Real mode to protected mode inside the timer ISR

This rocks:


It’s the insane little trampoline I wrote last year in order to make real-mode BIOS calls from my toy protected mode OS, Metalkit. It’s full of all kinds of awesome and scary things.

So today, I just had occasion to try making a BIOS call from inside the timer interrupt, and it works! (Both in a VMware VM and on the physical laptop I tried it on.) Woohoo!

So now I have this spiffy little app that tests VESA BIOS palette manipulation:


Here’s a screenshot of it running in VMware and QEMU. It doesn’t work correctly in QEMU. Not sure why yet- it could just be that their VESA BIOS doesn’t support command 0x09.

If you want to try it yourself (on a VM or a physical machine), here’s a 4 kB precompiled binary. You can either use it as a floppy disk image or a GRUB multiboot image.

(Yes, this is a great example of the sort of dorky thing that gets me excited on a regular basis 😉