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| Original file line number | Diff line number | Diff line change |
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| The Framebuffer Console | ||
| ======================= | ||
|
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| The framebuffer console (fbcon), as its name implies, is a text | ||
| console running on top of the framebuffer device. It has the functionality of | ||
| any standard text console driver, such as the VGA console, with the added | ||
| features that can be attributed to the graphical nature of the framebuffer. | ||
|
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| In the x86 architecture, the framebuffer console is optional, and | ||
| some even treat it as a toy. For other architectures, it is the only available | ||
| display device, text or graphical. | ||
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| What are the features of fbcon? The framebuffer console supports | ||
| high resolutions, varying font types, display rotation, primitive multihead, | ||
| etc. Theoretically, multi-colored fonts, blending, aliasing, and any feature | ||
| made available by the underlying graphics card are also possible. | ||
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| A. Configuration | ||
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| The framebuffer console can be enabled by using your favorite kernel | ||
| configuration tool. It is under Device Drivers->Graphics Support->Support for | ||
| framebuffer devices->Framebuffer Console Support. Select 'y' to compile | ||
| support statically, or 'm' for module support. The module will be fbcon. | ||
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| In order for fbcon to activate, at least one framebuffer driver is | ||
| required, so choose from any of the numerous drivers available. For x86 | ||
| systems, they almost universally have VGA cards, so vga16fb and vesafb will | ||
| always be available. However, using a chipset-specific driver will give you | ||
| more speed and features, such as the ability to change the video mode | ||
| dynamically. | ||
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| To display the penguin logo, choose any logo available in Logo | ||
| Configuration->Boot up logo. | ||
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| Also, you will need to select at least one compiled-in fonts, but if | ||
| you don't do anything, the kernel configuration tool will select one for you, | ||
| usually an 8x16 font. | ||
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| GOTCHA: A common bug report is enabling the framebuffer without enabling the | ||
| framebuffer console. Depending on the driver, you may get a blanked or | ||
| garbled display, but the system still boots to completion. If you are | ||
| fortunate to have a driver that does not alter the graphics chip, then you | ||
| will still get a VGA console. | ||
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| B. Loading | ||
|
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| Possible scenarios: | ||
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| 1. Driver and fbcon are compiled statically | ||
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| Usually, fbcon will automatically take over your console. The notable | ||
| exception is vesafb. It needs to be explicitly activated with the | ||
| vga= boot option parameter. | ||
|
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| 2. Driver is compiled statically, fbcon is compiled as a module | ||
|
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| Depending on the driver, you either get a standard console, or a | ||
| garbled display, as mentioned above. To get a framebuffer console, | ||
| do a 'modprobe fbcon'. | ||
|
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| 3. Driver is compiled as a module, fbcon is compiled statically | ||
|
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| You get your standard console. Once the driver is loaded with | ||
| 'modprobe xxxfb', fbcon automatically takes over the console with | ||
| the possible exception of using the fbcon=map:n option. See below. | ||
|
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| 4. Driver and fbcon are compiled as a module. | ||
|
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| You can load them in any order. Once both are loaded, fbcon will take | ||
| over the console. | ||
|
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| C. Boot options | ||
|
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| The framebuffer console has several, largely unknown, boot options | ||
| that can change its behavior. | ||
|
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| 1. fbcon=font:<name> | ||
|
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| Select the initial font to use. The value 'name' can be any of the | ||
| compiled-in fonts: VGA8x16, 7x14, 10x18, VGA8x8, MINI4x6, RomanLarge, | ||
| SUN8x16, SUN12x22, ProFont6x11, Acorn8x8, PEARL8x8. | ||
|
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| Note, not all drivers can handle font with widths not divisible by 8, | ||
| such as vga16fb. | ||
|
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| 2. fbcon=scrollback:<value>[k] | ||
|
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||
| The scrollback buffer is memory that is used to preserve display | ||
| contents that has already scrolled past your view. This is accessed | ||
| by using the Shift-PageUp key combination. The value 'value' is any | ||
| integer. It defaults to 32KB. The 'k' suffix is optional, and will | ||
| multiply the 'value' by 1024. | ||
|
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| 3. fbcon=map:<0123> | ||
|
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| This is an interesting option. It tells which driver gets mapped to | ||
| which console. The value '0123' is a sequence that gets repeated until | ||
| the total length is 64 which is the number of consoles available. In | ||
| the above example, it is expanded to 012301230123... and the mapping | ||
| will be: | ||
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| tty | 1 2 3 4 5 6 7 8 9 ... | ||
| fb | 0 1 2 3 0 1 2 3 0 ... | ||
|
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| ('cat /proc/fb' should tell you what the fb numbers are) | ||
|
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| One side effect that may be useful is using a map value that exceeds | ||
| the number of loaded fb drivers. For example, if only one driver is | ||
| available, fb0, adding fbcon=map:1 tells fbcon not to take over the | ||
| console. | ||
|
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||
| Later on, when you want to map the console the to the framebuffer | ||
| device, you can use the con2fbmap utility. | ||
|
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| 4. fbcon=vc:<n1>-<n2> | ||
|
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| This option tells fbcon to take over only a range of consoles as | ||
| specified by the values 'n1' and 'n2'. The rest of the consoles | ||
| outside the given range will still be controlled by the standard | ||
| console driver. | ||
|
|
||
| NOTE: For x86 machines, the standard console is the VGA console which | ||
| is typically located on the same video card. Thus, the consoles that | ||
| are controlled by the VGA console will be garbled. | ||
|
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| 4. fbcon=rotate:<n> | ||
|
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| This option changes the orientation angle of the console display. The | ||
| value 'n' accepts the following: | ||
|
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||
| 0 - normal orientation (0 degree) | ||
| 1 - clockwise orientation (90 degrees) | ||
| 2 - upside down orientation (180 degrees) | ||
| 3 - counterclockwise orientation (270 degrees) | ||
|
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| The angle can be changed anytime afterwards by 'echoing' the same | ||
| numbers to any one of the 2 attributes found in | ||
| /sys/class/graphics/fb{x} | ||
|
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| con_rotate - rotate the display of the active console | ||
| con_rotate_all - rotate the display of all consoles | ||
|
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| Console rotation will only become available if Console Rotation | ||
| Support is compiled in your kernel. | ||
|
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| NOTE: This is purely console rotation. Any other applications that | ||
| use the framebuffer will remain at their 'normal'orientation. | ||
| Actually, the underlying fb driver is totally ignorant of console | ||
| rotation. | ||
|
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||
| --- | ||
| Antonino Daplas <adaplas@pol.net> |
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