Interrupts when switching back to real mode

[pranavappu007]

Hello, I am writing an OS for hobby an it doesn't support interrupts in 32-bit mode. However, I plan to implement exception handling, and maybe rewrite keyboard driver. But I'm loading my kernel from USB so using BIOS for it. I switch back to real mode for that.

But I have a doubt; If I set up a new IDT when switching to 32-bit mode, does returning to real mode automatically loads default address for BIOS IVT(00h)? If not, how to load it? Also, do I have to reload IDT(using lidt) when jumping back to 32-bit mode again?

[alexfru]

If I set up a new IDT when switching to 32-bit mode, does returning to real mode automatically loads default address for BIOS IVT(00h)?

No.

If not, how to load it?

You use LIDT again.

Also, do I have to reload IDT(using lidt) when jumping back to 32-bit mode again?

And again. Now is a good time for you to start reading the CPU documentation. The answers to most of your questions are there.

[pranavappu007]

So I use lidt to load IVT and IDT. So just like IDT, you write the size of IVT which is 0x3FF and then address which is 0h and load with LIDT?

[nullplan]

You know, reading the CPU documentation is actually really helpful here. It would tell you that the reset value for the IDTR has a base address of 0, yes, but a length of 65535. I have no idea how it would ever access anything past 0x3ff, since an interrupt vector is 4 bytes in real mode and there are at most 256 of those around, but that is the reset value. Indeed the CPU documentation would tell you that there is no IVT, the IVT is just what we call the IDT in real mode.