Linux Braille Console — The Linux Kernel 6.14.4-gnu-4-vanilla documentation

# 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 Documentation/admin-guide/serial-console.rst), and for braille device (in Device Drivers ‣ Accessibility support ‣ Console on braille device).

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 Documentation/admin-guide/serial-console.rst.

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/PAGE-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 Documentation/admin-guide/serial-console.rst.

For now, only the VisioBraille device is supported.

Samuel Thibault <samuel.thibault@ens-lyon.org>