LCDML 1.2

LCDML project (or Liquid Crystal Display Markup Language) is a description language based on XML and used to describe the text that should be displayed on a LCD. It supports both static and dynamic text messages and bar charts and allows to implement all kinds of (complex) status output on a display.

A LCDML player (e.g. iowlcdml in the iowlcd package) uses a LCDML input file and then displays the pages defined there. Each page will be displayed for a specified duration, then the next page is displayed. This allows to use LCDML to describe lots of status messages on different pages and its output will be displayed with time multi-plexing.

Each page defined in LCDML contains regions. The regions are rectangular boxes defined on the text screen on the LCD where text output can be placed. A region is by default static, i. e. the contents displayed is generated if the page is constructed and keeps its contents until the page is no longer displayed. Other regions can be defined to be updated more often during the display of the page. These dynamic regions allow to update its contents more often during the lifetime of a page.

In a region text and bar charts can be defined. A text can be either defined directly, read from a file, or be the output of a shell command. The last method is very useful for creating status outputs defined in LCDML. The shell command is executed each time the region is updated. Similar to text output, the bar charts can be defined in regions, too. Both vertical and horizontal bars arranged in groups are supported. The values displayed in a bar can also be generated from a command output. LCDML allows to filter command output with regular expressions to extract the values from verbose output.

As a convenience and performance feature, the command output can be also stored as strings. The strings can then be used and filtered for different values and applied in different texts and bars in a regions without re-evaluating the command.