Systems - Operating Systems - Lecture Slides, Slides of Computer Science

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I/O Systems Chapter 13 Docsity.com I/O Systems • I/O Hardware • Application I/O Interface • Kernel I/O Subsystem • Transforming I/O Requests to Hardware Operations • Streams • Performance Docsity.com A Typical PC Bus Structure Gist s||-Ge a re monitor processor a cache pea ea f— memory SCSI controller IDE disk controller expansion bus keyboard interface (ask) Gist) parallel serial port port Docsity.com  Device |/O Port Locations on PCs (partial) I/O address range (hexadecimal) device 000-—00F DMA controller 020-021 interrupt controller 040-043 timer 200-20F game controller 2F8—2FF serial port (secondary) 320-32F hard-disk controller 378-37F parallel port 3D0-3DF graphics controller 3FO-3F7 diskette-drive controller 3F8—3FF serial port (primary) Docsity.com Polling • Determines state of device – command-ready – busy – Error • Busy-wait cycle to wait for I/O from device Docsity.com Intel Pentium Processor Event-Vector Table vector number description (Coy DC) eco) no (Oo Op) On) eS co) nS) =) co) 19-31 32-255 divide error debug exception null interrupt breakpoint INTO-detected overflow bound range exception invalid opcode device not available double fault coprocessor segment overrun (reserved) invalid task state segment segment not present stack fault general protection page fault (Intel reserved, do not use) floating-point error alignment check machine check (Intel reserved, do not use) maskable interrupts Docsity.com Direct Memory Access • Used to avoid programmed I/O for large data movement • Requires DMA controller • Bypasses CPU to transfer data directly between I/O device and memory Docsity.com Six Step Process to Perform DMA Transfer 1. device driver is told to transfer disk data to buffer at address X . DMA controller 2. device driver tells transfers bytes to disk controller to buffer X, increasing transfer C bytes memory address from disk to buffer and decreasing C at address X until C = 0 . when C = 0, DMA interrupts CPU to signal transfer completion DMA/bus/ interrupt controller x memory IDE disk controller 3. disk controller initiates DMA transfer 4. disk controller sends e¢ disk} (disk) each byte to DMA controller Docsity.com Characteristics of |/O Devices aspect variation example RR raneiennnacie character terminal block disk sequential modem access method ae CD-ROM transfer schedule eee ae asynchronous keyboard hatin dedicated tape g sharable keyboard device speed latency seek time transfer rate delay between operations read only CD-ROM \/O direction write only graphics controller read-write disk Docsity.com Block and Character Devices • Block devices include disk drives – Commands include read, write, seek – Raw I/O or file-system access – Memory-mapped file access possible • Character devices include keyboards, mice, serial ports – Commands include get, put – Libraries layered on top allow line editing Docsity.com Network Devices • Varying enough from block and character to have own interface • Unix and Windows NT/9x/2000 include socket interface – Separates network protocol from network operation – Includes select functionality • Approaches vary widely (pipes, FIFOs, streams, queues, mailboxes) Docsity.com Two I/O Methods requesting process waiting A ,fequesting process | device driver device driver interrupt handler i interrupt handler Tt hardware i— data transfer — hardware --data transfer —Ct time —» Synchronous time ————> Asynchronous Docsity.com Kernel I/O Subsystem • Scheduling – Some I/O request ordering via per-device queue – Some OSs try fairness • Buffering - store data in memory while transferring between devices – To cope with device speed mismatch – To cope with device transfer size mismatch – To maintain “copy semantics” Docsity.com Device-status Table device: keyboard status: idle device: laser printer status: busy device: mouse status: idle device: disk unit 1 status: idle request for > laser printer address: 38546 length: 1372 device: disk unit 2 status: busy request for disk unit 2 file: xxx operation: read address: 43046 length: 20000 request for disk unit 2 file: yyy operation: write address: 03458 length: 500 Docsity.com Error Handling • OS can recover from disk read, device unavailable, transient write failures • Most return an error number or code when I/O request fails • System error logs hold problem reports Docsity.com I/O Protection • User process may accidentally or purposefully attempt to disrupt normal operation via illegal I/O instructions – All I/O instructions defined to be privileged – I/O must be performed via system calls • Memory-mapped and I/O port memory locations must be protected too Docsity.com Use of a System Call to Perform |/O system call n © to Docsity.com I/O Requests to Hardware Operations • Consider reading a file from disk for a process: – Determine device holding file – Translate name to device representation – Physically read data from disk into buffer – Make data available to requesting process – Return control to process Docsity.com request iO systom call <n cai, ae yes send request to deviee driver, block process if appropriate I process request, issue commands to controller, configure contrcller to book url interrupted deviee-contioller commands monitor device, interrupt when /O completed user process kernel VO subsystem kernel VO subsystem device driver interrupt handler device controller Life Cycle of An I/O Request VO completed Input data available, or coutout completed retum from system call transfer data (if appropriate) to procass, retum completion of error code determine which VO completed, incicate siate chiang to VO subsysiet receive interrupt, store data in device-driver butter it input, signal to unblock device driver interrupt time VO completed generate interrupt Docsity.com STREAMS • STREAM – a full-duplex communication channel between a user-level process and a device in Unix System V and beyond • A STREAM consists of: – STREAM head interfaces with the user process – driver end interfaces with the device – zero or more STREAM modules between them. • Each module contains a read queue and a write queue • Message passing is used to communicate between queues Docsity.com Intercomputer Communications —— — character — network typed system call packet | received — ale 3/8 zie sls 3 ae £2 8|3 £(= interrupt interrupt network generated handled adapter fig 2/¢ s =|5 o|8 interrupt interrupt interrupt handled generated generated A___ network is eaetworkcas fis a5 device network device driver adapter driver Rernel device rerael network driver lsubdaemon a\s a\s 8/s Ea =/= —\s gla Al ae context context kernel network kernel BeGeea| switch aemon | ewitch sending system receiving system Docsity.com Improving Performance • Reduce number of context switches • Reduce data copying • Reduce interrupts by using large transfers, smart controllers, polling • Use DMA • Balance CPU, memory, bus, and I/O performance for highest throughput Docsity.com Device-Functionality Progression new algorithm w velopment cost abstraction application code kernel code device-driver code device-controller code (hardware) increased flexibili device code (hardware) Docsity.com