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ScienceDirectProcedia Engineering 00 (2014) 000–000

www.elsevier.com/locate/procedia

“APISAT2014”, 2014 Asia-Pacific International Symposium on Aerospace Technology, APISAT2014

Assessment Model of the Architecture of the Aerospace Embedded Computer

Wei Hana,b,c, Xiaoying Baia, Jianchun Xieb,c*

aDep. of Computer Science & Technology, No.1, Tsinghua Yuan, Haidian District, Beijing 100084, ChinabAVIC Computing Technique Research Institute, No.15, Jinye 2 steet, Yanta District, Xi’an 710065, China

cAviation Key Laboratory of Science and Technology on Airborne and Missileborne Computer, No.15, Jinye 2 street, Yanta District, Xi’an 710065, China

Abstract

Typical aerospace embedded computers have many characters in common, especially in the aspect of the design of computer architecture. To evaluate this category of computers, 3 typical aerospace embedded computers were sampled and their characters of architecture and common technology were analyzed. Eight characters of architecture were concluded, and three evaluation dimensions were proposed. A basic guideline and a practical reference value or design were attached to each architecture character. The relationship was analyzed among the final assessment result, the evaluation dimensions and the architecture characters. Any aerospace embedded computer can be scored according to the assessment model for various estimate requirements. The evaluating method and progress were illustrated through one kind of advanced aerospace embedded computer's evaluation case. The case indicates that the assessment model is clear, effective and practical. It can provide some guidance for the design and performance analysis of aerospace embedded computers.© 2014 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA).

Keywords: aerospace embedded computer; architectural assessment; modular; net-centric

1. Introduction

These years, avionics is developing from combined system structure to Integrated Modular Avionics. The main design idea is to make full use of the fast development of micro-electronics to share a unique backbone network. In the network, several standard modular resources are connected in the large-scale avionics. The uniform support platform for information processing and message passing deeply integrates the avionics functions, improves in

* * Corresponding author.Tel.: +86-29-89186496; +86-10-62794935; fax: +86-029-89186001E-mail address: hanw12@mails.tsinghua.edu.cn

1877-7058 © 2014 The Authors. Published by Elsevier Ltd.Peer-review under responsibility of Chinese Society of Aeronautics and Astronautics (CSAA).

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functionality and performance, and saves cost[1]. Space electronics has a similar developing trend. It must adapt the requirements of high-performance, high reliability, intelligence, and miniaturization by sharing data, high-speed reliable network, functional integration and modularity. Spacecrafts such as satellite and airship run on track for a long time, exposed to the heat and radiation from the astrospace, so the reliability of the embedded computer is a big issue[2].

The assessment model or method of the computer architecture primarily includes Modular Open System Approach(MOSA), computer system reference architecture, health status and reliability assessment et.al. Fundamental MOSA principles are about affordable or adaptable capability. The MOSA Process applies to the development of an adaptable product or service in the engineering development domain. MOSA maturity model is a staged representation model. It identifies the practice that is the foundation to implement effective MOSA process.[3]

There is a series of reference architectures. The OSI Reference Model is a communication reference model which defines the layers of the software and their functions. Open Systems Architectures(OSA) of the Open Systems Architectures Working Group, introduces their hardware and real-time. ARINC 651/653 defines the communications in the bottom three layers of Application/Executive/Hardware, where Application/Executive (APEX) is defined. Generic Open Architecture(GOA), is intended to classify interfaces to transit open standards to military avionics.

These models or methods guide the hardware and software design of embedded computer systems and have a great influence. But they are not very fit for the aerospace embedded computer, since they are not very pertinent to the subject or are limited to a certain aspect.

To solve the problems mentioned above, an assessment model of the architecture of the aerospace embedded computer is proposed in this paper. Based on the analysis of the typical aerospace embedded computer, the assessment model contains classification principal of the architectural metrics. According to the assessment model, an aerospace embedded computer can get an explicit score for the architecture.

2. Architecture and common technology of typical embedded computer

Three categories of embedded computer are analyzed for the architectural characters and common technologies. They are A380 flight control computer, missile guidance control system and SpaceBus4000 electronic system. Figure 1 shows the architectures of these computers.

a. A380 flight control computer b. Missile Guidance Control System c. SpaceBus4000 Electronic System

Fig 1 Typical architecture of the aerospace embedded computer

Table 1 shows the architectural characters of these computers, and refers to some details of their design.

