I think I was pretty impressed with myself when I managed to crash my PC into an infinite loop of displaying green smiley faces (just a coincidence, honest!) from the boot sector of a floppy disk. And it wasn't supposed to be an infinite loop anyway.
Then there was the time I got my real CPU into protected mode. I had spent weeks battling through incomplete online tutorials and muddled reference information (half of which made reference to DOS) before even drafting up my GDT, then I finally got to the stage where I got executable code out of the thing and got Bochs to display an "A" (this time without infinite loop) without triple-faulting. Then I booted my real PC from it.
Now my next milestone is to get the kernel to load a user program and run it... (actually not too far off, relatively speaking)
Octocontrabass wrote:
My most recent? Writing to video memory from the boot sector of a floppy disk.
...on a Macintosh Quadra 605.
You're also into old Macs? I've got a Performa 475 (coincidentally the home version of the Quadra 605), but I haven't done any low-level work on it. I enjoy the Macintosh for what it is: unsurpassable, in my opinion. Anyway, are you on the 68kMLA forums? (I am.)