JP4890909B2 - Communication system and communication method. - Google Patents

Description

  The present invention relates to a communication system and a communication method, and more particularly to a multi-master communication system and a communication method.

  In recent years, a multi-master communication system has been attracting attention in which a plurality of communication nodes are connected to a bus and the plurality of communication nodes can transmit data onto the bus when the bus is released.

In such a multi-master communication system, as shown in FIG. 6 , an unspecified number of communication nodes 1A, 1B, and 1C are connected to a common bus. The communication circuit does not have an arbitration circuit, and each communication node monitors the bus usage status to determine whether transmission is possible. As a multi-master communication system that does not have a bus use right arbitration circuit, for example, there is a Controller Area Network (CAN) used for in-vehicle LANs and the like.

Each communication node in the communication system of the multi-master takes a configuration as shown in FIG. The CPU 14 connected to the internal bus 17, the main RAM 15 used for storing data processed by the CPU 14, the external I / F 16 for acquiring information from the sensor 3 provided outside the communication node, and the CAN bus 2 communication CAN control block 4 for controlling

  The CAN control block 4 includes a shift register 13 that converts serial data of the CAN bus 2 into parallel data or converts parallel data from the CAN controller 11 into serial data, and a message buffer that includes a transmission buffer and a reception buffer for holding data to be transmitted and received. 12 includes a CAN controller 11 that controls data exchange between the shift register 13 and the message buffer 12.

As shown in FIG. 8 , the CAN controller 11 receives a frame (consisting of ID, DLC, transmission data, etc.) from the message buffer and supplies it to the shift register 13, and transfers the reception data to the message buffer. It is comprised from the function and the control circuit 111 which controls these.

  Since such a multi-master communication system represented by CAN does not have a common arbitration circuit that controls network communication, each CAN controller 11 performs arbitration to check the bus use state each time a frame is transmitted. It is necessary to start communication after going. Arbitration is performed when a communication node that intends to transmit a frame outputs a transmission ID on the CAN bus 2, compares the transmission ID output by the communication node with the transmission ID that appears on the CAN bus 2, and when they match, When the right to use the bus is obtained, the remaining frames (DLC, transmission data) are transmitted, and if they do not match, a transmission ID with a high priority from another communication node is output. As described above, the transmission is stopped once.

Data transmission from the communication node to the CAN bus 2 (frame transmission) is processed according to the flow shown in FIG. When a communication node in which data with a transmission request exists in the message buffer 12 reads the data (transmission ID, transmission DLC, transmission data, transmission request, etc.) in the message buffer 12 into the transmission temporary buffer 112, the transmission preparation is completed. Then, the process proceeds to step S51 for checking the state of the bus. In step S51, if the bus is busy, that is, if it is being used by another communication node, the bus state check is repeated until the bus is in an idle state. If it is detected that the bus is in an idle state, the process proceeds to step S52. The transmission of the frame in step S52 includes a transmission ID indicating the priority order of the frames (as described above, arbitration is performed by comparing transmission IDs), a data length code (DLC) indicating the length of data, data, and transmission data. Cycle Redundancy Code (CRC) for checking whether the received data is matched, and End Of Frame (EOF) indicating the end of the frame are performed in this order, and the process moves to step S53 when EOF is transmitted. In step S53, it is confirmed whether or not an error frame transmitted by a communication node that has failed to receive the transmitted frame is received. If no error frame is received, the process proceeds to step S54 to transmit the communication node that transmitted the frame. When the phase is completed and an error frame is received, the communication node that has transmitted the frame temporarily stops transmission and proceeds to step S55. In step S55, an error counter value indicating the number of error detections is confirmed. If the error counter value has not reached the specified value, the process proceeds to step S51, and retransmission of the frame that failed to be transmitted is executed. When the value reaches the specified value, the process proceeds to step S56 and enters a bus off state in which communication on the bus cannot be performed. In step S56, the communication node in the bus off state monitors the bus and satisfies a certain condition, for example, confirming that the bus is idle a specified number of times, or proceeds to step S57 after a predetermined time has elapsed. Then, after returning to communication, the process proceeds to step S51, and retransmission of the frame that failed to be transmitted is executed. In this way, retransmission of a frame that has failed to be transmitted is performed.

Next, data reception on CAN bus 2 (frame reception) is processed by the flow shown in FIG. 10. When there is a frame output from a communication node other than itself on the CAN bus 2, the communication node starts receiving the frame, and proceeds to step S71. In step S71, it is detected whether or not there is an error in the received frame. If there is an error, the process proceeds to step S72 to output an error frame on the CAN bus 2. If there is no error, step S71 is performed. The process proceeds to S73. In step S73, a communication node other than itself outputs an error frame on the CAN bus 2 to detect whether it has been received. If an error frame is detected, the process proceeds to step S74 to discard the received frame. If no error frame is detected, the frame is assumed to have been received normally, and the process proceeds to step S75 to complete the reception.

