This is a project I worked on about 11 months ago -- it's very incomplete, and barely usable. I was compelled to put up the code for others to look at after Steven Troughton-Smith mentioned there were no examples of the mouse driver code from Chadderz's Simple USB Driver. That mouse driver was written for this project, so it seemed appropriate to finally post the code.
This is a modified version of the Squeak Smalltalk virtual machine to be booted from the bare metal. The kernel.img is the VM, and it will initialize the serial port (for lots of debugging), initialize the frame buffer, use CSUD to attempt to interface with the keyboard & mouse (very flakey). It (ab)uses ATAGs to have the Raspberry Pi firmware load the Squeak image for it to run. If all goes well, it should boot into a fully usable Squeak system in a few seconds. And when all goes bad, there's at least a watchdog timer to help reboot the system
For those that just want to play with it and not deal with compiling, there is:
https://raw.github.com/pablomarx/Raspbe ... -ready.zip
One should be able to unzip that onto an SD card and have the RPI boot into Squeak.
The project owes a lot to various forum members here -- it's been too long so I can't remember everybody whose posts were instrumental in getting this up and running. But I do remember it was Alex Chadwick's Baking Pi that led me to trying this out in the first place. Many thanks to Alex for his excellent tutorial.