Invalidity detection electronic control unit, in-vehicle network system, and communication method

1. An invalidity detection electronic control unit connected to a bus used by a plurality of electronic control units to communicate with one another in accordance with controller area network (CAN) protocol,

wherein each of the plurality of electronic control units includes a reception error counter, and configured to:

increment a value of the reception error counter when each of the plurality of electronic control units receives an error frame from the bus, and

decrement the value of the reception error counter when each of the plurality of electronic control units receives a normal frame from the bus,

the invalidity detection electronic control unit comprising:

a receiver that receives a frame for which transmission is started; and

a transmitter that transmits the error frame on the bus before a tail end of the frame is transmitted if the frame received by the receiver meets a predetermined condition indicating invalidity and transmits the normal frame that conforms to the CAN protocol on the bus after the error frame is transmitted.

2. The invalidity detection electronic control unit according to claim 1 , further comprising:

a communication interface connected to the bus;

a CAN controller connected to the communication interface, the CAN controller controlling communication on the bus in accordance with the CAN protocol; and

a CPU that controls the CAN controller to realize the receiver and the transmitter.

3. The invalidity detection electronic control unit according to claim 1 , wherein when the bus enters an idle state for the first time after the transmission of the error frame, the transmitter transmits the normal frame.

4. The invalidity detection electronic control unit according to claim 1 , wherein the transmitter transmits normal frames equal in number to the number of the transmitted error frames.

5. The invalidity detection electronic control unit according to claim 1 , wherein the normal frame transmitted by the transmitter after an error frame is transmitted is a data frame having a data field with a length of zero.

6. The invalidity detection electronic control unit according to claim 1 , wherein an ID indicated by an ID field of the normal frame transmitted by the transmitter after an error frame is transmitted is an ID for which a process to be performed is not defined by any one of electronic control units connected to the bus other than the invalidity detection electronic control unit after the electronic control unit identifies the ID.

7. The invalidity detection electronic control unit according to claim 1 , wherein if the transmitter receives a normal frame that does not meet the predetermined condition from the bus after the transmission of the error frame and before the transmission of the normal frame, the transmitter stops transmitting the normal frame.

8. The invalidity detection electronic control unit according to claim 1 , wherein the invalidity detection electronic control unit is connected to a plurality of buses, and the invalidity detection electronic control unit has a function of forwarding a frame received from one of the buses to the other,

wherein if the received frame meets the predetermined condition, the invalidity detection electronic control unit stops forwarding the frame, and

wherein if a frame received by the receiver meets the predetermined condition, the transmitter transmits an error frame on the bus from which the frame has been received before the tail end of the frame is transmitted and transmits the normal frame on the bus after the error frame is transmitted.

9. The invalidity detection electronic control unit according to claim 1 , wherein the transmitter transmits a normal frame if the transmission of the normal frame fails.

10. The invalidity detection electronic control unit according to claim 9 , wherein the transmitter transmits normal frames which are more in number than a value obtained by subtracting, from the number of the transmitted error frames, the number of normal frames that do not meet the predetermined condition and that are received from the bus after the error frames are transmitted.

11. The invalidity detection electronic control unit according to claim 9 , wherein if the transmission of the normal frame fails, the transmitter transmits a normal frame having an ID field indicating an ID that is smaller than an ID indicated by an ID field of the normal frame.

12. An in-vehicle network system comprising:

a plurality of electronic control units that communicate with one another via a bus in accordance with a controller area network (CAN) protocol; and

an invalidity detection electronic control unit connected to the bus,

wherein the invalidity detection electronic control unit includes a receiver that receives a frame for which transmission is started and a transmitter that transmits an error frame on the bus before a tail end of the frame is transmitted if the frame received by the receiver meets a predetermined condition indicating invalidity and transmits a normal frame that conforms to the CAN protocol on the bus after the error frame is transmitted,

wherein each of the plurality of electronic control units includes a CAN controller that includes a reception error counter and that controls communication on the bus in accordance with the CAN protocol, wherein each of the plurality of electronic control units increments a value of the reception error counter when each of the plurality of electronic control units receives an error frame from the bus, and wherein each of the plurality of electronic control units decrements the value of the reception error counter when each of the plurality of electronic control units receives a normal frame from the bus.

13. A communication method for use in an in-vehicle network system including a plurality of electronic control units that communicate with one another via a bus in accordance with a controller area network (CAN) protocol,

wherein each of the plurality of electronic control units includes a reception error counter, and configured to:

increment a value of the reception error counter when each of the plurality of electronic control units receives an error frame from the bus, and

decrement the value of the reception error counter when each of the plurality of electronic control units receives a normal frame from the bus,

the communication method comprising:

receiving a frame for which transmission is started; and

transmitting the error frame on the bus before a tail end of the frame is transmitted if the received frame meets a predetermined condition indicating invalidity and transmitting the normal frame that conforms to the CAN protocol on the bus after the error frame is transmitted.