oe7drt-website/content/posts/2023-05-28-backlight-control-on-a-lenovo-x1-carbon/index.md

+++
# vim: ft=markdown
title = 'Backlight control on a Lenovo X1 Carbon'
summary = '''These two scripts let the X1 switch to a predefined setting for
battery or ac mode. It also remembers the last used setting for either mode.'''
date = '2023-05-28T17:35:45+02:00'
# lastmod = ''
categories = [ 'computerstuff' ]
tags = [ 'freebsd', 'script' ]

+++

I like to have my computer reduce the screen brightness when it's not
connected to an external power source.

## powersave.sh

This is (mainly) used to control Intel SpeedStep®. I tend to save my custom
applications and scripts in `$HOME/bin`. Saved as `$HOME/bin/powersave.sh`.

```sh
#! /bin/sh

case $( sysctl -n hw.acpi.acline ) in

  (0) # BATTERY
    doas sysctl dev.hwpstate_intel.0.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.1.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.2.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.3.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.4.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.5.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.6.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.7.epp=100 1> /dev/null 2> /dev/null
    #backlight 20 1> /dev/null 2> /dev/null
    backlight $(cat ${HOME}/.backlight-bat) 1> /dev/null 2> /dev/null
    ;;

  (1) # AC
    doas sysctl dev.hwpstate_intel.0.epp=0   1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.1.epp=50  1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.2.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.3.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.4.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.5.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.6.epp=100 1> /dev/null 2> /dev/null
    doas sysctl dev.hwpstate_intel.7.epp=100 1> /dev/null 2> /dev/null
    #backlight 100 1> /dev/null 2> /dev/null
    backlight $(cat ${HOME}/.backlight-ac) 1> /dev/null 2> /dev/null
    ;;

esac
```

The script is run by a line in my personal cron table. A little delay (up to
a minute) is expected.

```crontab
* * * * * ~/bin/powersave.sh
```

## xbl

A script to modify different backlight settings depending on the connected
power source. Saved as `$HOME/bin/xbl`.

```sh
#! /bin/sh

print_usage () {
  echo >&2 "usage: $(basename ${0}) [0..100]"
  exit 1
}

# check if argument given or not (list or set value)
if [ $# -eq 1 ]
then
  # set value (select between ac or bat mode)
  # check if argument is integer between 0,100
  if [ "$1" -eq "$1" ] 2>/dev/null
  then
    if [ "$1" -ge 0 ] && [ "$1" -le 100 ] 2>/dev/null
    then
      # argument given and between 0,100
      case $( sysctl -n hw.acpi.acline ) in
        (0) # BATTERY
          echo "$1" > ${HOME}/.backlight-bat
          ;;
        (1) # AC
          echo "$1" > ${HOME}/.backlight-ac
          ;;
      esac
      backlight "$1"
    else
      # arg not between 0 and 100
      print_usage
    fi
  else
    # arg not an integer
    print_usage
  fi
else
  # no args given, only list values
  case $( sysctl -n hw.acpi.acline ) in
    (0) # BATTERY
      current=bat
      ;;
    (1) # AC
      current=ac
      ;;
  esac

  for status in ac bat
  do
    if [ "${status}" = "${current}" ]
    then
      echo -e "${status}: ★ \t$( cat ${HOME}/.backlight-${status} )" | tr "[:lower:]" "[:upper:]"
    else
      echo -e "${status}:\t$( cat ${HOME}/.backlight-${status} )" | tr "[:lower:]" "[:upper:]"
    fi
  done
fi
```