JP2010081152A - Communication device, communication system, communication method, and can node - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid unnecessary bus-off, in a CAN (Controller Area Network) system. <P>SOLUTION: In a CAN controller of each node connected to a CAN bus, an error state control part controls whether a current error state continues or shifts from the current error state to another error state by using count values of a reception error counter and a transmission error counter as determination conditions. When the current error state is in an error active state and the determination conditions cause the error state control part to continue the error active state, a transmission timing control part controls a transmission interval so that a minimum transmission interval is set longer than that specified for the error active state when the count value of the reception error counter reaches a predetermined value or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a communication technique in a CAN (Controller Area Network) system.

  A variety of electronic control systems such as engine ignition timing control, gearboxes, and ABS (Anti-Block System) are installed in recent automobiles. There are problems such as an increase in the number of wires and duplication of sensors as the number of installed systems increases. Further, as a result of pursuing higher performance, it becomes necessary to control these systems in an integrated or coordinated manner.

  In order to perform integration or coordinated control, it is necessary to perform data communication between the systems. CAN (Controller Area Network) is a communication protocol developed for this purpose, and is used not only in automobiles but also in a wide range of fields such as ships and medical devices. Here, the CAN protocol will be briefly described.

  FIG. 9 is a schematic diagram illustrating a connection example of a CAN system. As shown in FIG. 9, the CAN system 10 includes a plurality of CAN nodes (hereinafter simply referred to as nodes) 12 connected by a CAN bus 14. The CAN bus 14 is composed of two wires (wire 16 and wire 18), and a CAN controller (not shown) at each node determines the level of the bus based on the potential difference between the two wires of the CAN bus 14. . The sending node 12 can send a message to another node 12 by changing this level.

  When the CAN bus 14 is free except for a node in a bus-off state, which will be described later, all nodes 12 connected to the CAN bus 14 can start transmitting messages. The node that started transmission gets the transmission right. When a plurality of nodes start transmission at the same time, the node that transmits the message with the highest priority obtains the transmission right. The priority order will be described together with the frame structure defined by the CAN protocol.

  The CAN protocol defines five types of frames: a data frame, a remote frame, an error frame, an overload frame, and an inter frame space. The data frame is a frame for sending a message from the transmitting node (transmitting node) to the receiving node (receiving node), and the remote frame is a frame for requesting a message having the same priority to the transmitting node. is there. The error frame is a frame for notifying other nodes of an error when an error is detected, and the overload frame is a frame for notifying the reception node that reception preparation is not completed, and is an interframe space. Is a frame for separating the data frame and the remote frame from the previous frame. Here, the format of the data frame will be described as an example.

  FIG. 10 shows a standard format of a data frame defined by the CAN protocol. As shown, the CAN data frame includes a plurality of fields. “SOF” and “EOF” are fields indicating the start and end of a frame, respectively. The “arbitration field” is a field indicating the priority order of frames, and indicates the priority order and stores an identification ID. When a plurality of nodes start transmission at the same time, arbitration is performed based on the ID of each transmitted data frame. As a result of the arbitration, the node that transmits the data frame having the ID with the highest priority continues transmitting as it is, and the other nodes immediately stop transmitting and proceed to the receiving operation. The control field is a field indicating the reserved bits and the number of bytes of data, and the data field is the content of the message. The CRC field is a field for checking a frame transmission error, and the ACK field is a field indicating a signal for confirmation of normal reception.

  Each node 12 includes a transmission error counter and a reception error counter that count transmission errors and reception errors, respectively. Refer to the CAN protocol standard for the timing and number of counts up and down of the transmission error counter and the reception error counter. In general, the transmission error counter counts up when a transmission error is detected, and transmission can be performed normally. Sometimes it counts down. Similarly, the reception error counter counts up when a reception error is detected, and counts down when normal reception is possible.

  Each node transitions between three error states of an error active state, an error passive state, and a bus off state according to the count value (REC) of the reception error counter and the count value (TEC) of the transmission error counter. The error active state is a state in which communication on the bus can be normally joined, and the error passive state is a state in which an error is more likely to occur than the error active state. Nodes in the error passive state are more restricted during transmission than nodes in the error active state. The bus off state is a state in which an error is more likely to occur than the error passive state, and a node in this state is prohibited from performing all transmission and reception operations and cannot participate in communication on the bus. Here, the difference between the error active state and the error passive state will be described with emphasis on the transmission interval.

