1、 ISO/IEC 24740 Edition 1.0 2008-01 INTERNATIONAL STANDARD Information technology Responsive link (RL) ISO/IEC 24740:2008(E) THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2008 ISO/IEC, Geneva, Switzerland All rights reserved. Unless otherwise specified, no part of this publication may be reproduc
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8、feedback on this publication or need further assistance, please visit the Customer Service Centre FAQ or contact us: Email: csciec.ch Tel.: +41 22 919 02 11 Fax: +41 22 919 03 00 ISO/IEC 24740 Edition 1.0 2008-01 INTERNATIONAL STANDARD Information technology Responsive link (RL) INTERNATIONAL ELECTR
9、OTECHNICAL COMMISSION J ICS 35.200 PRICE CODE ISBN 2-8318-9542-1 2 24740 ISO/IEC:2008(E) CONTENTS FOREWORD.4 INTRODUCTION.5 1 Scope.7 2 Normative reference.7 3 Definitions, terms and abbreviations.7 3.1 Terms and definitions 7 3.2 Abbreviations 8 4 Conformance8 5 Responsive Link structure 8 5.1 Outl
10、ine of Responsive Link8 5.2 OSI reference model .9 6 Layer 1 (physical layer) 9 6.1 Separate transmission of data and event.9 6.2 Physical interface9 7 Layer 2 (data link layer)10 7.1 Error correction .10 7.1.1 General .10 7.1.2 CODEC .10 7.1.3 Error correction encoding 10 7.1.4 Bit stuffing .10 7.1
11、5 NRZI encoding 11 7.2 Frame format.11 7.2.1 Packet.11 7.2.2 Frame11 7.2.3 Setup pattern.11 7.2.4 Idle pattern11 7.2.5 Bit synchronization and clock rate .11 7.2.6 Error handling12 7.3 Automatic reconfiguration (plug and play)12 8 Layer 3 (network layer).12 8.1 Packet overtaking function 12 8.2 Res
12、ponsive Link packet format12 8.2.1 Header format .12 8.2.2 Priority.13 8.2.3 Data packet .13 8.2.4 Event packet .14 8.3 Routing .15 8.3.1 General .15 8.3.2 Routing table.15 8.3.3 Independent routing of data and event.16 8.3.4 Priority-based routing 16 9 Layer 4 (transport layer) .16 9.1 Priority rep
13、lacement for packet acceleration/deceleration 16 9.2 Multi-link .17 24740 ISO/IEC:2008(E) 3 9.3 Stream data transmission17 Annex A (informative) Characteristics of real-time communications18 Annex B (informative) Real-time scheduling.19 Annex C (informative) An implementation of the Responsive Link
14、interface20 Annex D (informative) Examples of implementation .21 D.1 An implementation of the Responsive Link switch.21 D.2 An implementation of overtaking buffers .22 Annex E (informative) Examples of routing of data and event.23 E.1 An example of independent routing of data and event.23 E.2 An exa
15、mple of priority based routing.23 Bibliography24 Figure 1 A humanoid robot.6 Figure 2 Logical interface of Responsive Link 9 Figure 3 Header format13 Figure 4 Data packet format.13 Figure 5 Trailer format of data packet 13 Figure 6 Event packet format .14 Figure 7 Trailer format of event packet.15 F
16、igure 8 Routing table .16 Figure B.1 EDF scheduling 19 Figure C.1 Responsive Link connector and cable.20 Figure D.1 A Responsive Link switch .21 Figure D.2 An overtaking buffer .22 Figure E.1 An example of routing.23 Table 1 Syndrome and error digits .10 Table 2 Frame format 11 Table A.1 Syndrome an
17、d error digits18 Table C.1 Maximum cable length .20 4 24740 ISO/IEC:2008(E) INFORMATION TECHNOLOGY RESPONSIVE LINK (RL) FOREWORD 1) ISO (International Organization for Standardization) and IEC (International Electrotechnical Commission) form the specialized system for worldwide standardization. Nati
18、onal bodies that are members of ISO or IEC participate in the development of International Standards. Their preparation is entrusted to technical committees; any ISO and IEC member body interested in the subject dealt with may participate in this preparatory work. International governmental and non-
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26、ublication of, use of, or reliance upon, this ISO/IEC publication or any other IEC, ISO or ISO/IEC publications. 9) Attention is drawn to the normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 10) Atten
27、tion is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. International Standard ISO/IEC 24740 was prepared by subcommittee 25: Interconnectio
28、n of information technology equipment, of ISO/IEC joint technical committee 1: Information technology. This International Standard has been approved by vote of the member bodies, and the voting results may be obtained from the address given on the second title page. This publication has been drafted
29、 in accordance with the ISO/IEC Directives, Part 2. 24740 ISO/IEC:2008(E) 5 INTRODUCTION The Responsive Link standard defines a real-time communication protocol between computers networked in a machine or in a site with point-to-point interfaces. Complex machines, such as robots, automobiles and net
30、work routers, have a growing demand for distributed processing. In addition, modernization of facilities such as factories, offices, schools and homes is creating a ubiquitous computing environment. Unlike conventional PC applications for documentation and internet applications that exchange texts w
31、ithout hard time constraints, these types of cooperative computing require real-time and reliable responses to physical events occurring in the real world. Although most conventional real-time systems employ a single processor that invokes tasks corresponding to outside events, the need for distribu
