FreeBSD/Linux Kernel Cross Reference
sys/Documentation/braille-console.txt

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

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