HL-OS

This site is very simplistic. I just want to show off what I've been working on lately. It's a very minimalist operating system. I wrote it in High Level Assembly. A couple of years back when I tried to get my head around assembly programming, I discovered HLA on the web and was intrigued by its advertised ease of entry into an understanding about how the machine works inside. But after learning assembly I wasn't happy, because everything I wrote was still dependent on the OS I was running on, so I sort of knew what my programs did in machine terms, but not how the multitasking and all the hardware stuff was made to get going.

I found it was time to learn about operating systems. But not just from a theoretical point (I did have that in the college). After a little bit more research I found out about Minix. I got myself a copy of the Minix Book, which turnt out to be an excellent investment.

When it came to actually writing some code on my own, I recalled HLA and was curious whether it would actually be possible to code an OS in it. On the HLA newsgroup I was told it was possible, the only catch being that you can't use HLA to write 16-bit code. So you would indeed need some other compiler to code the very first few instructions of your would-be OS in to make your machine switch into protected mode, but from there on, HLA is all you need. I personally love HLA because it gives me the power to write "real assembly" whenever I see fit, but also to express myself on a higher level, with control structures, structs, and the likes.

But getting back to my OS, what I've got going for the moment is the following:

machine starts and reads first 512 bytes from disk

machine reads rest of the kernel from disk

machine uses BIOS to retrieve memory map

machine switches over to protected mode

machine sets up clock and keyboard interrupts

machine sets up rudimentary multitasking

machine sets up 3 simple commands: cls, say, and uptime

Below I will provide the source plus the compiled "kernel". If you want to compile the kernel yourself, you will need to install NASM and HLA on your Linux box. Then uncompress the files into a folder of your choice and type:

make bootdisk.bin

You will need to copy the content of this file to the very start of a floppy disk. You can then restart your machine from this floppy into the kernel. Alternatively, you can start the emulator of your choice (Bochs, qemu, VirtualBox, and the likes) and provide bootdisk.bin as a virtual floppy to boot from.

A few words about the multitasking: I don't as of yet have any meaningful tasks. So all I did was write two very simple tasks that just increment a register in a tight loop, over and over again. They look like this:

procedure task1;
begin task1;
    forever
        cli;
        putstring("1");
        sti;
    endfor;
    endfor;
end task1;

procedure task2;
begin task2;
    forever
        cli;
        putstring("2");
        sti;
    endfor;
end task2;

The multitasking functionality is however still very rudimentary. The user cannot launch new processes as of yet. But the most fundamental functions and mechanisms to for this exists already. Take the following function call (it's commented out in main.hla):

createProcess(0,50,&task1,$14700,$14700,NO_BASE,0,$b8000,$110000,$fffff,$fffff,0,$fffff,$1,$ffff0);

This will create a new process in the process table with:

privilege 0
a quantum of 50 clockticks
a starting address equal to &task1
a code segment (where the cs register points) that starts at absolute memory offset $14700 and has a limit of $fffff (page-granular)
a data segment (where the ds register points) that starts at absolute memory offset $14700 and has a limit of $fffff (page-granular)
an empty (zeroed-out) es register
a data segment (where the fs register points) that starts at absolute memory offset 0 and has a limit of $fffff (page-granular)
a data segment (where the gs register points) that starts at absolute memory offset $b8000 and has a limit of $1 (page-granular)
a stack segment (where the ss register points) that starts at absolute memory offset $110000 and has a limit of $ffff0 (page-granular)

This function returns the index into pproctab for the new process in eax. You can then enqueue this new process with:

enqueue(pproctab[eax], 5, FRONT);

The above call would enqueue the process at the front of scheduling queue 5 (There exists a maximum of NO_SCHEDQUEUES scheduling queues).

If you uncommend the four lines down the bottom of main.hla you can see how the two processes are created and run.

I will also shortly describe the commands that I've implemented so far:

this clears the screen

will repeat what you tell it to (e.g. "say something")

uptime

will display the hours, minutes and seconds passed since sytem startup

I will also include a precompiled version of bootdisk.bin, in case you want to see it roll but can't compile the source. Click here to learn more about the source.

Download here:

MyOS.zip

bootdisk.bin

I have also written some basic documentation about the source code. Please click here.

mail to: webmaster {at} com-eu-nication.eu