IRQ_SLAVE          15 picirq.c       static ushort irqmask = 0xFFFF & ~(1<<IRQ_SLAVE);
IRQ_SLAVE          52 picirq.c         outb(IO_PIC1+1, 1<<IRQ_SLAVE);
IRQ_SLAVE          67 picirq.c         outb(IO_PIC2+1, IRQ_SLAVE);           // ICW3