32、ted processing architecture is inevitable for the larger-scale systems mentioned above, because operational targets are physically separated and scalable processing power becomes necessary as the number of components increases. For distributed nodes to cooperate in real-time, an interconnecting netw
33、ork shall realize real-time communication. The Responsive Link provides such real-time communication between computers by providing dual full-duplex communication channels, fixed-size prioritized packets, packet overtaking based on priority, and automatic error correction. Real-time An operation of
34、a dynamic system is called a real-time operation if the combined reaction- and operation-time of the task is shorter than the allowed maximum delay, with respect to circumstances outside the operation. A system is said to be a hard real-time system if the correctness of an operation depends not only
35、 on logical correctness, but also on the time at which it is performed. An operation performed after the deadline is, by definition, incorrect, and has no value. In a soft real-time system the value of an operation declines steadily after the deadline expires. Whether a system is hard real-time or s
36、oft real-time and how much time is allowed before a deadline are application dependent. Although it is known that static estimation of the time required for generating a response is important for a computer to output a response before a deadline, such static estimation is often very difficult or imp
37、ossible. Instead, most real-time systems rely on priority-based scheduling. Real-time scheduling As real-time scheduling algorithms, the earliest deadline first (EDF) scheduler, the rate monotonic (RM) scheduler and their variations have been established, as explained in Annex B. These algorithms co
38、mmonly schedule tasks based on priorities determined by margins to deadlines. Thus, an important function is preemption, i.e. the scheduler deprives the execution privilege of the lower-priority task and allows the higher-priority task to run. In order to realize real-time communication, a function
39、similar to task preemption shall also be employed in communication. There are several methods for this communication preemption: provision of two separate channels for high- and low-priority packets, setting different communication paths according to priority and assigning a shorter path for high-pr
40、iority communication, and allowing higher-priority packets to overtake lower-priority packets. Responsive Link has all of these capabilities. Important features Responsive Link has the following distinctive features that allow realization of real-time communication. Separation of data transmission a
41、nd event transmission (see Annex A). Prioritized routing: When multiple packets with different priority levels are sent to the same destination, different routes can be set in order to realize exclusive communication lines or detours (see Annex E). Priority-based packet overtaking: The packet with t
42、he highest priority overtakes the other packets at each node (see Annex B and Annex D). 6 24740 ISO/IEC:2008(E) Packet acceleration/deceleration using priority replacement: Packet priority can be replaced with a new priority at each node in order to accelerate/decelerate packets under distributed co
43、ntrol and realize real-time communication. Fixed packet size: 64-byte data and 16-byte event. Point-to-point serial link (see Annex A). Independent routing of the data link and the event link (see Annex E). Hardware forward error correction to prevent retransmission. Other useful features are as fol
44、lows: variable link speeds (533, 267, 133, 66,7, 33,3, 16,7 and 8,3 Mbit/s), automatic reconfiguration (plug & play), topology free, low latency (240 ns required to pass through one routing node at 66,7 Mbit/s). Typical applications and operations As a typical application of the Responsive Link, Fig
45、ure 1 shows a distributed control configuration of a humanoid robot. The electronic control part of the humanoid robot consists of several control nodes with local sensing and actuating devices. The distributed controllers are connected to each other by Responsive Link. In this figure, rectangles re
46、present node controllers, and dotted lines show the Responsive Link cable, which is a point-to-point serial link. For a humanoid robot to walk stably, a servo loop of 1 ms or shorter is needed. In this configuration, the farthest two nodes can exchange a 16-byte packet within 5 s. Since the time is
47、guaranteed not to fluctuate, the distributed control of a humanoid is considered to be sufficiently possible. Figure 1 A humanoid robot 24740 ISO/IEC:2008(E) 7 INFORMATION TECHNOLOGY RESPONSIVE LINK (RL) 1 Scope This International Standard specifies the communications protocol and interface of Respo
48、nsive Link, the real-time communication for parallel/distributed control. This standard corresponds approximately to the functions specified in layer 1 to layer 4 of the OSI reference model. The purpose of this standard is to facilitate the development and use of Responsive Link in real-time systems
49、 by providing a common data protocol. This standard provides a real-time communication protocol for interconnections among distributed real-time systems, including embedded systems, control systems, amusement systems, robot systems and intelligent buildings. 2 Normative reference The following referenced document is indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the