主飞控计算机Maj or Control Computer

主飞控计算机

Fl i ght Control

Acti vator

主飞控计算机Vi ce Control Computer

BCM

Brake horn

BCMFCDC

FWS

CDS

Yaw rudder bal ance

Yaw rudder

Pi tch Bal anceSwi cth

Si de horn

Bri dge connecti on

MPC755 CPU

Storage

FPGAI nterface Servo

Control

Gui dance acceptan

ce

I nert i a sensi t i ve uni t

Radi o hei ght

Gui dance antenna

El ectri c motor

Radi o al ti meter antenna

Gui de head

. . .

SMU

North data i nterface

South data i nterface

Pl atf orm data i nterface

Power

Output mul ti pl exer

I nput matri x

Sunl i ght sensor

React i on wheel . . .

. . . . . .

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Table 1Architecture characters

Typical embedded computer

Architecture character

Description

Airbus A380 flight control computer[4]

Modularity Main and vice flight control computer is made up of command channel and supervisor channel distribution and comparison modules

Functionality integration

PRIM integrates auto flight and flight guidance function, besides flight control tasks.

Open interfaces It has AFDX interface，which implements software download, warning signal and subsystem communication and other functions.

Dissimilar redundancy technology

Main flight control system contains 3 main flight control computers and 3 auxiliary ones. Each computer has 2 channels which adopt different CPU and program language provided by different manufacturer.

A certain missile[5] guidance and control system

Modularity It is many modules: power module, processing module, bus communication module, A/D module, etc

Integration design considering the hardware resource as a whole, making integrated design of electronic devices in every subsystem.

miniaturization Combine similar functional modules, arrange modularized functional card and inertial sensor component in one cabinet to form a compact structure.

SpaceBus4000 satellite borne electronic system[6]

functional integration

Satellite Management Unit(SMU)runs gesture and track control software and satellite affair management software, and has gesture and track control and heat control and other functions.

Network-centric Data Bus Network(DBN)connects SMU、platform devices and effective load devices.

Modularity SMU and 3 data interface units are all modularized.

redundancy technology

Modules in SMU are warm or cold backup. DBN is able to manage 6 redundant RS485 buses.

Airspace embedded computers has a variety of architectures because of different supporting platform, reliability requirement and function complexity. Nevertheless, there are many interlinked technology characters between them. The modular design is widespread, in other words, Line Replace Module(LRM) is the basis of the hardware. These modules are usually not complete computers, e.g. operating module, I/O module and net module. LRM can work with the system, and it can be diagnosed off the system while other LRMs is working. LRM can be replaced and recovered in the system[7]. The maintainability of the system is improved by diagnosing bad modules. Net-centric design is another common technique. Network has always been the infrastructure of the computer system and grows into definitive network such as AFDX, Fibre Channel(FC), Space Wire bus and Time Triggered Ethernet(TTE) bus. Then comes integrated design, which strengthens integrated functions and information sharing. One single system or module implements the function of several original systems or modules.

Aerobat determines the architecture design of the embedded computer to a great extent. The former 3 embedded computers all concern flight or gesture control but has a great difference. For aerobat like guided missile that has limited utility time and frequency, the embedded computer need to control the cost of production. Miniaturization is applied, and similar function unit are combined, so the cabinet of the computer becomes small and light. To the contrary, if the aerobat has a long life or frequently functions, the embedded computer needs reliability and maintainability. Redundancy technology is applied to achieve a long service life. We take these two directions as control of cost in the whole life of the embedded computer.

Additionally, typical aerospace embedded computer architecture has the following techniques in common: Application of Commercial Off The Shelf(COTS). Application of COTS in the components, processors and

networks to reduce the cost of the production. Following open standards. Adhering to public interface specification, bus protocol, etc. It is convenient to

expand, upgrade and reconfigure the system.

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High-performance. Efficient Data processing is achieved by full use of computing resources and network resources.

3. Assessment modeling

Based on the common technologies of the aerospace embedded computer architecture, we set up an assessment model in the aspects (or evaluation dimensions) of common architecture, cost control and development oriented, as shown in Figure 2. Modular, Net-centric and Integration are all general ideas of architecture design, so they can be put to category “Common architecture”. Intensivism and Longevity are two approaches to control cost of the product in the whole life. Other characters of the aerospace embedded computers are classified as development oriented. Application of COTS reduces cost and takes the advantage of the continuous sufficient supplies of electron devices. Open standards can help the system to expand and upgrade. High-performance makes it possible that the system can be upgraded and meet new requirements in the future.

