5 Device Management

Input/Output Devices Output Device Processor Input Device

The Device Driver Interface … write(…); Device Interface Terminal Driver Printer Driver Disk Driver Terminal Controller Printer Controller Disk Controller

Device Management Organization Application Process System Interface File Manager Device-Independent Device-Dependent 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

Overlapping the Operation of a Device and the CPU . . . 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

Gantt Chart A Gantt chart is a graphical representation of the duration of tasks against the progression of time. http://www.ganttchart.com/

Gantt Chart Gantt charts are useful tools for planning and scheduling projects. Gantt charts allow you to assess how long a project should take. Gantt charts lay out the order in which tasks need to be carried out. Gantt charts help manage the dependencies between tasks. Gantt charts determine the resources needed.

Gantt Chart Gantt charts are useful tools when a project is under way. Gantt charts monitor progress. You can immediately see what should have been achieved at a point in time. Gantt charts allow you to see how remedial action may bring the project back on course.

Henry Laurence Gantt (1861-1919) was a mechanical engineer, management consultant and industry advisor. Henry Laurence Gantt developed Gantt charts in the second decade of the 20th century. Gantt charts were used as a visual tool to show scheduled and actual progress of projects. Accepted as a commonplace project management tool today, it was an innovation of world-wide importance in the 1920s.  Gantt charts were used on large construction projects like the Hoover Dam started in 1931 and the interstate highway network started in 1956.

Henry Gantts contribution to the management process is honored today through the Henry Laurence Gantt Medal.  The award established in 1929 is given for distinguished achievement in management and for service to the community.

Overlapping CPU-Controller Operations in a Process I/O Ctlr t1 t2 t3 t4 t5 t6 t7 t8 t9

Overlapping Processing and I/O I/O Ctlr t1 t2 t3 t4

I/O strategies 1. Direct I/O with Polling. 2. DMA I/O with Polling. 3. Direct I/O with Interrupt. 4. DMA I/O with Interrupt.

Polling I/O Read Operation read(device, …); 1 Data System Interface read function 5 write function 2 3 4 Hardware Interface Command Status Data Device Controller

Direct I/O with Polling (IN) 1. The application process requires a read operation. 2. The device driver queries the status register to determine if the device is idle, if the device is busy, the driver waits for it to be idle. 3. The driver stores an input command into the controller’s command register, thereby, starting the device. 4. The driver repeatedly reads the status register while waiting for the device to complete its operation. 5. The driver copies the contents of the controller’s data register(s) into process’s space.

Direct I/O with Polling (OUT) 1. Process requests an output operation. 2. Driver status register, busy? Wait. 3. Driver copies data from user space memory controller’s data registers. 4. The driver stores an output command into the command register, thereby starting the device. 5. The driver repeatedly reads the status register while waiting for the device to complete the operation.

Interrupt-driven I/O Operation 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

Interrupt Driven I/O Operation 1. Process requests a read operation 2. Top half of the driver queries the status register, idle? -> Yes! -> Wait! 3. If no longer busy, the driver stores command into the controller’s command register and thereby starting the device for read operation. 4. When read driver completes its work, information regarding the op -> device status table.

Device Status Table contains an entry for each device in the system. 5. Eventually, the driver completes the operation and interrupt the CPU and cause the interrupt handler to run. 6. The interrupt handler determines which device caused the interrupt. It then branches to the device handler for that device. 7. The device handler retrieves the pending I/O status information from the device status table. 8. The device handler copies the contents of the controller’s data registers into the user process’s space (memory). 9. The device handler-behaving as the bottom half of the device driver invoked by the application process-thus returns control to the application process.

Device Independent Function Call Trap Table funci(…) dev_func_i(devID, …) { // Processing common to all devices … switch(devID) { case dev0: dev0_func_i(…); break; case dev1: dev1_func_i(…); case devM: devM_func_i(…); }; }

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

Handling Interrupts Device driver J Device interrupt handler J Device status table int read(…) { // Prepare for I/O save_state(J); out dev# // Done (no return) } void dev_handler(…) { get_state(J); //Cleanup after op signal(dev[j]); return_from_sys_call(); } J Interrupt Handler Device Controller

Handling Interrupts(2) Device driver J Device interrupt handler J int read(…) { … out dev# // Return after interrupt wait(dev[J}); return_from_sys_call(); } void dev_handler(…) { //Cleanup after op signal(dev[j]); } Interrupt Handler Device Controller

The Pure Cycle Water Company Customer Office Water Company Returning the Empties Water Producer Water Consumers Delivering Water

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

Double Buffering in the Driver Process Process A B A B Driver Controller Controller A B A B Hardware Device Device

Circular Buffering To data consumer Buffer i Buffer j From data producer

A Generic Communications Device Bus Generic Controller Communications Controller Local Device Cabling connecting the controller to the device Device Printer Modem Network

Rotating Media Cylinder (set of tracks) Track (Cylinder) Sector (a) Multi-surface Disk (b) Disk Surface (b) Cylinders

Storage Device Driver SCSI API Controller (SCSI) Magnetic Disk 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

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

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

UART universal asynchronous receiver- transmitter

Serial Port Device Driver Software on the CPU Bus Interface UART API 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 ...

Switched Telephone Network 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 Serial Device RS-232 Modem 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

Logical Communication 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

The USB Process When the host powers up, it queries all of the devices connected to the bus and assigns each one an address. This process is called enumeration -- devices are also enumerated when they connect to the bus. The host also finds out from each device what type of data transfer it wishes to perform:

Interrupt - A device like a mouse or a keyboard, which will be sending very little data, would choose the interrupt mode. Bulk - A device like a printer, which receives data in one big packet, uses the bulk transfer mode. A block of data is sent to the printer (in 64-byte chunks) and verified to make sure it is correct. Isochronous - A streaming device (such as speakers) uses the isochronous mode. Data streams between the device and the host in real-time, and there is no error correction.

MS Disk Description-Boot Sector

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