runtime configuration options. Any OPC client can send a new firmware configuration packet using this command. If the supplied data is shorter than the firmware's configuration buffer, only the provided bytes will be changed.
Byte | **Set Firmware Configuration** command
------ | ------------------------------------------
0 | Channel Number (0x00, reserved)
1 | Command (0xFF, System Exclusive)
2 - 3 | Data length (Configuration Length + 4)
4 - 5 | System ID (0x0001, Fadecandy)
6 - 7 | SysEx ID (0x0002, Set Firmware Configuration)
8 - … | Configuration Data
Current firmwares support the following configuration options:
Byte Offset | Bits | Description
----------- | ------ | ------------
0 | 7 … 2 | (reserved)
0 | 3 | Manual LED control bit
0 | 2 | 0 = LED shows USB activity, 1 = LED under manual control
0 | 1 | Disable keyframe interpolation
0 | 0 | Disable dithering
1 … 62 | 7 … 0 | (reserved)