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# ASUS C302

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The Asus C302 (also known as Asus C302C and Asus C302CA) is a Chromebook, which can have Linux installed. Here are some pointers on the smooth running of Arch Linux.

## Installation

Add `acpi_osi=Linux intel_iommu=on,igfx_off` to your kernel parameters.

`intel_iommu=on,igfx_off` is from BBS#228604, to prevent the following error from appearing in the output of dmesg:

    [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun

The CPU is an Intel Core M3, so install intel-ucode.

## Kernel Modules

In e.g. /etc/modprobe.d/skylake.conf

    # Needed, for the nau8825 kernel sound modules to initialize
    blacklist snd_hda_intel

    options tpm_tis interrupts=0

## Screen

The screen is 12.5 inches diagonally. At 1920x1080 resolution, this is 176 DPI, which is HiDPI.

In ~/.xinitrc, to set the screen dimensions (measured in millimetres):

    xrandr --fbmm 277x156

### Vsync

For proper vsync (including e.g. fullscreen Youtube in Firefox) in XFCE, install xfwm4-gitAUR, and enable XFCE's compositor.

Proper vsync also requires xf86-video-intel, rather than modesetting.

In /etc/X11/xorg.conf.d/20-intel.conf

    Section "Device"
        Identifier "Intel Graphics"
        Driver "intel"
    EndSection

### Screen Flipping

To use the laptop in tent mode, the following script will flip both the screen and touch input:

    #!/bin/dash

    set_normal() {
    	r="normal"
    	ctm="1 0 0 0 1 0 0 0 1"

    }

    set_upside_down() {
    	r="inverted"
    	ctm="-1 0 1 0 -1 1 0 0 1"
    }

    line=$(xrandr | grep '^eDP.* connected ')
    screen=$(printf "%s" "$line" | cut -d" " -f1)

    if $(printf "%s" "$line" | grep -q ' inverted (normal') ; then
    	set_normal
    else
    	set_upside_down
    fi

    xrandr --output "$screen" --rotate "$r"
    xinput set-prop "Elan Touchscreen" "Coordinate Transformation Matrix" $ctm

## Keyboard

To use the top row of Chromebook keys as useful keys in xorg, use e.g.:

In ~/.Xmodmap

    keycode   9 = Escape NoSymbol Escape
    keycode  22 = BackSpace BackSpace BackSpace BackSpace Delete NoSymbol Delete
    keycode  37 = Control_L NoSymbol Control_L
    keycode  50 = Shift_L NoSymbol Shift_L
    keycode  66 = Caps_Lock NoSymbol Caps_Lock
    keycode  67 = Home F1 Home F1 F1 F1 XF86Switch_VT_1
    keycode  68 = End F2 End F2 F2 F2 XF86Switch_VT_2
    keycode  69 = Prior F3 Prior F3 F3 F3 XF86Switch_VT_3
    keycode  70 = Next F4 Next F4 F4 F4 XF86Switch_VT_4
    keycode  71 = Delete F5 Delete F5 F5 F5 XF86Switch_VT_5
    keycode  72 = XF86MonBrightnessDown F6 XF86MonBrightnessDown F6 F6 F6 XF86Switch_VT_6
    keycode  73 = XF86MonBrightnessUp F7 XF86MonBrightnessUp F7 F7 F7 XF86Switch_VT_7
    keycode  74 = XF86AudioMute F8 XF86AudioMute F8 F8 F8 XF86Switch_VT_8
    keycode  75 = XF86AudioLowerVolume F9 XF86AudioLowerVolume F9 F9 F9 XF86Switch_VT_9
    keycode  76 = XF86AudioRaiseVolume F10 XF86AudioRaiseVolume F10 F10 F10 XF86Switch_VT_10
    keycode 111 = Up Up Up Up Prior Prior
    keycode 112 = Prior NoSymbol Prior
    keycode 113 = Left Left Left Left Home Home
    keycode 114 = Right Right Right Right End End
    keycode 115 = End NoSymbol End
    keycode 116 = Down Down Down Down Next Next
    keycode 117 = Next NoSymbol Next
    keycode 118 = Insert NoSymbol Insert
    keycode 119 = Delete NoSymbol Delete
    keycode 124 = XF86PowerOff NoSymbol XF86PowerOff
    keycode 167 = XF86Forward NoSymbol XF86Forward
    keycode 182 = XF86Close NoSymbol XF86Close
    keycode 191 = XF86ScreenSaver NoSymbol XF86ScreenSaver

