Linux's Auxiliary Displays' tree at Miguel Ojeda's homepage

v2007-10-10
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State of the Auxiliary Displays' tree (drivers/auxdisplay/*)

• Maintained
• Location: Mainline Linux since 2.6.21.
• Known bugs: 0
• Patchs at -mm: 0

About the Auxiliary Displays' tree (drivers/auxdisplay/*)

The Auxiliary Displays tree - since Linux 2.6.21, located at drivers/auxdisplay/* and maintained by Miguel Ojeda - contains Linux's device drivers for auxiliary (not for normal use) displays (whatever kind), like cfag12864b, a tiny 128x64 LCD.

There are three kinds of device drivers in the tree:

• Controller Device Driver - Like the ks0108, used by display device drivers.
• Display Device Driver - Like the cfag12864b, used by framebuffer device drivers.
• Framebuffer Device Driver - Like the cfag12864bfb, used by programs at userspace.

Currently, there are the following device drivers in the tree:

• ks0108
  • Description: Samsung's ks0108 LCD controller driver (through a parallel port)
  • Depends: parport
  • License: GNU General Public License version 2
  • Author: Copyright (C) Miguel Ojeda <miguel.ojeda.sandonis at gmail dot com>
  • Date: 2006-10-31
  • Maintainer: Miguel Ojeda <miguel.ojeda.sandonis at gmail dot com>

• cfag12864b
  • Description: Crystalfontz 128x64 2-colors LCD B-Series driver
  • Depends: ks0108
  • License: GNU General Public License version 2
  • Author: Copyright (C) Miguel Ojeda <miguel.ojeda.sandonis at gmail dot com>
  • Date: 2006-10-31
  • Maintainer: Miguel Ojeda <miguel.ojeda.sandonis at gmail dot com>

• cfag12864bfb
  • Description: Crystalfontz 128x64 2-colors LCD B-Series framebuffer driver
  • Depends: cfag12864b
  • License: GNU General Public License version 2
  • Author: Copyright (C) Miguel Ojeda <miguel.ojeda.sandonis at gmail dot com>
  • Date: 2006-10-31
  • Maintainer: Miguel Ojeda <miguel.ojeda.sandonis at gmail dot com>

Currently, there is support for the following auxiliary displays:

• Crystalfontz 128x64 2-colors LCD B-Series
  • Controller: ks0108 (through a parallel port)
  • Display: cfag12864b
  • Framebuffer: cfag12864bfb

If you need more specific information, technical details, check Documentation/auxdisplay/* tree in the kernel source. If you found a bug, discovered some way to improve the driver or just you have some suggestion, please e-mail me.

Project improvements over the time will be reflected in this page as well as in the Documentation.

If you would like to contribute with new drivers or patches, please e-mail it to the LKML and CC me. If your patch is accepted, I will add an entry in the above list.

About the cfag12864b LCD Device Driver...

Although you may think the wiring specified at Documentation/auxdisplay/cfag12864b is poor, I chose such one because it is compatible with LCDStudio's wiring (Microsoft Windows), so you won't need to change if you want to switch to Linux. Sadly, with such wiring there is not any way to probe for the LCD: the module gets loaded and starts working no matter what is connected to the parport; so I suggest using the driver as a module: To start it, type "# modprobe cfag12864bfb"; to stop it, type "# modprobe -r cfag12864bfb".

If you need some example code to start playing with the LCD, see Documentation/auxdisplay/cfag12864b-example.c

Hints:

• The small voltage source (like 5V or 12 V) needed for LED backlighting can be taken from the PC power source, there is no need for external power sources.
• You can use any framebuffer related software with cfag12864bfb. For example, you can use fbcon (fb-console attacher) and login using your tiny LCD.

As an eye candy, here it is a video frame ("screenshot") of the cfag12864b LCD drawing two moving functions (sine and cosine) refreshing at about 10 Hz. Please note that pixels being animated are shaded, therefore it is harder to see them. However, axes are clearly visible as they are fixed.