After testing: # gcc inlineasm.c inlineasm.c: Assembler messages: inlineasm.c:7: Error: suffix or operands invalid for `out' [root@debian-johnny] ~/workspace/test # cat inlineasm.c #include <stdio.h> int main () { unsigned int val = 5, tmp = 10; asm volatile ("outb $0x27, %%al" : : "a" (0xb2), "b"(val), "c" (tmp) ); } It seems the source of outb instruction cannot be a constant. Is there a AT&T instructions document for x86? BRs, H. Johnny > Why not just: > ("outb $0x27, %%al" : : "a" (0xb2), "b"(val), "c" (tmp)); > -- > js > Faculty of Informatics, Masaryk University > Suse Labs, Novell > -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html