Device Management

1. Device Management

2. Serial Port CPU Memory Serial Device • Printer • Terminal • Modem • Mouse • etc.

3. 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 • ...

4. 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

5. 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

6. Exploiting the Phone Network Logical Communication CPU CPU Memory Comm Device Comm Device Memory Modem Modem Phone Phone Switched Telephone Network

7. 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

8. Rotating Storage Track (Cylinder) Sector Top View of a Surface

9. MS Disk Description

10. 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

11. Device Management Organization Application Process System Interface File Manager Device Driver Hardware Interface Command Status Data Device Controller

12. 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)

13. 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

14. Read with Polling read(device, …); 1 Data System Interface read function 5 write function 2 3 4 Hardware Interface Command Status Data Device Controller

15. 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

16. 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)

17. Reconfigurable Drivers System call interface open(){…} read(){…} Entry Points for Device j etc. Other Kernel services Driver for Device j

18. NT Driver Organization

19. 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

20. 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

21. 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

22. 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

23. Direct Memory Access Primary Memory Primary Memory CPU CPU Controller Controller Device Device

24. 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

25. Hardware Buffering Process Process Controller Controller Data A B Device Device Process reads bi-1 Controller reads bi Unbuffered

26. 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

27. Buffering in the Driver Process A B Driver Controller A B Hardware Device

28. Buffering in the Driver Process Process A B A B Driver Controller Controller A B A B Hardware Device Device

29. A Ring Buffer To data consumer Buffer i Buffer j From data producer

30. Compute vs I/O Bound Compute-bound Time I/O-bound

31. 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

32. 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

33. 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

34. 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