hal_input − control HAL pins with any Linux input device, including USB HID devices


loadusr hal_input [-KRAL] inputspec ...


hal_input is an interface between HAL and any Linux input device, including USB HID devices. For each device named, hal_input creates pins corresponding to its keys, absolute axes, and LEDs. At a fixed rate of approximately 10ms, it synchronizes the device and the HAL pins.


The inputspec may be in one of several forms:

A string S

A substring or shell-style pattern match will be tested against the "name" of the device, the "phys" (which gives information about how it is connected), and the "id", which is a string of the form "Bus=... Vendor=... Product=... Version=...". You can view the name, phys, and id of attached devices by executing less /proc/bus/input/devices. Examples:

"Vendor=001f Product=0001"

A number N

This opens /dev/input/eventN. Except for devices that are always attached to the system, this number may change over reboots or when the device is removed. For this reason, using an integer is not recommended.

When several devices are identified by the same string, add ":N" where N is the index of the desired device. For example, if Mouse matches input3 and input10, then Mouse and Mouse:0 select input3. Specifying mouse:1 selects input10.

For devices that appear as multiple entries in /dev/input, these indices are likely to stay the same every time. For multiple identical devices, these indices are likely to depend on the insertion order, but stay the same across reboots as long as the devices are not moved to different ports or unplugged while the machine is booted.

If the first character of the inputspec is a "+", then hal_input requests exclusive access to the device. The first device matching an inputspec is used. Any number of inputspecs may be used.

A subset option may preceed each inputspec. The subset option begins with a dash. Each letter in the subset option specifies a device feature to include. Features that are not specified are excluded. For instance, to export keyboard LEDs to HAL without exporting keys, use

hal_input -L keyboard ...


EV_KEY (buttons and keys). Subset -K

EV_ABS (absolute analog inputs). Subset -A

EV_REL (relative analog inputs). Subset -R

EV_LED (LED outputs). Subset -L


For buttons

input.N.btn-name bit out

input.N.btn-name-not bit out

Created for each button on the device.

For keys



Created for each key on the device.

For absolute axes

input.N.abs-name-counts s32 out

input.N.abs-name-position float out

input.N.abs-name-scale parameter float rw

input.N.abs-name-offset parameter float rw

input.N.abs-name-fuzz parameter s32 rw

input.N.abs-name-flat parameter s32 rw

input.N.abs-name-min parameter s32 r

input.N.abs-name-max parameter s32 r

Created for each absolute axis on the device. Device positions closer than flat to offset are reported as offset in counts, and counts does not change until the device position changes by at least fuzz. The position is computed as position = (counts - offset) / scale. The default value of scale and offset map the range of the axis reported by the operating system to [-1,1]. The default values of fuzz and flat are those reported by the operating system. The values of min and max are those reported by the operating system.

For relative axes

input.N.rel-name-counts s32 out

input.N.rel-name-position float out

input.N.rel-name-reset bit in

input.N.rel-name-scale parameter float rw

input.N.rel-name-absolute parameter s32 rw

input.N.rel-name-precision parameter s32 rw

input.N.rel-name-last parameter s32 rw

Created for each relative axis on the device. As long as reset is true, counts is reset to zero regardless of any past or current axis movement. Otherwise, counts increases or decreases according to the motion of the axis. counts is divided by position-scale to give position. The default value of position is 1. There are some devices, notably scroll wheels, which return signed values with less resolution than 32 bits. The default value of precision is 32. precision can be set to 8 for a device that returns signed 8 bit values, or any other value from 1 to 32. absolute, when set true, ignores duplicate events with the same value. This allows for devices that repeat events without any user action to work correctly. last shows the most recent count value returned by the device, and is used in the implementation of absolute.

For LEDs

input.N.led-name bit out

input.N.led-name-invert parameter bit rw

Created for each LED on the device.


By default, the input devices may not be accessible to regular users--hal_input requires read-write access, even if the device has no outputs. To change the default permission of a device, add a new file to /etc/udev/rules.d to set the device’s GROUP to "plugdev". You can do this for all input devices with this rule:

SUBSYSTEM=="input", mode="0660", group="plugdev"

You can also make more specific rules for particular devices. For instance, a SpaceBall input device uses the ’spaceball’ kernel module, so a udev entry for it would read:

DRIVER=="spaceball", MODE="0660", GROUP="plugdev"

the next time the device is attached to the system, it will be accessible to the "plugdev" group.

For USB devices, the udev line would refer to the device’s Vendor and Product values, such as

SYSFS{idProduct}=="c00e", SYSFS{idVendor}=="046d", MODE="0660", GROUP="plugdev"

for a particular logictech-brand mouse.

For more information on writing udev rules, see udev(8).


The initial state of keys, buttons, and absolute axes are erroneously reported as FALSE or 0 until an event is received for that key, button, or axis.