In-vehicle relay device, flow control method, and computer program

Abstract

To easily suppress buffer leakage in the low-speed transmit buffer. [Solution] An in-vehicle relay device according to one aspect of the present disclosure comprises: a first port which is the physical port of the first frame described below; a second port which is the physical port of the second frame described below; a relay processing unit which performs relay processing to determine the output port of the received frame and protocol conversion to convert the format of the received frame to the format of the transmitting side, wherein the relay processing unit transmits the second frame from the second port when the amount of the transmit buffer of the first port is equal to or greater than a threshold, with an identifier representing the transmission priority set to a predetermined value. First frame: A communication frame that conforms to the first communication protocol and contains an identifier indicating the transmission priority. Second frame: A communication frame containing an identifier indicating transmission priority, conforming to a second communication protocol with a higher maximum transmission speed than the first communication protocol.

Description

Technical Field

[0004] , ,

[0005]

[0001] The present disclosure relates to an in-vehicle relay device, a flow control method, and a computer program.

Background Art

[0002] Patent Document 1 describes an in-vehicle communication system that enables coexistence of an ECU (Electric Control Unit) compliant with CAN and an ECU compliant with Ethernet by adopting an in-vehicle relay device that performs protocol conversion between CAN (Control Area Network: registered trademark) and Ethernet (registered trademark). Patent Document 2 describes a flow control device that has a buffer for each priority, sets a threshold for each buffer, and sends a transmission stop instruction and a restart instruction. [[ID=##]]

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, buffer leakage of the low-speed side transmission buffer, which is a concern when the flow from the high-speed side Ethernet to the low-speed side CAN increases, is not assumed. As a measure to prevent the above buffer leakage, it is conceivable to apply the flow control device of Patent Document 2 to the in-vehicle communication system. However, in such an in-vehicle communication system, there is a problem that the cost becomes high because it is necessary to modify the software of a large number of ECUs so that the stop instruction and restart instruction for each priority can be discriminated.

[0005] In view of the aforementioned conventional problems, this disclosure aims to provide an in-vehicle relay device, etc., that can easily suppress buffer leakage in the low-speed transmission buffer. [Means for solving the problem]

[0006] An in-vehicle relay device according to one aspect of the present disclosure is an in-vehicle relay device comprising: a first port which is the physical port of the first frame described below; a second port which is the physical port of the second frame described below; a relay processing unit which performs relay processing to determine the output port of a received frame and protocol conversion to convert the format of the received frame to the format of the transmitting side, wherein the relay processing unit transmits the second frame from the second port when the amount of the transmit buffer of the first port is equal to or greater than a threshold, with an identifier representing the transmission priority set to a predetermined value.

[0007] First frame: A communication frame that conforms to the first communication protocol and contains an identifier indicating the transmission priority. Second frame: A communication frame containing an identifier indicating transmission priority, conforming to a second communication protocol with a higher maximum transmission speed than the first communication protocol.

[0008] This disclosure can be implemented not only as a system and apparatus having the characteristic configuration described above, but also as a program for causing a computer to execute such characteristic configuration. Furthermore, this disclosure can be implemented as a semiconductor integrated circuit that implements part or all of the system and apparatus. [Effects of the Invention]

[0009] According to this disclosure, an in-vehicle relay device, etc., can be obtained that can easily suppress buffer leakage in the low-speed transmission buffer. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a network configuration diagram showing an example of an in-vehicle communication system. [Figure 2]Figure 2 is a block diagram showing an example of the internal configuration of CGW. [Figure 3] Figure 3 is an explanatory diagram illustrating the challenges of CGW and an example of a proposed solution. [Figure 4] Figure 4 is a flowchart showing an example of flow control. [Figure 5] Figure 5 shows an example of a correspondence table. [Modes for carrying out the invention]

[0011] <Summary of the embodiments of this disclosure> The embodiments of this disclosure are outlined below.