The assessment result is a level among 0~8, which is the addition of the evaluation dimensions. The level of Common Architecture is the minimum of that of Modular, Net-centric and Integration, as the worst architectural character determines the common architecture level. The level of Cost Control is the maximum of that of Intensivism and Longevity, for either approach is enough to achieve the target. The level of Development Oriented is the medium of that of COTS, Openness and High-performance, for the average of the 3 characters counts but is not necessary. The classification of the characters is described in Section 2.1 to 2.3.

Modul ar Level 0~3Net-centri c Level 0~3I ntegrati on Level 0~3I ntensi vi sm Level 0~3Longevi ty Level 0~3COTS Level 0~2Openness Level 0~2Hi gh-performance Level 0~2

AssessmentModel of

theArchi tectur

e ofEmbeddedComputer

(Level 0~8)

CommonArchi tecture

MI N（ ）

Cost ControlMAX（ ）

Devel opmentOri entedMedi um（ ）

Fig. 2 Assessment Model

3.1. Common Architecture

Common Architecture is characterized by modular, net-centric and integration, and the latters are all indispensible. Good modular design has to partition the system into administrable, reliable and maintainable modules. Usually, modules are independent from each other by well-defined interfaces to ensure that they can be developed and maintained independently. Net-centric demands that the system have centralized high-speed network to share information and integration needs resources shared and function integrated through the networks and middleware. Table 2 shows the evaluation demission’s classification and guidelines.[8]

Table 2. Evaluation of Common Architecture

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Architecture Character

Level Guideline Reference

Modular

0 Few modules Number of modules are no more than 2

1 good partition of modules Containing Power management, data processing and IO modules

2 good partition and independency of modules Data processing function are divided, modules can be developed, tested, verified and maintained independently

3 Good partition, independency and maintenance of modules Modules have fault detection and isolation mechanism

Net-centric

0 Lack of connectivity, little shared information

1 Normal connectivity, considerable shared information，low data switch speed，good certainty

Data switch speed is below 10Mbps[9]

2 full connectivity, considerable shared information, high speed data switch good certainty and extension

Data switch speed is above 10Mbps

3 centralized high speed network adhere to open standards a high speed network connects above 80% units of data acquisition, processing and display

Integration

0 little shared resource

1 some common modules, many shared resources, many functions integrated

General processing module and network switch module act as common modules

2 Reliable integration Fault isolation mechanisms such as partition operating system

3 Real-time middleware to support application partition and system upgrading

Primary functional modules have real-time middleware

3.2. Cost Control

The evaluation dimension of Cost Control has two different approach, that is, intensivism and longevity. Application domain determines which approach is reasonable. Intensivism stresses constructing the computer system with a low cost, keeping short life cycle of production, reducing the volume, weight and power of the computer. Simplification, combination and reuse of the function or component are the major methods for intensivism. Longevity is mainly supported by reliability and maintainability. The dependable computer architecture is based on three dimensions: integrity level, fault-tolerant scope and redundancy scope[10]. Table 3 shows the evaluation demission’s classification and guidelines.

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Table 3. Evaluation of Cost Control

Architecture Character

Level Guideline Reference

Intensivism

0 Little simplified design

1 Reduce redundant component, performance is just enough for requirement

Redundant components are no more than 10%

2 miniaturizes system, combination of similar functions and structure

great differences of function and structure between subsystems

3 Other approaches to control the expense. COTS, SW reuse, etc.

Longevity

0 General reliability and maintainability

1 Good reliability High quality components, derated design ,good system software safety

2 Good reliability and maintainability, redundancy and fault-tolerant

Easy to detect and replace fault module

3 complete service support mature development method and tools

3.3.Development oriented

The evaluation dimension of development oriented consists of application of COTS, Openness and high performance. These architectural characters are optional and independent from Common Architecture. They are prepared for new requirements and upgrading of the system. Table 4 shows the evaluation demission’s classification and guidelines.

Table 4. Evaluation of development oriented

Architecture Character

Level Guideline Reference

COTS[11]

0 Low application rate below 20%

1 Average application rate; error detection and fault-tolerant

between 20%~50%

2 High application rate; validation of dependability above 50%

Openness[12]

0 little open standards

1 Good hardware openness open data bus and interface standards

2 Good software openness open API standards

High performance

0 low speed of data processing and transmission

1 High speed of data processing and transmission(real-time OS support)

processing speed above 400MIPS, transmission speed above 10Mbps

2 Effective parallel processing and balanced task dispatch

parallel processing among cores, processors or modules

4. Architectural assessment case

We study and evaluate F-35 Joint Strike Fighter’s Integrated Core Processor(ICP) to reveal the architectural assessment method. ICP adopts 7 categories of standard modules and a unified Fibre Channel(FC) as its network. In the aspect of Common Architecture; redundant technique and dynamical reconfiguration technique are applied to control the cost. Wide application of COTS and open standards prepare ICP for the system upgrade and new requirements[13]. Table 5 shows the process and reasons for the classification. Each architectural character gets the score for the reasons showed in Table 5. The dimensions (Common Architecture, Cost Control and Development

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Oriented) are respectively the minimum, maximum and medium of their architectural characters’ scores. The final level is a sum of the dimensions. The assessment result is the highest level, that is 8 Level.

