USING HASH TABLES FOR SYNCHRONIZATION IN COMMUNICATIONBETWEEN THE CAN PROTOCOL AND IEEE 802.15.4

Marcos Antonio Estremote∗, Nobuo Oki†

∗Department of Electrical EngineeringSao Paulo State University

lha Solteira, Sao Paulo State, Brasil

†Department of Electrical EngineeringSao Paulo State University

lha Solteira, Sao Paulo State, Brasil

Emails: estremot@gmail.com, nobuo@dee.feis.unesp.br

Abstract— This paper proposes the development of an heterogeneous system using the microcontroller(AT90CAN 128) where the protocol model CAN and the IEEE standard 802.15.4 are connected. This moduleis able to manage and monitor sensors and actuators using CAN network and, by means the 802.15.4 standard(ZigBee), communicate with others network modules. The control in the synchronization of data between thetwo protocols (CAN and IEEE 802.15.4) is performed using the technique of hash tables. It is used to improvenetwork performance and avoid stack overflow in the communication between the two technologies.

Keywords— CAN Bus, IEEE 802.15.4, Hash Table, ZigBee.

Resumo— Este artigo propoe o desenvolvimento de um sistema heterogeneo usando o microntrolador(AT90CAN 128) onde protocolo do modelo CAN e o padrao IEEE 802.15.4 sao conectados. Este modulo ecapaz de gerenciar e monitorar sensores e atuadores usando a rede CAN e, por meio do padrao IEEE 802.15.4(ZigBee), comunicacar com os outros modulos da rede. O controle na sincronizacao dos dados entre os dois pro-tocolos (CAN e IEEE 802.15.4) e executado utilizando a tecnica de programacao de tabelas de dispersao. Ela eusada para aperfeicoar o desempenho da rede e evitar estouro de pilha na comunicacao entre as duas tecnologias.

Palavras-chave— Barramento CAN, Padrao IEEE 802.15.4, Tabelas de Dispersao, ZigBee.

1 Introduction

The use of wireless communication networks is nomore an optional tool but a necessity for residencemonitoring, automobiles and automated processcontrols. As it deals with wired networks trans-ducers, the networks CAN (Controller Area Net-work) are utilized in modern automobiles, med-ical instrumentation, in tactical vehicles, in theautomation processes, in the metropolitan trans-port and in factory control. This system is utilizedin a connection among node sensors with a lowcost through a wired network. Most, if not all, ofcritical infrastructure control systems make use ofCAN in some point of the network, to connect re-mote sensors and to control actuators of a system,or to connect multiple controllers using a commoninterface. The wireless standard, IEEE 802.15.4,commercially known as ZigBee, was designed tooperate with low data rates, with security andnetwork configurations low cost. This network iscommonly known as LR-WPAN (Low-Rate Wire-less Personal Area Network), is utilized in domes-tic networks, medical instrumentation and otherapplications requiring low power remote sensors,in order to lengthen the battery life time and mini-mize maintenance sensor. Two key elements of thestandard IEEE 802.15.4 LR-WPAN can be distin-guished: operation at low power and implementa-tion of inherent safety.

A network node is represented by a point of

interconnection with a structure or independentnetwork technology utilized for its development.The intelligent transducers networks are, some-times, composed by a central node, routable nodesand terminal nodes independent if they are usedin wired or wireless networks. The terminal nodesare used to perform data acquisition from thesensors or actuators control, such information issent to nodes or routers to the central node forstorage, analysis and visualization. The routablenodes eliminate collisions, obsolete packages andpermit the adaptation to different physical net-work technologies, so it is possible to convert thewired technology into a wireless network or thewireless network to a wired network, as an exam-ple, CAN network (Controller Area Network) towireless network ZigBee.