[0012] (1) An in-vehicle relay device according to one aspect of this embodiment includes a first port which is the physical port for the first frame described below, a second port which is the physical port for the second frame described below, a relay processing unit which performs relay processing to determine the output port of the received frame and protocol conversion to convert the format of the received frame to the format of the transmitting side, wherein the relay processing unit transmits the second frame from the second port when the amount of the transmit buffer of the first port is equal to or greater than a threshold, with an identifier representing the transmission priority set to a predetermined value.

[0013] First frame: A communication frame that conforms to the first communication protocol and contains an identifier indicating the transmission priority. Second frame: A communication frame containing an identifier indicating transmission priority, conforming to a second communication protocol with a higher maximum transmission speed than the first communication protocol.

[0014] According to the in-vehicle relay device of this embodiment, when the amount of the transmit buffer of the first port is greater than or equal to a threshold, the relay processing unit transmits a second frame with an identifier set to a predetermined value from the second port. As a result, the in-vehicle communication device (e.g., ECU) connected to the second port will not transmit a second frame with a lower priority than the predetermined value. Therefore, even without modifying the software of the in-vehicle communication device connected to the second port, it becomes possible to transmit pressure to the in-vehicle communication device. Thus, it becomes possible to easily suppress buffer overflow in the transmission buffer of the first port, which is the low-speed side.

[0015] (2) In the in-vehicle relay device of (1) above, the first ports are plural, and when the buffer amount of any one of the plural first ports is equal to or greater than a threshold value, the relay processing unit may transmit the second frame from the second port. In this way, it is possible to easily suppress buffer overflow for the transmission buffers of all the first ports.

[0016] (3) In the in-vehicle relay device of (1) or (2) above, the second ports are plural, and the relay processing unit may determine the value of the identifier applied to the second frame according to the reception buffer amounts of the plural second ports. In this way, compared with the case where the value of the identifier is a fixed value, it is possible to flexibly adjust the degree of transmission suppression for the in-vehicle communication device (for example, ECU) connected to the second port.

[0017] (4) In the in-vehicle relay device of (3) above, the relay processing unit may determine the value of the identifier so that the transmission priority increases for the second port with a larger reception buffer amount. In this way, it is possible to gradually increase the degree of transmission suppression for the in-vehicle communication device (for example, ECU) connected to the second port, which is estimated to have a high transmission frequency.

[0018] (5) In the in-vehicle relay device of (4) above, the relay processing unit may increase the transmission frequency of the second frame for the second port with a larger reception buffer amount. In this way, compared with the case where the transmission frequency of the second frame is constant, it is possible to increase the degree of transmission suppression for the in-vehicle communication device (for example, ECU) connected to the second port.

[0019] (6) In the in-vehicle relay devices described in (1) to (5) above, the payload of the second frame may store an identifier other than the identifier and the actual data section. In this way, the second frame used for transmission suppression can also be used for data transmission from the in-vehicle relay device to the in-vehicle communication device (e.g., ECU) connected to the second port.

[0020] (7) In the in-vehicle relay devices described in (1) to (6) above, the first communication protocol may be CAN, and the second communication protocol may be CAN-FD (CAN with flexible data rate). In this case, it becomes possible to send pressure to an in-vehicle communication device (e.g., an ECU) that complies with CAN-FD without modifying its software. Therefore, buffer leakage in the transmission buffer of the low-speed CAN port can be easily suppressed.

[0021] (8) In the in-vehicle relay device described in (7) above, the identifier may be a CANID. The reason is that CAN and CAN-FD use CANID as an identifier to indicate the transmission priority.

[0022] (9) A method according to one aspect of this embodiment is a flow control method executed by the in-vehicle relay device described in (1) to (8) above. Therefore, the flow control method of this embodiment has the same effects as the in-vehicle relay device described in (1) to (8) above.

[0023] (10) A computer program according to one aspect of this embodiment is a computer program for causing a computer to function as an in-vehicle relay device as described in (1) to (8) above. Therefore, the computer program of this embodiment has the same effects as the in-vehicle relay devices described in (1) to (8) above.