In the CAN system, except for the node in the bus off state, all the nodes other than the node that has transmitted the frame currently flowing on the CAN bus receive this frame. In the CAN protocol, a shortest period from the end of transmission of a frame flowing on the CAN bus to the transmission of the next frame is provided, and transmission from any node is not possible during this period. In this specification, the period from the end of transmission of a frame currently flowing on the CAN bus to the start of transmission of the next frame is referred to as “transmission interval”, and the shortest transmission interval defined by the CAN protocol is referred to as “minimum transmission interval”. "
For the error active state, an intermission period is defined as the minimum transmission interval for both continuous transmission and non-continuous transmission. “Continuous transmission” means that the node that has transmitted the frame that currently flows on the CAN bus continues to transmit, and “non-continuous transmission” means that a node other than the node that has transmitted the frame currently flowing on the CAN bus Means to send.
The intermission period is usually 3 bits, hereinafter referred to as the first interval. A node in this state can transmit at any reception side or transmission side of the current frame after a 3-bit intermission period from the end of transmission of the frame. When a node in this state detects an error, it outputs an active error flag to notify the other nodes of the error.

For the error passive state, a minimum transmission interval that differs depending on whether the transmission is discontinuous or continuous is defined. In the case of non-continuous transmission, the minimum transmission interval is defined as a 3-bit intermission period as in the error active state. On the other hand, in the case of continuous transmission, there is a restriction to place a suspend transmission period after the intermission period. The suspend transmission period is usually 8 bits. That is, in the case of continuous transmission, an 11-bit minimum transmission interval that combines the intermission period and the suspend mission period is defined. Hereinafter, the minimum transmission interval of 11 bits is referred to as a second interval.
Therefore, if the node in the error passive state is the receiving side of the frame currently flowing on the CAN bus, it can transmit if the first interval of 3 bits has passed since the end of transmission of the frame. If it is the transmission side of the frame, transmission cannot be performed unless the second interval of 11 bits elapses from the transmission end time of the frame.
In addition, there is a restriction that active error notification is not performed for the error passive state. For example, when a node in the error passive state detects an error, the error is notified by outputting a passive error flag, but if no other error active node detects an error, the entire bus is It is determined that there were no errors.

  The above three error state transitions are made based on the count values of the transmission error counter and the reception error counter. As shown in FIG. 11, when the count value TEC of the transmission error counter and the count value REC of the reception error counter are both 0 to 127, the node is in an error active state, and either TEC or REC is 128 to If it is 255, the node is in an error passive state. Regardless of the REC, when the TEC becomes 256 or more, the node enters the bus off state and is disconnected from the communication on the CAN bus.

  In this way, in the CAN, an error state corresponding to the degree that an error is likely to occur is specified, and a restriction according to the error state is added to the transmission / reception operation of the node, thereby preventing communication by the node that is likely to cause an error. To avoid.

  In recent years, the amount of traffic on the CAN system has been increasing, and if bus-off frequently occurs, communication with the node is interrupted until recovery, and the efficiency of the entire system decreases. Therefore, it is desirable to avoid unnecessary bus-off as much as possible.

  Errors in the CAN system include errors due to noise and other disturbances, and errors due to internal node failures, driver failures, disconnection failures, and the like. A bus off due to an error caused by a disturbance corresponds to an unnecessary bus off.

Patent Document 1 discloses a method of determining whether a disturbance or a node failure. This method monitors whether or not the state of a node that has become error passive continues for a predetermined time. When the error passive state continues for a predetermined time, it is determined that the node is faulty.
JP 2004-348274 A

  Patent Document 1 does not disclose a measure after determining whether or not a node has failed. For example, when it is determined that a node is not failed by the method of Patent Document 1, the node is in a bus-off state. It is conceivable to prevent transition and avoid unnecessary bus off.

  By the way, in the CAN protocol, the transmission error counter of the node is incremented by “8” when a transmission error occurs, but is decremented by “1” when transmission is successful. That is, a node in the error passive state cannot make a transition from the error passive state to the error active state unless transmission is successful a considerable number of times. For example, when a node has a TEC of 250 and has a high possibility of transitioning to a bus-off state, that is, in a state where the bus-off risk is high, if a transmission succeeds many times in succession, the bus-off risk is increased. Although it can be avoided, even if a transmission error occurs only once due to disturbance, the TEC becomes 258 and the bus is turned off.

  However, as described above, in the CAN protocol, the first in the case of non-continuous transmission to a node in an error passive state in order to reduce interference with other nodes by a failed node. On the other hand, in the case of continuous transmission, it is specified that the second interval is set rather than the first interval. That is, the node in the error passive state is delayed in transmission timing as compared with the other nodes performing continuous transmission in the error active state regardless of the priority order indicated by the ID. In this case, a node whose bus-off risk has increased has a small chance of avoiding the bus-off by increasing the number of times of normal transmission even though the node itself has no failure. In this case, according to the method of Patent Document 1, it is determined that the node has a failure, and unnecessary bus-off occurs.

  One aspect of the present invention is a communication device connected to a CAN (Controller Area Network) bus and capable of transitioning between a plurality of error states. The communication apparatus includes a reception error counter, a transmission error counter, an error state control unit, and a transmission interval control unit.

  The error state control unit controls whether the current error state continues or transitions from the current error state to another error state using the count values of the reception error counter and the transmission error counter as determination conditions.

