Principles of I/O Hardware

• There exists a large variety of I/O devices:
  • Many of the with different properties
  • They seem to require different interfaces to manipulate and manage them
• We don't want a new interface for every device
• Diverse, but similar interfaces leads to code duplication
• Challenge: Uniform and efficient approach to I/O
• Common concepts
  • port
  • bus
  • controller (host adapter)
• each port is given a special address (see Table 1)
• communication, use an assembly instruction (high-level languages only work with main memory) to read/write a port; e.g., OUT port, reg: writes the value in CPU register reg to I/O port port
• protection, users should have access to some I/O devices but not to others
• I/O instructions control devices
• Devices have addresses, used by
  • direct I/O instructions
  • memory-mapped I/O

Table 1: Device I/O Port Locations on PCs (Partial).

I/O address range (hexadecimal)	Device
000-00F	DMA Controller
020-021	Interrupt Controller
040-043	Timer
200-20F	Game Controller
2F8-2FF	Serial port (secondary)
320-32F	Hard disk Controller
378-37F	Parallel port
3D0-3DF	Graphics Controller
3F0-3F7	Diskette drive Controller
3F8-3FF	Serial port (primary)