linux/Documentation/braille-console.txt
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   1                       Linux Braille Console
   2
   3To get early boot messages on a braille device (before userspace screen
   4readers can start), you first need to compile the support for the usual serial
   5console (see serial-console.txt), and for braille device (in Device Drivers -
   6Accessibility).
   7
   8Then you need to specify a console=brl, option on the kernel command line, the
   9format is:
  10
  11        console=brl,serial_options...
  12
  13where serial_options... are the same as described in serial-console.txt
  14
  15So for instance you can use console=brl,ttyS0 if the braille device is connected
  16to the first serial port, and console=brl,ttyS0,115200 to override the baud rate
  17to 115200, etc.
  18
  19By default, the braille device will just show the last kernel message (console
  20mode).  To review previous messages, press the Insert key to switch to the VT
  21review mode.  In review mode, the arrow keys permit to browse in the VT content,
  22page up/down keys go at the top/bottom of the screen, and the home key goes back
  23to the cursor, hence providing very basic screen reviewing facility.
  24
  25Sound feedback can be obtained by adding the braille_console.sound=1 kernel
  26parameter.
  27
  28For simplicity, only one braille console can be enabled, other uses of
  29console=brl,... will be discarded.  Also note that it does not interfere with
  30the console selection mechanism described in serial-console.txt
  31
  32For now, only the VisioBraille device is supported.
  33
  34Samuel Thibault <samuel.thibault@ens-lyon.org>
  35
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