Sitara Linux LCDC fbdev User Space

Sitara Linux Software Developer's Guide

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LCDC: fbdev User Space

Usage and Verification

fbset is a utility that can be used to verify and set display parameters.

Here is an example output of fbset when run on the terminal of an AM335x General Purpose EVM:

/ # fbset
mode "800x480-40"
# D: 21.429 MHz, H: 21.956 kHz, V: 40.139 Hz
geometry 800 480 800 960 32
timings 46666 64 64 32 32 48 3
accel false
rgba 8/16,8/8,8/0,0/0
endmode
/ #

In 24bpp configuration, testing can be done by dumping bmp image (header stripped 800*480.bmp) on LCD

$cat 800*480.bmp > /dev/fb0

Framebuffer console blankes out after blanking interval. Framebuffer console blanking and unblanking can be set via below sysfs interfaces.

to unblank:
$echo "0" > /sys/class/graphics/fb0/blank
to blank:
$echo "4" > /sys/class/graphics/fb0/blank

Application Interface

To configure and use a framebuffer device, the following interfaces are needed. Note that most of the configuration will occur via IOCTLs.

open ()
To open a framebuffer device
close ()
To close a framebuffer device
ioctl ()
To send ioctl commands to the framebuffer driver.
mmap ()
To obtain the framebuffer region as mmap'ed area in user space.

Supported Standard IOCTLs

FBIOGET_VSCREENINFO, FBIOPUT_VSCREENINFO
These I/O controls are used to query and set the so-called variable screen info. This allows an application to query or change the display mode, including the color depth, resolution, timing etc. These I/O controls accept a pointer to a struct fb_var_screeninfo structure. The video mode data supplied in the fb_var_screeninfo struct is translated to values loaded into the display controller registers.

FBIOGET_FSCREENINFO
This I/O control can be used by applications to get the fixed properties of the display, e.g. the start address of the framebuffer memory. This I/O control accepts a pointer to a struct fb_fix_screeninfo.

FBIOGETCMAP, FBIOPUTCMAP
These I/O controls are used to get and set the color-map for the framebuffer. These I/O controls accept a pointer to a struct fb_cmap structure.

FBIO_BLANK
This I/O control is used to blank or unblank the framebuffer console.

Fbdev-Display Application Flow

Archived Versions

• Sitara Linux SDK 08.00.00.00