ECE232: Hardware Organization and Design Lecture 29: Computer - PowerPoint PPT Presentation

ECE232: Hardware Organization and Design Lecture 29: Computer Input/Output Adapted from Computer Organization and Design , Patterson & Hennessy, UCB

Announcements ECE Honors Exhibition  Wednesday, April 30 • 3:00-4:00 PM • M5 • SDP Demo Day  10AM-2PM, Friday, April 25 • Gunness Student Center • ECE Picnic (tickets in ECE office/Eliza)  3-7PM, Friday, April 25 • Hadley Young Men’s Club • ECE Banquet (tickets in ECE office/Eliza)  6-9PM, Friday, May 2 • Courtyard Marriott, Hadley • ECE232: Computer I/O 2

Overview Input and output are fundamental for computer operation  Typically much slower than computation • Two types of transfer  Polling – processor constantly checks for data • Interrupts – processor is interrupted from activity • Need to understand the requirements of data transfer  Tied to computer organization (bus, interfaces, etc) • I/O bandwidth is important (how fast, how much) • Most interfaces today are standardized (USB, monitor, Ethernet)  ECE232: Computer I/O 3

Anatomy: 5 components of any Computer Keyboard, Processor Devices Memory Mouse Control Input Disk Datapath Output Processor Display , Printer Cache interrupts Memory - I/O Bus I/O I/O I/O Main Controller Controller Controller Memory Graphics Disk Disk Network ECE232: Computer I/O 4

Handling IO Users like to connect devices to their computers  • Keyboard, mouse, printer… External devices may require attention from processor at  unpredictable times • CPU doesn’t know when you’re about to hit a key IO devices can be very fast or very slow  Need to have a flexible way to control all devices  ECE232: Computer I/O 5

I/O Device Examples and Speeds I/O Speed: bytes transferred per second  (from mouse to display: million-to-1) Device Behavior Partner Data Rate (Mbit/sec) Keyboard Input Human 0.0001 Mouse Input Human 0.0038 Laser Printer Output Human 3.2000 Magnetic Disk Storage Machine 240-2560 Modem I or O Machine 0.016-0.064 Network-LAN I or O Machine 100-1000 Graphics Display Output Human 800-8000 ECE232: Computer I/O 6

Hardware Solution (875 Chipset) Pentium 4 processor System bus (800 MHz, 604 GB/sec) DDR 400 AGP 8X Memory (3.2 GB/sec) (2.1 GB/sec) Graphics controller Main output hub DDR 400 CSA memory (north bridge) (3.2 GB/sec) (0.266 GB/sec) DIMMs 1 Gbit Ethernet 82875P (266 MB/sec) Serial ATA Parallel ATA (150 MB/sec) (100 MB/sec) CD/DVD Disk Serial ATA Parallel ATA (150 MB/sec) (100 MB/sec) Tape Disk I/O AC/97 controller (1 MB/sec) hub Stereo (south bridge) (20 MB/sec) (surround- 82801EB 10/100 Mbit Ethernet USB 2.0 sound) (60 MB/sec) PCI bus . . . (132 MB/sec) ECE232: Computer I/O 7

Disk Device Terminology Several platters, with information recorded magnetically on  both surfaces (usually) Inner Outer Arm Head Sector Track Track Actuator Platter Bits recorded in tracks, which in turn are divided into sectors  (e.g., 512 Bytes) Actuator moves head (end of arm, 1/surface) over track  ( “seek” ), select surface, wait for sector rotate under head, then read or write • “ Cylinder ”: all tracks under heads ECE232: Computer I/O 8

Disk Device Performance Disk Latency = Seek Time + Rotation Time + Transfer Time  + Controller Overhead Seek Time - depends on no. tracks arm moves, seek speed  Average no. tracks arm moves?  • Sum all possible seek distances from all possible tracks / total # • Assumes average seek distance is random • Disk industry standard benchmark Rotation Time - depends on rotation speed, how far sector is  from head 1/2 time of a rotation  • Example: 7200 Revolutions Per Minute  120 Rev/sec • 1 revolution = 1/120 sec  8.33 milliseconds • 1/2 rotation (revolution)  4.16 ms Transfer Time - depends on data rate (bandwidth) of disk  (bit density), size of request ECE232: Computer I/O 9

Disk Performance Model /Trends Capacity  + 100%/year (2X/1 yr) • Transfer rate (BW)  + 40%/year (2X/2 yrs) • Rotation + Seek time  – 8%/year (1/2 in 10 • yrs) MB/$  > 100%/yr (2X/<1.5 yr) • ECE232: Computer I/O 10

