[deliverable/linux.git] / Documentation / fb / framebuffer.txt

			The Frame Buffer Device
			-----------------------

Maintained by Geert Uytterhoeven <geert@linux-m68k.org>
Last revised: May 10, 2001


0. Introduction
---------------

The frame buffer device provides an abstraction for the graphics hardware. It
represents the frame buffer of some video hardware and allows application
software to access the graphics hardware through a well-defined interface, so
the software doesn't need to know anything about the low-level (hardware
register) stuff.

The device is accessed through special device nodes, usually located in the
/dev directory, i.e. /dev/fb*.


1. User's View of /dev/fb*
--------------------------

From the user's point of view, the frame buffer device looks just like any
other device in /dev. It's a character device using major 29; the minor
specifies the frame buffer number.

By convention, the following device nodes are used (numbers indicate the device
minor numbers):

      0 = /dev/fb0	First frame buffer
      1 = /dev/fb1	Second frame buffer
	  ...
     31 = /dev/fb31	32nd frame buffer

For backwards compatibility, you may want to create the following symbolic
links:

    /dev/fb0current -> fb0
    /dev/fb1current -> fb1

and so on...

The frame buffer devices are also `normal' memory devices, this means, you can
read and write their contents. You can, for example, make a screen snapshot by

  cp /dev/fb0 myfile

There also can be more than one frame buffer at a time, e.g. if you have a
graphics card in addition to the built-in hardware. The corresponding frame
buffer devices (/dev/fb0 and /dev/fb1 etc.) work independently.

Application software that uses the frame buffer device (e.g. the X server) will
use /dev/fb0 by default (older software uses /dev/fb0current). You can specify
an alternative frame buffer device by setting the environment variable
$FRAMEBUFFER to the path name of a frame buffer device, e.g. (for sh/bash
users):

    export FRAMEBUFFER=/dev/fb1

or (for csh users):

    setenv FRAMEBUFFER /dev/fb1

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


2. Programmer's View of /dev/fb*
--------------------------------

As you already know, a frame buffer device is a memory device like /dev/mem and
it has the same features. You can read it, write it, seek to some location in
it and mmap() it (the main usage). The difference is just that the memory that
appears in the special file is not the whole memory, but the frame buffer of
some video hardware.

/dev/fb* also allows several ioctls on it, by which lots of information about
the hardware can be queried and set. The color map handling works via ioctls,
too. Look into <linux/fb.h> for more information on what ioctls exist and on
which data structures they work. Here's just a brief overview:

  - You can request unchangeable information about the hardware, like name,
    organization of the screen memory (planes, packed pixels, ...) and address
    and length of the screen memory.

  - You can request and change variable information about the hardware, like
    visible and virtual geometry, depth, color map format, timing, and so on.
    If you try to change that information, the driver maybe will round up some
    values to meet the hardware's capabilities (or return EINVAL if that isn't
    possible).

  - You can get and set parts of the color map. Communication is done with 16
    bits per color part (red, green, blue, transparency) to support all 
    existing hardware. The driver does all the computations needed to apply 
    it to the hardware (round it down to less bits, maybe throw away 
    transparency).

All this hardware abstraction makes the implementation of application programs
easier and more portable. E.g. the X server works completely on /dev/fb* and
thus doesn't need to know, for example, how the color registers of the concrete
hardware are organized. XF68_FBDev is a general X server for bitmapped,
unaccelerated video hardware. The only thing that has to be built into
application programs is the screen organization (bitplanes or chunky pixels
etc.), because it works on the frame buffer image data directly.

For the future it is planned that frame buffer drivers for graphics cards and
the like can be implemented as kernel modules that are loaded at runtime. Such
a driver just has to call register_framebuffer() and supply some functions.
Writing and distributing such drivers independently from the kernel will save
much trouble...


3. Frame Buffer Resolution Maintenance
--------------------------------------

Frame buffer resolutions are maintained using the utility `fbset'. It can
change the video mode properties of a frame buffer device. Its main usage is
to change the current video mode, e.g. during boot up in one of your /etc/rc.*
or /etc/init.d/* files.

Fbset uses a video mode database stored in a configuration file, so you can
easily add your own modes and refer to them with a simple identifier.


