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ddr4-guide.md

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DDR4 DIMMs

Driver API and source code available in liquidctl.driver.ddr4.

Support for these DIMMs in only available on Linux. Other requirements must also be met:

  • i2c-dev kernel module has been loaded
  • r/w permissions to the host SMBus /dev/i2c-* device
  • specific unsafe features have been opted in
  • the host SMBus is supported: currently only i801 (Intel mainstream & HEDT)

Jump to a specific section:

DIMMs with a standard temperature sensor

Supports modules using TSE2004-compatible SPDD EEPROMs with temperature sensor.

Unsafe features:

Initialization

Not required for this device.

Retrieving the DIMM's temperature

# liquidctl status --unsafe=smbus,ddr4_temperature
DDR4 DIMM2
└── Temperature    30.5  °C

Corsair Vengeance RGB

Unsafe features:

Initialization

Not required for this device.

Retrieving the DIMM's temperature

# liquidctl status --verbose --unsafe=smbus,vengeance_rgb
Corsair Vengeance RGB DIMM2
└── Temperature    30.5  °C

Controlling the LED

Each module features a few non-addressable RGB LEDs. The table bellow summarizes the available channels, modes and their associated number of required colors.

Channel Mode Colors
led off 0
led fixed 1
led breathing 1–7
led fading 2–7

The LED colors can be specified using any of the supported formats.

The speed of the breathing and fading animations can be adjusted with --speed; the allowed values are slowest, slower, normal (default), faster and fastest.

# liquidctl set led color breathing ff355e 1ab385 speed=faster --unsafe=smbus,vengeance_rgb
                ^^^       ^^^^^^^^^ ^^^^^^^^^^^^^ ^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
              channel        mode      colors        speed        enable unsafe features

# liquidctl set led color fading "hsv(90,85,70)" "hsv(162,85,70)" --unsafe=smbus,vengeance_rgb
# liquidctl set led color fixed ff355e --unsafe=smbus,vengeance_rgb
# liquidctl set led color off --unsafe=smbus,vengeance_rgb

Inherent unsafeness of I2C and SMBus

Reading and writing to System Management (SMBus) and I²C buses is inherently more risky than dealing with, for example, USB devices. On typical desktop and workstation systems many important chips are connected to these buses, and they may not tolerate writes or reads they do not expect.

While SMBus 2.0 has some limited ability for automatic enumeration of devices connected to it, unlike simpler I²C buses and SMBus 1.0, this capability is, effectively, not safely available for us in user space.

It is thus necessary to rely on certain devices being know to use a specific address, or being documented/specified to do so; but there is always some risk that another, unexpected, device is using that same address.

The enumeration capability of SMBus 2.0 also brings dynamic address assignment, so even if a device is know to use a particular address in one machine, that could be different on other systems.

On top of this, accessing I²C or SMBus buses concurrently, from multiple threads or processes, may also result in undesirable or unpredictable behavior.

Unsurprisingly, users or programs dealing with I²C/SMBus devices have occasionally crashed systems and even bricked boards or peripherals. In some cases this is reversible, but not always.

For all of these reasons liquidctl requires users to opt into accessing I²C/SMBus devices, which can be done by enabling the smbus unsafe feature. Other unsafe features may also be required for the use of specific devices, based on other know risks specific to a particular device.

Note that a feature not being labeled unsafe, or a device not requiring the use of additional unsafe features, does in no way assure that it is safe. This is especially true when dealing with I²C/SMBus devices.

Finally, liquidctl may list some I²C/SMBus devices even if smbus has not been enabled, but only if it is able to discover them without communicating with the bus or the devices.