Lecture 33OutlineI/O Systems 1I/O Systems 2I/O Systems 3I/O Hardware 1I/O Hardware 2I/O Hardware 3I/O Hardware 4Application I/O Interface 1Application I/O Interface 2Application I/O Interface 3Application I/O Interface 4Application I/O Interface 5Application I/O Interface 6Application I/O Interface 7Application I/O Interface 8Kernel I/O Subsystem 1Kernel I/O Subsystem 2Kernel I/O Subsystem 3System Performance 1System Performance 2System Performance 3Monday, April 4 CS 470 Operating Systems - Lecture 33 1Lecture 33Schedule for rest of term posted.Optional project posted. Can be used to replace one project grade.Questions?Monday, April 4 CS 470 Operating Systems - Lecture 33 2OutlineI/O systemsI/O hardwareApplication I/O interfaceKernel I/O subsystemSystem performanceMonday, April 4 CS 470 Operating Systems - Lecture 33 3I/O SystemsMain jobs of a computerProcessingI/OOften the primary job is I/O with incidental processingWeb browsingDocument editingMonday, April 4 CS 470 Operating Systems - Lecture 33 4I/O SystemsI/O devices are diverse - mouse, disk, monitor - so various methods are needed to control them. Collectively, they are known as the I/O subsystem that separates the rest of the kernel form the complexities of managing I/O.Monday, April 4 CS 470 Operating Systems - Lecture 33 5I/O SystemsConflicting trendsIncreasing standardization of software/hardward interfaces makes is easier to incorporate new devicesI/O devices are becoming more diverse, unlike any previous devices.Details and oddities of differing devices are encapsulated in device drivers that allow the OS to provide a uniform device-access interface.Monday, April 4 CS 470 Operating Systems - Lecture 33 6I/O HardwareNot too much detail; covered in CS 320General categories:StorageTransmissionHuman interfaceSpecial I/O - sensors, actuatorsCommunicate with computer via port or busMonday, April 4 CS 470 Operating Systems - Lecture 33 7I/O HardwareController is a piece of electronics that operates a port, bus, or device.Sometimes a separate card, e.g. SCSI host adapter, network interface cardSometimes built into the device, e.g. disk controllerCommunication is through special I/O commands that write to registers at I/O port addresses or through memory-mapped I/O.E.g. PC graphics controller uses I/O ports for basic operations, but maps screen memory for direct writes.Monday, April 4 CS 470 Operating Systems - Lecture 33 8I/O HardwareInteraction (or handshaking) between devices is done through polling or interrupts.Polling is fast (read, mask, branch on 0), but wasted processing if event does not happen often.Interrupts only happen when events happen, but must have fast dispatch and ability to mask interrupts for critical sections or higher-priority interrupts.Monday, April 4 CS 470 Operating Systems - Lecture 33 9I/O HardwareDirect-memory access (DMA) controller is used to handle large transfers to memory so that CPU does not have to watch status bits and/or load data one word at a time.Monday, April 4 CS 470 Operating Systems - Lecture 33 10Application I/O InterfaceAs with other software-engineering problems, approach is to abstract and encapsulate behavior. Drivers provide a standardized set of functions - an interface - for various generic I/O devices.Lots of different classes of drivers.Monday, April 4 CS 470 Operating Systems - Lecture 33 11Application I/O InterfaceKernelKernel I/O SubsystemEIDEdevicedriverEthernetdevicedriverUSBdevicedriverPCI busdevicedrivergraphicsdevicedriverATAPIdevicedriverEIDEdevicecontrollerEthernetdevicecontrollerUSBdevicecontrollerPCI busdevicecontrollergraphicsdevicecontrollerATAPIdevicecontrollerhard disk networkmousekeyboardmemory monitor CD/DVDsoftwarehardware.........Monday, April 4 CS 470 Operating Systems - Lecture 33 12Application I/O InterfaceUnfortunately, each OS has its own standards for device-driver interface, so many devices ship with multiple drivers. Or are usable only with certain OS'sLess so now that many devices use USB for wired and Bluetooth for wireless interaction.Monday, April 4 CS 470 Operating Systems - Lecture 33 13Application I/O InterfaceDevices vary on many dimensionsdata transfer mode: character (e.g. terminal) vs. block (e.g. disk)access method: sequential (e.g. modem) vs. random (e.g. CD-ROM)transfer schedule: synchronous (e.g. tape) vs. asynchronous (e.g. keyboard)device speed: few bytes/sec (e.g. modem) vs. few gigabytes/sec (e.g. Ethernet)I/O direction: read-only (e.g. CD-ROM) vs. write-only (e.g., monitor) vs. read-write (e.g. disk)Monday, April 4 CS 470 Operating Systems - Lecture 33 14Application I/O InterfaceMost OS's support several general categories of devices.Block devices: read/write/seek operations. Sometimes raw I/O with direct access to controller. Sometimes direct I/O with no buffering or locking, but all other services.Character streams: single-character get/put operations. Buffered, concept of a line. Editing is built on top of these.Monday, April 4 CS 470 Operating Systems - Lecture 33 15Application I/O InterfaceNetwork devices use socket interface: create, bind, connect, listen, accept, selectClocks and timers: operations to get current time, get elapsed time, set timer to trigger operation X at time T. Interface is not standardized. Interrupt rates are 18-60 ticks/sec. Heavily used by the OS and real-time applications.Most OS's have an escape (or backdoor) command that will pass arbitrary commands to a device. E.g. Unix ioctl( ) system call.Monday, April 4 CS 470 Operating Systems - Lecture 33 16Application I/O InterfaceBlocking vs. non-blocking I/O. Most physical actions are asynchronous, but most system calls are blocking, since they are easier to understand and use.Some user-level processes need non-blocking I/O to do "simultaneous" I/O operations. E.g. keyboard and display, or video read and display.Monday, April 4 CS 470 Operating Systems - Lecture 33 17Application I/O InterfaceSometimes there is a difference between non-blocking and asynchronousNon-blocking: call attempts to perform an operation and returns in a short amount of time with indication of how far it got.Asynchronous: call returns immediately without waiting for I/O to complete. Notification is given when operation complete. (Event interrupt.)Threads can be used to provide simultaneous