The transmission interval control unit controls the error state control unit so that the current error state is an error active state included in the plurality of error states, and the determination condition continues the error active state. In some cases, the transmission is performed so that the minimum transmission interval is longer than the minimum transmission interval specified for the error active state, on condition that the count value of the reception error counter is equal to or greater than the predetermined value. Control the interval.
Another aspect of the present invention includes a transmission error counter that counts the number of occurrences of a transmission error and a reception error counter that counts the number of occurrences of a reception error, and the count value of the transmission error counter or the reception error counter is a first reference When a value larger than the value is indicated, if the frame flowing on the CAN bus is output from another node, frame transmission from the own node starts after the first period has elapsed since the transmission of the frame was completed. If the frame flowing on the CAN bus is output from the own node, frame transmission from the own node is started after a lapse of a second period longer than the first period from the end of transmission of the frame. It is a CAN node. In this CAN node, the count value of the transmission counter is less than or equal to the first reference value, and the count value of the reception counter is less than or equal to the first reference value and indicates a value greater than or equal to the second reference value that is smaller than the first reference value. First, frame transmission from the own node is started after the elapse of a third period, which is a period longer than the first period from the end of transmission of the frame flowing through the CAN bus.

  It is also effective as an aspect of the present invention that the communication apparatus and the CAN node in the above aspect are replaced with a method or a program that causes a computer to operate as the apparatus or the node. A system including a plurality of apparatuses or CAN nodes according to the above aspect is also effective as an aspect of the present invention.

  According to the technology of the present invention, unnecessary bus-off can be avoided and communication efficiency can be improved in a CAN system.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, each element described as a functional block for performing various processes in the drawings used in the following description can be configured with a processor, a memory, and other circuits in terms of hardware, and in terms of software It is realized by a program recorded in a memory or loaded. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof, and is not limited to any one. Further, for easy understanding, in these drawings, only those necessary for explaining the technique according to the present invention are shown.

  As a result of earnest research to avoid unnecessary bus-off risk in the CAN system, the present inventor has found that the count value REC of the reception error counter of one node and the height of the bus-off risk of another node. I found that there is a relationship. Regarding this, first, the fluctuation of the error count value in the CAN system will be described with reference to FIG.

  As shown in FIG. 1, the transmitting node increments the TEC by “8” in every case where the TEC should be incremented, and decrements the TEC by “1” if the transmission is successful. On the other hand, the receiving node may increment REC by “8”, but may increment REC by only “1” as indicated by “1” in FIG. Therefore, during the occurrence of disturbance, the increase in the TEC of the transmitting node tends to be faster than the increase in the REC of the receiving node, and the TEC increases greatly as the number of transmissions increases.

  The transmission node decrements the TEC by “1” once it can be normally transmitted, but continuously transmits the message if the message has accumulated due to the previous transmission failure. By the way, if the transmitting node is already in the error passive state, the minimum transmission interval at the time of continuous transmission is set longer than that of the node in the error active state. Therefore, before arbitration, the node loses to the node in the error active state and cannot transmit. This is increasing the risk of bus-off.

  On the other hand, as described above, during the disturbance occurrence period, the REC of the receiving node increases although the degree is smaller than the TEC of the transmitting node. That is, when the REC of the receiving node increases due to the occurrence of a disturbance, if there is a node with a large number of transmissions in the same CAN system, this node may increase the TEC and increase the bus-off risk.

The inventors of the present application pay attention to this and propose the following method. For a node in the error active state, even if the TEC and REC do not satisfy the condition for transitioning to the error passive state (TEC> 127 or REC> 127), the REC becomes a predetermined threshold value of 127 or less, for example, 120 or more. The minimum transmission interval of the node is controlled to be longer than the minimum transmission interval determined for the node in the error active state.
Therefore, according to the technique of the present invention, a node whose TEC is 127 or less and whose REC is smaller than the above threshold value has a minimum transmission interval in an error active state according to the CAN protocol in both cases of continuous transmission and non-continuous transmission. The first interval of 3 bits defined for the first interval. On the other hand, a node having a TEC of 127 or less and a REC of not less than the above threshold and 127 or less has a minimum transmission interval longer than the first transmission interval in both cases of continuous transmission and non-continuous transmission. In order to distinguish from the second transmission interval (11 bits), which is the minimum transmission interval at the time of continuous transmission defined by the CAN protocol for the error passive state, the minimum transmission interval in this case is hereinafter referred to as a third transmission interval. .
FIG. 2 shows a minimum transmission interval of a node in an error active state when the technique of the present invention is applied. For comparison, the minimum transmission interval of a node in an error passive state is also shown.
As shown in FIG. 2, the minimum transmission interval of the node in the error passive state is the second interval of 11 bits at the time of continuous transmission and the first interval of 3 bits at the time of non-continuous transmission as defined by the CAN protocol. is there.
The minimum transmission interval of the node in the error active state varies depending on the count value REC of the reception counter. Specifically, when REC is smaller than a predetermined threshold, the minimum transmission interval is the first interval of 3 bits in both cases of continuous transmission and non-continuous transmission as defined by the CAN protocol. On the other hand, when REC becomes equal to or greater than a predetermined threshold value, the minimum transmission interval is a third interval longer than the first interval of 3 bits in either continuous transmission or non-continuous transmission.

