Exchanges data with device Manages all I/O Signals Device when data available May signal CPU when complete Uses bus In bursts during exchange For duration of exchange Acts as surrogate for main CPU Advantage I/O independent of CPU Unburdens CPU Disadvantage Higher cost Complex Control and Synchronization Similar to internal exchange Three types external interchange possible Event Shared Variable Message Observe these are abstractions Within each type Variety of related signals Event is change in state of signal of interest Usually assumed to be single signal Generally asynchronous to executing process occurrence of event Simultaneously activates Functions procedures to tasks Linked to it Occurrence of May or may not be stored in some way Becomes important issue in real time systems Acquired in several ways Sampled One example called polling to normal control flow Synchronous
Exchanges data with device Manages all I/O Signals Device when data available May signal CPU when complete Uses bus In bursts during exchange For duration of exchange Acts as surrogate for main CPU Advantage I/O independent of CPU Unburdens CPU Disadvantage Higher cost Complex Control and Synchronization Similar to internal exchange Three types external interchange possible Event Shared Variable Message Observe these are abstractions Within each type Variety of related signals Event is change in state of signal of interest Usually assumed to be single signal Generally asynchronous to executing process occurrence of event Simultaneously activates Functions procedures to tasks Linked to it Occurrence of May or may not be stored in some way Becomes important issue in real time systems Acquired in several ways Sampled One example called polling Synchronous to normal control flow
Input-Output0.docx