Modelling, simulation, and performance analysis of a CAN FD system with SAE benchmark based message set

Transcription

1 Modelling, simulation, and pefomance analysis of a CAN FD system with SAE benchmak based message set Mahmut Tenuh, Panagiotis Oikonomidis, Peiklis Chachalakis, Elias Stipidis Mugla S. K. Univesity, TR; visiting eseache, VRC, Univesity of Bighton, UK Vetonics Reseach Cente (VRC), Univesity of Bighton, UK Abstact. The inceasing amount of electonic contol units (ECUs) and message taffic in in-vehicle and industial communication netwoks cause a ising demand fo highe bandwidth and low message esponse times. As a pominent eal-time distibuted contol netwok, CAN esponds to this demand with the CAN FD potocol which povides impoved bandwidth and payload capacities. CAN FD povides pefomance impovements mainly in two ways: fistly, by inceasing the bit-ate in the data-phase of the fame, which esults in faste message tansmission; secondly, by inceasing the payload size, which povides bette payload to ovehead atio. In a contol netwok, it is cucial to meet the citical timing equiements of had eal-time tasks. Simulating a eal-time system is an impotant pocess to investigate the timing behaviou and analyse the pefomance of system. This study povides the pefomance analysis of a CAN FD system with SAE Benchmak based message set, compised of both timetiggeed and event-tiggeed messages. In ode to investigate the pefomance impovements, the models fo both CAN and CAN-FD systems have been developed in Matlab Simulink envionment. The message delay and bus utilisation esults obtained with the simulation models show that the CAN-FD potocol povides high pefomance impovements to meet the equiements of eal-time contol systems. Intoduction Contolle Aea Netwok (CAN) is an asynchonous seial communication bus initially intoduced fo in-vehicle communication applications. Due to its low cost and obust potocol stuctue it has also become a widespead fieldbus in industial applications. CAN applies a pioity based medium access method which guaanties immediate bus access to the bus fo the highest pioity messages. Howeve, the lowe pioity messages may expeience extensive bus access delays especially unde heavy bus load and low tansmission bit-ate conditions. Inceasing amount of Electonic Contol Units (ECUs) and message taffic equie highe tansmission speeds in the netwok. Howeve, the CAN potocol limits the message tansmission speed to 1 Mbps at maximum 40 m bus length due to its pioity based abitation mechanism and acknowledgement method [1]. The potocols like Time Tiggeed Potocol (TTP) [2] and Flexay [3] use highe tansmission speeds in ode to meet the eal-time communication equiements. In ode to meet the demand fo highe tansmission speed in CAN, the CAN FD potocol has been developed [4][5]. CAN FD impoves the potocol capabilities by using highe bit-ates to tansmit the payload and, by inceasing the payload size. In this way, CAN FD povides inceased bandwidth capacity and bette data to ovehead atio. CAN FD uses the existing CAN envionment without equiing significant changes in hadwae and softwae stuctue in ode to povide a smooth tansition fom CAN to CAN FD. It is an impotant subject to model and simulate a system in ode to evaluate its behaviou and pefomance. In this study, a CAN FD system with the SAE benchmak based message set is modelled and simulated. In ode to compae the pefomance impovements, a CAN model with the same message set has also been developed. The simulation esults ae investigated to evaluate the pefomance impovements achieved by CAN FD. The esults show that CAN FD povides consideably impoved pefomance esults 07-12

