Chapter 13-1 I/O SystemsChapter 13-1: I/O SystemsI/O SystemsIntroductionI/O HardwarePortsPort Picture – older deviceMore Modern Port ViewDevice I/O Port Locations on PCs (partial)BusesBuses: Parallel and Serial; Internal and External; Blurring with new technologies…Bus Topology - NetworkExamples of Internal Computer BusesExamples of External BusesBuses - lastlyA Typical PC Bus StructureDevice ControllersDevice Controllers - 2Setting Up I/O – CPU Communications with Device ControllersPort I/O and Memory Mapped I/OI/O Ports – Themselves <book>Programmed I/O : Interrupt-Driven I/O <different source>Polling Protocol (a.k.a. ‘busy waiting.’)Issues in PollingInterrupts – How they WorkEnd of Chapter 13-1Chapter 13-1 I/O SystemsChapter 13-1 I/O Systems13.2Silberschatz, Galvin and Gagne ©2005Operating System ConceptsChapter 13-1: I/O SystemsChapter 13-1: I/O SystemsChapter 13-1I/O HardwareChapter 13-2Application I/O InterfaceKernel I/O SubsystemTransforming I/O Requests to Hardware OperationsStreamsPerformance13.3Silberschatz, Galvin and Gagne ©2005Operating System ConceptsI/O SystemsI/O SystemsOne of the more difficult chapters.This chapter pulls together many things we’ve had, but in significantly more detail.It is divided into some key sections:An overviewI/O HardwareApplication I/O InterfaceKernel I/O SystemTransforming I/O Requests to Hardware OperationsStreamsPerformanceThese will keep us busy. I plan to cover almost all of these sections and will supplement from other sources as I feel the need arises.13.4Silberschatz, Galvin and Gagne ©2005Operating System ConceptsI.I.IntroductionIntroductionImportant to realize just how much of a constraint I/O operations place on a ‘computing system.’Yet I/O is, of course, essential, as we know that the I/O responsibilities include the management and control of I/O operations and devices in an overall computing system where overall performance and efficiency are king.The reality is that I/O devices differ markedly in capability, design, interfacing, and technologies along with the software and hardware that control these.Authors approach I/O operations in the context of an I/O Subsystem – part of the kernel, but treated separately from the rest of the kernel.I/O Subsystem is very complicated.ever-emerging new technologies in the form of specialized I/O devices Gives rise for significant standardization of interfacing and operations.Have basic hardware interfacing elements: ports, buses, and I/O device controllersBut great variability in how all these each define different ways to accommodate I/OHardware must facilitate data transfer with an operating system that craves performance and is software! So, how does the complexity of input / output actually get accommodated such that high performance is maintained in accommodating the slowest, yet perhaps the most essential activity in a computing system: input/output.We will look at all this in detail…13.5Silberschatz, Galvin and Gagne ©2005Operating System Concepts2.2.I/O HardwareI/O HardwarePutting I/O devices into ‘boxes’ we typically haveStorage devices (disks, tapes, etc.)Transmission devices (network cards, modems)Human-interface devices (screens, keyboards, mice, joysticks…)Devices all communicate over cables (or air) with the machine using ‘standard’ connections: Ports, Buses (daisy chained or shared host adaptor), and Device Controllers. They are all different, and I want to diverge and consider them in a bit more detail…13.6Silberschatz, Galvin and Gagne ©2005Operating System ConceptsPortsPortsThe CPU and its supporting circuitry provide Memory-mapped I/O, which involves a range of memory addresses simply set aside and are mapped to device registers.Reads and writes to these memory addresses cause the data to be transferred to and from the device registers. A computer using memory-mapped I/O accesses hardware by reading and writing to specific memory locations using the same assembler language instructions that the computer would normally use to access memory.So to accommodate the I/O devices, areas of CPU’s addressable space must be reserved for I/O (even temporarily) rather than memory. We will return later with more on memory-mapped I/OBut the thinking of memory-mapped I/O can be applied to other devices such as the serial and parallel ports used to connect modems and printers to a computer.Here, the CPU transfers data through these devices by reading and writing a few device registers called an I/O port. Port-mapped I/O usually requires the use of special instructions which are specifically designed to perform I/O operations, such as the IN and OUT instructions found on Intel microprocessors.Here, I/O devices have a separate address space from general memory – either accomplished by an extra I/O pin on the CPU’s physical interface or an entire bus dedicated to I/OI/O ports are simply a few registers supporting data transfer from I/O devices and main memory.Very specific I/O instructions are executed to allow this data transfer to take place between these registers and main memory.So, simply consider a port as a set of hardware addresses whose contents are accessed via specific low-level instructions (ahead).If we access hardware through ports, we are dealing with the hardware directly. Mistakes may be disastrous, however, because there is no validation whether your input is correct or not – in general.I/O ports only accept numbers (byte – 8 bits; or word (16 or 32 bits) This input depends on the hardware you want to deal with.More interest: A computer using memory-mapped I/O accesses hardware by reading and writing to specific memory locations – using the same assembler language instructions that the computer would normally use to access memory.(Access: not every port has both read and write access. Some have read only; some only write access.Interestingly, there may be a port register, which you may view as an array of data inside the hardware)13.7Silberschatz, Galvin and Gagne ©2005Operating System ConceptsPort Picture – older devicePort Picture – older deviceThis picture shows an internal view of some of the I/O ports on the right and a covered view on the left. On the back of computers are several I/O ports. Above, on the very