  In this way, except for the minimum transmission interval, while maintaining the error active state of the node in which the REC is equal to or greater than the threshold in the error active state, the number of transmissions is different from that node, and the bus off risk is caused by disturbance. It is possible to give the increased node many transmission opportunities based on arbitration based on the priority order, and it is possible to reduce the bus off risk of the node.

In addition, if the other node is not a disturbance and the risk of bus-off is increased due to its own problem, the node will cause many transmission errors, so the TEC will increase and it will go into the bus-off state sooner. The effect of transition is also obtained.
Here, the specific length of the third interval used in the technique of the present invention will be examined while comparing the case where the technique of the present invention is applied and the case where the technique of the present invention is not applied. An example is a case where there are a node A in an error passive state and a node B in an error active state, each having a transmission message and continuously transmitting. For simplicity, it is assumed that there are only node A and node B on the system. Further, in the following description and illustration, a frame transmitted by the node A and a frame transmitted by the node B are respectively represented by a “frame” attached with “A” and a “frame” attached with “B”. A frame transmitted after the priority adjustment is indicated by a dotted frame, and a frame transmitted without the priority adjustment is indicated by a solid rectangle.
FIG. 3 is a timing chart showing three patterns that can occur within a period in which three frames are transmitted after the end of transmission of the frame A0 from the node A when the present invention is not applied.
In this case, after the node A transmits the frame, the node B always obtains and transmits the transmission right of the next frame. Further, after node B transmits a frame, either node A or node B obtains the right to transmit the next frame through priority arbitration.
<Pattern 1>
Since node A is in the error passive state and the minimum interval during continuous transmission is the second interval (11 bits including the intermission period and the suspended transmission period), the first interval from the transmission end time (t0) of frame A0 is When the intermission period of the interval (3 bits) elapses (time point t1), the frame B1 is transmitted from the node B without passing through the priority order arbitration.
At the time t3 when the intermission period has passed from the transmission end time t2 of the frame B1, priority order arbitration for the node A and the node B to obtain the transmission right is performed.
Although both the node A and the node B may obtain the transmission right, in this pattern, the node A obtains the transmission right and transmits the frame A1.
At the time t5 when the intermission period has passed from the transmission end time t4 of the frame A1, the frame B2 is transmitted from the node B without passing through the priority order arbitration.
<Pattern 2>
At time t1, as in the case of pattern 1, frame B1 is transmitted from node B without passing through priority arbitration.
At the time t3, unlike the pattern 1, the node B obtains the transmission right through the priority order arbitration and transmits the frame B2.
Unlike the pattern 1, the node A and the node B perform priority arbitration at the time t5 when the intermission period has passed from the transmission end time t4 of the frame B2. In this pattern, the node A obtains the transmission right and transmits the frame A1.
<Pattern 3>
This is the same as pattern 2 up to the transmission end time t4 of frame B2. At the time t5, unlike the pattern 2, the node B obtains the transmission right and transmits the frame B3.
Thus, when node A transmits a frame, node B always obtains the right to transmit the next frame without passing through priority arbitration. After node B transmits a frame, either node A or node B obtains the right to transmit the next frame through priority arbitration. Therefore, the probability that node A can transmit is lower than that of node B.
In the case of the example illustrated in FIG. 3, the probability that the node A can transmit during the transmission of 3 frames from time t0 is 2/9.
FIG. 4 is a timing chart showing five patterns that can occur within a period in which three frames are transmitted after transmission of the frame A0 from the node A when the present invention is applied. In the technology of the present invention, when the count value REC of the reception counter of the node in the error active state is 127 or more, the minimum transmission interval of the node is set to a third interval longer than the 3-bit first interval. Therefore, FIG. 4 shows only the case where the REC of the node B is equal to or greater than the 127 threshold value. In the example of FIG. 4, the length of the third interval is set to the minimum interval for continuous transmission defined by the CAN protocol for the error passive state, that is, 11 bits of the third interval.
In this case, after node A transmits a frame, either node A or node B obtains the right to transmit the next frame through priority arbitration. In addition, after node B transmits a frame, node A always obtains the transmission right for the next frame and transmits it.
<Pattern 1>
Node A is in an error passive state, and the minimum transmission interval during continuous transmission is a second interval of 11 bits. In addition, although the node B is in an error active state, the minimum transmission interval becomes a third interval (here, 11 bits having the same length as the second interval) by applying the technique of the present invention. Therefore, at the time t1 when 11 bits have passed since the time t0, priority order arbitration is performed for the node A and the node to obtain a transmission right.
Although both the node A and the node B may obtain the transmission right, in this pattern, the node A obtains the transmission right and transmits the frame A1.
Similarly, at time point t4 when 11 bits have passed from the transmission end time point t2 of the frame A1, the node A obtains the transmission right and transmits the frame A2 through priority arbitration. In addition, at time t8 when 11 bits have passed since the transmission end time t6 of the frame A2, the node A obtains the transmission right and transmits the frame A3 through priority arbitration.
