Latest revision as of 12:16, 18 January 2023

On this page you will find usefull informations to have a working Linux Framebuffer on your board.

Introduction

Linux Framebuffer is the lowest level (standardized) API for userspace programs to access video capabilities of the system you're running on. It allows you to directly "draw" your graphics in the video memory. Some higher level librairies can be put on top of the Framebuffer for more portability: SDL, Qt/Embedded, GTK, DirectFB, etc...

Kernel configuration

Note: Framebuffer is already configured (for Sharp LQ043 LCD on APF9328 and for Chimei LW700 on APF27/APF51) in standard/default Armadeus kernel image. APF28 has a boot option to choose the LCD.

Instructions to configure Linux kernel were moved to Talk:FrameBuffer and are only given as references or if you want to change the default LCD.

Userland

• Framebuffer device can be accessed with /dev/fb0.

• You can activate some tools from the Buildroot's menuconfig:

 $ make menuconfig

 Package Selection for the target
     ...
     Graphic libraries and applications (graphic/text)  ---> 
     ...
         [*] fbgrab
         [*] fbtest
         [*] fbv
     ...
        ---> Graphic libraries and applications (graphic/text)  
            ---> fbset/fbv/fbgrab

Note: As explain on LinuxInstall page, to compile fbtest, libnetpbm10-dev must be installed in your host system

• For example to grab a snapshot of the framebuffer:

# fbgrab /tmp/snapshot.png

• For example to display an image using standard image file formats PNG, GIF...:

# fbv myimage.png

Tips

Login/Console

• To stop blinking cursor:

 # echo 0 > /sys/class/graphics/fbcon/cursor_blink

also possible at boot time (with 3.x recent kernels):

BIOS> setenv extrabootargs vt.global_cursor_default=0

• To make it blinking again:

 # echo 1 > /sys/class/graphics/fbcon/cursor_blink

• To have a login on LCD, add these line in /etc/inittab of your rootfs:

# Set up a getty on LCD
tty1::respawn:/sbin/getty 38400 tty1

Screenshot

• To grab a screenshot of a running Framebuffer application, use FBGrab

Sleep

• To enter in Framebuffer sleep mode:

 # echo 1 > /sys/class/graphics/fb0/blank

• To leave Framebuffer sleep power mode:

 # echo 0 > /sys/class/graphics/fb0/blank

• To set "sleep mode"/screensaver entering time (where X is a time in minute; 0 = never):

 # echo -e '\033[9;X]' > /dev/tty1    (from serial console)

or

 # echo -e '\033[9;X]'    (from framebuffer console)

or to set it at each boot, use /etc/inittab:

 tty1::sysinit:echo -e '\033[9;X]'

Other usefull ESC sequences

• To (definitly) hide cursor:

 # echo -e '\033[?17;0;0c' > /dev/tty1    (from serial console)

or

 # echo -e '\033[?17;0;0c'    (from framebuffer console)

• inverse screen on:

 # echo -e '\033[?5h' > /dev/tty1

• inverse screen off:

 # echo -e '\033[?5l' > /dev/tty1

• To erase the screen

echo -e '\033[2J' > /dev/tty1 (from serial console)

Links

• How to change the Linux boot logo
• How to play with Framebuffer overlay on APF6
• How to configure soft cursor
• http://linux-fbdev.sourceforge.net/
• Linux console ESC sequences
• http://directfb.org/
• Blackfin wiki page on the subject