The ZigBee is a standard for wireless net-working technology that works at low power andability to connect a large number of devices ona single network. The ZigBee technology worksin the frequency range 2.4 GHz unlicensed. Zig-Bee offers only low-latency communication be-tween devices without the need for network syn-chronization delays of working with a set of pro-tocols for high-level communication based on thepattern IEEE 802.15.4 (for Information Technol-ogy, 2003). Wireless networks using ZigBee tech-nology operate using different types of communi-cation topologies, point-multipoint, peer-to-peerand mesh. Such features allow them to be ap-

plied in several environments, such as: precisionagriculture, medicine, domestic applications, in-dustrial and climate analysis.

The CAN is based on multi-master architec-ture in which all drivers have equals rights andmaster functionality, characteristics that perme-ate equal rights in the transmission medium beingcapable of always sending a message according to aneed to respond to an event. The features of CANnetwork are: operation range of until 1Mbps forshort distances, CAN uses message short of until8 bytes for each message, flexibility configurationand network control by priority in the messages.

Based on features of the wireless networkIEEE 802.15.4 standard and the wired networkCAN in this paper presents the network node thatallows integrate two protocols distinct one used inwired network and other in wireless. The het-erogeneous network node is capable of obtainingdata from a CAN network and converts them toa standard wireless network. The nodes imple-mented were made using the In Fig. 1 shows theschematic with two nodes black those were imple-mented in laboratory.

This work was divided into four sections, sec-tion 1, it described introduction about the project,the section 2 shows the characteristics of wirelessprotocols and CAN. The Section 3 shows the de-velopment of the system. In Chapter 4 the im-plementation and testing, in the last section, theconsideration of the work.

2 Heterogeneous Network Node

An easy way to comply with the conference paperformatting requirements is to use this documentas a template and simply type your text into it.

The network nodes with CAN and ZigBeewere divided in two parts: the first was realizedstudy of protocol and development of the commu-nication between modules using the ZigBee andthe second the study of the features, protocols anddevelopment of CAN network. Section A presentsthe features and specification of CAN network andsection B presents the ZigBee network.

1. Wireless network - ZigBee

The IEEE 802.15.4 standard is a simplepacket data protocol for lightweight wireless net-works and specifies the MAC and PHY networkinglayers. ZigBee technology takes full advantage ofthe IEEE 802.15.4 standard and adds the logicalnetwork, security and application software. Zig-Bee technology provides static and dynamic star,cluster tree and mesh networking structures thatallow large area network coverage, scalable net-works and single point-of-failure avoidance. Now,customers do not have to be tied to complex,costly proprietary solutions that increase their de-sign time.

The MAC frame format for IEEE 802.15.4standard can be showed in Table 1 that has thefollowing components (Semiconductor, 2009):

• MHR- responsible by control frame, sequencenumber and address information.

• MAC payload- it has variable length, which con-tains specifics information about the frame.Acknowledgement frames do not contain apayload.

• MFR- contains the FCS.

LR-WPAN defines 4 frame structures: beaconframe, data frame, acknowledgement frame andMAC command frame (Ergen, 2004). This fieldvariable describes the frame structures, where, inthis project was used the data frame to changethe protocol CAN to ZigBee in the server nodeand send the data for others ZigBee nodes untilarrive client node. In the client node is changedthe ZigBee data to the CAN protocol to manage-ment of the intelligent transducers.

1. Controll Area Network - CAN

The CAN standard is presents resolution ISO11898 of the International Organization Standard-ization. Nowadays, there are two standards ofCAN network, the CAN 2.0 A with identificationof 11bits and CAN 2.0 B with identification of 29bits. The CAN based on OSI model using thephysical layer and link layer can be implementedin the chip all system leaving the application layerto be developed. The CAN specifies three typesof buses, with a wire, in which determining thebit 0 and 1 is performed by the potential differ-ence held between the wire and the vehicle carcass.With the two wires buses is defined as CAN Hand CAN L in which the potential difference ismade through two wires and other four-wire bus,in which two wires CAN H and CAN L are fol-lowed by two more power wires Vcc and GND,illustrate in Fig 2. The medium access control isdone by the CSMABA protocol (Collision Mul-tiple Sense Access/Bitwise Arbitration) in whichworks similarly to the CSMACD (Collision Multi-ple Sense AccessCollision Detect), however, whena collision occurs times are determined in accord-ing to the priority of each node.

