UM0851 datasheet(193/245 Pages) STMICROELECTRONICS

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UM0851

Audio/video drivers

Doc ID 16604 Rev 2

193/245

Figure 53.

Framebuffer layer of Linux

The kernel's frame buffer interface thus allows applications to be independent of the specific

characteristics of the underlying graphics hardware. Applications can run unchanged over

diverse types of video hardware if they and the display drivers conform to the framebuffer

interface.

If standard GUIs (Graphic User Interface) such as MiniGUI, MicroWindows are used, LCD

device drivers must be implemented as Linux framebuffer device drivers in addition to those

low level operations which only deal with commands provided by LCD controllers.

The device is accessed through special device nodes, usually located in the /dev directory,

and have names such as /dev/fb0 (or /dev/fb/0), /dev/fb1 etc.

The framebuffer devices are also `normal' memory devices, this means one can read and

write their contents. You can, for example, even make a screen snapshot by:

# cat /dev/fb0 > myfile

Application software that uses the frame buffer device (e.g. the X server), uses /dev/fb0 by

default.

An alternative frame buffer device can be specified by setting the environment variable

$FRAMEBUFFER to the path name of a frame buffer device, for example:

# export FRAMEBUFFER=/dev/fb1 (for sh/bash users)

# setenv FRAMEBUFFER /dev/fb1 (for csh users)

After this the X server will use the second frame buffer:

# export FRAMEBUFFER=/dev/fb1

(for sh/bash users)

Framebuffer

driver 1

Video card 1

Framebuffer

driver N

Video card N

... video cards using

different graphics

controllers

Common Framebuffer API

GUIs, consoles,

movie players etc.

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