asdbctl

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Apple Studio Display Brightness Control +++++++++++++++++++++++++++++++++++++++ This small command line utility allows for changing the brightness of one or more Apple Studio Display(s) attached to a Linux or Windows PC.

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Tool to get or set the brightness for Apple Studio Displays

Usage: asdbctl [OPTIONS] <COMMAND>

Commands:
  get   Get the current brightness in %
  set   Set the current brightness in %
  up    Increase the brightness
  down  Decrease the brightness
  help  Print this message or the help of the given subcommand(s)

Options:
  -s, --serial <SERIAL>  Serial number of the display for which to adjust the brightness
  -h, --help             Print help

Getting started

Prebuild releases are not available. Only Rust is required to build from source.

.. code-block:: bash

git clone https://github.com/juliuszint/asdbctl.git && cd asdbctl
# either just run from here
cargo run --release -- help
# or install with
cargo install --path .

Troubleshooting

In case regular users are not allowed to access raw HID devices, you can use the udev rule in the rules.d directory.

Technical details

Dumping the USB traffic on macOS with Wireshark and setting the proper filters will show the USB Control transfers to set the brightness

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bmRequestType: 0x21
bRequest     : 0x9
wValue       : 0x0301
wIndex:      : 0x000c
wLength      : 0x7

with this data package when setting it to the minimum brightness value

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[ 0x01, 0x90, 0x01, 0x00, 0x00, 0x00, 0x00 ]

The 0x90 and 0x01 are the brightness value encoded with the least significant byte first (LSB).

Its possible to operate the Studio Display in 3 different USB configurations and Linux will use the first. This means that the USB interface number for controlling the brightness is not 0xc (extracted from the dump) but 0x7.

Decoded HID Report Descriptor

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Apple Studio Display HID report descriptor

# device 0:0
# 0x05, 0x80,                    // Usage Page (Monitor)                0
# 0x09, 0x01,                    // Usage (Monitor Control)             2
# 0xa1, 0x01,                    // Collection (Application)            4
# 0x85, 0x01,                    //  Report ID (1)                      6
# 0x06, 0x82, 0x00,              //  Usage Page (VESA Virtual Controls) 8
# 0x09, 0x10,                    //  Usage (Brightness)                 11
# 0x16, 0x90, 0x01,              //  Logical Minimum (400)              13
# 0x27, 0x60, 0xea, 0x00, 0x00,  //  Logical Maximum (60000)            16
# 0x67, 0xe1, 0x00, 0x00, 0x01,  //  Unit (SILinear: cm⁻² * cd)         21
# 0x55, 0x0e,                    //  Unit Exponent (-2)                 26
# 0x75, 0x20,                    //  Report Size (32)                   28
# 0x95, 0x01,                    //  Report Count (1)                   30
# 0xb1, 0x42,                    //  Feature (Data,Var,Abs,Null)        32

# 0x05, 0x0f,                    //  Usage Page (Vendor Usage Page 0x0f) 34
# 0x09, 0x50,                    //  Usage (Vendor Usage 0x50)          36
# 0x15, 0x00,                    //  Logical Minimum (0)                38
# 0x26, 0x20, 0x4e,              //  Logical Maximum (20000)            40
# 0x66, 0x10, 0x01,              //  Unit (None)                        43
# 0x55, 0x0d,                    //  Unit Exponent (-3)                 46
# 0x75, 0x10,                    //  Report Size (16)                   48
# 0xb1, 0x42,                    //  Feature (Data,Var,Abs,Null)        50

# 0x06, 0x82, 0x00,              //  Usage Page (VESA Virtual Controls) 52
# 0x09, 0x10,                    //  Usage (Brightness)                 55
# 0x16, 0x90, 0x01,              //  Logical Minimum (400)              57
# 0x27, 0x60, 0xea, 0x00, 0x00,  //  Logical Maximum (60000)            60
# 0x67, 0xe1, 0x00, 0x00, 0x01,  //  Unit (SILinear: cm⁻² * cd)         65
# 0x55, 0x0e,                    //  Unit Exponent (-2)                 70
# 0x75, 0x20,                    //  Report Size (32)                   72
# 0x95, 0x01,                    //  Report Count (1)                   74
# 0x81, 0x02,                    //  Input (Data,Var,Abs)               76

# 0xc0,                          // End Collection                      78

R: 79 05 80 09 01 a1 01 85 01 06 82 00 09 10 16 90 01 27 60 ea 00 00 67 e1 00 00 01 55 0e 75 20 95 01 b1 42 05 0f 09 50 15 00 26 20 4e 66 10 01 55 0d 75 10 b1 42 06 82 00 09 10 16 90 01 27 60 ea 00 00 67 e1 00 00 01 55 0e 75 20 95 01 81 02 c0
N: device 0:0
I: 3 0001 0001

Related projects

Other projects that helped along the way were LG-ultrafine-brightness_ and acdcontrol_.

.. _acdcontrol: https://github.com/yhaenggi/acdcontrol .. _LG-ultrafine-brightness: https://github.com/ycsos/LG-ultrafine-brightness