NAME¶

SYNOPSIS¶

DESCRIPTION¶

ddcutil communicates with monitors implementing MCCS (Monitor Control Command Set) using the DDC/CI protocol on the I2C bus. Normally, the video driver for the monitor exposes the I2C bus as devices named /dev/i2c-n. Alternatively, ddcutil can communicate with USB connected monitors implementing the USB Monitor Control Class Specification.

The Monitor Control Command Set describes a collection of Virtual Control Panel (VCP) features that a monitor can implement. Each feature is identified using a single byte. For example, feature x10 is the brightness control.

In general, the monitor settings that can be controlled by ddcutil are a superset of what can be changed using the buttons on a monitor and its on screen display. The specific capabilities vary from monitor to monitor.

A particular use case for ddcutil is as part of color profile management. Monitor calibration is relative to the monitor color settings currently in effect, e.g. red gain. ddcutil allows color related settings to be saved at the time a monitor is calibrated, and then restored when the calibration is applied.

Another common use case is to switch the monitor input source.

This man page includes only abbreviated documentation of trace and other program diagnostic facilities.

For extended documentation, use the "--help" option, and see http://www.ddcutil.com.

COMMANDS¶

detect Report monitors

vcpinfo [ feature-code | feature-group ]

Describe VCP feature codes that ddcutil knows how to interpret

capabilities

Query the monitor's capabilities string

getvcp [ feature-code | feature-group ]

Report a single VCP feature value, or a group of feature values

setvcp [+|-] feature-code new-value

Set a single VCP feature value. If + or - is specified, it must be surrounded by blanks, and indicates a relative value change of a Continuous VCP feature.

dumpvcp filename

Save color profile related VCP feature values in a file. If no file name is specified, one is generated and the file is saved <describe location>

loadvcp filename

Set VCP feature values from a file. The monitor to which the values will be applied is determined by the monitor identification stored in the file. If the monitor is not attached, nothing happens.

environment

Probe the ddcutil installation environment.

scs

Issue DDC/CI Save Current Settings request.

usbenv

Probe USB aspects of the ddcutil installation environment.

probe

Explore the capabilities and features of a single monitor.

interrogate

Collect maximum information for problem diagnosis.

chkusbmon

Tests if hiddev device is a USB connected monitor, for use in udev rules.

COMMAND ARGUMENTS¶

A feature-code is specified by its 2 character hex feature number, with or without a leading "0x", e.g. 0x10, 10

feature-group

The following are the most useful feature groups recognized. For a complete list, use the --help option.

ALL|KNOWN

All feature codes understood by ddcutil

COLOR

Scan color related feature codes

PROFILE

Subset of color related feature codes that are saved and restored by dumpvcp and loadvcp

SCAN

Scan all possible feature codes 0x00..0xff, except those known the be write-only

Feature group names can be abbreviated to the first 3 characters. Case is ignored. e.g. COL, pro

new-value

A decimal number in the range 0..255, or hexadeciaml number in the range x00..xff.

OPTIONS¶

-d,--display

display-number logical display number (starting from 1)

-b,--bus

bus-number I2C bus number

-a,--adl adapterIndex.displayIndex

ADL adapter and display indexes

--hiddev

device number hiddev device number

-u,--usb busnum.devicenum

USB bus and device numbers

-g,--mfg

3 letter manufacturer code

-l,--model

model name

-n,--sn

serial number. (This is the "serial ascii" field from the EDID, not the binary serial number.)

-e,--edid

256 hex character representation of the 128 byte EDID. Needless to say, this is intended for program use.

Options to control the amount and form of output.

-t, --terse, --brief

Show brief detail. For command getvcp, the output is in machine readable form.

-v, --verbose

Show extended detail

-U, --show-unsupported

Normally, getvcp does not report unsupported features when querying a feature-group. This option forces output.

--show-table | --no-table

Normally, getvcp does not report Table type features when querying a feature-group. --show-table forces output. --no-table is the default.

--rw, --ro, --wo

Limit getvcp or vcpinfo output to read-write, read-only, or (for vcpinfo) write-only features.

--mccs MCCS version

Tailor vcpinfo output to a particular MCCS version, e.g. 2.1

Options for diagnostic output.

--stats [all|errors|tries|calls|elapsed|time]

Report execution statistics. If no argument is specified, or ALL is specified, then all statistics are output. elapsed is a synonym for time. calls implies time.
I2C bus communication is an inherently unreliable. It is the responsibility of the program using the bus to manage retries in case of failure. This option reports retry counts and various performance statistics.

--ddc

Reports DDC protocol errors. These may reflect I2C bus errors, or deviations by monitors from the MCCS specification.

Options for program information.

-h,--help

Show program help.

-V, --version

Show program version.

Options to tune execution:

--maxtries (max-read-tries, max-write-read-tries, max-multi-part-tries)

Adjust the number of retries

--force-slave-address

Take control of slave addresses on the I2C bus even they are in use.

-f, --force

Do not check certain parameters.

--verify

Verify values set by setvcp or loadvcp. (default)

--noverify

Do not verify values set by setvcp or loadvcp.

--async

If there are multiple monitors, initial checks are performed in multiple threads, improving performance.

--nodetect

If the monitor is specified by its I2C bus number (option --busno) skip the monitor detection phase, improving performance.

EXECUTION ENVIRONMENT¶

NVIDIA PROPRIETARY DRIVER¶

Copy file /usr/local/share/ddcutil/data/90-nvidia-i2c.conf to directory /etc/X11/xorg.conf.d

sudo cp /usr/local/share/ddcutil/data/90-nvidia-i2c.conf /etc/X11/xorg.conf.d

This file will work "out of the box" if you do not have an /etc/X11/xorg.conf file. If you do, adjust the Identifier value in the file to correspond to the value in the master xorg.conf file.

(Note that the above instructions assume that datadir was set to /usr/local/share when ddcutil was installed. YMMV)

For further discussion of Nvidia driver settings, see http://www.ddcutil.com/nvidia.

AMD PRORIETARY DRIVER¶

To see if your copy of ddcutil was built with fglrx support, issue the command:
ddcutil --version

ADL identifies monitors using an adapter-number/display-number pair. To select a monitor using these numbers, specify the --adl option with a period separating the adapter-number and display-number, e.g.
--adl 0.1

VIRTUAL MACHINES¶

EXAMPLES¶

Identify all attached monitors.

ddcutil getvcp supported

Show all settings that the default monitor supports and that ddcutil understands.

ddctpp getvcp 10 --display 2
Query the luminosity value of the second monitor.

ddcutil setvcp 10 30 --bus 4

Set the luminosity value for the monitor on bus /dev/i2c-4.

ddcutil vcpinfo --verbose

Show detailed information about VCP features that ddcutil understands.

ddcutil interrogate > ~/ddcutil.out

Collect maximum information about monitor capabilities and the execution environment, and direct the output to a file.

DIAGNOSTICS¶

Requesting help is regarded as success.

SEE ALSO¶

AUTHOR¶