JP 2000-36361 A

  Here, there is a communication node A that has output a large number of transmission errors on the bus, that is, there is a communication node A that has repeatedly generated errors during frame transmission, and that communication node A is trying to transmit a frame. think about.

As shown in the timing chart of FIG. 11 , the communication node A performs frame transmission in the order of ID A, DLC, data A, and CRC. At this time, if the communication node C fails to receive a frame due to detection of a CRC error, the communication node C transmits an error frame on the CAN bus 2. The communication node A that has detected a transmission failure by receiving the error frame output on the CAN bus 2 increments the number of error detections, and when the number of error detections reaches a specified value, active communication is performed. By entering the bus off state, which is a block state, the communication node A returns to communication after a predetermined time has elapsed, considering that there may be noise and other obstructions on the bus at the current time. Until this time, the retransmission is suspended. This is performed in order to temporarily disconnect a communication node that frequently generates errors from the bus and improve the use efficiency of the bus. For this reason, in a communication system that requires real-time performance, the retransmission of a frame to be sent from the communication node A to the communication node C is delayed, causing a communication delay problem.

  Even if communication between communication node A and communication node C is not established due to the influence of distance and noise on the network (if an error occurs), other nodes on the network (in this case communication) Node B) failed to receive at any single node on the bus (in this case, communication node C) even though it successfully received ID, DLC, and data that should be stored in the message buffer. This causes a problem of discarding the received frame. That is, the frame from the communication node A is a frame that should be received by both the communication nodes B and C, and when the communication node B is normally received and an error occurs in the communication node C, not only the communication node C, There arises a problem that a frame normally received by the communication node B is also discarded.

  The communication system according to the present invention is a communication system comprising a bus and first to third communication nodes connected to the bus, wherein the first communication node includes a transmission buffer for storing a first transmission frame. A first control circuit for adding transfer information to the first transmission frame and outputting the first transmission frame to which the transfer information is added as a second transmission frame to the bus, and The communication node includes a reception buffer that stores the second transmission frame output from the first communication node as a reception frame, and the second transmission frame output from the first communication node received by the third communication node. And detecting whether an error frame output from the third communication node is transmitted on the bus and detecting the error. A second control circuit for confirming whether or not the transfer information is included in a frame, wherein the second control circuit detects the error frame on the bus and transmits the transfer information in the received frame. When it is confirmed that the first transmission frame is included in the reception frame, the first transmission frame is output to the bus. The communication method according to the present invention is a communication method for first to third communication nodes to communicate via a bus, wherein the first communication node stores a first transmission frame, and the first communication node stores the first transmission frame. Transfer information is added to a transmission frame, and the first transmission frame with the transfer information added is output as a second transmission frame to the bus, and the second communication node is output from the first communication node. The second transmission frame is stored as a reception frame, and is output from the third communication node when an error is detected in the output second transmission frame from the first communication node received by the third communication node. And whether or not an error frame is transmitted on the bus, and whether or not the transfer information is included in the received frame. When the error frame is detected and it is confirmed that the transfer information is included in the received frame, the first transmission frame included in the received frame is output to the bus. .

  With such a configuration, transfer information can be added to a transmission frame from a specific communication node, and a transmission frame to which the transfer information is added can be transferred by another communication node.

  As described above, it is possible to notify other communication nodes that a frame is a transfer request frame, and to transfer when the received frame is a frame for which transfer is requested, thereby improving communication efficiency. .

  In the communication system of the present invention, among a plurality of communication nodes (also referred to as communication modules or communication circuits) connected on the bus, a node that requests transfer and a node that has a function of executing transfer are arranged. Can be realized. More specifically, in the case of a communication node having a function of adding and transmitting information that is a frame requesting transfer to a frame in error, and when the received frame is a frame for which transfer is requested This can be realized by connecting a communication node having a function of transferring the received frame to the bus. In a multi-master communication system, since arbitration is performed using an ID, there may be a plurality of communication nodes that request transfer. However, if there are a plurality of communication nodes that perform transfer, a frame having the same ID may be used. Since there is a possibility of collision from being output from a plurality of communication nodes, one communication node that performs transfer is preferable.

  A configuration of a CAN controller according to an embodiment of the present invention will be described with reference to FIGS. Here, an example will be described in which information on whether or not a frame is requested to be transferred and whether or not it is a transferred frame is included in a bit that is not used by DLC in the frame.

