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.

Gernot Heiser 2002-08-07