4. The X Server
---------------

The X server (XF68_FBDev) is the most notable application program for the frame
buffer device. Starting with XFree86 release 3.2, the X server is part of
XFree86 and has 2 modes:

  - If the `Display' subsection for the `fbdev' driver in the /etc/XF86Config
    file contains a

	Modes "default"

    line, the X server will use the scheme discussed above, i.e. it will start
    up in the resolution determined by /dev/fb0 (or $FRAMEBUFFER, if set). You
    still have to specify the color depth (using the Depth keyword) and virtual
    resolution (using the Virtual keyword) though. This is the default for the
    configuration file supplied with XFree86. It's the most simple
    configuration, but it has some limitations.

  - Therefore it's also possible to specify resolutions in the /etc/XF86Config
    file. This allows for on-the-fly resolution switching while retaining the
    same virtual desktop size. The frame buffer device that's used is still
    /dev/fb0current (or $FRAMEBUFFER), but the available resolutions are
    defined by /etc/XF86Config now. The disadvantage is that you have to
    specify the timings in a different format (but `fbset -x' may help).

To tune a video mode, you can use fbset or xvidtune. Note that xvidtune doesn't
work 100% with XF68_FBDev: the reported clock values are always incorrect.


5. Video Mode Timings
---------------------

A monitor draws an image on the screen by using an electron beam (3 electron
beams for color models, 1 electron beam for monochrome monitors). The front of
the screen is covered by a pattern of colored phosphors (pixels). If a phosphor
is hit by an electron, it emits a photon and thus becomes visible.

The electron beam draws horizontal lines (scanlines) from left to right, and
from the top to the bottom of the screen. By modifying the intensity of the
electron beam, pixels with various colors and intensities can be shown.

After each scanline the electron beam has to move back to the left side of the
screen and to the next line: this is called the horizontal retrace. After the
whole screen (frame) was painted, the beam moves back to the upper left corner:
this is called the vertical retrace. During both the horizontal and vertical
retrace, the electron beam is turned off (blanked).

The speed at which the electron beam paints the pixels is determined by the
dotclock in the graphics board. For a dotclock of e.g. 28.37516 MHz (millions
of cycles per second), each pixel is 35242 ps (picoseconds) long:

    1/(28.37516E6 Hz) = 35.242E-9 s

If the screen resolution is 640x480, it will take

    640*35.242E-9 s = 22.555E-6 s

to paint the 640 (xres) pixels on one scanline. But the horizontal retrace
also takes time (e.g. 272 `pixels'), so a full scanline takes

    (640+272)*35.242E-9 s = 32.141E-6 s

We'll say that the horizontal scanrate is about 31 kHz:

    1/(32.141E-6 s) = 31.113E3 Hz

A full screen counts 480 (yres) lines, but we have to consider the vertical
retrace too (e.g. 49 `lines'). So a full screen will take

    (480+49)*32.141E-6 s = 17.002E-3 s

The vertical scanrate is about 59 Hz:

    1/(17.002E-3 s) = 58.815 Hz

This means the screen data is refreshed about 59 times per second. To have a
stable picture without visible flicker, VESA recommends a vertical scanrate of
at least 72 Hz. But the perceived flicker is very human dependent: some people
can use 50 Hz without any trouble, while I'll notice if it's less than 80 Hz.

Since the monitor doesn't know when a new scanline starts, the graphics board
will supply a synchronization pulse (horizontal sync or hsync) for each
scanline.  Similarly it supplies a synchronization pulse (vertical sync or
vsync) for each new frame. The position of the image on the screen is
influenced by the moments at which the synchronization pulses occur.

The following picture summarizes all timings. The horizontal retrace time is
the sum of the left margin, the right margin and the hsync length, while the
vertical retrace time is the sum of the upper margin, the lower margin and the
vsync length.