[0024] <Details of Embodiments of the Invention> The embodiments of the present invention will be described in detail below with reference to the drawings. At least some of the embodiments described below may be combined in any way.

[0025] [Example of an in-vehicle communication system configuration] Figure 1 is a network configuration diagram showing an example of the configuration of the in-vehicle communication system 100. As shown in Figure 1, the in-vehicle communication system 100 according to this embodiment is an in-vehicle LAN (Local Area Network) built inside the vehicle 1. The in-vehicle communication system 100 includes a CGW (Central Gateway) 10, a TCU (Telematics Control Unit) 20, and multiple ECUs 30, 40 as communication nodes that constitute the network.

[0026] The TCU20 is a wireless communication unit that handles data communication with external servers operated by the vehicle manufacturer. By communicating with the TCU20, the external server can share information with vehicle 1 in near real-time. ECUs 30 and 40 are electronic control units for vehicles that control various in-vehicle equipment such as sensors or actuators within the vehicle 1. ECUs 30 and 40 are communication nodes that constitute the in-vehicle communication system 100, and from a communication standpoint, they are a type of "in-vehicle communication device".

[0027] Focusing on the controlled objects, the types of ECUs 30 and 40 include engine control ECUs, transmission control ECUs, power steering control ECUs, air conditioning control ECUs, and AV (Audio / Visual) system control ECUs. The ECUs 30 and 40 take measurement information from sensors connected to them (such as speed sensors, acceleration sensors, temperature sensors, and pressure sensors) into the system and control various actuators connected to them (such as electric motors) based on the measurement information.

[0028] Focusing on the communication protocol, the in-vehicle communication system 100 is a network in which ECUs 30 that perform communication compliant with the "first communication protocol" and ECUs 40 that perform communication compliant with the "second communication protocol" coexist. In this embodiment, both the first communication protocol and the second communication protocol shall conform to the following conditions.

[0029] Condition 1: Adopt a protocol that uses arbitration to determine transmission priority based on the number of identifiers in the communication frame. Condition 2: The maximum transmission speed of the second communication protocol is greater than the maximum transmission speed of the first communication protocol.

[0030] In this embodiment, as an example, the first communication protocol is CAN and the second communication protocol is CAN-FD. In CAN and CAN-FD, collision resolution is performed in CAMA / CR (Carrier Sense Multiple Access with Collision Resolution) at each communication node, prioritizing the transmission of data with smaller CANIDs. Therefore, CAN and CAN-FD satisfy condition 1.

[0031] The maximum transmission speed of CAN-FD is 8 Mbps in standard mode, while the maximum transmission speed of CAN is typically 1 Mbps. Therefore, both CAN and CAN-FD meet condition 2. However, CAN and CAN-FD are just examples, and any protocol other than CAN may be used for the first communication protocol and a protocol other than CAN-FD for the second communication protocol, as long as conditions 1 and 2 are met.

[0032] ECU30 is an ECU that performs communication compliant with CAN (Canal Communication Protocol). Hereinafter, a communication frame compliant with CAN will be referred to as a "CAN frame" or "first frame," and an ECU that performs communication compliant with CAN will be referred to as a "C-ECU" or "first ECU." ECU40 is an ECU that performs communication compliant with CAN-FD (Second Communication Protocol). Hereinafter, a communication frame compliant with CAN-FD will be referred to as a "CAN-FD frame" or "Second frame," and an ECU that performs communication compliant with CAN-FD will be referred to as "F-ECU" or "Second ECU."

[0033] C-ECU30 is connected to CGW10 via CAN bus 50 (hereinafter referred to as "first bus 50"). F-ECU40 is connected to CGW10 via CAN bus 60 (hereinafter referred to as "second bus 60"). The first bus 50 and the second bus 60 are twisted-pair cables containing high and low transmission lines. Multiple first ECUs 30 can be connected in a line configuration to one first bus 50. Multiple second ECUs 40 can be connected in a line configuration to one second bus 60.

