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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Device Interfaces

• Devices are controlled via special device registers, typically:
  • status register, to obtain device status,
  • control register, to send commands to device
    status and control registers are at the same address,
  • data register(s) to pass data/command parameters.
• Number of registers is normally small,
  data and parameter buffers are passed in memory, address specified in data registers
• Device registers are either memory mapped or accessed via I/O instructions
• Devices access only physical memory, i.e. bypass the MMU.