  As shown in FIG. 1, the CAN controller 11A of the transmission side communication node requesting the transfer is incremented by receiving an error frame on the CAN bus 2 when the communication node transmits a frame. A control circuit 111A having a specified value register 1112 that holds a specified value to be compared with the value of 1111 and the error counter 1111; a transmission temporary buffer 113 that holds a transmission ID, transmission DLC, transmission data, and transmission request from the message buffer Is provided. The control circuit 111A rewrites the transmission DLC based on the value of the error counter 1111 and the value of the specified value register, compares the ID of the received frame with the transmission ID held in the transmission temporary buffer 113, and matches. In this case, a function for clearing the transmission request of the transmission temporary buffer 113 is provided.

  As shown in FIG. 2, the CAN controller 11B of the receiving communication node requested to transfer the frame (reception ID, DLC, received data) from the shift register 13 when the communication node receives the frame. A reception temporary buffer 112 to be held, a DLC decoding circuit 121 for decoding the DLC of the received frame, a control circuit 111B for controlling the DLC of the reception temporary buffer and a transfer request.

  That is, the CAN controller of the communication node on the transmission side involved in the transfer has a control circuit having a function of adding information on whether or not to request the transfer to the frame, and the CAN controller of the communication node on the reception side related to the transfer is Transfer can be realized by including a decoding circuit for decoding whether or not the received frame is a frame for which transfer is requested, and a reception temporary buffer for temporarily storing the received frame.

  Next, the operation of the transmission side and reception side communication nodes will be described with reference to the flowcharts of FIGS.

  The control circuit 111A in the CAN controller 11A of the transmission side communication node fetches the data from the message buffer to the transmission temporary buffer 113 when there is a transmission request, that is, when there is data having a transmission request in the message buffer, Preparation for transmission is performed, and the process proceeds to step S60. In step S60, the control circuit 111A determines whether or not the CAN bus 2 is in an idle state based on whether data is output on the CAN bus 2. If not, the control circuit 111A repeatedly checks the bus state to When the state is detected, the process proceeds to step S61. In step S61, the control circuit 111A compares the error counter 1111 and the value of the set value register 1112 to determine whether or not it is immediately before the bus off state. If it is immediately before the bus off state, the process proceeds to step S63. If not, the process proceeds to step S62. In step S63, the control circuit 111A embeds information for requesting frame transfer to an arbitrary communication node on the bus in the bit of the transmission DLC, transmits the frame onto the CAN bus 2, and proceeds to step S64. In step S62, the control circuit 111A transmits the transmission frame onto the CAN bus 2 as in the conventional case, and proceeds to step S64. In step S64, the control circuit 111A receives (RxD) and monitors the data on the bus to determine whether an error frame is transmitted for the frame transmitted on the CAN bus 2 in step S62 or 63. If it is detected and no error frame is detected, the process proceeds to step S65, and if it is detected, the process proceeds to step S66. When the process proceeds to step S65, the control circuit 111A completes the transmission on the assumption that the transmission of the frame has ended normally, and clears the transmission request of the transmission temporary buffer 113. In step S66, the control circuit 111A checks the value of the error counter 1111 indicating the number of times of error detection, and if this value has reached the specified value set in the specified value register, the control circuit 111A proceeds to step S67, which is a bus off state. Subsequently, the process proceeds to step S68. In step S68, the control circuit 111A receives data on the bus to determine whether or not the transfer frame has been normally transmitted by another communication node, that is, whether or not an error frame has been detected for the transmission of the transfer frame. If an error frame is detected and no error frame is detected, the process proceeds to step S65 assuming that the transfer has been performed normally. If an error frame is detected, the process proceeds to step S69. In step S69, the control circuit 111A returns to the communication after a predetermined time for returning the communication has elapsed, and retransmits the frame that failed to be transmitted.

  In step S81, the control circuit 111B of the CAN controller 11B of the communication node on the receiving side starts reception in response to the output of data (frame) on the CAN bus 2, and receives the frame on the CAN bus 2. If the frame received in the temporary buffer 112 and received by the communication node has an error, it is detected by, for example, CRC check. If there is an error, the process proceeds to step S82. The process proceeds to S82. In step S82, since an error is detected in the received frame, the control circuit 111B outputs an error frame to the CAN bus 2. In step S83, the control circuit 111B detects whether or not an error frame has been transmitted on the CAN bus 2 from another communication node. When the error frame is transmitted, the process proceeds to step S84, and the error frame is transmitted. If not, the process proceeds to step S85. In step S84, the control circuit 111B detects the DLC of the frame stored in the reception temporary buffer 112 by the DLC decoding circuit 121. If the received frame is a transfer request frame as a result of decoding, the control circuit 111B proceeds to step S86. If the received frame is not a transfer request frame, the process proceeds to step S87. In step S86, the control circuit 111B sets a transfer request flag in the reception temporary buffer 112, rewrites the DLC of the frame captured in the reception temporary buffer 112 from the transfer request frame to the normal frame, and transmits (transfers) to the CAN bus 2. )I do. In step S87, the control circuit 111B discards the frame held in the reception temporary buffer and completes reception.

