Input/Output

Techniques

Programmed I/O

• CPU has direct control over I/O
  • Continuously sense status – Poll
  • Read/write commands
  • Transferring data
• CPU waits for I/O module to complete operation
• Wastes CPU time

Interrupt Driven I/O

CPU does its own work without waiting. When I/O device is ready, interrupts CPU.

Steps:

• CPU issues read command
• I/O module gets data from peripheral whilst CPU does other work
• I/O module interrupts CPU
• CPU requests data
• I/O module transfers data

Direct Memory Access (DMA)

DMA transfers data directly to/from memory without CPU intervention.