Device Management Input/Output Devices

Device Management

Input/Output Devices

The Device Driver Interface

Device Management Organization

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

Overlapping the Operation of a Device and the CPU

Overlapping CPU-Controller Operations in a Process

Overlapping Processing and I/O

Polling I/O Read Operation

Interrupt-driven I/O Operation

Device Independent Function Call

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 Device Drivers

Handling Interrupts

Handling Interrupts(2)

The Pure Cycle Water Company

Hardware Buffering

Double Buffering in the Driver

Circular Buffering

A Generic Communications Device

Rotating Media

Storage Device

Compute vs 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

Serial Port

Serial Port

Adding a Modem

Serial Communication

Data Networks

MS Disk Description

NT Driver Organization

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