Figure 2: Example of CAN network.

The CAN has several attractive features foruse in automotive or industrial environments, such

Figure 1: System implemented in laboratory.

Table 1: General MAC

Oct: 1 1 0/2 0/2/8 0/2 0/2/8 Var. 2

Frame ControlSeq. Dest.

Dest.Sour.

Sour FrameF

Num PAN PAN CID ID S

Address FieldMHR MAC MFR

as: Multi-master, error detection, retransmissionof data after corruption of messages, the distinc-tion between temporary errors and permanent er-rors, consistency of data, prioritization of mes-sages and multiplex with the time synchronization((CIA), n.d.).

The CAN can be described by two formats:the standard and base frame format define as2.0A, and the extended 2.0B. The difference be-tween A and B is that the Version A supportsthe format 11 bits to identifier field and the Ver-sion B support length of 29 bits to identifier field.For the development of the heterogeneous networknode was used the version 2.0A that is describedby Table 2 (Jaman and Hussain, 2007).

Table 2: CAN Protocols version 2.0 A.

Length (bits) Field Name1 Start-of-frame11 A identifier for the data1 Remote Transmission Request1 Identifier extension bit1 Reserved bit4 Data length code

0-8 bytes Data field15 Cyclic Redundancy Check1 CRC delimiter1 ACK slot1 ACK delimiter7 End-of-frame

For the development of the node modulewas used for programming Atmel’s AVR Stu-dio, recording module STK 500, STK 501, ra-dio transceiver RZ502 and the microcontrollerAT90CAN128.

3 Project Development

In wireless sensor network the node is a point onthe network with the ability to manage the datarelated to an application involving sensors and ac-tuators. The model has the ability to manage thesensors / actuators through a bus and send thecollected information using the serial port (RS-232) to a remote base station. It is relevant toemphasize that to reach the base station wirelesssensor network, information can jump by severalpoints until the final destination. Fig. 3 showsa schematic of the system for the interfacing andcommunication network of wireless sensors to thewired network (Hongiang and Shuangyou, 2008).

In Fig. 3, Block 1 is illustrated the CAN busin which they can attach a mesh of sensors andactuators; a CAN network will have interfacingwith the microcontroller proposed. The networkworks in high data rate up to 1Mbps and reliably,because of the CAN does not work with commu-nications address, the microcontroller will have toperform a conversion to packet format to the for-mat of IEEE 802.15.4 and may thus be sent toother meshes of sensors and actuators of the wire-less network (E. Ding and Zhou, 2007).

So that the battery power of sensors is op-timized, the IEEE 802.15.4 standard is used forinterfacing with other software modules wirelessnetwork. The conversion done by the microcon-troller shown in Fig. 3, Block 2, it is also held be-tween the ZigBee standard for CAN network illus-trated in Table 2 of that figure. One feature thatshould be emphasized is that the Zigbee operateswith transfer rates of up to 250 Kbps messages,which will be needed for a bidirectional commu-

Figure 3: Detailing of the implemented communication module.

nication, which the packets of the IEEE 802.15.4are also processed in the format of the CAN pro-tocol for being recognized by the sensors and actu-ators. Communication between the two moduleswork reliably and there is a confirmation of receiptby the client module, a feature called handshacke.For communication between the modules is beingused RZ502 kit (radio transceiver) with supportfor standard Zigbee.