[0034] The CGW10 has the following multiple types of communication ports: Port 1 CPi: A physical port for CAN frames (first frame). "i" represents a port number from 1 to m. Port 2 FPj: A physical port for CAN-FD frames (second frame). "j" is a port number ranging from 1 to n. Third port TP: A physical port for communicating with external communication devices of vehicle 1.

[0035] Therefore, the first bus 50 is connected to the first port CPi, and the second bus 60 is connected to the second port FPj. Additionally, a communication cable (such as a LAN cable) used for communication with the TCU20 is connected to the third port TP.

[0036] CGW10 has routing functions to distribute the destination of communication frames received from ECU30 and 40, protocol conversion functions to convert the format of communication protocols, and security functions to prevent unauthorized access from external sources. Therefore, CGW10 is a type of "in-vehicle relay device" that performs routing of communication frames based on CANID and protocol conversion of communication frames transmitted and received between C-ECU30 and F-ECU40.

[0037] [Example of CGW configuration] Figure 2 is a block diagram showing an example of the internal configuration of CGW10. As shown in Figure 2, the CGW10 includes a relay processing unit 11, a first transceiver 12C, and a second transceiver 12F as electronic components housed in the enclosure. The CGW10 also has physical ports provided on the wall of the enclosure: a first port CPi (i=1,2...m), a second port FPj (j=1,2...n), and a third port TP.

[0038] The relay processing unit 11 is a communication module that performs Layer 2 signal processing on CAN frames and CAN-FD frames, and includes a controller 13, memory 14, and a plurality of buffers 15. The multiple buffers 15 include a transmit buffer CTBi and a receive buffer CRBi that correspond one-to-one with the first port CPi, and a transmit buffer FTBj and a receive buffer FRBj that correspond one-to-one with the second port FPi.

[0039] The controller 13 controls the retrieval of data from the transmit buffer CTBi, receive buffer CRBi, transmit buffer FTBj, and receive buffer FRBj.

[0040] The first transceiver 12C is a transceiver that performs Layer 1 signal processing related to CAN frames. The first transceiver 12C encodes the CAN frame input from the transmit buffer CTBi to generate a differential signal and outputs the differential signal to the first port CPi. The first transceiver 12C reconstructs a CAN frame from the differential signal input from the first port CPi and outputs the CAN frame to the receive buffer CRBi.

[0041] The second transceiver 12F is a transceiver that performs Layer 1 signal processing related to CAN-FD frames. The second transceiver 12F encodes the CAN-FD frame input from the transmit buffer FTBj to generate a differential signal, and outputs the differential signal to the second port FPj. The second transceiver 12F reconstructs the CAN-FD frame from the differential signal input from the second port FPj and outputs the CAN-FD frame to the receive buffer FRBj.

[0042] The controller 13 may consist of, for example, one or more CPUs (Central Processing Units). However, the controller 13 may also include an FPGA (Field Programmable Gate Array), or it may consist of an FPGA without implementing a CPU. The controller 13 reads the computer program 16 from the memory 14 and executes predetermined communication processing according to the read program 16.

[0043] The memory 14 may be composed of a non-volatile recording medium such as an EEPROM (Electrically Erasable Programmable ROM). Memory 14 stores not only the computer program 16 for communication processing, but also a relay table 17 used for routing and a correspondence table 18 used for flow control. A specific example of the correspondence table 18 (see Figure 5) will be described later.

[0044] The computer program 16 stored in memory 14 includes a program that causes the controller 13 to perform the following processes. 1) Relay processing 2) Protocol conversion 3) Arbitration 4) Flow control

[0045] "Relay processing" is the process of determining the output port of the received frame based on the output destination for each CANID defined by the relay table 17. "Protocol conversion" is the process of converting the format of a received frame to the destination's format when the communication protocols of the receiving and transmitting devices are different. Therefore, protocol conversion includes the process of converting CAN frames to CAN-FD frames and the process of converting CAN-FD frames to CAN frames.

