Gypsum is a super-simplistic graphics display server for Android, designed to provide a display to a Bluetooth RFCOMM-connected headless device for the Navi project. It was originally designed as part of the Navi project to be run on Google Glass (though it works on virtually any Android device), with a paired Intel Edison as the core “mote” of the wearable system.
Gypsum’s design is heavily influenced by Common Lisp and it’s base
representation type, s-expressions. Currently incoming s-expressions are parsed
in through Java’s highly inefficient StreamTokenizer class – this needs to
change, and will likely move to a native C/C++ implementation, one that makes
use of a proper lisp reader, possibly even implemented entirely in ecl.
Note: Gypsum and the Gypsum display protocol are in constant flux. This code is pre-alpha quality, and has not seen much testing. I can prove that it works for me, but it may not work for your usage goals.
Building Gypsum is fairly simplistic at the moment. You’ll need the following prerequisites:
- Apache Ant
- Android SDK (at least API 19 – Google Glass extensions are largely unused)
- Java JDK (at least 1.5)
Building is done entirely through the command line. Once you have the prerequisites installed, you’ll need to do the following inside the root of the source tree:
$ android update project -p . -n Gypsum -t android-19- Start your AVD instance, or connect a real device via USB. If using an AVD, wait for it to finish starting and ensure “debug over USB” is turned on in the Developer menu first.
$ ant debug install- Start Gypsum from the Android launcher.
At this point, one of two things will happen, depending on what kind of device Gypsum is running on.
Since there’s no effective way of testing Gypsum via a “loopback Bluetooth” connection, it’s approximated via a local TCP socket. You’ll need to connect to the local port for your AVD instance and redirect TCP socket 5555 to your host machine before you can connect.
Once that’s done, you should be able to issue s-expressions to the Gypsum
instance running on the device via telnet localhost <redirected-port>.
On a real device, Gypsum actually listens over an RFCOMM instance. How you connect to it is implementation defined. Most Nexus devices (running bluedroid) start numbering their RFCOMM connections at port number 5.
Gypsum registers itself as the UUID 199d6fc0-adcb-11e4-a32c-6c4008a5fbd2, so
an SDP scan for that service UUID should turn up the proper port.