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1、教育部顧問室 資通訊科技人才培育先導型計畫 車載資通訊嵌入式系統,VI. ARM嵌入式系統原理與實作,2,Embedded System Overview ARM Embedded Systems ARM Processor Fundamentals ARM Instruction Set Efficient C Programming,ARM Embedded System,Embedded System Design: A Unified Hardware/Software Introduction Frank Vahid, and Tony D. Givargis, John Wiley
2、, 2002, ISBN: 0-471-38678-2,3,Outline,Embedded Systems Overview Design Challenge Optimizing Design Metrics Technologies Processor technologies IC technologies Design technologies Tradeoffs Summary,4,Embedded Systems Overview,Computing systems are everywhere Most of us think of “desktop” computers PC
3、s Laptops Workstations Mainframes Servers But theres another type of computing system Far more common.,5,Embedded Systems Overview (Cont.),Embedded computing systems Computing systems embedded within electronic devices Hard to define. Nearly any computing system other than a desktop computer Billion
4、s of units produced yearly, versus millions of desktop units Perhaps 50 per household and per automobile,Computers are in here.,and here.,and even here.,Lots more of these, though they cost a lot less each.,6,A “short list” of embedded systems,And the list goes on and on,Anti-lock brakes Auto-focus
5、cameras Automatic teller machines Automatic toll systems Automatic transmission Avionic systems Battery chargers Camcorders Cell phones Cell-phone base stations Cordless phones Cruise control Curbside check-in systems Digital cameras Disk drives Electronic card readers Electronic instruments Electro
6、nic toys/games Factory control Fax machines Fingerprint identifiers Home security systems Life-support systems Medical testing systems,Modems MPEG decoders Network cards Network switches/routers On-board navigation Pagers Photocopiers Point-of-sale systems Portable video games Printers Satellite pho
7、nes Scanners Smart ovens/dishwashers Speech recognizers Stereo systems Teleconferencing systems Televisions Temperature controllers Theft tracking systems TV set-top boxes VCRs, DVD players Video game consoles Video phones Washers and dryers,7,Some Common Characteristics of Embedded Systems,Single-f
8、unctioned Executes a single program, repeatedly Tightly-constrained Low cost, low power, small size, fast, etc. Reactive and real-time Continually reacts to changes in the systems environment Must compute certain results in real-time without delay,8,An Embedded System Example Digital Camera,Single-f
9、unctioned - always a digital camera Tightly-constrained - Low cost, low power, small, fast Reactive and real-time - only to a small extent,9,Design Challenge Optimizing Design Metrics,Obvious design goal: Construct an implementation with desired functionality Key design challenge: Simultaneously opt
10、imize numerous design metrics Design metric A measurable feature of a systems implementation,10,Design Challenge Optimizing Design Metrics (Cont.),Common metrics NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system Unit cost: the monetary cost of manufacturin
11、g each copy of the system, excluding NRE cost Size: the physical space required by the system e.g. bytes for software, gates or transistors for hardware Performance: the execution time or throughput of the system Power: the amount of power consumed by the system Flexibility: the ability to change th
12、e functionality of the system without incurring heavy NRE cost,11,Design Challenge Optimizing Design Metrics (Cont.),Common metrics (continued) Time-to-prototype: the time needed to build a working version of the system Time-to-market: the time required to develop a system to the point that it can b
13、e released and sold to customers Maintainability: the ability to modify the system after its initial release Correctness : the functionality implemented correctly Safety: the probability that the system will not cause harm,12,Design Metric Competition - Improving One May Worsen Others,Expertise with
14、 both software and hardware is needed to optimize design metrics Not just a hardware or software expert, as is common A designer must be comfortable with various technologies in order to choose the best for a given application and constraints,Hardware,Software,13,Time-to-Market: a Demanding Design M
15、etric,Time required to develop a product to the point it can be sold to customers Market window Period during which the product would have highest sales Average time-to-market constraint is about 8 months Delays can be costly,14,Revenue Losses Due to Delayed Market Entry,Simplified revenue model Pro
16、duct life = 2W, peak at W Time of market entry defines a triangle, representing market penetration Triangle area equals revenue Loss The difference between the on-time and delayed triangle areas Percentage revenue loss = (On-time - Delayed) / On-time) * 100%,15,Revenue Losses Due to Delayed Market E