  +----------+---------------------------------------------+----------+-------+
  |          |                ↑                            |          |       |
  |          |                |upper_margin                |          |       |
  |          |                ↓                            |          |       |
  +----------###############################################----------+-------+
  |          #                ↑                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |   left   #                |                            #  right   | hsync |
  |  margin  #                |       xres                 #  margin  |  len  |
  |<-------->#<---------------+--------------------------->#<-------->|<----->|
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |yres                        #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                |                            #          |       |
  |          #                ↓                            #          |       |
  +----------###############################################----------+-------+
  |          |                ↑                            |          |       |
  |          |                |lower_margin                |          |       |
  |          |                ↓                            |          |       |
  +----------+---------------------------------------------+----------+-------+
  |          |                ↑                            |          |       |
  |          |                |vsync_len                   |          |       |
  |          |                ↓                            |          |       |
  +----------+---------------------------------------------+----------+-------+

The frame buffer device expects all horizontal timings in number of dotclocks
(in picoseconds, 1E-12 s), and vertical timings in number of scanlines.


6. Converting XFree86 timing values info frame buffer device timings
--------------------------------------------------------------------

An XFree86 mode line consists of the following fields:
 "800x600"     50      800  856  976 1040    600  637  643  666
 < name >     DCF       HR  SH1  SH2  HFL     VR  SV1  SV2  VFL

The frame buffer device uses the following fields:

  - pixclock: pixel clock in ps (pico seconds)
  - left_margin: time from sync to picture
  - right_margin: time from picture to sync
  - upper_margin: time from sync to picture
  - lower_margin: time from picture to sync
  - hsync_len: length of horizontal sync
  - vsync_len: length of vertical sync

1) Pixelclock:
   xfree: in MHz
   fb: in picoseconds (ps)

   pixclock = 1000000 / DCF

2) horizontal timings:
   left_margin = HFL - SH2
   right_margin = SH1 - HR
   hsync_len = SH2 - SH1

3) vertical timings:
   upper_margin = VFL - SV2
   lower_margin = SV1 - VR
   vsync_len = SV2 - SV1

Good examples for VESA timings can be found in the XFree86 source tree,
under "xc/programs/Xserver/hw/xfree86/doc/modeDB.txt".


7. References
-------------

For more specific information about the frame buffer device and its
applications, please refer to the Linux-fbdev website:

    http://linux-fbdev.sourceforge.net/

and to the following documentation:

  - The manual pages for fbset: fbset(8), fb.modes(5)
  - The manual pages for XFree86: XF68_FBDev(1), XF86Config(4/5)
  - The mighty kernel sources:
      o linux/drivers/video/
      o linux/include/linux/fb.h
      o linux/include/video/


8. Mailing list
---------------

There is a frame buffer device related mailing list at kernel.org:
linux-fbdev@vger.kernel.org.

Point your web browser to http://sourceforge.net/projects/linux-fbdev/ for
subscription information and archive browsing.


9. Downloading
--------------

All necessary files can be found at

    ftp://ftp.uni-erlangen.de/pub/Linux/LOCAL/680x0/

and on its mirrors.

The latest version of fbset can be found at

    http://www.linux-fbdev.org/ 

  
10. Credits                                                       
----------                                                       
                
This readme was written by Geert Uytterhoeven, partly based on the original
`X-framebuffer.README' by Roman Hodek and Martin Schaller. Section 6 was
provided by Frank Neumann.

