[Bassetlug mailing] Writing an OS

[MJ.Wells]

The following link has a lot of information about the structure of an OS:

wiki.osdev.org/Main_Page

Particularly you might like to try:

wiki.osdev.org/Bare_Bones

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Looking at the Rpi information it seems that a sensible kernel to write 
is a FORTH Interpreter. you can write the main interpreter in about 100 
bytes of assembler code. I wrote one back in the 1980's and the concepts 
involved are simple and straight forward. A FORTH interpreter can be 
regarded as an Operating System in its own right with the addition of a 
suitable dictionary.

At the moment I have two issues with this:

a) We will have to use the UART to do RS232 serial in order to talk to 
the Pi from a computer using a USB to serial port device. I have still 
to solve the issue raised with the RS232 because the  Rpi is 3v3 so we 
need to do some level shifting. I have only designed RS232 work down to 
5v before. I have seen articles talking about the solution to this and 
so it is not a big problem.

b) I don't yet understand how the framebuffer works so that we can get 
output to the screen. This is not initially a problem until we want to 
use graphics as to start with we can use the RS232 link to a computer as 
both the input and output console.

It may be possible to adapt the Linux kernel sources for the USB, screen 
and Ethernet. As we get into this it is will not be beyond us to do this 
if they are fairly freestanding and not intimately entwined into Linux 
as we have a great deal of expertise in the group now. However, I am 
hoping that the foundation bring out a kernel module to handle the 
peripherals on the RPI.

Martin