Chrome OS uses the open-source BRLTTY library to provide support for refreshable braille displays.
We typically ship with a stable release build of BRLTTY plus some cherry-picked patches.
First, follow the public Chromium OS Developer Guide to check out the source. At a minimum you'll need to create a chroot. You do not need to build everything from source. You do need to start the devserver.
Next, flash your device to a very recent test build. Internally at Google you can do this with the following command when the dev server is running, where CHROMEBOOK_IP_ADDRESS is the IP address of your Chromebook already in developer mode, and $BOARD is your Chromebook's board name.
cros flash ssh://CHROMEBOOK_IP_ADDRESS xbuddy://remote/$BOARD/latest-dev/test
The BRLTTY files can be found in this directory:
third_party/chromiumos-overlay/app-accessibility/brltty
The first thing you‘ll need to do is edit the ebuild symlink to change the revision number. The real file is something like brltty-5.4.ebuild, but the revision will be something like brltty-5.4-r5.ebuild. You’ll need to increment it.
To increment it from r5 to r6, you'd do something like this:
rm brltty-5.4-r5.ebuild ln -s brltty-5.4.ebuild brltty-5.4-r6.ebuild git add brltty-5.4-r6.ebuild
The changes we make are all patches against a stable release of brltty. To add a new patch, put it in the files/ directory and reference it in brltty.bashrc
Once you're done adding patches or making other changes, flash it to your device like this:
emerge-$BOARD brltty cros deploy CHROMEBOOK_IP_ADDRESS brltty
After that, reboot your Chromebook and verify that brltty works.
To upload a change, use repo, something like this:
repo start <branch_name> . git commit -a BUG=chromium:12345 TEST=Write what you tested here repo upload .
Note that you shouldn't need to run cros_workon.