<Pattern 2>
This pattern is the same as pattern 1 up to the transmission end time t6 of frame A2.
At the time t8, unlike the case of the pattern 1, the node B obtains the transmission right and transmits the frame B1 through the priority order arbitration.
<Pattern 3>
This pattern is the same as pattern 1 until the transmission end time t2 of frame A1.
At the time t4, unlike the case of the pattern 1, the node B obtains the transmission right and transmits the frame B1 through the priority order arbitration.
At this time, in order to transmit the next frame, the node B needs to have a third interval of 11 bits from the transmission end time t6 of the frame B1. On the other hand, in order to transmit the frame next to the frame B1, the node A has to leave only the first 3-bit interval from the time point t6. Therefore, the frame A2 is transmitted from the node A without passing through the priority order arbitration at the time t7 when the first interval of 3 bits has passed from the transmission end time t6 of the frame B1.
<Pattern 4>
Node B obtains a transmission right through priority arbitration at time t1, and transmits frame B1.
At the time point t3 when the first interval of 3 bits has passed from the transmission end time point t2 of the frame B1, the frame A1 is transmitted from the node A without passing through the priority order arbitration.
At the time t7 when 11 bits have passed from the transmission end time t5 of the frame A1, priority order arbitration between the node A and the node B is performed. In this pattern, the node A obtains the transmission right and transmits the frame A2.
<Pattern 5>
This pattern is the same as the pattern 4 until the transmission end time t5 of the frame A1.
At the time t7, unlike the case of the pattern 4, the node B obtains the transmission right and transmits the frame B2 through the priority order arbitration.
Thus, after node A transmits a frame, either node A or node B obtains the right to transmit the next frame through priority arbitration. After node B transmits a frame, node A always obtains and transmits the next frame transmission right. Therefore, the probability that node A can transmit is higher than that of node B.
In the case of the example shown in FIG. 4, the probability that the node A can transmit during the transmission of 3 frames from time t0 is 2/3. This is a higher probability than in the case shown in FIG.
FIG. 5 is a timing chart showing patterns that can occur within a period in which three frames are transmitted after the transmission of the frame A0 from the node A when the present invention is applied, as in FIG. A difference from the case of FIG. 4 is that the length of the third interval is longer than the first interval of 3 bits and shorter than the second interval of 11 bits. In this example, the third interval is 6 bits.
In this case, there is one possible pattern as shown in FIG.
Node A is in an error passive state, and the minimum transmission interval during continuous transmission is a second interval of 11 bits. Although the node B is in an error active state, the minimum transmission interval becomes longer than the first interval and shorter than the second interval (here, 6 bits) by applying the technique of the present invention. Therefore, the frame B1 is transmitted from the node B without passing through the priority order arbitration at the time t1 when the third 6-bit interval has passed from the time t0.
When the node A transmits a frame after the frame B1, it is necessary to put 3 bits in the first interval. On the other hand, when transmitting a frame after the frame B1, the node B needs to put 6 bits in the third interval. Therefore, the frame A1 is transmitted from the node A without passing through the priority order arbitration at the time t3 when 3 bits have passed from the transmission end time t2 of the frame B1.
Then, at time point t5 when 6 bits of the third interval have passed since the transmission end time point t4 of the frame A1, the frame B2 is transmitted from the node B without passing through priority order arbitration.
That is, after node A transmits a frame, node B always obtains and transmits the transmission right for the next frame. In addition, after node B transmits a frame, node A always obtains the right to transmit the next frame. In the case of the example shown in FIG. 5, the probability that node A can transmit during the transmission of 3 frames from time t0 is 1/3. This is also a higher probability than in the case shown in FIG.
Although not shown, when the third interval is longer than 11 bits of the second interval, the probability that node A can transmit is 100%, and node B cannot transmit while node A continuously transmits. .
As described above, when the count value REC of the reception counter of the node B in the error active state is equal to or larger than the predetermined threshold, the minimum transmission interval of the node becomes a third interval longer than the first interval of 3 bits, Node A in the error passive state has a higher probability of transmission. Therefore, if the bus A risk increases due to disturbance, the node A can avoid the bus OFF risk by increasing the number of transmissions. This is an effect obtained even when the third interval is shorter than the minimum transmission interval (second interval of 11 bits) at the time of continuous transmission specified for the error passive state.
The longer the third interval, the higher the probability that node A can transmit. By the way, when the third interval is longer than the minimum transmission interval (second interval of 11 bits) at the time of continuous transmission defined for the error passive state, while node A is continuously transmitting, node B Cannot transmit at all even though it is in the error active state. This has a large impact on the system.
When the third interval is 11 bits having the same length as the second interval, the probability that the node A can transmit is higher than when the third interval is smaller than the second interval. Since priority order arbitration with the node B is performed, there is a possibility of transmission to the node B as well. By doing so, it is possible to suppress the influence on the system while exhibiting the effects of the technology of the present invention. Therefore, when applying the technique of the present invention, it is preferable to make the third interval the same length as the second interval.
Based on the above description, embodiments of the present invention will be described.

