BRLTTY gives a braille user access to the text consoles of a Linux/Unix system. It runs as a background process (daemon) which operates a refreshable braille display, and can be started very early in the system boot sequence. It enables a braille user, therefore, to easily independently handle aspects of system administration such as single user mode entry, file system recovery, and boot problem analysis. It even greatly eases such routine tasks as logging in.
BRLTTY reproduces a rectangular portion of the screen (referred to within this document as `the window') as braille text on the display. Controls on the display can be used to move the window around on the screen, to enable and disable various viewing options, and to perform special functions.
BRLTTY provides the following capabilities:
underlineto indicate specially highlighted text.
blinking(rates individually settable) for cursor, special highlighting underline, and/or capital letters.
To date, BRLTTY runs under Linux and Solaris. While ports to other Unix-like operating systems aren't currently planned, we do welcome any interest in such projects.
This software has been tested on a variety of Linux systems:
This software has been tested on the following Solaris systems:
On Linux, BRLTTY can inspect the content of the screen
completely independently of any logged in user.
It does this by using a special device
which provides easy access to the contents of the current virtual console.
This device was introduced in version 1.1.92 of the Linux kernel,
and is normally called either
(on systems with
devfs it's called
For this reason, Linux kernel 1.1.92 or later is required
if BRLTTY is to be used in this way.
A patch for the
screen program is provide
It allows BRLTTY to access
screen's screen image via shared memory,
and, therefore, allows BRLTTY to be used quite effectively on platforms
which don't have their own screen content inspection facility.
The main weakness of the
screen approach is that
BRLTTY can't be started until the user has logged in.
In order for BRLTTY to successfully communicate with the refreshable braille display, the correct driver (serial, parallel, USB) must be configured into the kernel. If the driver requires special options, then they must be supplied. If it's built into the kernel, then its options must be:
/etc/conf.modulesby some older distributions).
BRLTTY only works with text-based consoles and applications.
It can be used with
but not with any application which
either uses special VGA features
or requires a graphics console (like the X Window system).
You must also, of course, possess a supported refreshable braille display (see section Supported Braille Displays for the complete list). We hope that additional displays will be supported in the future, so, if you have any vaguely technical programming information for a device which you'd like to see supported, then please let us know (see section Contact Information).
Finally, you need tools to build the executable from its source:
The development tools provided with standard Unix distributions should suffice.
If you have problems,
then contact us and we'll compile a binary for you.