Input/Output Control: Exceptions, Interrupts, and Data Transfer in Computer Systems, Study notes of Introduction to Sociology

Download Input/Output Control: Exceptions, Interrupts, and Data Transfer in Computer Systems and more Study notes Introduction to Sociology in PDF only on Docsity! 3/11/2002 CSE 141 - Input/Output Input/Output Control Datapath Memory Processor Input Output Memory Input Output Network Control Datapath Processor CSE 141 - Input/Output2 Exceptions and Interrupts Terminology isn’t consistent. We’ll define: • Exceptions: any unexpected change in control flow Branches and jumps are not considered exceptions. • Exceptions are classified as either: – Internal Interrupts: Exception caused by something in the execution pipeline. • arithmetic overflow • illegal instruction • divide by zero • user program invoking the OS – External Interrupts: ones caused by something else. • I/O device signals completion to CPU • memory parity error • timer signal • low battery warning CSE 141 - Input/Output5 Giving Commands to I/O Devices • Two methods are used to address I/O devices: – Special I/O instructions – Memory-mapped I/O • Special I/O instructions specify a device number and a command • Memory-mapped I/O: – Each I/O device is given a portion of the real address space To prevent chaos, these addressed aren’t mapped to users’ virtual memory. – Read and writes to those addresses (by the OS) are interpreted as commands by the I/O device CSE 141 - Input/Output6 I/O Device Notifying the OS • The OS needs to know when: – The I/O device has completed an operation – The I/O operation has encountered an error • This can be accomplished in two different ways: – Polling: • The I/O device put information in a status register • The OS periodically check the status register – I/O Interrupt: • Whenever an I/O device needs attention from the processor, it issues an interrupt to the processor. CSE 141 - Input/Output7 Polling • Advantage: – Simple: the processor is in control and does all the work • Disadvantage: – Polling overhead can consume a lot of CPU time yes busy wait loop is an inefficient way to use the CPU unless the device is very fast! but checks for I/O completion can be dispersed among computation intensive code CPU IOC device Memory Is the data ready? read data store data yes no done? no