Table 5. Assessment of ICP

Final Level Dimension Character Reason

8

Common Architecture(3)

Modular 3 reasonable module categories, module independence and fault-tolerant, Line Replace Module(LRM)

Net- centric 3 common resources shared by FC;2GB/s speed; low firm latency

Integration 3 Radar, electronic warfare and other tasks integrated; General Processor and Net Switch as shared modules; Integrity OS and CORBA support

Cost Control(3)

Intensivism 0 great deal of redundancy

Longevity 3Double ICP design, FC and 1394B as redundant channels; applications configured to different partitions by security level; real-time fault-tolerant and LRM; development support

Development Oriented(2)

COTS 2 great deal of commercial techniques, like PowerPC processors

Openness 2 FC and 1394 bus as major module interfaces; good layer software design and API openness of Integrity OS; wide application of COTS

High performance 2

system real-time reaction supported by real-time processors, network and OS; high speed data transmission; parallel processing among modules; efficient dispatch of tasks

5. Conclusion

Embedded computer design standardization is improving in the aerospace domain, and there are more and more commons of architectural characters. Advanced aerospace embedded computer characters are summarized in this paper. According to the summery, the assessment model is built, by which the ICP of F-35 is evaluated. The process and result of the assessment shows that the provided architectural assessment model is efficient and practical. We hope the work can provide some reference for the designers and purchaser of the aerospace embedded computers.

Future work may introduce the variety of requirements for the embedded computers and provide criteria and evaluating method of the balanced design.

Acknowledgements

Professor Yaorong Zhou told us the development history of avionics system, and supplied us with some useful references, which helped us a lot. Linting Bai read this paper and gave many advices to make some sentences read smoothly. Thank them and all the others who have helped this paper.

Reference

[1] Zhang Fengming, et al, Research on Architecture of Integrated Modular Avionics, Electronics Optics & Control, 2009, 16(9): 47-51.

8 Wei Han/ Procedia Engineering 00 (2014) 000–000

[2] Xiaopeng Li;Baidong Jin;Ti Zhou;Zhenggao Liu, Study on transmitting reliability of satellite-station data links based on transmitting environment influence model, in:Quality, Reliability, Risk, Maintenance, and Safety Engineering (ICQR2MSE), 2012 International Conference , 2012.

[3] M. Jakovijevic, Modular Open System Approach(Mosa) and Ttp-Based Platforms for Aerospace Control Systems, in:Proceeding of 25th Digital Avionics Systems Conference, 2006.

[4] Niu Wensheng, The Airborne computer technology,. Xi’an: Aviation Industry Publishing, 2013.[5] Xie Yanwu, Integrated Guidance-Control System for Winged Missile, Ordnance Industry Automation, 2012, 31(11): 38-40.[6] Ye Yuanfei, Lv Nan, Huang Xianlong, et al. Applications of Advanced Avionics in Communication Satellite Platform, Aerospace Control and

Application, 2011, 37(1): 45-49.[7] Jin Yanzhong, Lu Yongji, Yang Lin. Research on LRM and It’s Key Technologies of Military Aircraf, Aircraft Design, 2009, 29(3): 33-36.[8] Zhu Xiaofei, Huang Yongkui. Analysis and View of Standard for Integrated Modular Avionics, AVIONICS TECHNOLOGY, 2010, 41(4): 17-

22.[9] Liu Shiquan, Juan Yang, Cai Jieming, et al. Research on the Application Development of 1553B Bus, ELECTRONICS & PACKAGING,

2013, 13(12): 11-15.[10] Kong Deqi, Li Yahui, Guo Peng. Development of dependable embedded computer systems, Journal on Communications, 2013, 34(Z1): 170-

175.[11] Xing Kefei, He Wei, Yang Jun. Study on Space Application Technique of COTS Components, Computer Measurement & Control, 2011,

19(7): 1741-1745.[12] Ding Quanxin. Remarks on Standards of Integrated Module Avionic System, Electronics Optics & Control, 2013, 20(6):1-3.[13] Luo Rui, Li Guozhu. Development of the F-35 Avionics System, Ship Electronic Engineering, 2012, 32(8): 21-23.