[0046] "Arbitration" is the process of determining transmission priority based on the identifier (CANID) of the communication frame. In CAN and CAN-FD arbitration, a smaller CANID value is determined to have a higher transmission priority. "Flow control" is a control mechanism that suppresses buffer leakage of communication frames. In this embodiment, the transmission buffer CTBi, which corresponds to the first port CPi (the low-speed side), is targeted for suppression. The details of the flow control (see Figure 4) will be described later.

[0047] [Challenges and Solutions of CGW] Figure 3 is an explanatory diagram illustrating the challenges of CGW10 and an example of a solution. As shown in Figure 3, this assumes that CGW10 relays communication frames from the high-speed CAN-FD second bus 60 to the low-speed CAN second bus 50.

[0048] In this case, for example, if a burst transmission occurs on the second bus 60, the capacity of the transmit buffer CTBi of the first port CPi connected to the first bus 50 may be exceeded, potentially causing the CAN frame (first frame) to be lost. Therefore, in CGW10, which accommodates both CAN and CAN-FD, it is necessary to perform flow control on the high-speed side F-ECU (second ECU) 40 to suppress the transmission of CAN-FD frames (second frames).

[0049] Therefore, in this embodiment, when the amount of data accumulated in the transmit buffer CTBi exceeds a predetermined threshold Th, CGW10 performs a "pressure transmission" from the second port FPj connected to the second bus 60. Specifically, CGW10 continuously transmits the "suppression frame SF" defined below from the second port FPj. Suppression frame SF:CANID contains a predetermined value (for example, "0x300" in this case) in the CAN-FD frame (second frame).

[0050] Upon receiving the suppression frame SF described above, the F-ECU (second ECU) 40, through communication arbitration in accordance with CAN-FD, will cease sending lower-priority CAN-FD frames (second frames) with a CANID value greater than 0x300. Therefore, by continuously transmitting suppression frames SF to the high-speed side, buffer leakage can be suppressed in the transmission buffer CTBi of the CAN frame (first frame), which is on the low-speed side.

[0051] In this way, by continuously transmitting suppression frames SF and applying transmission suppression to the high-speed side F-ECU (second ECU) 40, it is possible to prevent the buffer size of the low-speed side transmission buffer CTBi from becoming excessive. Furthermore, in order to transmit the suppression frame SF as quickly as possible, it is preferable that the controller 13 of the CGW10 outputs the suppression frame SF to the second transceiver 12F without placing it in the transmit buffer FTBj.

[0052] Incidentally, in Ethernet backpressure using "PAUSE frames," the communication node that receives the frame temporarily suspends its transmission process. In contrast, in the pressure transmission of this embodiment, the transmission of CAN-FD frames (second frames) with a higher priority than the CANID value written in the suppression frame SF is permitted. Furthermore, since the arbitration function of CAN-FD is utilized, there is the advantage that flow control can be achieved without modifying the software of the F-ECU (second ECU) 40.

[0053] As a suppression frame (SF), for example, a meaningless frame containing padding data in the payload could be used. However, as shown in Figure 3, a CAN-FD frame may be adopted in which a CANID different from the header section's CANID (=0x300) and the actual data section are stored in the payload. If a suppression frame SF in this data format is adopted, the suppression frame SF can also be used for data transmission from CGW10 to F-ECU (second ECU) 40.

[0054] [Flow control details] Figure 4 is a flowchart showing an example of the flow control performed by the controller 13 of CGW10. The controller 13 of CGW10 performs the processing shown in the flowchart in Figure 4 at predetermined control cycles C (e.g., 10 seconds).

[0055] As shown in Figure 4, the controller 13 first obtains the buffer amount BA of the transmit buffer CTBi, which is the slow side of all operating devices (step ST11). Next, the controller 13 determines whether or not there is a transmit buffer CTBi whose acquired buffer amount BA is equal to or greater than a predetermined threshold Th (e.g., 90%) (step ST12).