  FIG. 6 shows a CAN system 100 according to an embodiment of the present invention. The CAN system 100 conforms to the CAN protocol, and a plurality of CAN nodes (hereinafter simply referred to as nodes) 120 are connected by a CAN bus 110.

  FIG. 7 shows the node 120 in the CAN system 100 shown in FIG. The node 120 includes a transceiver 122, a CPU 124, a peripheral chip 126, and a CAN controller 130. The CPU 124, the peripheral chip 126, and the CAN controller 130 are connected by a local bus 128.

  The transceiver 122 is connected to the CAN bus 110, receives a frame on the CAN bus 110, transfers the frame to the CAN controller 130, and outputs a frame transmitted from the CAN controller 130 to the CAN bus 110. All transmission / reception between the node 120 and the CAN bus 110 is performed through the transceiver 122.

  The CAN controller 130 includes a bit stream control unit 132, an error state control unit 134, a reception error counter 136, a transmission error counter 138, a transmission timing control unit 140, a message handler 150, and a message buffer 152. The message buffer 152 further includes a reception buffer 154 and a transmission buffer 156.

  The bit stream control unit 132 has a function of detecting whether or not an error has occurred in communication (transmission / reception). When a communication error occurs, the bit stream control unit 132 notifies the error state control unit 134 to that effect. The bit stream control unit 132 also notifies the error state control unit 134 to the effect when the communication is normally completed. Further, the bit stream control unit 132 outputs an EOF signal indicating reception completion to the transmission timing control unit 140 when reception is completed and an EOF signal indicating transmission completion when the transmission is completed. Further, the bit stream control unit 132 transfers the received frame (reception frame) to the message handler 150 and sends the frame (transmission frame) from the message handler 150 to the CAN bus 110 via the transceiver 122. Note that the timing at which the bit stream control unit 132 sends the frame to the CAN bus 110 is controlled by the transmission timing control unit 140.

  The message handler 150 is connected between the bit stream control unit 132 and the message buffer 152, stores the received frame transferred from the bit stream control unit 132 in the reception buffer 154 in the message buffer 152, and stores the received frame stored in the transmission buffer 156. The transmission frame for transmission is output to the CAN controller 130. The reception frame stored in the reception buffer 154 is provided to the CPU 124 and the peripheral chip 126 later via the local bus 128. The untransmitted transmission frame stored in the transmission buffer 156 is received from the CPU 124 or the peripheral chip 126 via the local bus 128.

  The error state control unit 134 controls count-up or count-down of the reception error counter 136 and the transmission error counter 138 based on the signal received from the bitstream control unit 132. Specifically, when a reception error notification signal is received from the bitstream control unit 132, a signal to be incremented is output to the reception error counter 136, and when a transmission error notification is received, a signal to be incremented is output to the transmission error counter 138. To do. Further, when a signal that has been successfully received from the bit stream control unit 132 is received, a signal that is decremented to the reception error counter 136 is output, and when a signal that has been successfully transmitted is received, a signal that is decremented to the transmission error counter 138 Is output.

  Further, the error state control unit 134 manages the error state of the node 120 based on the count value REC of the reception error counter 136 and the count value TEC of the transmission error counter 138. Specifically, as shown in FIG. 11, the error state of the node 120 is transitioned between an error active state, an error passive state, and a bus off state based on REC and TEC.

  The error state control unit 134 notifies the transmission timing control unit 140 of a signal indicating the current error state of the node 120 (error state notification signal). The reception error counter 136 also notifies the transmission timing control unit 140 of the current REC.

  The transmission timing control unit 140 controls the timing of transmission from the node 120, specifically, from the CAN controller 130 to the CAN bus 110. This control is based on the EOF signal from the bit stream control unit 132 and the error status. Based on the error state notification signal from the control unit 134 and the REC from the reception error counter 136.

  FIG. 8 shows a configuration example of the transmission timing control unit 140. The transmission timing control unit 140 includes a transmission timing timer 141, a suspend transmission timer 142, a comparator 143, an OR gate 144 with an inverting input, and a selector 145.