2 fo the system in ode to meet eal-time equiements. CAN and CAN FD oveview CAN basics CAN is a pominent eal-time netwok technology in automotive and industial applications. The potocol has standad CAN and extended CAN fame fomats, which have 11 bit and 29 bit identifies espectively. In this study, the standad CAN potocol is used in simulation models. Figue 1 shows the standad CAN message fame. The CAN potocol applies a medium access method known as CSMA/CA with non-destuctive bit-wise abitation. In this mechanism, evey message has an identifie which also indicates the pioity of the message. In case of two o moe messages stating tansmission at the same time, the abitation mechanism ensues that the highest pioity message has the immediate access, and the lowe pioity messages ae tansmitted late accoding to thei pioities. This method povides immediate access fo the highest pioity messages, howeve the lowe pioity messages may expeience long delays. The esponse time fo message m m is whee Jm is the queuing jitte, the latest queuing time of message mm on the host CPU. Wm includes the queuing delay due to the highe pioity messages and the blocking time due to a lowe pioity message that has aleady taken the bus since the potocol is non-peemptive. Cm is the time taken to tansmit message mm on the bus [6][7][8]. The CAN potocol is subject to bit stuffing in ode to keep synchonisation duing message tansmission. Accoding to bitstuffing ule, afte the tansmission of evey five bits with the same polaity, a bit with the opposite polaity is inseted. Theefoe, the message tansmission time (Cm) with wostcase bit stuffing fo a standad CAN fame is 47 is the fixed fom size of a CAN fame excluding the payload. (34 +8s m )/4 is the floo opeato giving the stuff bit numbe fo the payload and the 34-bit pat of fixed fom field of the fame that is subject to bit stuffing, and τα is the bus bit-time [6]. The inceasing amount of ECUs and message taffic make it necessay fo the CAN potocol to use highe tansmission bit-ates in ode to meet the eal-time application equiements. Howeve, the tansmission speed is limited to 1 Mbps fo the CAN potocol. CAN FD basics In ode to povide highe tansmission speeds to solve the bandwidth poblem in CAN, the CAN FD potocol has been intoduced [4][5]. The CAN FD potocol impoves the system pefomance in two ways: fistly, by using highe bit-ates to tansmit the payload, and secondly, by inceasing the payload size up to 64 bytes. The bus speed is limited fo the CAN potocol since the bit-wise abitation mechanism and acknowledgement method do not allow highe tansmission bit-ates on the bus. Howeve, the payload can be tansmitted with highe bit-ates in ode to achieve highe tansmission speeds. Theefoe, the CAN FD potocol divides the message fame into two phases as the Abitationphase and the Data-phase. Figue 2 shows the stuctue of a message fame with 11-bit identifie. The abitation phase of the message is tansmitted with standad CAN bit-ate fom the Stat Of Fame (SOF) bit to the Bit-Rate Switch bit (BRS). The tansmission speed is switched to the highe data-phase bit-ate at the sample point of BRS bit on sampling a ecessive level. At the sample point of CRC delimite, the bus speed is switched back to the abitation-phase bit-ate. The Extended Data Length (EDL) bit indicates that the fame is in the CAN FD fomat. whee sm is the payload size in bytes

3 S O F Abitation Field 11-bit Identifie R T R I D E Contol Field 6-bit 0 Data Field CRC Field DLC 0-8 Bytes 15-bit ACK Field EOF IFS 1b 1b 1b 7-bit 3-bit Figue 1: Standad CAN message fame. S O F Abitation Field 11-bit Identifie 1 I ACK Contol Field Data Field CRC Field Field EOF IFS 9-bit E D L B R S E SI D E 0 DLC 0-64 Bytes bits 1b 1b 1b 7-bit 3-bit Abitation Phase Data Phase Abitation Phase S O F 11-bit Identifie 1 I E D D E L 0 B RS 1b 1b 7-bit 3-bit Abitation Phase Data Phase Figue 2: CAN FD message fame. Abitation Phase The bit stuffing pocess is also applied in CAN FD potocol with mino changes. In the CRC field, fixed stuff bits ae used in ode to impove the eo detection capability of the potocol [4][9]. In CAN FD, CRC field is 17 bits plus 4 fixed stuff bits fo payload sizes up to 16 bytes, and 21 bits plus 5 fixed stuff bits fo payload sizes lage than 16 bytes. Theefoe, the message tansmission time with wost-case bit-stuffing [10] can be witten as whee s ab is the numbe of bits subject to bit-stuffing in the fist abitation-phase, whee the second abitation phase is not subject to bit stuffing. The total numbe of bits in the abitation-phase is 29, including the BRS bit and excluding the CRC delimite bit. τ α is the abitation-phase bit-time. The data-phase, excluding the payload, is 28 bits in length, which compises 27 bits of a CAN FD fame plus 1 stuff bit that may be inseted due to the BRS, ESI, and DLC bits. sm is the payload size in bytes. τ α is the data-phase bit-time. The EDL, 0, and BRS bits contain 1, 0, and 1, espectively, emaining 13 bits fo bit stuffing in the field befoe the fist bit-ate switch [10]. In the wost-case bit stuffing, the s ab /4 opeato can poduce 3 stuff bits, esulting in 32 bits. Theefoe, the equation can be simplified as Although the bit stuffing pocess inceases message size and consequently message tansmission time, it is necessay in ode to keep synchonisation duing tansmission. Thee ae some studies suggesting solutions to decease the effect of bit stuffing such us in [11]. Modelling and Simulation In ode to investigate the system pefomance impovements with the CAN FD potocol, the CAN and CAN FD models with the SAE benchmak based message set have been developed. The SAE benchmak message set oiginally includes 53 signals. In [6], the signals have been piggybacked and the set includes 17 messages. Table 1 shows the SAE benchmak based message set. The set includes piggybacked messages of the SAE benchmak, compised of both peiodic and spoadic messages [6]. Message M1 and M11 ae event-tiggeed, and messages fom M7 to M10 includes event-tiggeed signals piggybacked and tansmitted peiodically

