kernel/ramdisk/test.c

void io_out_byte(unsigned short port, unsigned char data) {
    asm volatile ("outb %0, %1" :  : "a"(data), "Nd"(port));
}

int _start() {
//    asm("int $0x01");
    while (1){
        io_out_byte(0x3F8, 'A');
    }
}