wiki:lcd4linux_conf

CONFIGURATION

The config file (default: /etc/lcd4linux.conf) contains the configuration and layout of LCD4Linux. Starting with 0.10, the format changed a lot, and is now much more flexible.

Any text on a line after a hash character ('#') (and empty lines) will be ignored (If you want to use '#' in a value (think of X11-colors), you have to quote it with a backslash). Empty lines and lines containing only whitespace characters will be ignored, too.

The file consists of sections, subsections and parameters. Section and parameter names are not case sensitive. A key must not contain whitespace.

A parameter looks like this:

name value

BIG FAT WARNING: Every value from the config file is treated as an expression, and therefore will be evaluated. This means that normally you have to enclose a value in single quotes so that it evaluates to a string!

Some examples:

name1 value1
name2 'value2'
name3 '2+3'
name4 2+3
name5 '42'
name6 42

name1 will be evaluated from the expression 'value1', which will return 0 (or an empty string), which is normally not what you want (except when value1 is the name of a variable).
name2 will return the string 'value2', which is what you want.
name3 will return the string '2+3'
name4 will evaluate the expression '2+3', and will return 5
name5 will evaluate to the string '42' (or the number 42 in numeric context)
name6 gives exactly the same result as name5

Sections looks like this:

section_a {
   name1 value1
}
section_b name_b {
   name2 value2
}
section_c name_c {
   name3 value3
   section_d {
      name4 value4
   }
}

So a section may or may not have a name!

Sections can be written in a compact form, so the following is fully equivalent to the example above:

section_a.name1 value1
section_b:name_b.name2 value2
section_c:name_c.name3 value3
section_c:name_c.section_d.name4 value4

Sections and section names are concatenated with a colon (':'); sections, subsections and keys are concatenated with a dot ('.')

Here's a more real-world example: the following two entries (from a wiring configuration) are equivalent:

Wire.EX   'STROBE'
Wire.IOC1 'SELECT'
Wire.IOC2 'AUTOFD'
Wire.GPO  'INIT'
Wire {
   EX   'STROBE'
   IOC1 'SELECT'
   IOC2 'AUTOFD'
   GPO  'INIT'
}

Section selection

Note that there's a difference between name value { } and name value: The first defines a section, the second a parameter, but both have the same name! This is used to select a specific section.

Take a look at this:

Display My_20x4 {
   ...
}

Display My_16x2 {
   ...
}

Display My_16x2

You define two display sections with different names, and afterwards select one of the sections.


Special sections

some sections have a special meaning:

Display: Display-specific configuration, depends on the display and driver used.
Plugin: Configuration for specific plugins (rarely used)
Widget: Definition of Widgets
Layout: How and where widgets are placed on the display
Variables: Definition of variables


Minimalistic example configuration

Display HD44780-20x2 {
    Driver  'HD44780'
    Model   'generic'
    UseBusy  1
    Port    '/dev/parport0'	
    Size    '20x2'
    Wire {
	RW      'AUTOFD'
	RS      'INIT'
	ENABLE  'STROBE'
	ENABLE2 'GND'
	GPO     'GND'
    }
}


Widget CPU {
    class  'Text'
    expression  uname('machine')
    prefix 'CPU '
    width  9
    align  'L'
    update tick
}

Layout Default {
    Row1 {
        Col1 'CPU'
    }
}

Variables {
   tick 500
}

Display 'HD44780-20x2'
Layout  'Default'

There is at least one Display section, which describes and configures your display.
You have some Widget sections, which define what and how data is displayed.
Widgets are placed on the display in the Layout section.


Security

Because of security reasons (the configuration may contain usernames/passwords for mail accounts) the config file is assured to be:

  • file is a normal file (or /dev/null)
  • file owner is owner of program
  • file is not accessible by group
  • file is not accessible by other

So if you run lcd4linux as root, /etc/lcd4linux.conf has to be:

chmod 600
chown root.root

Last modified 8 years ago Last modified on 04/01/10 23:30:35