stevix*

*it doesn't work as well with my name as it did with Linus

This is a long term project in which I hope to build a simple operating system for the Raspberry Pi.

Setup

See doc/Setup.md.

Status

An OS is a huge undertaking, and there are lots of milestones to reach before you can really claim to have an OS. Here are the things I currently have accomplished.

• Simple HDMI framebuffer, with line drawing
• Framebuffer console output
• Serial input/output, on both the Mini UART and PL011 UART
• Simple printf formatting for either serial or framebuffer

Some things that are on the horizon:

• Support more format specifiers in string formatting (not a very high priority right now)
• Process abstraction, with time slices and scheduling. No memory protections yet. Separate stack.
• Memory segmentation
• USB keyboard input (a major undertaking)
• FAT32 filesystem implementation

This would get me to my first milestone. Here is the current set of milestones that I have in mind:

1. A minimal shell that supports keyboard input. Basic utilities to explore the file system (probably read-only). Future features will be exposed as commands until I have the ability to create an init process.
2. The ability to enter "user-mode" and run something. This will require me to figure out the MMU and how I will manage memory for processes (even though process won't actually exist yet).
3. A real "process" abstraction, complete with a system call interface and a few system calls. At this point, the process code will likely be copied from the kernel image into the user-mode memory space, rather than trying to support ELF.
4. A real "file" abstraction, with an implementation that supports the console. At this point, a process should be able to read and write to the console as its "stdin" and "stdout".
5. Some sort of scheduling system (brain-dead simple first). The important thing is to be able to set time slices, run the process in a time slice, and then transition back into kernel-mode in order to schedule something else.
6. Some form of interrupt handling that respects processes. This way, the USB driver could use interrupts to get input.
7. A real user-mode shell as init!
8. Process management system calls so that you can create a new process.
9. ELF support? Some sort of format for storing executables.

Like I said, this is a truly long-term project.

License, Credits

There are a lot of great resources that have helped me:

• Baking Pi
• dwelch67's collection of bare-metal examples
• BCM2835 perpiherals datasheet
• PrimeCell UART (PL011) datasheet

I'd like to release this under Revised BSD, as per usual.