17、ntry (Cont.),Example: market rise angle is 45 degrees Area = 1/2 * base * height On-time = 1/2 * 2W * W Delayed = 1/2 * (W-D+W)*(W-D) Percentage revenue loss = (D(3W-D)/2W2)*100% Try some examples Lifetime 2W=52 wks, delay D=4 wks (4*(3*26 4)/2*262) = 22% Lifetime 2W=52 wks, delay D=10 wks (10*(3*26
18、 10)/2*262) = 50% Delays are costly!,16,NRE and Unit Cost Metrics,Costs: Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system total cost = NRE cost + unit cost * # of un
19、its per-product cost = total cost / # of units = (NRE cost / # of units) + unit cost,Example NRE=$2000, unit=$100 For 10 units total cost = $2000 + 10*$100 = $3000 per-product cost = $2000/10 + $100 = $300,17,NRE and Unit Cost Metrics (Cont.),Compare technologies by costs Technology A: NRE=$2,000, u
20、nit=$100 Technology B: NRE=$30,000, unit=$30 Technology C: NRE=$100,000, unit=$2 best technology choice will depend on quantity,18,The Performance Design Metric,Performance: how long the system takes to execute our desired tasks Most widely-used measure, most abused Clock frequency, instructions per
21、 second not good measures Digital camera example a user cares about how fast it processes images, not clock speed or instructions per second Two main measures of performance: Latency (response time): Time between task start and end e.g., Cameras A and B process images in 0.25 seconds Throughput: num
22、ber of tasks that can be processed per second e.g. Camera A processes 4 images per second Speedup of A over B = As performance / Bs performance e.g. throughput speedup = 8/4 = 2 (A is 2 times faster than B),19,Three Key Embedded System Technologies,Technology A manner of accomplishing a task, especi
23、ally using technical processes, methods, or knowledge Three key technologies for embedded systems Processor technology IC technology Design technology,20,Processor Technology,The architecture of the computation engine used to implement a systems desired functionality Processor does not have to be pr
24、ogrammable “Processor” not equal to general-purpose processor,Application-specific,Registers,Custom ALU,Datapath,Controller,Program memory,Assembly code for: total = 0 for i =1 to ,Control logic and State register,Data memory,IR,PC,Single-purpose (“hardware”),Datapath,Controller,Control logic,State
25、register,Data memory,index,total,+,IR,PC,Register file,General ALU,Datapath,Controller,Program memory,Assembly code for: total = 0 for i =1 to ,Control logic and State register,Data memory,General-purpose (“software”),21,Processor Technology (Cont.),Processors vary in their customization for the pro
26、blem at hand,total = 0 for i = 1 to N loop total += Mi end loop,General-purpose processor,Single-purpose processor,Application-specific processor,Desired functionality,22,General-Purpose Processors,Programmable device suitable for a variety of applications Also known as “microprocessor” Features Pro
27、gram memory General datapath with large register file and general ALU,Desired functionality,General-purpose processor,23,General-Purpose Processors (Cont.),When used in an embedded system: Benefits: Low time-to-market and NRE costs High flexibility Unit cost may be low in small quantities Performanc
28、e may be fast for computation-intensive applications Drawbacks: Unit cost may be relatively high for large quantities Performance may be slow for certain applications Size and power may be large “Pentium” the most well-known, but there are hundreds of others,24,Single-Purpose Processors,Digital circ
29、uit designed to execute exactly one program a.k.a. coprocessor, accelerator or peripheral Features Contains only the components needed to execute a single program No program memory,Desired functionality,Application-specific processor,25,Single-Purpose Processors (Cont.),When used in an embedded syst
30、em: Benefits: Unit cost may be low for large quantities Performance may be fast Size and power may be small Drawbacks: High time-to-market and NRE costs low flexibility Unit cost may be high for small quantities Performance may not match general-purpose processors for some applications,26,Applicatio
31、n-Specific Processors,Programmable processor optimized for a particular class of applications having common characteristics Compromise between general-purpose and single-purpose processors Features Program memory Can optimize datapath for application class Add special functional units for common ope
32、rations Eliminate other infrequently used units,Desired functionality,Single-purpose processor,27,Application-Specific Processors (Cont.),Benefits flexibility, good performance, size and power Drawbacks: large NRE costs to build the processor and a compiler Two well-known types of ASIPs: Microcontro
33、llers A microprocessor optimized for embedded control applications digital signal processors A microprocessor designed to perform common operations on digital signals,IR,PC,Registers,Custom ALU,Datapath,Controller,Program memory,Assembly code for: total = 0 for i =1 to ,Control logic and State regis