In Fig. 3, Block 3 it is shown the microcon-troller module for interfacing between the 802.15.4standard and the CAN network of wireless sensornetwork. This module is the concatenation of thefeatures of Fig. 4, Block 1 with Block 2 of. Forimplementation we used the tools and kits: AVRStudio 4 (WinAVR) module STK500, STK501 ex-pansion kit, a radio transceiver integrated circuitand RZ502 with AT90CAN128 TQFP package.For the testing phase will be implemented sensorsfor monitoring temperature and humidity, besidesdriving devices such as motors, lights, heaters etc.

In researches held in the laboratory of In-tegrated Circuits, Faculty of Engineering of IlhaSolteira (Department of Electrical Engineering) aserial communication was implemented succeed-ing in capturing and recognition of the messages.Also, we studied the exchange communicationmessages using the IEEE 802.15.4 (Zigbee) be-tween two nodes of a peer network, as shown inFig. 4. Another analysis performed in the labo-ratory was the communication between a PC andRZ502 communication module using the standardserial interface RS-232, in which the data weresuccessfully transferred. The test software for thiscommunication was prepared using the Java lan-guage. Java has a library JAVAX.COMM thatencourages the implementation of systems for thispurpose. Because it is a synchronous communi-cation it was held the following configuration onboth devices (microcomputer/RZ502): 9600 bits/ second, 8 data bits, parity N (None) and 1 stopbit.

4 Test Implementation

The integration of heterogeneous protocols is com-plex because it requires a great effort to synchro-nize the transmission and reception of data, know-ing that, the wireless standard IEEE 802.15.4 asalready stated, it operates at a transmission rateof up to 250 Kbps while the CAN protocol at arate considerably higher than 1 Mbps, which cancause malfunction of the system and even loss ofcritical system information.

For synchronization of data between CANprotocol and IEEE 802.15.4 Protocol was adoptedhash tables because the data transfer rate of theCAN protocol is considerably higher than IEEE802.15.4. The possibility of using hash tablesto control the allocation of memory in microcon-trollers are techniques of data structure accepted(Palsberg, 2005).

Hash table is a special data structure, whichcombines search keys to values. The goal is, froma simple key, do a quick search and get the desiredvalue. Hash tables, if well designed, can be usedto get a table element in the order shown. Theway to solve the problem of spending too muchmemory, but still ensuring quick access is throughthe use of hash tables.

Figure 4, shows the transmission of tem-perature data, monitored by the wired networkfor wireless sensor network (IEEE 802.15.4), weadopted a function to the dispersion of the datacollected within the proposed structure, thusguaranteeing, direct access to information andeliminating duplicate information unnecessary.

Figure 4: Schematic of the model implementedusing the hash table to synchronization and datastore.

When the information is collected by the tem-perature sensor, this information can be sent tothe base station using the wireless network. Duethe difference in the rate of transmission betweenthe CAN protocols and IEEE 802.15.4 be differ-ent, the use of a simple linked stack could resultin a stack overflow quickly. With the use of datastructures and based on the concept of hash tableshas been defined a hash function that indicatesthe correct position which the data collected willbe stored in structure. The spread function f(x)seeks to define a function that reduces the colli-sions of the information collected, and provides aconstant value in the search, given the fact thatwe already know where the information within thevector. This work we defined a hash function givenby f(x) = 63%temp, where temp is the tempera-ture value and prime number 63 which defines theamount of structure elements of Array.

In model describe was applying the hash func-tion f(x) and checked if in the position f(x) ofarray (Array[f(x)]) there is some element, if thearray position there is some element, this elementis discarded. However, if the position Array[f(x)]is empty the information is allocated and the ad-dress of Array[f(x)] is assigned to queue elementsto be sent by the IEEE 802.15.4 protocol, andconsequently released from the queue (linked list).With this strategy, have a linked list that in thepessimistic case of the hash function will take n+1memory locations, and more n+1 positions of theArray.

