User:Anotheridiot/Getting Started

Picking the design

When you first get started you need to make a few choices before you start on your kernel, they are described below.

BIOS or UEFI?

When you start writing your OS you have to pick between BIOS or UEFI, BIOS was a far less standardized thing, and UEFI is standardized pretty well. UEFI is used on more modern devices, but is also more complex.

Custom Bootloader

This is mostly where the BIOS vs UEFI stuff comes in, when you write a custom bootloader for UEFI you get a well defined standard API and all of that. With BIOS you get legacy device support. UEFI is far better and easier for writing a custom bootloader and is far less limited.

Language

No matter what you will need a little bit of assembly for a lot of stuff like ISRs. But the primary language used in OS development is C, and sometimes C++, though C is better suited for it since it integrates with assembly a lot better and does not have "runtime" features built into the language such as try and catch, global constructors and such.

Kernel Design

If this is your first time writing an OS you should look at Kernel and the design types of a kernel, I personally recommend monolithic, no loading drivers, its all built into the kernel.

Making the OS

A little warning, this part is by far the most complex part because you need to do so much to get something that is barely functional.

The Bootloader

The bootloader is what loads your kernel, you should know this by now, assuming you make your own bootloader, you first need to base it on your BIOS/UEFI, when you do this for the BIOS you want to load your kernel, read the filesystem, jump to either 32 bit mode or 64 bit mode (check if its supported on the CPU first) then load your kernel from memory by jumping to it, you also need to setup the Global Descriptor Table.

The Kernel

The kernel is the most important part, the heart of your OS. Here is the (rough) order you need to make things in

1. Printing text with some form of Formatted Printing (printing out hex and decimal, with of course strings and characters would be good enough)
2. A fully functional GDT, when you load your kernel from UEFI the GDT is left in a state that is not known, which means it could be anything, so set it yourself.
3. Interrupt handing, you would need the 8259 PIC setup for Interrupts and the IOAPIC and APIC for the more advanced stuff related to ACPI
4. The actual Interrupt Descriptor Table.
5. Multithreaded Kernel (not Symmetric Multiprocessing which is using multiple cores, but instead using Threads)
6. A PS/2 Keyboard driver
7. A simple Shell (usually for debugging)
8. Logging
9. Error Handling that can recover the system from something that could be a fatal system issue if not handled correctly
10. A IDE driver for disk access
11. A VFS
12. A filesystem
13. A system API (using interrupts that ring3 can use)
14. Getting to Ring 3
15. Running ELF applications