Fall 2006 1 EE 333 Lillevik 333f06-l22 University of Portland School of Engineering Computer Organization Lecture 22 Project 6 Hard disk drive Bus arbitration.

Fall 2006

Lillevik 333f06-l22 1University of Portland School of Engineering

EE 333

Computer OrganizationLecture 22

Project 6Hard disk driveBus arbitration

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Project 6

• Due: Friday, December 1• Microprogram the instruction set• Complete MDP16 design• Execute a simple program• Extra credit for additional instructions

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MDP16 execution

Program stores 0x25, 0x35, and 0x45 at 0x100, 0x101, 0x102 and reads the numbers back

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MicroROM contents

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Example trace

$0 = 0x100 for address of sw

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Example trace, continued.

Mem[100] = 0x25, Mem[101] = 0x35, Mem[102] = 0x45

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Example trace, continued.

Now load 0x100, 0x101, 0x102 into $1

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Computer components

• Input: receives information from external world

• Output: transmits information to external world

• Memory: holds programs and data

• Data path: physical route that carries info

• Control: coordinates overall flow of info

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System Bus

The bus interconnects system agents

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System view of a computer

One Agent at-a-time owns the bus

···

Signal 0

Signal n

Agent 0 Agent n···

BusSignal 1

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Agents

• Goal: perform some function (memory, I/O, etc.)• Types

– Master: can own the bus, assert signals– Slave: only responds when requested by master

• Operations– Memory or I/O space– Read or write– Interrupt

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What type of agent?

Agent Master SlaveCPU Y N

Memory

Disk

Display

Keyboard

Printer

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Moving-head disk

Disk buses include EIDA, SATA, SCSI

Performance = seek time + latency time + transfer time

NOTE: Unique location denoted CHS cylinder, head, sector

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Disk features

• Platter: magnetically coated disk• Side: one of two platter surfaces• Arm: lever arm that swings across platter• Head: sensor that reads/writes data on platter• Track: circular region on platter• Cylinder: collection of tracks with same radius• Sector: region of a track, basic unit of data (B)

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Disk performance

• Seek: time to move arm• Latency (rotational): time for platter to rotate to

requested sector• Transfer: time to move data across bus

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High-end disk example

Buffer = disk cacheHost = PC disk controller

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Find disk bandwidth, transfer time?CLK = 100 ns, 32-bit data bus, 5 clocks/bus cycle, 512B sector

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Find the disk average latency?Twelve 5 cm platters, 7200 rpm, 120 GB

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System view of a computer

One Agent at-a-time owns the bus

···

Signal 0

Signal n

Agent 0 Agent n···

BusSignal 1

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Example bus control signals?

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Bus cycle (phases)

1. Arbitration: owner defined

2. Address: ID of memory or I/O provided

3. Data: information transferred

4. Response: indicates completion of cycle

Bus phases similar to instruction steps

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Bus timing

Clk

Breq

Bgnt

Ack

Data Bus Driven

ARB ADR DATA RESP

Address Bus Driven

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Bus timing example

Shared signals driven by different agents

DataRdy

Ack

Data

ReadReq 13

4

57

642 2

DiskMem

Disk

Disk-Adr Mem-data

Mem

Bus Cycle

A little more complex

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Bus arbitration

• Serial: priority in-out, Request-Grant, sent from agent-to-agent (daisy-chain)

• Parallel: each agent asserts unique request (centralized), one grant asserted

• Distributed– Self-selection: agent codes combined to identify

owner– Collision detection: request repeated after a delay

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Serial arbiter

Each priority circuit ripples to next in line

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Design the priority circuit?Req Pin Gnt Pout

0 0

0 1

1 0

1 1

Gnt =Pout =

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Centralized arbitration

More & fast logic, flexible algorithm

Device 1 Device 2 Device n•••

Central Arbiter

Req

1

Gnt

1

Req

2

Gnt

2

Req

n

Gnt

n

Fixed, round-robin, multi-level, etc.

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Fixed centralize arbiter

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Simple RR arbiter

00

10

11

01

Req2 Req1Req3

Req0

Gntn = Staten Reqn

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What type of agent?Agent Master Slave

CPU Y N

Memory N Y

Disk Y Y

Display Y Y

Keyboard N Y

Printer N Y

High-performance agents are often Masters

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Find disk bandwidth, transfer time?

snsclkTcycle 5.010055

sMBs

bytess

bitsBW 0.8105.0

45.0

326

sssMB

BytesT tor 641064

8512

6sec

CLK = 100 ns, 32-bit data bus, 5 clocks/bus cycle, 512B sector

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Find the disk average latency?Twelve 5 cm platters, 7200 rpm, 120 GB

min7200

minsec60

21

revTlatency

004167.000833.021

ms167.4

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Example bus control signals

• Bus request, bus grant• Read, write• Memory space, I/O space• Address valid, data valid• Wait• Interrupt request, interrupt acknowledge

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Design the priority circuit?Req Pin Gnt Pout

0 0 0 0

0 1 0 1

1 0 0 0

1 1 1 0

Gnt = Req · PinPout = Req · Pin

Fall 2006 1 EE 333 Lillevik 333f06-l22 University of Portland School of Engineering Computer Organization Lecture 22 Project 6 Hard disk drive Bus arbitration.

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