The frame buffer device abstraction was designed by Martin Schaller.
Commit	Line	Data
1da177e4 LT	1	The Frame Buffer Device
	2	-----------------------
	3
	4	Maintained by Geert Uytterhoeven <geert@linux-m68k.org>
	5	Last revised: May 10, 2001
	6
	7
	8	0. Introduction
	9	---------------
	10
	11	The frame buffer device provides an abstraction for the graphics hardware. It
	12	represents the frame buffer of some video hardware and allows application
	13	software to access the graphics hardware through a well-defined interface, so
	14	the software doesn't need to know anything about the low-level (hardware
	15	register) stuff.
	16
	17	The device is accessed through special device nodes, usually located in the
	18	/dev directory, i.e. /dev/fb*.
	19
	20
	21	1. User's View of /dev/fb*
	22	--------------------------
	23
	24	From the user's point of view, the frame buffer device looks just like any
	25	other device in /dev. It's a character device using major 29; the minor
	26	specifies the frame buffer number.
	27
	28	By convention, the following device nodes are used (numbers indicate the device
	29	minor numbers):
	30
	31	0 = /dev/fb0 First frame buffer
	32	1 = /dev/fb1 Second frame buffer
	33	...
	34	31 = /dev/fb31 32nd frame buffer
	35
	36	For backwards compatibility, you may want to create the following symbolic
	37	links:
	38
	39	/dev/fb0current -> fb0
	40	/dev/fb1current -> fb1
	41
	42	and so on...
	43
	44	The frame buffer devices are also `normal' memory devices, this means, you can
	45	read and write their contents. You can, for example, make a screen snapshot by
	46
	47	cp /dev/fb0 myfile
	48
	49	There also can be more than one frame buffer at a time, e.g. if you have a
	50	graphics card in addition to the built-in hardware. The corresponding frame
	51	buffer devices (/dev/fb0 and /dev/fb1 etc.) work independently.
	52
	53	Application software that uses the frame buffer device (e.g. the X server) will
	54	use /dev/fb0 by default (older software uses /dev/fb0current). You can specify
	55	an alternative frame buffer device by setting the environment variable
	56	$FRAMEBUFFER to the path name of a frame buffer device, e.g. (for sh/bash
	57	users):
	58
	59	export FRAMEBUFFER=/dev/fb1
	60
	61	or (for csh users):
	62
	63	setenv FRAMEBUFFER /dev/fb1
	64
65	After this the X server will use the second frame buffer.
66
67
68	2. Programmer's View of /dev/fb*
69	--------------------------------
70
71	As you already know, a frame buffer device is a memory device like /dev/mem and
72	it has the same features. You can read it, write it, seek to some location in
73	it and mmap() it (the main usage). The difference is just that the memory that
74	appears in the special file is not the whole memory, but the frame buffer of
75	some video hardware.
76
77	/dev/fb* also allows several ioctls on it, by which lots of information about
78	the hardware can be queried and set. The color map handling works via ioctls,
79	too. Look into <linux/fb.h> for more information on what ioctls exist and on
80	which data structures they work. Here's just a brief overview:
81
82	- You can request unchangeable information about the hardware, like name,
83	organization of the screen memory (planes, packed pixels, ...) and address
84	and length of the screen memory.
85
86	- You can request and change variable information about the hardware, like
87	visible and virtual geometry, depth, color map format, timing, and so on.
88	If you try to change that information, the driver maybe will round up some
89	values to meet the hardware's capabilities (or return EINVAL if that isn't
90	possible).
91
92	- You can get and set parts of the color map. Communication is done with 16
93	bits per color part (red, green, blue, transparency) to support all
94	existing hardware. The driver does all the computations needed to apply
95	it to the hardware (round it down to less bits, maybe throw away
96	transparency).
97
98	All this hardware abstraction makes the implementation of application programs
99	easier and more portable. E.g. the X server works completely on /dev/fb* and
100	thus doesn't need to know, for example, how the color registers of the concrete
101	hardware are organized. XF68_FBDev is a general X server for bitmapped,
102	unaccelerated video hardware. The only thing that has to be built into
103	application programs is the screen organization (bitplanes or chunky pixels
104	etc.), because it works on the frame buffer image data directly.
105
106	For the future it is planned that frame buffer drivers for graphics cards and
107	the like can be implemented as kernel modules that are loaded at runtime. Such