Disk Performance Calculate time to read 1 sector (512B) for UltraStar 72 using  advertised performance; sector is on outer track Disk latency = average seek time + average rotational delay  + transfer time + controller overhead = 5.3 ms + 0.5 * 1/(10000 RPM) + 0.5 KB / (50 MB/s) + 0.15 ms = 5.3 + 3.0 + 0.01 + 0.15 ms = 8.46 ms ECE232: Computer I/O 11

Instruction Set Architecture for I/O Some machines have special input and output instructions  Alternative model (used by MIPS):  • Input: ~ reads a sequence of bytes • Output: ~ writes a sequence of bytes Memory also a sequence of bytes, so use loads for input,  stores for output • Called “ Memory Mapped Input/Output ” A portion of the address  address 0 space dedicated to communication paths to Input or Output devices (no memory there) These addresses are not  regular memory, instead, cmd reg. 0xFFFF0000 they correspond to data reg. registers in I/O devices 0xFFFFFFFF ECE232: Computer I/O 12

Memory Mapped IO Make control registers and I/O device data registers appear  to be part of the system’s main memory • Reads and writes to the mapped region of the memory are translated by memory controller hardware into accesses of hardware device • Makes it easy to support variable numbers/types of devices – just map them onto different regions of memory Accessing I/O device registers and memory can be done by  accessing data structures via the device pointers • Most device drivers are now written in C/C++. Memory mapped I/O makes this feasible without any changes to the way a CPU is programmed ECE232: Computer I/O 13

Processor-I/O Speed Mismatch 1 GHz microprocessor can execute 1000 million load or  store instructions per second, or 4 million KB/s data rate • I/O devices from 0.01 KB/s to 30,000 KB/s Input: device may not be ready to send data as fast as the  processor loads it • Also, might be waiting for human to act Output: device may not be ready to accept data as fast as  processor stores it What to do?  ECE232: Computer I/O 14

Processor Checks Status before Acting: Polling Path to device generally has 2 registers:  • 1 register says it’s OK to read/write (I/O ready), often called Control Register • 1 register that contains data, often called Data Register Processor reads from Control Register in loop, waiting for  device to set Ready bit in Control reg to say its OK (0  1) Processor then loads from (input) or writes to (output) data  register • Load from device/Store into Data Register resets Ready bit (1  0) of Control Register ECE232: Computer I/O 15

Cost of Polling? Assume: a 1 GHz processor takes 400 clock cycles for a  polling operation (call polling routine, accessing the device, and returning). Determine % of processor time for polling • Mouse: polled 30 times/sec - not to miss user movement • Hard disk: transfers data in 16-byte chunks and can transfer at 8 MB/second. No transfer can be missed Mouse Polling Clocks/sec = 30 * 400 = 12000 clocks/sec  % Processor for polling = 12*10 3 /1*10 9 = 0.0012%   Polling mouse has little impact on processor Times Polling Disk/sec = 8 MB/s /16B = 500K polls/sec  Disk Polling Clocks/sec  = 500K * 400 = 200,000,000 clocks/sec % Processor for polling:  • 2*10 8 /1*10 9 = 20%  Unacceptable ECE232: Computer I/O 16

What is the alternative to polling? Interrupt Wasteful to have processor spend most of its time “spin -  waiting” for I/O to be ready Wish we could have an unplanned procedure call that would  be invoked only when I/O device is ready Solution: use exception mechanism to help I/O. Interrupt  program when I/O ready, return when done with data transfer Polling is like picking up the phone every few seconds to see if you have a call. Interrupt is like letting the phone ring ECE232: Computer I/O 17

I/O Interrupt Controller sends interrupt to the processor along with  additional information • which device • nature of interrupt: error, no paper, no ink,… Processor halts execution of current program  Saves State  Processor looks up which handler to start from the interrupt  information When interrupt is handled, returns to program state and  resumes ECE232: Computer I/O 18

Interrupt Driven Data Transfer Memory  add sub (1) I/O user interrupt program and (2) save PC or (3) interrupt service addr (4)  read interrupt store service ... routine (5) jr ECE232: Computer I/O 19

Benefit of Interrupt-Driven I/O 500 clock cycle overhead for each transfer, including  interrupt. Find the % of processor consumed if the hard disk is only active 5% of the time If interrupt rate = polling rate  • Disk Interrupts/sec = 8 MB/s /16B = 500K interrupts/sec • Disk Polling Clocks/sec = 500K * 500 = 250,000,000 clocks/sec • % Processor used during transfers: 250*10 6 /1*10 9 = 25% If disk active 5%  5% * 25%  1.25% busy  ECE232: Computer I/O 20