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Is int21 not for dos interupts?

Some pascal code:

procedure WriteChr(Chr: Char);
begin
asm
PUSH Ax

MOV Al, Chr
MOV Ah, 0Eh
INT 10h

POP Ax
end;
end;

function ReadChr: Char;
var
Key: Char;
begin
asm
PUSH Ax

XOR Ax, Ax
INT 16h

{Result}
MOV Key, Al

POP Ax
end;

ReadChr := Key;
end;

This should work in real mode but i don't use protected mode yet.

IDT defined?

Silenger: Maybe you misundstood me. What i wrote is my own OS, not in DOS. But thanks anyway!
Guest: Yes, i had set up the IDT.

what does exactly set_intr do ? keep in mind that C code usually trash some registers such as eax & edx... so you should not declare your driver as a plain C function, but at least have an asm stub code that will

pusha
call handler
popa
iretd

by the by, C function also ignores it should return differently from a handler (it will perform a RET instead of an iretd )

Thank you Clicker! What you said is absolutely right. I DID put my c code into the IDT directly, and that was the fault.
Now my kernel works well. Here you may get the source of my OS:
http://chong2.3322.net/myos/

Regards
Sysfree