(This list can be pruned.)

~/.Xmodmap will be loaded by /etc/X11/xinit/xinitrc, which effectively runs:

    xmodmap ~/.Xmodmap

### Keyboard Backlight

To be able to change the keyboard backlight brightness as a normal user, run as root:

    b="/sys/devices/platform/GOOG0002:00/leds/chromeos::kbd_backlight/brightness"
    chgrp users "$b" &&
    chmod 660 "$b" &&
    echo 6 > "$b"

It is a value between 0 (off) and 100 (full brightness). The default on ChromeOS is 25. 6 is a reasonable lower value.

ChromeOS is able to disable the keyboard backlight, when the keyboard is not being used - that functionality does not appear to be available in the Linux kernel, but can be replicated in a simple script, with the aid of xprintidle, e.g.:

    #!/bin/dash

    set_keyboard_backlight() {
    	printf "%s" "$1" > "/sys/devices/platform/GOOG0002:00/leds/chromeos::kbd_backlight/brightness"
    	b="$1"
    }

    b=0

    while true ; do
    	pgrep ^Xorg > /dev/null || exit 0

    	seconds_to_sleep=10
    	idle_millis=$(xprintidle)
    	if [ "$idle_millis" -gt 10000 ] ; then
    		nb=0
    		seconds_to_sleep=5
    	else
    		nb=25
    		seconds_to_sleep=15
    	fi

    	if [ "$nb" -ne "$b" ] ; then
    		set_keyboard_backlight "$nb"
    	fi

    	echo "nb=$nb, sleeping for $seconds_to_sleep"
    	sleep "$seconds_to_sleep"
    done

## Touchpad

As of libinput 1.12.0-2, the touchpad works nicely with all of:

- Tapping:
  - 1-finger tap = "left" button
  - 2-finger tap = "right" button
  - 3-finger tap = "middle" button

- Clickpad (clicking the lower portion of the touchpad):
  - Left side = "left" button
  - Right side = "right" button
  - Middle = "middle" button

## Mouse

Due to the limited amount of USB ports, a Bluetooth mouse is a good option. The Logitech M590 mouse works great.

Run "bluetoothctl power on &" at startup, e.g. in ~/.xinitrc

In e.g. /etc/X11/xorg.conf.d/99-mouse.conf

    Section "InputClass"
        Identifier "Logitech M590"
        MatchIsPointer "on"
        MatchDevicePath "/dev/input/event*"
        Driver "libinput"
        Option "AccelProfile" "flat"
    EndSection

Then, the "speed" of the mouse can be set using the XFCE GUI, in "Settings - Mouse", setting the "acceleration" to e.g. 2.0

## Sound

Sound is a work in-progress. Sound is reliable when using headphones only.

Save the audio firmware as /lib/firmware/9d70-CORE-COREBOOT-0-tplg.bin (filesize 23120 bytes).

To set audio to a sensible level, run in ~/.xinitrc:

    amixer -q -c0 sset Headphone 70% &

### PulseAudio

To prevent audio "clicks", comment out "load-module module-suspend-on-idle" in /etc/pulse/default.pa and /etc/pulse/system.pa

## Coil Whine

There is occasional coil whine, which can be greatly reduced by running:

    printf "1" > /sys/devices/system/cpu/intel_pstate/no_turbo

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- Chrome OS devices

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