Since the number of interrupts available is chip specific and the interrupt vector table always
ends at the last byte of memory, the interrupt numbers corresponds
to the interrupt vectors in reverse order of address. For example,
interrupt 1 will use the interrupt vector at 0xfffc, interrupt 2 will
use the interrupt vector at 0xfffa, and so on. However, interrupt
0 (the reset vector at 0xfffe) is not redefinable in this way; instead
see section for details on customizing startup.