Next, a frame on a communication system including a communication node A having a transmission-side CAN controller requesting transfer and a communication node B having a receiving-side CAN controller requested to transfer is transmitted. It will be described with reference to a timing chart shown in FIG. 5 for transfer.

  There is a communication node A that outputs a frame (data) that causes an error many times on the bus, and the count value of the error frame is a value that must be requested to be transferred, for example, the value immediately before the bus off state. The communication node A transmits a frame for which transfer is requested, that is, a frame in which a value indicating that transfer is requested to the DLC is transmitted, and the communication node B existing on the same CAN bus 2 receives the frame and receives the CAN bus. Consider the case of forwarding on 2.

  The communication node A transmits frames to the CAN bus 2 in the order of ID A, DLC, data A, and CRC. When the communication node C receives data on the CAN bus 2 and detects an error at the CRC reception stage, the communication node C transmits an error frame to the CAN bus 2.

  By receiving this error frame, the communication node A shifts to the bus off state immediately before the bus off state, and shifts to a passive state that confirms the state of the CAN bus 2 (does not transmit). The communication node B detects that there is another communication node on the CAN bus 2 that has failed to receive the frame due to the reception of the error frame from the CAN bus 2 regarding the frame that has been normally received by itself. Since the received frame is a transfer frame in which a method of requesting transfer to the DLC is embedded, transmission of the transfer frame is transmitted in the order of ID A, DLC, data A, and CRC. At this time, in the communication node A in the bus off state, the reception of the frame requested to be transferred is compared with the frame on the CAN bus 2 and the frame stored in the transmission temporary buffer which has failed to be transmitted, and the transmission of the transfer frame is performed. Is detected without the transmission of the error frame, that is, when the transfer frame from the communication node B is normally received by the communication node C, the bus is returned from the bus off state and held in the transmission temporary buffer. Clear the frame transmission request and cancel the retransmission of the frame.

  As described above, according to the present invention, the real-time property of communication is improved, the occupation of the bus by a single communication node can be reduced, and the communication node that is in the bus off state is quickly returned to communication. The effect that it can be made can be acquired.

  In the embodiment, the CAN has been described as an example. However, the present invention is not limited to this, and the present invention can be applied to any multi-master communication system. The gist of the present invention is applicable to other communication systems. Needless to say, the present invention can be applied without departing from the scope of the present invention.

  In addition, although an example has been described in which information indicating whether or not the frame is a transfer request frame to the DLC in the frame is embedded, the communication node that received the frame requests the transfer, not limited to the DLC. As long as the information can determine whether the frame is a frame to be transmitted or not, it may be anywhere in the frame.

  In the case of CAN, since there is a bit that is not specified in the protocol in the DLC in the frame, the present invention can be realized without changing the protocol by using the bit in the DLC. Is possible.

The block diagram which shows the CAN controller of the transmission side of one Example of this invention. The block diagram which shows the CAN controller of the receiving side (transfer side) of one Example of this invention. The operation | movement flowchart of the control circuit of the transmission side of FIG. FIG. 3 is an operation flowchart of a control circuit on the receiving side in FIG. 2. The timing diagram which showed the timing of transmission, transfer, and reception by this invention. 1 is a schematic diagram of a multi-master communication system using CAN. The block diagram of the conventional communication node. The block diagram of the conventional CAN controller. The operation | movement flowchart of the control circuit of the conventional transmission side. The operation | movement flowchart of the control circuit of the conventional receiving side. The timing diagram which showed the timing of the conventional transmission and reception.

