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PROTOCOL.md

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Reverse engineered USB protocol of the NZXT Kraken X61

Basic knowledge of the USB protocol is assumed. Example codes use the PyUSB Python module.

Initialization

The device has to be initialized with the following control message:

Request Type Request Value Index Length
0x40 2 0x0002 0 0

Python code:

dev.ctrl_transfer(0x40, 2, 0x0002)

Messages

Messages sent by the host

The first byte of messages sent by the host is the message type:

Type Description Length in bytes
0x10 Color 19
0x12 Fan speed 2
0x13 Pump speed 2

Notes:

  • The pump speed doesn't seem to be too responsive
  • The Windows software always matches the pump and fan speeds
  • While the Windows software lets you set the speed to as low as 25%, it actually won't send messages containing speeds less than 30% to the device

Color message

Byte Meaning
1-3 Color (RGB)
4-6 Alternate color (RGB)
7-10 0x0000003c
11 Alternating interval (sec)
12 Blinking interval (sec)
13 Enabled (on/off)
14 Alternating mode (on/off)
15 Blinking mode (on/off)
16-18 0x000001

Notes:

  • Byte 10 has something to do with alternating mode, values <= 0x20 stop the color change
  • Changing byte 18 to anything other than 0x01 ramps up the speed to 100%
  • Newer versions of CAM (checked in 3.5.50) no longer allow changing the blinking and alternating interval

Fan speed message

Byte Meaning
1 Fan speed percentage (30-100)

Pump speed message

Byte Meaning
1 Pump speed percentage (30-100)

Status message sent by the cooler

Byte Meaning
0-1 Fan speed (RPM)
2-7 ?
8-9 Pump speed (RPM)
10 Liquid temperature (°C)
11-31 ?

Communication

Every transaction begins with the following control message:

Request Type Request Value Index Length
0x40 2 0x0001 0 0

Python code:

dev.ctrl_transfer(0x40, 2, 0x0001)

Afterwards, one of the following sequence of bulk messages are sent to endpoint 0x02:

  • a color message
  • a pump speed message followed by a fan speed message

Python code:

dev.write(2, [13, 50])
dev.write(2, [12, 50])

Finally, a status message of 64 bytes is read from the device (endpoint 0x82).

Python code:

status = dev.read(0x82, 64)
fan_speed = 256 * status[0] + status[1]
pump_speed = 256 * status[8] + status[9]
liquid_temperature = status[10]