The transmission timing timer 141 includes an error state notification signal, an EOF signal indicating that normal transmission from the CAN controller 130 has ended (hereinafter referred to as “transmission EOF”), and an EOF signal indicating the completion of reception of a frame transmitted by another node (hereinafter referred to as “EOF signal”). Receive EOF) is input, and transmission timing defined by the CAN protocol is generated according to the error state indicated by the error state notification signal. Specifically, in the error active state, timing is started when the transmission EOF or the reception EOF is received, and when the first interval of 3 bits is reached, the first timing signal T1 is output to the selector 145. That is, at this time, the minimum transmission interval indicated by the first timing signal T1 is 3 bits in both cases of continuous transmission and non-continuous transmission.
In the error passive state, the minimum transmission interval indicated by the first timing signal T1 is 3 bits at the time of non-continuous transmission and 11 bits at the second interval at the time of continuous transmission.

The suspend transmission timer 142 starts timing when it receives either the transmission EOF or the reception EOF, and outputs the second timing signal T2 to the selector 145 when the third interval is reached. In the present embodiment, the third interval is 11 bits having the same length as the second interval.
That is, in any case of continuous transmission and non-continuous transmission, the minimum transmission interval indicated by the second timing signal T2 is 11 bits.

  The selector 145 selects either the first timing signal T <b> 1 or the second timing signal T <b> 2 as the transmission timing signal T based on the output S of the OR gate with inverting input, and outputs it to the bit stream control unit 132. Specifically, the first timing signal T1 is selected when the output S of the OR gate with inverting input 144 is High, and the second timing signal T2 when the output S of the OR gate with inverting input is Low. Select.

  The error state notification signal from the error state control unit 134 is input to the OR gate 144 with an inverting input, and the output S1 of the comparator 143 is inverted and input. In the present embodiment, the error state notification signal is low when the node 120 is in the error active state, and is high when the node 120 is in the error passive state.

  The comparator 143 compares the count value REC of the reception error counter 136 with a preset threshold value (for example, 120) smaller than the threshold value “127” for transition to the error passive state, and outputs a signal S1 indicating the comparison result. To do. The output S1 of the comparator 143 is Low when REC is smaller than the threshold, and is High when REC is equal to or larger than the threshold.

The operation of the transmission timing control unit 140 will be described together.
When the node 120 is in the error passive state, the output S of the OR gate 144 with the inverting input becomes High regardless of the output S1 of the comparator 143. Therefore, the first timing signal T1 is selected as the transmission timing signal T. Thereby, the minimum interval at the time of continuous transmission becomes 11 bits, and the minimum transmission interval at the time of non-continuous transmission becomes 3 bits.
When the node 120 is in the error active state and the output S1 of the comparator 143 is Low because REC is smaller than the threshold value, the output S of the OR gate 144 with an inverting input becomes High. Therefore, the first timing signal T1 is selected as the transmission timing signal T. As a result, the minimum transmission interval is 3 bits in both cases of continuous transmission and non-continuous transmission.
On the other hand, when the node 120 is in the error active state and the output S1 of the comparator 143 is High because REC is equal to or higher than the threshold, the output S of the OR gate 144 with an inverting input becomes Low. Therefore, the second timing signal T2 is selected as the transmission timing signal T. As a result, the minimum transmission interval is 11 bits in both cases of continuous transmission and non-continuous transmission.

  By doing so, if the REC exceeds a threshold value in the error active state, the minimum transmission interval of the node 120 becomes the same as the minimum transmission interval defined for the node in the error passive state. Therefore, in the CAN system 100, if there is a node in an error passive state with an increased bus-off risk, the node can perform transmission based on arbitration based on priority. Therefore, the node can get a chance to reduce the bus-off risk if the bus-off risk is increased due to disturbance, and if the bus-off risk is increased due to its own failure, the node transitions to the bus-off quickly. can do.

  The present invention has been described above based on the embodiment. The embodiment is an exemplification, and various changes and increases / decreases may be added without departing from the gist of the present invention. It will be understood by those skilled in the art that modifications to which these changes and increases / decreases are also within the scope of the present invention.

It is a figure which shows the fluctuation | variation of the transmission error counter defined by a CAN protocol, and a reception error counter. It is a figure which shows the minimum transmission space | interval at the time of applying the technique concerning this invention. It is a figure which shows the example of the frame transmission timing when not applying the technique concerning this invention. It is a figure which shows the example of the frame transmission timing at the time of applying the technique concerning this invention (the 1). It is a figure which shows the example of the frame transmission timing at the time of applying the technique concerning this invention (the 2). It is a figure which shows the CAN system concerning embodiment of this invention. It is a figure which shows the node in the CAN system shown in FIG. It is a figure which shows the transmission timing control part in the node shown in FIG. It is a figure which shows the example of a connection of a CAN system. It is a figure which shows the standard format of the data frame defined by the CAN protocol. It is a figure which shows the transition of the error state of the node in a CAN system, and the relationship between a reception error count value and a transmission error count value.