The implementation and configuration of theproposed protocol has been defined by laboratorytests. Figure 5 illustrates the communication ofa block composed of a display to visualize thecaptured charge by a temperature sensor (LM35)and monitored by an attached module (slave) ofa wireless sensor network and send them to a co-ordinator node (control unit) network using theIEEE 802.15.4.

Figure 5: Slave node monitoring temperature us-ing wireless communication ZigBee.

Figure 6 illustrates the simulation of themanagement of master/slave communication us-ing a software model to test offered by ATMEL(AVR414), whose programming language Javawire. This software was adapted so that data col-

lection, both in transmission and reception couldbe executed automatically, thus providing greaterflexibility for the network of smart transducers.

Figure 6: AVR414 application (client) adapted forcommunication with the network coordinator.

Figure 7 illustrates the reception of data sentby the slave node by the coordinator and this isresponsible for triggering the actuators of the sys-tem based on the information provided by sensorsconnected to the wireless network system ZigBee.In tests, the temperature was controlled using sen-sors of some fans (actuators) for the cooling sys-tem.

Figure 7: AVR414 Application (coordinated)modified to control and monitor data from clientdevices.

Finally, in Fig. 8 is defined monitoring tests ofsensors and actuators using CAN bus. Also, as inthe 802.15.4 standard, we used temperature sen-sors for data acquisition. The display shows thedata collected and monitoring using the Hyper-Terminal application operating system WindowsXP.

Authors G. Gaderer and Mahmood (2008)and Rauchhaupt (2002) indicate the possibilityof integrating technology with the IEEE 802.15.4standard CAN. It is based on these statements,that it is underway the creation of a heteroge-neous protocol capable of performing communica-tion and control technologies with different char-acteristics. One of the problems encountered inthe implementation is to perform the synchro-nization between the technologies, because they,both, work with transmission rates in different bus(CAN - 1 Mbps; 802.15.4 - 250 Kbps) as stated

Figure 8: Monitoring bank of sensors using theprotocol CAN Bus.

above. To implement the study, an integrated cir-cuit AT90CAN128 of ATMEL was used.

5 Conclusion

In this study, we presented the development ofa network node capable of integrating two differ-ent protocols (CAN and IEEE 802.15.4) for com-municating and managing a wireless sensor net-work (WSN) using the TQFP package with micro-controller AT90CAN128 from ATMEL. The nodehas characteristics of being embedded and au-tonomous, making the routing of each packet toits specified interface. For this, each interface isidentified by an address similar to the MAC ad-dress used in computer networks.

Through conducted studies, the lack of de-vices that allow the monitoring of various sen-sors in areas of relatively large scope is impossiblebecause of the complexity in interconnecting allnodes ((CIA), n.d.). With this objective the cre-ation of a network interconnecting the CAN nodewith 802.15.4 wireless standard is proposed. Theyuse the CAN network reliability for the monitoringof sensors and data transmission to other networknodes and also the standard IEEE 802.15.4, whichis reliable in data transmission, and has acceptablelevels of immunity to interference in industrial en-vironments; it can achieve higher distances, be-sides managing the lifetime of the battery sensorinterconnected to the network sensors.

In developing the logical part of the hardware,it is used the modules from ATMEL (STK 500,STK 501 and antenna RZ502) and the tool AVRStudio also from the same company.

At the end of the project, it is intended toimplement a structure that can be used for var-ious purposes such as monitoring homes (smarthomes), tracking of vehicles, checking tempera-ture and weather conditions in planting of differ-ent crops etc.

For future works, it is proposed to developa portable software for managing nodes throughthe JAVA programming language, because it isfree and can be used in Web applications, desktop,mobile phones etc.

Acknowledgment

We acknowledge the Department of Electrical En-gineering, Faculty of Engineering of Ilha Solteira- FEISUNESP, we also thank the Graduate Pro-gram in Electrical Engineering from UniversidadeEstadual Paulista “Julio de Mesquita Filho”, andfinally, the Laboratory for Integrated Circuits.

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