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iichid - Generic HID layer for FreeBSD

iichid is a set of abstract HID drivers for FreeBSD. All the drivers use evdev protocol to communicate with userland applications like libinput and xf86-input-evdev. hidbus is used to connect HID drivers with transport backends (usbhid for USB and iichid for I2C) and allows multiple HID drivers to attach to a single physical device.

Current drivers and respective HID devices supported by them are following:

  • hms - HID mouses. Physical relative devices with roller or optical sensor are supported as well as virtual absolute devices like VBox, Bhyve and VMWare mices.
  • hmt - MS Windows 7+ compatible Multi-touch devices like touchscreens and precission touchpads.
  • hconf - Mouse/touchpad mode switches on precission touchpads.
  • hkbd - HID keyboards. AT-key subset.
  • hskbd - Simple evdev-only HID keyboard driver.
  • hpen - Generic / MS Windows compatible HID pen tablets.
  • hcons - Consumer page AKA Multimedia keys.
  • hsctrl - System Controls page (Power/Sleep keys).
  • hgame - Game controllers including Xbox360-compatible and joysticks.
  • hidraw - Export raw HID data in uhid(4) and Linux hidraw-compatible way.

System requirements

FreeBSD 12.1+. Recent (any from 2020) CURRENT or 12-STABLE are preferred.

Downloading

This project does not have a special home page. The source code and the issue tracker are hosted on the Github:

https://github.com/wulf7/iichid

Building

To build driver, cd in to extracted archive directory and type

$ make

You need the sources of the running operating system under /usr/src

Installing

To install file already built just type:

$ sudo make install

and you will get the compiled module installed in /boot/modules

To load the module at a boot time, add both I2C driver module (it is usually an ig4) and HID module iichid to kld_list variable in /etc/rc.conf.

To handle keyboards in single user mode and at the early stages of booting process, iichid should be loaded at kernel startup. Add following lines to /boot/loader.conf in that case:

ig4_load="YES"
iicbus_load="YES"
iichid_load="YES"

Configure Xorg

Generally speaking, it is a bad idea to use static Xorg configuration for evdev devices due to dynamic unit number assignment. The simplest way to get new devices recognized by Xorg-server is to rebuild it with DEVD (since 1.20.7) or UDEV autoconfiguration backend enabled.

Static configuration is still possible. Add following snippet to a file under /usr/local/etc/X11/xorg.conf.d/

Section "InputDevice"
	Identifier "HID device"
	Driver "libinput"
	Option "Device" "/dev/input/event6"
	Option "AutoServerLayout" "true"
EndSection

You may need to run sudo libinput list-devices to find out unit number belonging to given device. Note that it can change across reboots.

usbhid

USB transport backend can (and usually does) interfere with OS built-in USB HID drivers like uhid, ukbd, ums and wmt. Which one will be active is depend on the order of loading, so genarally you should load iichid.ko from bootloader. In the case if the module is loaded with kldload it is necessary to issue

$ sudo usbconfig -d ugenX.X reset

command to force ugenX.X device reprobe at operating system run time. ugenX.X to reprobe can be found with issuing of simple usbconfig command:

$ sudo usbconfig

It is possible to build iichid with USB support disabled with following command:

$ make -DDISABLE_USBHID

I2C transport backend sampling (polling) mode

Currently iichid is unable to utilize GPIO interrupts on i386 and amd64 platforms due to absence of INTRNG support in PIC drivers and can not use any interrupts on 12.1-RELEASE due to inability of ig4 driver to work in ithread context in 12.1. In this case it fallbacks to so called sampling mode with periodic polling of hardware by driver. It is possible to check mode with following command:

$ sysctl dev.iichid.0.sampling_rate_slow

Any positive number returned means that sampling mode is enabled.

Unfortunatelly, using of sampling mode leads to lose of some data and often results in glitches. Most known are "drift of inactive mouse pointer" and "stuck of single finger touch". iichid has some internal hacks to workaround them but they are not reliable.

Choosing of optimal sampling rate for I2C transport.

Sampling rate is set to 60Hz by default. Although mostly it just works, in some cases e.g. if device internal scan rate lower than polling frequence it results in reading of empty reports, doubling of them or other unwanted effects.

Typically driver polling frequency should be set to about 0.9 of device internal scan rate. The simplest way to measure it is to run a Linux live distro from USB flash than execute evemu-record utility and choose your I2C device. Than you should convert inter-report interval duration to Hz and set 0.9 of that value as sampling_rate_fast parameter with following command

$ sudo sysctl dev.iichid.0.sampling_rate_fast=<poll freq>

If your device is supported by hmt driver, scan rate can be obtained by analyze of hardware timestamps. To enable them HQ_MT_TIMESTAMP quirk should be set for HID device. At first get vendor and product IDs with following command:

$ devinfo -rv | grep 'hmt.* bus=0x18'

It will return something like: hmt0 pnpinfo page=0x000d usage=0x0004 bus=0x18 vendor=0x06cb product=0x1941 ...

Then add following line to /boot/loader.conf replacing 0x6cb and 0x1941 with vendor and product values from previous command output.

hw.hid.quirk.0="0x18 **0x6cb** **0x1941** 0 0xffff HQ_MT_TIMESTAMP"

That will enable output of hardware timestamps in hmt driver after reboot. Reboot than attach evemu-record to proper node and touch device surface. You willl see something like this on stdout:

E: 33.569577 0004 0005 1152000	# EV_MSC / MSC_TIMESTAMP        1152000
E: 33.569577 0000 0000 0001	# ------------ SYN_REPORT (1) ---------- +18ms
E: 33.587771 0004 0005 1161000	# EV_MSC / MSC_TIMESTAMP        1161000
E: 33.587771 0000 0000 0001	# ------------ SYN_REPORT (1) ---------- +18ms
E: 33.605326 0004 0005 1170000	# EV_MSC / MSC_TIMESTAMP        1170000
E: 33.605326 0000 0000 0001	# ------------ SYN_REPORT (1) ---------- +18ms

Scan rate can be calculated with simple formula:

scan_rate = 1000000 / (MSC_TIMESTAMP(X) - MSC_TIMESTAMP(X-1))

where MSC_TIMESTAMP(X) and MSC_TIMESTAMP(X-1) are values taken from two consecutive events. In aforementioned example, optimal polling frequency is expected to be

sampling_rate_fast = 0.9 × 1000000 ÷ (1161000 − 1152000) = 100 (Hz)

It is possible to use double of scan_rate as sampling rate with increasing of dev.iichid.0.sampling_hysteresis to 3 or 4 to filter out missing samples. Tuning of this value requires enabling of debug output in I2C transport and lies out of scope of this README. Generally, sampling_hysteresis should be left as 1 if sampling frequency lower or equal 0.9 of device scan rate.

Bug reporting

You can report bugs at 'Project Issues' page https://github.com/wulf7/iichid/issues It is recommended to enclose console output of 'kldload iichid.ko' command with your report.

Some additional information that can be helpful especially if device has not been detected at all can be obtained with following commands:

$ devinfo -rv	# Very verbose
$ pciconf -lv
$ sudo usbconfig
$ dmesg

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Generic HID layer for FreeBSD. Including I2C and USB backends.

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