[0056] If the result of step ST12 is positive, the controller 13 determines the value of CANID to be written in the suppression frame SF (hereinafter referred to as "ID value") based on the buffer amount of the high-speed receiving buffer FRBi and the correspondence table 18 (step ST13). Next, the controller 13 starts transmitting pressure using the suppression frame SF (step ST14) and terminates the process. This causes the suppression frame SF, which contains the above ID value, to be continuously transmitted from the second port FPj.

[0057] If the result of step ST12 is negative, the controller 13 determines whether or not pressure transmission is currently being performed (step ST15). If the result of step ST15 is positive, the controller 13 stops the ongoing pressure transmission (step ST16) and terminates the process. As a result, the pressure transmission that was being performed in the previous control cycle C is stopped in the current control cycle C.

[0058] If the result of step ST15 is negative, the controller 13 skips step ST16 and terminates the process.

[0059] [Method for determining ID values ​​using a correspondence table] Figure 5 shows an example of the correspondence table 18. As shown in Figure 5, the correspondence table 18 used to determine the ID value of CANID can be either the first table 18A or the second table 18B.

[0060] Table 18A is a table-formatted data set containing the "Buffer Amount BA Range" column and the "CANID" column for the receive buffer FRBj. Table 18A defines the ID values ​​of CANID for each range of buffer size BA as follows: 80% ≤ BA < 90% → ID value = 0x200 90% ≤ BA < 95% → ID value = 0x100 95% ≤ BA → ID value = 0x50

[0061] If the first table 18A is adopted, the controller 13 will select a smaller ID value (higher priority ID value) the larger the buffer amount BA of the high-speed receive buffer FRBj. Consequently, the degree of transmission suppression for the F-ECU (second ECU) 40 will increase. The reason for this is that the larger the buffer size BA of the receive buffer FRBj, the higher the estimated frequency of CAN-FD frame (second frame) transmission, and therefore the degree of transmission suppression should be increased.

[0062] Table 18B, the second table, is a table-formatted data set that, in contrast to Table 18A, also includes a column for "Bus Load L". Table 2, 18B, defines the ID value of CANID and the bus load L value (hereinafter referred to as "L value") for each range of buffer amount BA as follows: 80% ≤ BA < 90% → ID value = 0x200, L value = 60% 90% ≤ BA < 95% → ID value = 0x100, L value = 70% 95% ≤ BA → ID value = 0x50, L value = 100%

[0063] When the second table 18B is adopted, the controller 13 selects a smaller ID value (higher priority ID value) the larger the buffer amount BA of the high-speed receive buffer FRBj, and increases the transmission frequency of the suppression frame SF so that it becomes the defined L value. Therefore, compared to the case where the transmission frequency of suppression frames SF is kept constant, the degree of transmission suppression to the F-ECU (second ECU) 40 can be increased.

[0064] The transmission frequency F of the suppression frame SF is calculated by the following equation (1). F = (L × B) / D ……(1) However, L: Bus load (% / 100) D: Data length per frame (bits) F: Frame transmission frequency (number of frames / second) B: Bus bandwidth (bits / second)

[0065] [Other variations] The embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present invention is not limited to the embodiments described above, and includes all modifications within the scope equivalent to the configurations described in the claims. In the embodiments described above, in addition to CAN and CAN-FD, FlexRay (Flexible Time-Triggered Protocol for Automotive Applications) may also be adopted.

[0066] FlexRay meets condition 1 because it employs a protocol that determines transmission priority based on the number of identifiers. Furthermore, FlexRay is a high-speed communication protocol suitable for real-time requests and has a higher maximum transmission speed than CAN-FD. Therefore, in the above embodiment, the first communication protocol may be CAN-FD and the second communication protocol may be FlexRay. Alternatively, the first communication frame may be CAN and the second communication protocol may be FlexRay. [Explanation of Symbols]

