hi! if you are using a protected mode model,
it may be impossible to call int 10 directly
and you may have to use dpmi for that.
all compilers for DOS offer ways to call BIOS
and other interrupts directly from C, which
is a lot more foolproof than using ASM here.
the next problem is whether you should use
RET here, that may be something C does for
you and it may be something more complex
than just calling RET, e.g. also preparing
and clearing up the stack before and after
the ASM part. you can try without the RET.
C compilers have various opinions about
whether and which registers you are allowed
to change, but int ax=0x0013 probably is
safe, changing only AX, as far as I remember.
Note that you write mov al,0x13, which
means you do NOT specify what AH should
be. this is a BAD idea. AH could be any
arbitrary value at that moment, so you
could be triggering any VGA BIOS int 10
thing instead of the one you intended.
Finally, your clear screen confuses the
graphics RAM segment 0xa000 with absolute
address 0xa0000 and relative offsets of
0 to 0xfa00 within that. It will depend
A LOT on which compiler and memory model
you use what the PROPER way to do this
will be for you. I can only tell that
the style you use right know is NOT okay
and will just overwrite data and crash.
Regards, Eric
I can’t for the love of god figure out why this is throwing the divide
by zero interrupt.
void setMCGA() {
_asm {
mov al, 0x13
int 0x10
ret
}
}
void setText() {
_asm {
mov al, 0x03
int 0x10
ret
}
}
void clearScreen(char color) {
int i;
for (i = 0xa000; i < 0xfa00; i++) {
char* byte = i;
*byte = color;
}
}
int main(int argc, char** argv) {
setMCGA();
clearScreen(255);
getchar();
setText();
return 0;
}
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