108	a driver just has to call register_framebuffer() and supply some functions.
109	Writing and distributing such drivers independently from the kernel will save
110	much trouble...
111
112
113	3. Frame Buffer Resolution Maintenance
114	--------------------------------------
115
116	Frame buffer resolutions are maintained using the utility `fbset'. It can
117	change the video mode properties of a frame buffer device. Its main usage is
118	to change the current video mode, e.g. during boot up in one of your /etc/rc.*
119	or /etc/init.d/* files.
120
121	Fbset uses a video mode database stored in a configuration file, so you can
122	easily add your own modes and refer to them with a simple identifier.
123
124
125	4. The X Server
126	---------------
127
128	The X server (XF68_FBDev) is the most notable application program for the frame
129	buffer device. Starting with XFree86 release 3.2, the X server is part of
130	XFree86 and has 2 modes:
131
132	- If the `Display' subsection for the `fbdev' driver in the /etc/XF86Config
133	file contains a
134
135	Modes "default"
136
137	line, the X server will use the scheme discussed above, i.e. it will start
138	up in the resolution determined by /dev/fb0 (or $FRAMEBUFFER, if set). You
139	still have to specify the color depth (using the Depth keyword) and virtual
140	resolution (using the Virtual keyword) though. This is the default for the
141	configuration file supplied with XFree86. It's the most simple
142	configuration, but it has some limitations.
143
144	- Therefore it's also possible to specify resolutions in the /etc/XF86Config
145	file. This allows for on-the-fly resolution switching while retaining the
146	same virtual desktop size. The frame buffer device that's used is still
147	/dev/fb0current (or $FRAMEBUFFER), but the available resolutions are
148	defined by /etc/XF86Config now. The disadvantage is that you have to
149	specify the timings in a different format (but `fbset -x' may help).
150
151	To tune a video mode, you can use fbset or xvidtune. Note that xvidtune doesn't
152	work 100% with XF68_FBDev: the reported clock values are always incorrect.
153
154
155	5. Video Mode Timings
156	---------------------
157
158	A monitor draws an image on the screen by using an electron beam (3 electron
159	beams for color models, 1 electron beam for monochrome monitors). The front of
160	the screen is covered by a pattern of colored phosphors (pixels). If a phosphor
161	is hit by an electron, it emits a photon and thus becomes visible.
162
163	The electron beam draws horizontal lines (scanlines) from left to right, and
164	from the top to the bottom of the screen. By modifying the intensity of the
165	electron beam, pixels with various colors and intensities can be shown.
166
167	After each scanline the electron beam has to move back to the left side of the
168	screen and to the next line: this is called the horizontal retrace. After the
169	whole screen (frame) was painted, the beam moves back to the upper left corner:
170	this is called the vertical retrace. During both the horizontal and vertical
171	retrace, the electron beam is turned off (blanked).
172
173	The speed at which the electron beam paints the pixels is determined by the
174	dotclock in the graphics board. For a dotclock of e.g. 28.37516 MHz (millions
175	of cycles per second), each pixel is 35242 ps (picoseconds) long:
176
177	1/(28.37516E6 Hz) = 35.242E-9 s
178
179	If the screen resolution is 640x480, it will take
180
181	640*35.242E-9 s = 22.555E-6 s
182
183	to paint the 640 (xres) pixels on one scanline. But the horizontal retrace
184	also takes time (e.g. 272 `pixels'), so a full scanline takes
185
186	(640+272)*35.242E-9 s = 32.141E-6 s
187
188	We'll say that the horizontal scanrate is about 31 kHz:
189
190	1/(32.141E-6 s) = 31.113E3 Hz
191
192	A full screen counts 480 (yres) lines, but we have to consider the vertical
193	retrace too (e.g. 49 `lines'). So a full screen will take
194
195	(480+49)*32.141E-6 s = 17.002E-3 s
196
197	The vertical scanrate is about 59 Hz:
198
199	1/(17.002E-3 s) = 58.815 Hz
200
201	This means the screen data is refreshed about 59 times per second. To have a
202	stable picture without visible flicker, VESA recommends a vertical scanrate of
203	at least 72 Hz. But the perceived flicker is very human dependent: some people
204	can use 50 Hz without any trouble, while I'll notice if it's less than 80 Hz.
205
206	Since the monitor doesn't know when a new scanline starts, the graphics board
207	will supply a synchronization pulse (horizontal sync or hsync) for each