Explanation of symbols

10 CAN System 12 Node 14 CAN Bus 16 Wire 18 Wire 100 CAN System 110 CAN Bus 120 Node 122 Transceiver 124 CPU
126 Peripheral chip 128 Local bus 130 CAN controller 132 Bit stream control unit 134 Error state control unit 136 Reception error counter 138 Transmission error counter 140 Transmission timing control unit 141 Transmission timing timer 143 Suspended transmission timer 143 Comparator 144 OR gate with inverted input 145 selector 150 message handler 152 message buffer 154 reception buffer 156 transmission buffer S1 output of comparator 143 S2 error status signal S output of OR gate 144 with inverting input T transmission timing signal T1 first timing signal T2 second timing signal

Claims (13)

A communication device connected to a CAN (Controller Area Network) bus and capable of transitioning between a plurality of error states,
A reception error counter,
A transmission error counter,
An error state control unit that controls whether the current error state continues or transitions from the current error state to another error state based on the count values of the reception error counter and the transmission error counter as determination conditions;
When the current error state is an error active state included in the plurality of error states, and the determination condition is to cause the error state control unit to control the error active state to continue, the The transmission interval is controlled so that the minimum transmission interval becomes a predetermined length longer than the minimum transmission interval defined for the error active state on condition that the count value of the reception error counter becomes equal to or greater than the predetermined value. A communication apparatus comprising: a transmission interval control unit.   The communication apparatus according to claim 1, wherein the predetermined length is equal to or less than a length of a minimum transmission interval at the time of continuous transmission defined for an error passive state included in the plurality of error states.   The communication apparatus according to claim 2, wherein the predetermined length is a length of a minimum transmission interval at the time of continuous transmission defined for an error passive state. In a communication system in which a plurality of communication devices are connected by a CAN (Controller Area Network) bus,
Each of the communication devices that can transition between a plurality of error states,
A reception error counter,
A transmission error counter,
An error state control unit that controls whether the current error state continues or transitions from the current error state to another error state based on the count values of the reception error counter and the transmission error counter as determination conditions;
When the current error state is an error active state included in the plurality of error states, and the determination condition is to cause the error state control unit to control the error active state to continue, the The transmission interval is controlled so that the minimum transmission interval becomes a predetermined length longer than the minimum transmission interval defined for the error active state on condition that the count value of the reception error counter becomes equal to or greater than the predetermined value. A communication system comprising a transmission interval control unit.   5. The communication system according to claim 4, wherein the predetermined length is equal to or less than a length of a minimum transmission interval at the time of continuous transmission defined for an error passive state included in the plurality of error states.   5. The communication system according to claim 4, wherein the predetermined length is a length of a minimum transmission interval at the time of continuous transmission defined for an error passive state. For a communication device connected to a CAN (Controller Area Network) bus and capable of transitioning between a plurality of error states,
An error state that controls whether the current error state continues or transitions from the current error state to another error state based on the count values of the reception error counter and the transmission error counter provided in the communication device Control process;
When the current error state is an error active state included in the plurality of error states, and the determination condition is to cause the error state control step to control the error active state to continue, The transmission interval is controlled so that the minimum transmission interval becomes a predetermined length longer than the minimum transmission interval defined for the error active state on condition that the count value of the reception error counter becomes equal to or greater than the predetermined value. A communication method comprising: a transmission interval control step.   The communication method according to claim 7, wherein the predetermined length is equal to or shorter than a minimum transmission interval length for continuous transmission defined for an error passive state included in the plurality of error states.   The communication method according to claim 8, wherein the predetermined length is a length of a minimum transmission interval at the time of continuous transmission defined for an error passive state. A transmission error counter that counts the number of occurrences of transmission errors;
A reception error counter that counts the number of occurrences of reception errors,
When the count value of the transmission error counter or the reception error counter indicates a value larger than the first reference value, if the frame flowing on the CAN (Controller Area Network) bus is output from another node, The frame transmission is started from the own node after the elapse of the first period from the end of transmission, and when the frame flowing in the CAN bus is output from the own node, the first frame is transmitted from the end of transmission of the frame. A CAN node that starts frame transmission from its own node after the elapse of a second period longer than the period,
When the count value of the transmission counter is less than or equal to the first reference value, and the count value of the reception counter is less than or equal to the first reference value and is greater than or equal to a second reference value that is smaller than the first reference value A CAN node which starts frame transmission from its own node after a lapse of a third period, which is a period longer than the first period from the end of transmission of a frame flowing on the CAN bus.   The CAN node according to claim 10, wherein the third period has a length equal to or shorter than the second period.   The CAN node according to claim 11, wherein the third period has the same length as the second period.   When the count value of the transmission counter is equal to or smaller than the first reference value and the count value of the reception counter is smaller than the second reference value, the transmission of the frame flowing on the CAN bus is completed. The CAN node according to any one of claims 10 to 11, wherein frame transmission from the own node is started after elapse of the first period.

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