[0067] 1 vehicle 10 CGW (Vehicle-mounted relay device) 11 Relay Processing Unit 12C Transceiver 1 12F 2nd Transceiver 13 Controllers 14 memory 15 buffers 16 Computer Programs 17 Relay Table 18 Compatible Tables 18A Table 1 18B Table 2 30 C-ECU (1st ECU) 40 F-ECU (Second ECU) 50 CAN bus (Bus No. 1) 60 CAN bus (2nd bus) 100 In-vehicle communication systems CPi Port 1 (physical port for CAN frames) FPj 2nd port (physical port for CAN-FD frames) TP 3rd port (physical port for external communication) CTBi Port 1 transmit buffer CRBi Receive buffer for port 1 FTBj second port transmit buffer FRBj Receive buffer for port 2

Claims

1. The first port, which is the physical port of the first frame shown below, The second port, which is the physical port of the second frame shown below, An in-vehicle relay device comprising a relay processing unit that performs relay processing to determine the output port of a received frame and protocol conversion to convert the format of the received frame to the format of the transmitting side, The relay processing unit, An in-vehicle relay device that, when the amount of the transmit buffer of the first port is equal to or greater than a threshold, transmits the second frame from the second port, in which an identifier representing the transmission priority is set to a predetermined value. First frame: A communication frame that conforms to the first communication protocol and contains an identifier indicating the transmission priority. Second frame: A communication frame containing an identifier indicating transmission priority, conforming to a second communication protocol with a higher maximum transmission speed than the first communication protocol.

2. The first port is multiple, The relay processing unit, The in-vehicle relay device according to claim 1, wherein the second frame is transmitted from the second port when the transmit buffer amount of any of the multiple first ports is equal to or greater than a threshold.

3. The aforementioned second port is multiple, The relay processing unit, The in-vehicle relay device according to claim 1, wherein the value of the identifier to be applied to the second frame is determined according to the amount of the receive buffer of a plurality of the second ports.

4. The relay processing unit, The in-vehicle relay device according to claim 3, wherein the value of the identifier is determined such that the transmission priority increases for the second port which has a larger receive buffer size.

5. The relay processing unit, The in-vehicle relay device according to claim 4, wherein the transmission frequency of the second frame is increased for the second port which has a larger receive buffer size.

6. The payload of the second frame described above includes: An in-vehicle relay device according to any one of claims 1 to 5, wherein an identifier other than the aforementioned identifier and an actual data section are stored.

7. The first communication protocol is CAN, The in-vehicle relay device according to any one of claims 1 to 5, wherein the second communication protocol is CAN-FD.

8. The in-vehicle relay device according to claim 7, wherein the identifier is a CANID.

9. The first port, which is the physical port of the first frame shown below, The second port, which is the physical port of the second frame shown below, A flow control method executed in an in-vehicle relay device, comprising a relay processing unit that performs relay processing to determine the output port of a received frame and protocol conversion to convert the format of the received frame to the format of the transmitting side, The steps include obtaining the transmit buffer size of the first port, A flow control method comprising the step of transmitting a second frame from the second port, in which an identifier representing the transmission priority is set to a predetermined value, when the acquired amount of the transmit buffer is equal to or greater than a threshold. First frame: A communication frame that conforms to the first communication protocol and contains an identifier indicating the transmission priority. Second frame: A communication frame containing an identifier indicating transmission priority, conforming to a second communication protocol with a higher maximum transmission speed than the first communication protocol.

10. The first port, which is the physical port of the first frame shown below, The second port, which is the physical port of the second frame shown below, A computer program for causing a computer to function as an in-vehicle relay device, comprising a relay processing unit that performs relay processing to determine the output port of a received frame and protocol conversion to convert the format of the received frame to the format of the transmitting side, The steps include obtaining the transmit buffer size of the first port, A computer program comprising the step of transmitting a second frame from the second port, in which an identifier representing the transmission priority is set to a predetermined value, if the acquired transmit buffer amount is greater than or equal to a threshold. First frame: A communication frame that conforms to the first communication protocol and contains an identifier indicating the transmission priority. Second frame: A communication frame containing an identifier indicating transmission priority, conforming to a second communication protocol with a higher maximum transmission speed than the first communication protocol.

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