4 CAN / CAN FD Bus Figue 3: Simplified epesentation of the simulation model. Messages fom M2 to M6, and fom M12 to M17 ae time-tiggeed messages. In the table, the messages ae placed in pioity ode fom the highest (M1) to the lowest (M17). T indicates the message peiod, while D indicates the deadline in milliseconds [6]. Table 1: SAE benchmak based message set. Message Size (bytes) T (ms) D (ms) M M M M M M M M M M M M M M M M M In the model development pocess, the SimEvents toolbox of Matlab Simulink softwae package has been used. Fist, a CAN model has been developed in ode to investigate the pefomance of the standad CAN potocol with the SAE based benchmak messages. Then, a CAN FD model has been developed in ode to compae the esults and evaluate the pefomance impovements achieved with the CAN FD potocol. In the modelling pocess, 11 bit identifie size of standad CAN potocol has been used. Figue 3 shows the simplified epesentation of the simulation model developed fo CAN and CAN FD systems. In the simulation model, one node is assigned fo each message. In ode to investigate the system pefomances, the models have been simulated at 1 Mbps, 500 kbps, 250 kbps, and 125 kbps tansmission bit-ates. In CAN FD, 5 Mbps is used as the data-phase tansmission bit-ate. Pefomance analysis In ode to evaluate the pefomance esults and compae the pefomance impovements achieved with the CAN FD potocol, both CAN and CAN FD models have been simulated at fou diffeent tansmission speeds. The esults fo wostcase and aveage message delays have been analysed and visualised in gaphs. As an impotant pefomance paamete, the bus utilisation esults have also been analysed. Wost-case message delay analysis The wost-case message delay o esponse time analysis is impotant in eal-time systems since it indicates the pefomance of the system to meet the deadline citeia. Figues fom 4 to 7 show the wost-case message delay gaphs fo 1 Mbps, 500 kbps, 250 kbps, and 125 kbps bus tansmission bit-ates. The gaph CAN max efeence epesents the message delay values given in [6]. These values ae used as a efeence to evaluate the esults obtained in simulations. The gaph CAN max epesents the wost-case delay values fo the CAN model