Explanation of symbols

1A, 1B, 1C Communication nodes 11, 11A, 11B CAN controllers 111, 111A, 111B Control circuit 112 Reception temporary buffer 113 Transmission temporary buffer 1111 Error counter 1112 Specified value register 121 DLC decoding circuit

Claims (20)

A communication system comprising a bus and first to third communication nodes connected to the bus,
The first communication node is
A transmission buffer for storing the first transmission frame;
A first control circuit for adding transfer information to the first transmission frame and outputting the first transmission frame to which the transfer information is added as a second transmission frame to the bus;
Have
The second communication node is
A reception buffer for storing the output second transmission frame output from the first communication node as a reception frame;
When an error is detected in the second transmission frame output from the first communication node received by the third communication node, an error frame output from the third communication node is transmitted on the bus. A second control circuit for detecting whether or not the transfer information is included in the received frame;
Have
When the second control circuit detects the error frame on the bus and confirms that the transfer information is included in the received frame, the first transmission frame included in the received frame To the bus,
Communications system.   The first control circuit determines whether the first communication node is immediately before shifting to the bus off state, and outputs the second transmission frame to the bus when it is immediately before shifting to the bus off state. The communication system according to claim 1. The first control circuit has an error counter that counts the number of times an error frame is received from the third communication node in response to transmission of the first transmission frame;
The communication system according to claim 2, wherein a value of the error counter is compared with a specified value to determine whether or not it is immediately before shifting to the bus off state. The specified value is a reference value for shifting to the bus off state when the value of the error counter reaches the specified value,
4. The communication system according to claim 3, wherein the first control circuit determines that it is immediately before shifting to the bus off state when the value of the error counter reaches the specified value.   5. The communication system according to claim 1, wherein the first control circuit shifts to a bus off state when an error frame is received from the third communication node in response to transmission of the second transmission frame. 6.   The communication system according to claim 5, wherein the first control circuit detects whether or not the first transmission frame is normally transmitted from the second communication node after transitioning to the bus off state.   When the first control circuit detects that the first transmission frame is normally transmitted from the second communication node, the first control circuit returns from the bus off state to the communication state and completes the transmission of the first transmission frame. The communication system according to claim 6.   When the first control circuit detects that the first transmission frame is not normally transmitted from the second communication node, the first control circuit returns to the communication state from the bus off state after a predetermined time elapses, and the first transmission circuit The communication system according to claim 6 or 7, wherein the frame is retransmitted.   When the second control circuit detects the error frame on the bus and confirms that the transfer information is not included in the reception frame, the second control circuit discards the reception frame from the reception buffer. The communication system according to any one of claims 1 to 8.   The communication system according to claim 1, wherein the second transmission frame is a frame in which the transfer information is embedded in the first transmission frame. A communication method for first to third communication nodes to communicate via a bus,
The first communication node is
Storing the first transmission frame;
Adding transfer information to the first transmission frame, and outputting the first transmission frame with the transfer information added to the bus as a second transmission frame;
The second communication node is
Storing the output second transmission frame output from the first communication node as a reception frame;
When an error is detected in the second transmission frame output from the first communication node received by the third communication node, an error frame output from the third communication node is transmitted on the bus. And whether or not the transfer information is included in the received frame,
When the error frame is detected on the bus and it is confirmed that the transfer information is included in the received frame, the first transmission frame included in the received frame is output to the bus.
Communication method.   The first communication node determines whether or not the first communication node is immediately before shifting to the bus off state, and outputs the second transmission frame to the bus when it is immediately before shifting to the bus off state. The communication method according to claim 11. The first communication node has an error counter that counts the number of times an error frame is received from the third communication node in response to transmission of the first transmission frame;
The communication method according to claim 12, wherein a value of the error counter is compared with a specified value to determine whether or not it is immediately before shifting to the bus off state. The specified value is a reference value for shifting to the bus off state when the value of the error counter reaches the specified value,
The communication method according to claim 13, wherein the first communication node determines that the error counter value is immediately before shifting to the bus off state when the error counter value is just before reaching the specified value.   The communication method according to claim 11, wherein the first communication node shifts to a bus off state when receiving an error frame from the third communication node in response to transmission of the second transmission frame.   The communication method according to claim 15, wherein the first communication node detects whether the first transmission frame is normally transmitted from the second communication node after transitioning to the bus off state.   When the first communication node detects that the first transmission frame is normally transmitted from the second communication node, the first communication node returns from the bus off state to the communication state and completes the transmission of the first transmission frame. The communication method according to claim 16.   When the first communication node detects that the first transmission frame is not normally transmitted from the second communication node, the first communication node returns to the communication state from the bus off state after a predetermined time elapses, and the first transmission node The communication method according to claim 16 or 17, wherein the frame is retransmitted. When the second communication node detects the error frame on the bus and confirms that the transfer information is not included in the received frame, the second communication node discards the stored received frame. The communication method according to claim 11.



  The communication method according to claim 11, wherein the second transmission frame is a frame in which the transfer information is embedded in the first transmission frame.

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