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Device Management. Serial Port. CPU. Memory. Serial Device. Printer Terminal Modem Mouse etc. Serial Port. Device Driver API. Device Driver Set UART parms read/write ops Interrupt hander. Software on the CPU. Bus Interface. UART API parity bits per byte etc.
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Serial Port CPU Memory Serial Device • Printer • Terminal • Modem • Mouse • etc.
Serial Port Device Driver API • Device Driver • Set UART parms • read/write ops • Interrupt hander Software on the CPU Bus Interface • UART API • parity • bits per byte • etc. Serial Device (UART) • RS-232 Interface • 9-pin connector • 4-wires • bit transmit/receive • ...
Adding a Modem CPU • Dialing & connecting • Convert analog voice to/from digital • Convert bytes to/from bit streams • Transmit/receive protocol Memory Serial Device Modem Phone Switched Telephone Network
Serial Communication • Device Driver • Set UART parms • read/write ops • Interrupt hander • Driver-Modem Protocol • Dialing & connecting • Convert analog voice to/from digital • Convert bytes to/from bit streams • Transmit/receive protocol Serial Device RS-232 Modem
Exploiting the Phone Network Logical Communication CPU CPU Memory Comm Device Comm Device Memory Modem Modem Phone Phone Switched Telephone Network
Data Networks • Technology focus includes protocols and software • (more on this later … Chapter 15 and beyond ...) Logical Communication CPU CPU Memory Network Device Network Device Memory Data Network
Rotating Storage Track (Cylinder) Sector Top View of a Surface
Storage Device Device Driver API • Driver • Get disk description • Set SCSI parms • read/write ops • Interrupt hander • SCSI API • commands • bits per byte • etc. Controller (SCSI) Magnetic Disk
Device Management Organization Application Process System Interface File Manager Device Driver Hardware Interface Command Status Data Device Controller
System Call Interface • Functions available to application programs • Abstract all devices (and files) to a few interfaces • Make interfaces as similar as possible • Block vs character • Sequential vs direct access • Device driver implements functions (one entry point per API function)
Example: BSD UNIX Driver open Prepare dev for operation close No longer using the device ioctl Character dev specific info read Character dev input op write Character dev output op strategy Block dev input/output ops select Character dev check for data stop Discontinue a stream output op
Read with Polling read(device, …); 1 Data System Interface read function 5 write function 2 3 4 Hardware Interface Command Status Data Device Controller
Read Using Interrupts read(device, …); 9 1 8b Data System Interface Device Status Table 4 7 Device Handler read driver 2 write driver 6 3 8a Interrupt Handler Hardware Interface 5 Command Status Data Device Controller
Driver-Kernel Interface • Drivers are distinct from main part of kernel • Kernel makes calls on specific functions, drivers implement them • Drivers use kernel functions for: • Device allocation • Resource (e.g., memory) allocation • Scheduling • etc. (varies from OS to OS)
Reconfigurable Drivers System call interface open(){…} read(){…} Entry Points for Device j etc. Other Kernel services Driver for Device j
NT Device Drivers • API model is the same as for a file • Extend device management by adding modules to the stream • Device driver is invoked via an Interrupt Request Packet (IRP) • IRP can come from another stream module • IRP can come from the OS • Driver must respond to minimum set of IRPs • See Part I of notes
Memory Mapped I/O Primary Memory Primary Memory Memory Addresses Device 0 Device 0 Memory Addresses Device 1 Device 1 Device Addresses Device n-1 Device n-1
CPU-I/O Overlap . . . startRead(dev_I, “%d”, x); . . . While(stillReading()) ; y = f(x) . . . . . . read(dev_I, “%d”, x); y = f(x) . . . Data on device Variable x Register Device dev_I Memory CPU
I/O - CPU Overlap App 1 App 2 I/O Ctlr t1 t2 t3 t4 Overlapping App 1’s I/O with App 2 App I/O Ctlr t1 t2 t3 t4 t5 t6 t7 t8 t9 Overlapping App CPU with its own I/O
Direct Memory Access Primary Memory Primary Memory CPU CPU Controller Controller Device Device
Buffering Customer Office Water Company Returning the Empties Water Producer Water Consumers Delivering Water • Water bottles are buffers • Office workers consume water from a buffer while • water company fills other buffers
Hardware Buffering Process Process Controller Controller Data A B Device Device Process reads bi-1 Controller reads bi Unbuffered
Hardware Buffering Process Process Process Controller Controller Controller Data A B A B Device Device Device Process reads bi-1 Controller reads bi Process reads bi Controller reads bi+1 Unbuffered
Buffering in the Driver Process A B Driver Controller A B Hardware Device
Buffering in the Driver Process Process A B A B Driver Controller Controller A B A B Hardware Device Device
A Ring Buffer To data consumer Buffer i Buffer j From data producer
Compute vs I/O Bound Compute-bound Time I/O-bound
Disk Optimizations • Transfer Time: Time to copy bits from disk surface to memory • Disk latency time: Rotational delay waiting for proper sector to rotate under R/W head • Disk seek time: Delay while R/W head moves to the destination track/cylinder • Access Time = seek + latency + transfer
Optimizing Seek Time • Multiprogramming on I/O-bound programs => set of processes waiting for disk • Seek time dominates access time => minimize seek time across the set • Tracks 0:99; Head at track 75, requests for 23, 87, 36, 93, 66 • FCFS: 52+ 64 + 51 + 57 + 27 = 251 steps
Optimizing Seek Time (cont) • Requests = 23, 87, 36, 93, 66 • SSTF: (75), 66, 87, 93, 36, 23 • 11 + 21 + 6 + 57 + 13 = 107 steps • Scan: (75), 87, 93, 99, 66, 36, 23 • 12 + 6 + 6 + 33 + 30 + 13 = 100 steps • Look: (75), 87, 93, 66, 36, 23 • 12 + 6 + 27 + 30 + 13 = 87 steps
Optimizing Seek Time (cont) • Requests = 23, 87, 36, 93, 66 • Circular Scan: (75), 87, 93, 99, 23, 36, 66 • 12 + 6 + 6 + home + 23 + 13 + 30 = 90 + home • Circular Look: (75), 87, 93, 23, 36, 66 • 12 + 6 + home + 23 + 13 + 30 = 84 + home