What should be implemented before multitasking?

[mrjbom]

Hi.
I want to implement multitasking in my OS, but I don't understand what I need to do before that.
Now I can work work with the keyboard and I have a primitive physical memory manager (divides the memory into pages and allocate the desired number of pages), is this enough to implement kernel multitasking? Or should I do something else?
I think so, but it's better to ask.

[AndrewAPrice]

Very close, you just need to implement interrupt handling. Return from the interrupt with a different set of registers (including the instruction pointer and stack pointer) to what you entered with.

Then, this interrupt could be fired from a timer or manually fired by a thread willing to give up control.

[iansjack]

I'd say that allocating memory as pages, rather than smaller amounts, is going to be a little wasteful. I'd recommend writing a memory allocator to hand out smaller chunks of (virtual) memory.

[mrjbom]

Very close, you just need to implement interrupt handling. Return from the interrupt with a different set of registers (including the instruction pointer and stack pointer) to what you entered with.

Then, this interrupt could be fired from a timer or manually fired by a thread willing to give up control.

I already have interrupts, I think I need to implement software interrupts somehow. I also need a timer with millisecond accuracy to switch between tasks. But I don't know what kind of watch will help me.

[AndrewAPrice]

I found the PIT very easy to use. It'll fire an interrupt on IRQ0.