5 The gaph CAN FD max epesents the wost-case delay values fo the CAN FD model. The delays ae shown in the gaphs in message pioity ode fom the highest (M1) to the lowest (M17). As can be seen fom the figues, CAN wostcase delay values obtained with simulation show discepancies fom the CAN efeence delay values. This is because the wost-case delay is vey ae in simulations, wheeas the efeence values ae obtained by analysis. The study in [12] pesents the evaluation and compaison of esults obtained by simulation and analysis. Howeve, at lowe tansmission bit-ates, the simulation and efeence esults pesent close delay values since at lowe tansmission speeds it is moe likely that the messages expeience the wost-case delays. Fom the gaphs, it can be seen that the CAN FD model povides consideable wost-case message delay pefomance impovement fo the system. This impovement is achieved due to the highe tansmission speed used in dataphase of the message fame. In ode to investigate the pefomance impovement in moe detail, the wostcase delay atio of each message in CAN to CAN FD is computed, and the message delay atios ae pesented in Table 2 as aveage, minimum, and maximum. The delay atios ae investigated at fou diffeent tansmission bit-ates. At 1 Mbps bit-ate, the aveage atio is 1.78, that is, the wost-case message delay with CAN FD is 1.78 times smalle on aveage than it is with CAN. The aveage atio at 500 kbps is 2, which means CAN FD has half wost-case message delay of CAN on aveage. The atio is 2.16 and 3.28 at 250 kbps and 125 kbps bit ates, espectively. These atios show the aveage wost-case message delay impovement achieved with the CAN FD potocol. The table also gives the minimum and maximum wost-case message delay atios. The minimum atio anges fom 1.66 to 2.5, while the maximum atio anges fom 1.98 to 6.00, which means CAN FD tansmits messages up to 6 times smalle wost-case message delays with the SAE benchmak based message set. Figue 4: Wost-case delays at 1 Mbps Figue 5: Wost-case delays at 500 kbps Figue 6: Wost-case delays at 250 kbps Figue 7: Wost-case delays at 125 kbps 07-16

6 Table 2: Wost-case message delay atios CAN /CAN FD Mbps Mbps Mbps Mbps Aveage Minimum Maximum Aveage message delay analysis Figues fom 8 to 11 show the aveage message delay values fo CAN and CAN FD models at fou diffeent bus bit-ates. As can be seen fom the figues, the dominant facto affecting the CAN aveage delay is the message tansmission time at 1 Mbps ant 500 kbps bus bit-ates. At 250 kbps bus bit-ate, the effect of abitation delay becomes noticeable in CAN as the lowe pioity messages expeience ising delays due to the inceased bus utilisation. At 125 kbps bus bit-ate, the effect of the abitation delay becomes vey obvious in CAN as the lowe pioity messages expeience vey high message delays. Howeve, the aveage message delays in CAN FD ae mostly affected by the tansmission time and only little effect of the abitation delay can be obseved at almost all bus bit-ates. The highest message tansmission time in CAN is obseved with message 7 as it has the lagest payload size in the message set, and the effect of payload diffeence is noticeable. Howeve, the payload size diffeence is not vey noticeable in CAN FD. This shows the pefomance impovement achieved with CAN FD due to the application of highe tansmission bit-ate in the data-phase of the message fame. This application povides enough bandwidth fo message tansmissions with lowe delays even at low abitation-phase bit ates. As can be seen fom the figues, even at 125 kbps, CAN FD aveage message delays ae compaatively much smalle than CAN delays, which become extensively high especially with lowe pioity messages. In ode to analyse pefomance impovements in moe detail, the atios also fo the aveage message delays have been computed and listed in Table 3 as aveage, minimum and maximum. Figue 8: Aveage delays at 1Mbps Figue 9: Aveage delays at 500 kbps Figue 10: Aveage delays at 250 kbps Figue 11: Aveage delays at 125 kbps 07-17

