1 The Framebuffer Console
2 =======================
3
4 The framebuffer console (fbcon), as its name implies, is a text
5 console running on top of the framebuffer device. It has the functionality of
6 any standard text console driver, such as the VGA console, with the added
7 features that can be attributed to the graphical nature of the framebuffer.
8
9 In the x86 architecture, the framebuffer console is optional, and
10 some even treat it as a toy. For other architectures, it is the only available
11 display device, text or graphical.
12
13 What are the features of fbcon? The framebuffer console supports
14 high resolutions, varying font types, display rotation, primitive multihead,
15 etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature
16 made available by the underlying graphics card are also possible.
17
18 A. Configuration
19
20 The framebuffer console can be enabled by using your favorite kernel
21 configuration tool. It is under Device Drivers->Graphics Support->Support for
22 framebuffer devices->Framebuffer Console Support. Select 'y' to compile
23 support statically, or 'm' for module support. The module will be fbcon.
24
25 In order for fbcon to activate, at least one framebuffer driver is
26 required, so choose from any of the numerous drivers available. For x86
27 systems, they almost universally have VGA cards, so vga16fb and vesafb will
28 always be available. However, using a chipset-specific driver will give you
29 more speed and features, such as the ability to change the video mode
30 dynamically.
31
32 To display the penguin logo, choose any logo available in Logo
33 Configuration->Boot up logo.
34
35 Also, you will need to select at least one compiled-in fonts, but if
36 you don't do anything, the kernel configuration tool will select one for you,
37 usually an 8x16 font.
38
39 GOTCHA: A common bug report is enabling the framebuffer without enabling the
40 framebuffer console. Depending on the driver, you may get a blanked or
41 garbled display, but the system still boots to completion. If you are
42 fortunate to have a driver that does not alter the graphics chip, then you
43 will still get a VGA console.
44
45 B. Loading
46
47 Possible scenarios:
48
49 1. Driver and fbcon are compiled statically
50
51 Usually, fbcon will automatically take over your console. The notable
52 exception is vesafb. It needs to be explicitly activated with the
53 vga= boot option parameter.
54
55 2. Driver is compiled statically, fbcon is compiled as a module
56
57 Depending on the driver, you either get a standard console, or a
58 garbled display, as mentioned above. To get a framebuffer console,
59 do a 'modprobe fbcon'.
60
61 3. Driver is compiled as a module, fbcon is compiled statically
62
63 You get your standard console. Once the driver is loaded with
64 'modprobe xxxfb', fbcon automatically takes over the console with
65 the possible exception of using the fbcon=map:n option. See below.
66
67 4. Driver and fbcon are compiled as a module.
68
69 You can load them in any order. Once both are loaded, fbcon will take
70 over the console.
71
72 C. Boot options
73
74 The framebuffer console has several, largely unknown, boot options
75 that can change its behavior.
76
77 1. fbcon=font:<name>
78
79 Select the initial font to use. The value 'name' can be any of the
80 compiled-in fonts: VGA8x16, 7x14, 10x18, VGA8x8, MINI4x6, RomanLarge,
81 SUN8x16, SUN12x22, ProFont6x11, Acorn8x8, PEARL8x8.
82
83 Note, not all drivers can handle font with widths not divisible by 8,
84 such as vga16fb.
85
86 2. fbcon=scrollback:<value>[k]
87
88 The scrollback buffer is memory that is used to preserve display
89 contents that has already scrolled past your view. This is accessed
90 by using the Shift-PageUp key combination. The value 'value' is any
91 integer. It defaults to 32KB. The 'k' suffix is optional, and will
92 multiply the 'value' by 1024.
93
94 3. fbcon=map:<0123>
95
96 This is an interesting option. It tells which driver gets mapped to
97 which console. The value '0123' is a sequence that gets repeated until
98 the total length is 64 which is the number of consoles available. In
99 the above example, it is expanded to 012301230123... and the mapping
100 will be:
101
102 tty | 1 2 3 4 5 6 7 8 9 ...
103 fb | 0 1 2 3 0 1 2 3 0 ...
104
105 ('cat /proc/fb' should tell you what the fb numbers are)
106
107 One side effect that may be useful is using a map value that exceeds
108 the number of loaded fb drivers. For example, if only one driver is
109 available, fb0, adding fbcon=map:1 tells fbcon not to take over the
110 console.
111
112 Later on, when you want to map the console the to the framebuffer
113 device, you can use the con2fbmap utility.
114
115 4. fbcon=vc:<n1>-<n2>
116
117 This option tells fbcon to take over only a range of consoles as
118 specified by the values 'n1' and 'n2'. The rest of the consoles
119 outside the given range will still be controlled by the standard
120 console driver.
121
122 NOTE: For x86 machines, the standard console is the VGA console which
123 is typically located on the same video card. Thus, the consoles that
124 are controlled by the VGA console will be garbled.
125
126 4. fbcon=rotate:<n>
127
128 This option changes the orientation angle of the console display. The
129 value 'n' accepts the following:
130
131 0 - normal orientation (0 degree)
132 1 - clockwise orientation (90 degrees)
133 2 - upside down orientation (180 degrees)
134 3 - counterclockwise orientation (270 degrees)
135
136 The angle can be changed anytime afterwards by 'echoing' the same
137 numbers to any one of the 2 attributes found in
138 /sys/class/graphics/fb{x}
139
140 con_rotate - rotate the display of the active console
141 con_rotate_all - rotate the display of all consoles
142
143 Console rotation will only become available if Console Rotation
144 Support is compiled in your kernel.
145
146 NOTE: This is purely console rotation. Any other applications that
147 use the framebuffer will remain at their 'normal'orientation.
148 Actually, the underlying fb driver is totally ignorant of console
149 rotation.
150
151 ---
152 Antonino Daplas <adaplas@pol.net>
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