A device that can be addressed to read data from or write data to the device.
A device (cpu) that can debugged using the built-in debugger
A device (peripheral) that can inspected using the built-in debugger
A device that can receive an interrupt. The interrupt_state_change() method
will be called whenever an interrupt signal changes goes high or low.
A device that can change state over time. The step() method will be called
by the containing System when the system clock advances. If an error occurs
with any device, the on_error() method will be called to display any state
information that might be helpful for debugging.