System with real-time checking of privilege levels and the system's state to allow access to internal resources of the system

摘要

A data processing apparatus has a plurality of execution status and is adapted to control in accordance with the respective execution conditions the allowance of the execution of an instruction requiring the reference to the internal resource. The processing apparatus also comprises a register for holding the execution status, and another register for holding information controlling the reference to the internal resource. A comparator responds to the contents of the first and second registers to output a signal indicating whether the reference is allowed or not. The output signal and a strobe signal are fed to a gate, which then controls an actual reference to the internal resource.