34、ter,Data memory,28,IC Technology,The manner in which a digital (gate-level) implementation is mapped onto an IC IC: Integrated circuit, or “chip” IC technologies differ in their customization to a design ICs consist of numerous layers (perhaps 10 or more) The bottom layers form the transistors The m
35、iddle layers form logic components The top layers connect these components with wires IC technologies differ with respect to who builds each layer and when,29,IC Technology (Cont.),Three types of IC technologies Full-custom/VLSI Semi-custom ASIC (gate array and standard cell) PLD (Programmable Logic
36、 Device),30,Full-Custom/VLSI,All layers are optimized for a particular embedded systems digital implementation Placing transistors to minimize interconnection lengths Sizing transistors to optimize signal transmissions Routing wires among transistors Benefits Excellent performance, small size, low p
37、ower Drawbacks High NRE cost (e.g., $300k), long time-to-market Usually used only in high-volume or extremely performance-critical applications,31,Semicustom ASIC (gate array and standard cell),Lower layers are fully or partially built Designers are left with finishing upper layers, such as routing
38、of wires and maybe placing some blocks Benefits Good performance, good size, less NRE cost than a full-custom ICs (perhaps $10k to $100k) Drawbacks Still require weeks to months to manufacture,32,PLD (Programmable Logic Device),All layers already exist Designers can purchase an IC Connections on the
39、 IC are either created or destroyed to implement desired functionality Field-Programmable Gate Array (FPGA) very popular Benefits Low NRE costs, almost instant IC availability Drawbacks Bigger than ASICs, expensive (perhaps $30 per unit), power hungry, slower Reasonable performance, well-suited to r
40、apid prototyping,33,Trends - Moores Law,The most important trend in embedded systems Predicted in 1965 by Intel co-founder Gordon Moore IC transistor capacity has doubled roughly every 18 months for the past several decades,Note: logarithmic scale,34,Graphical Illustration of Moores Law,1981,1984,19
41、87,1990,1993,1996,1999,2002,Leading edge chip in 1981,10,000 transistors,Leading edge chip in 2002,150,000,000 transistors,Something that doubles frequently grows more quickly than most people realize! A 2002 chip can hold about 15,000 1981 chips inside itself This trend of increasing chip capacity
42、has enabled the proliferation of low-cost, high-performance embedded systems,35,Design Technology,The manner in which we convert our concept of desired system functionality into an implementation,36,Ideal Top-Down Design Process, and Productivity Improvers,Libraries/IP: Incorporates pre-designed imp
43、lementation from lower abstraction level into higher level.,System specification,Behavioral specification,RT specification,Logic specification,To final implementation,Compilation/Synthesis: Automates exploration and insertion of implementation details for lower level.,Test/Verification: Ensures corr
44、ect functionality at each level, thus reducing costly iterations between levels.,Compilation/ Synthesis,Libraries/ IP,Test/ Verification,System synthesis,Behavior synthesis,RT synthesis,Logic synthesis,Hw/Sw/ OS,Cores,RT components,Gates/ Cells,Model simulat./ checkers,Hw-Sw cosimulators,HDL simulat
45、ors,Gate simulators,37,Ideal Top-Down Design Process,System specification The designer describes the desired functionality in some language, often a natural language like English, but preferably an executable language like C Behavioral specifications The designer refines system specification by dist
46、ributing portions of it among several general and/or single-purpose processors, yielding behavioral specifications for each processor. Register-transfer (RT) specifications The designer converts behavior on general-purpose processors to assembly code, and converts single-purpose processors to a conn
47、ection of register-transfer components and state machines.,38,Ideal Top-Down Design Process(Cont.),Logic specification The designer refines the RT specification of a single-purpose processor into a logic specification consisting of Boolean equations. Finally, the designer refines the remaining speci
48、fications into an implementation, consisting of machine code for general-purpose processors and a gate-level netlist for single-purpose processors.,39,Improving the Design Processor for Increased Productivity,Compilation/Synthesis Lets a designer specify desired functionality in an abstract manner a
49、nd automatically generates lower-level implementation details Libraries/IP Libraries involve reuse of preexisting implementations Intellectual property (IP) must be protected from copying Test/Verification Involves ensuring method of testing for correct functionality Simulation is the most common method,40,Design Productivity Exponential Increase,Exponential increase over the past few decades Source: the international technology roadmap for semiconductors,100,00