Subroutines and Parameters

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Subroutines and Parameters

• Call and return
• Parameter passing
• Return values
• Leaf subroutines
• Combining C and assembly modules

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Separate Assembly

• Separate Assembly Language Modules
• Command line parameters are passed like any
  others  
• External Data

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Example
include(macro_defs.m) ! Some symbolic constants
for readability. define(argc, i0)
define(argv, i1) local_vars
var(sum, 4) fmt .asciz "sum is d\n" !
Read-only string !
for printf . . .
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.align 4 begin st g0,
fp sum ! sum 0 b test
! while test nop !
Delay slot loop add fp, sum, o0 ! sum
call summer ld argv, o1
! ptr to 1st num test subcc argc, 1, argc !
argc-- bg,a loop add argv,
4, argv ! argv . . .
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. . . set fmt, o0
call printf ! printf(fmt, sum)
ld fp sum, o1 ! Delay slot
end_fn
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7. Instruction Encoding

• All instructions 32 bits long
• Three formats

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Format 1

• The call instruction

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Format 2

• Branch and sethi

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Format 3

• Arithmetic, Logical, Load, Store, etc.

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Computer ArchitectureA Quantitative Approach

• (Based on Hennessy and Patterson, 3rd Ed.)

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Fundamentals of Computer Design

• Improvement in computer performance comes from
  two areas
• Technological improvements
• Architectural improvements
• Since the 1980s development of new architectures
  has been encouraged by
• High-level languages
• Standardised operating systems

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Background

• Since 1985 new architectures have led to
  startling performance improvements
• Fig 1.1 (p. 3)
• Microprocessors rule!
• Workstations and PCs
• Minicomputers
• Mainframes
• Supercomputers

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Computing Markets

• Desktop machines
• Price/performance is critical
• Use newest technology
• Servers
• Availability, scalability, throughput
• Embedded computers
• Fastest growing market segment
• Huge range of price/performance
• Real-time requirements
• Memory and power are limited

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The Task of a Computer Designer

• Instruction Set Architecture
• Organisation
• Hardware

• Must meet functional requirements
• Intended application area
• Compatibility with existing software
• Support required for operating system(s)
• Standards (IEEE floating point, busses, networks,
  programming languages, etc.)

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Task of a Designer (cont.)

• Strive to minimise complexity and
  cost/performance ratio
• Track future trends

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Technology Trends

• Processors
• transistor counts increase /55 each year
• RAM
• rapid increase in density (but not speed)
• Disks
• density increases at 100 each year
• Networks
• bandwidth increasing rapidly

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Technology Trends (cont.)

• Life span of a processor /5 years
• Must plan for changes in technologies
• May design for future technology!
• Trends are continuous, but sometimes observed as
  discrete leaps
• E.g. transistor density ? on-chip caches

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Power

• A major headache!
• Packing more transistors closer together greatly
  increases power consumption
• 1970s microprocessors a few tenths of a watt
• 2GHz P4 100W

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Cost/Price Trends

• Critical for desktop and embedded markets
• Time
• Learning curve decreases price
• Volume
• Commodification
• Competition in high volume markets decreases price

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Cost Issues

• Complex and rapidly changing area
• Cost of integrated circuits
• Significant impact on cost differentiation
• Overall (desktop PC)
• Cabinet 6
• Processor and motherboard 37
• Processor 22
• I/O Devices 37
• Software 20

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Balancing Cost/Performance

• No one answer
• Supercomputers
• Cost is of little concern
• Some embedded areas (e.g. cell phones)
• Cost is critical
• Workstations and servers
• Cost and performance must be balanced

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