7 Table 3: Aveage message delay atios CAN /CAN FD Mbps Mbps Mbps Mbps Aveage Minimum Maximum At 1 Mbps tansmission bit-ate, mean message delay is 1.67 times smalle on aveage in CAN FD than it is in CAN. The aveage atio fo bit-ates fom 1 Mbps to 125 kbps anges fom 1.67 to 4.16, which means up to 4.16 times smalle aveage message delays ae achieved on aveage with CAN FD. The minimum atio anges fom 1.53 to 2.16, and the maximum atio anges fom 2.17 to 6.00, which means, as in wost-case delay atios, up to 6 times smalle aveage message delays ae achieved with CAN FD. Bus utilisation analysis Figue 12: Bus utilisation. Figue 12 shows the bus utilisation values fo CAN efeence, CAN, and CAN FD. Fom the figue, it can be seen that the CAN efeence and CAN gaphs show almost the same chaacteistics. The CAN FD gaph shows that the same message set is tansmitted with less bus utilisation with CAN FD. Bus utilisation affects the system pefomance. As the utilisation becomes highe, the delay caused by the abitation mechanism also gets highe. At high bus utilisation values, especially lowe pioity messages expeience extensive bus access delays as they have to wait fo the highe pioity messages to be tansmitted fist. This effect can be seen clealy at 125 kbps bus bit-ate, whee the bus utilisation is ove 80%. Howeve, the bus utilisation with CAN FD at the same bit-ate is just ove 40%, which is almost half that of CAN. The simulated bus utilisation values at bus bitates fom 1 Mbps to 125 kbps anges fom 10.3 to 82.5 fo CAN, and fom 6.7 to 43.8 fo CAN FD, espectively. The esults show that compaed to CAN, CAN FD povides faste message tansmission with less bus utilisation. Conclusion As the amount of ECUs and message taffic in automotive and industial applications incease, the moe need aises fo highe bandwidth and faste message tansmission. The CAN FD potocol povides a solution fo bit-ate limitation in CAN using highe tansmission bit-ates in data-phase of the message fame. In this study, modelling and simulation of the CAN and CAN FD systems with the SAE benchmak based message set have been ealised in ode to investigate the pefomance impovements achieved by the CAN FD potocol. The pefomance analysis have been ealised fo wostcase message delays, aveage message delays, and bus utilisations. The wost-case message delay analysis has shown that with the CAN FD model based on the SAE benchmak message set, fom 1.78 to 3.28 times smalle wost-case message delays on aveage can be achieved compaed to the CAN model. Similaly, fom 1.67 to 4.16 times smalle mean message delays on aveage has been obseved with CAN FD. In bus utilisation esults, almost half the bus utilisation values have been obseved with CAN FD. The simulation esults have evealed that the CAN FD potocol povides consideable pefomance impovements in message tansmission speed and bus utilisation compaed to CAN

8 Acknowledgement: This wok was suppoted by The Scientific and Technological Reseach Council of Tukey (TUBITAK). Mahmut Tenuh Mugla S. K. Univesity Depatment of Electical & Electonics Engineeing TR Mugla Panagiotis Oikonomidis Univesity of Bighton Vetonics Reseach Cente (VRC) Lewes Road GB-BN2 4GJ Bighton Peiklis Chachalakis Univesity of Bighton Vetonics Reseach Cente (VRC) Lewes Road GB-BN2 4GJ Bighton Elias Stipidis Univesity of Bighton Vetonics Reseach Cente (VRC) Lewes Road GB-BN2 4GJ Bighton Refeences [1] CAN Specification, Vesion 2.0, Robet Bosch GmbH, [2] H. Baue and G. Kopetz, The timetiggeed achitectue, Poc. IEEE, vol. 91, no. 1, pp , [3] FlexRay Communications System Potocol Specification, Vesion 3.0.1, the FlexRay Consotium, [4] F. Hatwich, CAN with flexible data-ate, in 13th Int. CAN Conf., 2012, pp [5] CAN with Flexible Data-Rate, specification vesion 1.0, Robet Bosch GmbH, [6] K. Tindell and A. Buns, Guaanteeing Message Latencies on Contol Aea Netwok (CAN), in 1st Int. CAN Conf., 1994, pp [7] K. W. Tindell, A. Buns, and A. J. Wellings, Calculating Contolle Aea Netwok (CAN) message esponse times, Contol Eng. Pact., vol. 3, no. 8, pp , [8] R. I. Davis, A. Buns, R. J. Bil, and J. J. Lukkien, Contolle aea netwok (CAN) schedulability analysis: Refuted, evisited and evised, Real-Time Syst., vol. 35, no. 3, pp , [9] A. Mutte, CAN FD and the CRC issue, CAN Newslette, no. 1, pp. 4 10, [10] U. D. Bodoloi and S. Samii, The Fame Packing Poblem fo CAN-FD, in 2014 IEEE Real-Time Systems Symposium, 2014, pp [11] G. Cena, I. C. Betolotti, T. Hu, and A. Valenzano, Fixed-length payload encoding fo low-jitte contolle aea netwok communication, IEEE Tans. Ind. Inf., vol. 9, no. 4, pp , [12] N. Navet, CAN in Automotive Applications: a Look Fowad, in 13 th Int. CAN Conf.,