208	scanline. Similarly it supplies a synchronization pulse (vertical sync or
209	vsync) for each new frame. The position of the image on the screen is
210	influenced by the moments at which the synchronization pulses occur.
211
212	The following picture summarizes all timings. The horizontal retrace time is
213	the sum of the left margin, the right margin and the hsync length, while the
214	vertical retrace time is the sum of the upper margin, the lower margin and the
215	vsync length.
216
217	+----------+---------------------------------------------+----------+-------+
be2a608b	218	\| \| ↑ \| \| \|
1da177e4	219	\| \| \|upper_margin \| \| \|
be2a608b	220	\| \| ↓ \| \| \|
1da177e4	221	+----------###############################################----------+-------+
be2a608b	222	\| # ↑ # \| \|
1da177e4 LT	223	\| # \| # \| \|
	224	\| # \| # \| \|
	225	\| # \| # \| \|
	226	\| left # \| # right \| hsync \|
	227	\| margin # \| xres # margin \| len \|
	228	\|<-------->#<---------------+--------------------------->#<-------->\|<----->\|
	229	\| # \| # \| \|
	230	\| # \| # \| \|
	231	\| # \| # \| \|
	232	\| # \|yres # \| \|
	233	\| # \| # \| \|
	234	\| # \| # \| \|
	235	\| # \| # \| \|
	236	\| # \| # \| \|
	237	\| # \| # \| \|
	238	\| # \| # \| \|
	239	\| # \| # \| \|
	240	\| # \| # \| \|
be2a608b	241	\| # ↓ # \| \|
1da177e4	242	+----------###############################################----------+-------+
be2a608b	243	\| \| ↑ \| \| \|
1da177e4	244	\| \| \|lower_margin \| \| \|
be2a608b	245	\| \| ↓ \| \| \|
1da177e4	246	+----------+---------------------------------------------+----------+-------+
be2a608b	247	\| \| ↑ \| \| \|
1da177e4	248	\| \| \|vsync_len \| \| \|
be2a608b	249	\| \| ↓ \| \| \|
1da177e4 LT	250	+----------+---------------------------------------------+----------+-------+
	251
	252	The frame buffer device expects all horizontal timings in number of dotclocks
	253	(in picoseconds, 1E-12 s), and vertical timings in number of scanlines.
	254
	255
	256	6. Converting XFree86 timing values info frame buffer device timings
	257	--------------------------------------------------------------------
	258
	259	An XFree86 mode line consists of the following fields:
	260	"800x600" 50 800 856 976 1040 600 637 643 666
	261	< name > DCF HR SH1 SH2 HFL VR SV1 SV2 VFL
	262
	263	The frame buffer device uses the following fields:
	264
	265	- pixclock: pixel clock in ps (pico seconds)
	266	- left_margin: time from sync to picture
	267	- right_margin: time from picture to sync
	268	- upper_margin: time from sync to picture
	269	- lower_margin: time from picture to sync
	270	- hsync_len: length of horizontal sync
	271	- vsync_len: length of vertical sync
	272
	273	1) Pixelclock:
	274	xfree: in MHz
	275	fb: in picoseconds (ps)
	276
	277	pixclock = 1000000 / DCF
	278
	279	2) horizontal timings:
	280	left_margin = HFL - SH2
	281	right_margin = SH1 - HR
	282	hsync_len = SH2 - SH1
	283
	284	3) vertical timings:
	285	upper_margin = VFL - SV2
	286	lower_margin = SV1 - VR
	287	vsync_len = SV2 - SV1
	288
	289	Good examples for VESA timings can be found in the XFree86 source tree,
	290	under "xc/programs/Xserver/hw/xfree86/doc/modeDB.txt".
	291
	292
	293	7. References
	294	-------------
	295
	296	For more specific information about the frame buffer device and its
	297	applications, please refer to the Linux-fbdev website:
	298
	299	http://linux-fbdev.sourceforge.net/
	300
	301	and to the following documentation:
	302
	303	- The manual pages for fbset: fbset(8), fb.modes(5)
	304	- The manual pages for XFree86: XF68_FBDev(1), XF86Config(4/5)
	305	- The mighty kernel sources:
	306	o linux/drivers/video/
	307	o linux/include/linux/fb.h
	308	o linux/include/video/
	309
	310
	311
	312	8. Mailing list
	313	---------------
314
c69f677c GU	315	There is a frame buffer device related mailing list at kernel.org:
c69f677c GU	316	linux-fbdev@vger.kernel.org.
1da177e4 LT	317
	318	Point your web browser to http://sourceforge.net/projects/linux-fbdev/ for
	319	subscription information and archive browsing.
	320
	321
	322	9. Downloading
	323	--------------
	324
	325	All necessary files can be found at
	326
	327	ftp://ftp.uni-erlangen.de/pub/Linux/LOCAL/680x0/
	328
	329	and on its mirrors.
	330
	331	The latest version of fbset can be found at
	332
0ea6e611	333	http://www.linux-fbdev.org/
1da177e4 LT	334
	335
	336	10. Credits
	337	----------
	338
	339	This readme was written by Geert Uytterhoeven, partly based on the original
	340	`X-framebuffer.README' by Roman Hodek and Martin Schaller. Section 6 was
	341	provided by Frank Neumann.
	342
	343	The frame buffer device abstraction was designed by Martin Schaller.