problem in multitasking theory

[Jef]

My multitasking theory works like this:
Is this correct?
Have I set/change TSS offset (looking in new task) in gdt?

If i am doing like this, i take an 0Dh exception once
EDIT: when i restore the GS register



while booting...
setups os_loop task
setups Clock_loop task
finally: jmp $

os_loop:
checks mouse, keyboard events
updates vga
jmp os_loop

clock_loop:
prints clock
jmp clock_loop

irq0:
saves old registers
load new registers
iretd

[Jef]

If i am doing like this, i take an 0Dh exception once
EDIT: when i restore the GS register

My mistake. I forgot to init GS on creating tasks. fixed.
Now working ok.

But i don't use TSS descriptor (and LTR command).
Is this used only when you use hardware multitasking?

[AJ]

Hi,

Yes - you will need to use LTR at least once per processor core if you want to be able to switch privilege level in the future. If you have your ring 0 stacks at the same location in virtual RAM, you can then forget about the TSS.

Cheers,
Adam

[Jef]

Hi,

Yes - you will need to use LTR at least once per processor core if you want to be able to switch privilege level in the future. If you have your ring 0 stacks at the same location in virtual RAM, you can then forget about the TSS.

Cheers,
Adam

right now i have only ring 0, and i am not using paging yet.
I want to put paging in my memory manager soon.
But i will keep all in ring 0 for now.

[AJ]

Fine - most people just get happy with ring 0 first. Once you need ring 3, it's really easy to add to your existing code. Simply:

1. Initialise the TSS and do an LTR in your run-once multitasking initialisation routine. You can load ESP0 here if you like.
2. If applicable, set ESP0 each time you switch task. Skip this step if you are using the paging method.

Good luck with the paging.

Cheers,
Adam

[Jef]

Fine - most people just get happy with ring 0 first. Once you need ring 3, it's really easy to add to your existing code. Simply:

1. Initialise the TSS and do an LTR in your run-once multitasking initialisation routine. You can load ESP0 here if you like.
2. If applicable, set ESP0 each time you switch task. Skip this step if you are using the paging method.

Good luck with the paging.

Cheers,
Adam

thanx