c++ asm statement for MCGA mode

gvp87 · 01-31-2008, 12:45 PM

void MCGA() {
asm("movl $0x13 %ax");
asm("int $0x10");
}

this is my function to set MCGA mode...for somereason it wont compile, but i've looked at like, every single HOWTO on asm and c++ inline asm, and still can't figure out what i'm doing wrong.

the compiler is telling me this:

Error: suffix or operands invalid for `mov'

Does anyone know how I can fix this??

Mara · 01-31-2008, 04:24 PM

Code:

void MCGA() {
asm("movl $0x13, %eax");
asm("int $0x10");
}

Two things: comma between the arguments and change of ax to eax because you use movl, not mov.

gvp87 · 02-01-2008, 08:32 AM

Thanks a lot! Omg i couldn't figure it out for the life of me and it was driving me crazy

Dox Systems - Brian · 02-04-2008, 08:31 AM

While using EAX works and won't hurt anything, it'd be more technically correct to just use MOV with AX, since that's all that BIOS call is looking for. But clearing the upper half of EAX isn't going to hurt anything either. The only real downside I can think of is future readability. Someone looking at the code might wonder "why on earth is EAX used? what might break if I change anything?, etc)