Communication method and communication device

Abstract

The present disclosure pertains to a communication method and a communication device that enable resolving a discrepancy between a transmission buffer and a reception buffer. A communication device according to the present disclosure transmits / receives a packet to / from a communication partner device by means of an A-PHY. When an ACK signal is received from the communication partner device and a packet of an MC number indicated by the ACK signal is not present in the transmission buffer, the communication device transmits, to the communication partner device, an ACK request signal for requesting an ACK signal that indicates the latest MC number present in the reception buffer of the communication partner device. The present disclosure can be applied to, for example, a communication system to which an in-vehicle camera is connected.

Description

Communication method and communication device

[0001] The present disclosure relates to a communication method and a communication device, and more particularly to a communication method and a communication device that can eliminate discrepancies between a transmission buffer and a reception buffer.

[0002] One of the standards defined by the Mobile Industry Processor Interface (MIPI) Alliance is the Automotive PHY (A-PHY) standard (see, for example, Non-Patent Document 1). A-PHY is a standard related to the physical layer of an in-vehicle SerDes (Serializer Deserializer).

[0003] MIPI Alliance Specification for A-PHY, version 1.1, MIPI Alliance, Inc., 9 August 2021.

[0004] The MIPI A-PHY standard does not specify the behavior when an ACK signal is received that indicates an MC (Message Counter) number that does not exist in the A-packet held in the transmit buffer. Therefore, there is a risk of a discrepancy occurring between the MC numbers of the A-packets held in the transmit buffer and the receive buffer.

[0005] The present disclosure has been made in view of such circumstances, and aims to eliminate the discrepancy between the transmission buffer and the reception buffer.

[0006] A communication method according to a first aspect of the present disclosure is a communication method including a communication device that transmits and receives packets to and from a communication partner device via A-PHY, receiving an ACK signal from the communication partner device, and, if the packet having the MC number indicated in the ACK signal is not present in a transmission buffer, transmitting an ACK request signal to the communication partner device requesting the ACK signal indicating the most recent MC number present in the reception buffer of the communication partner device.

[0007] A communication device according to a first aspect of the present disclosure includes a communication unit that transmits and receives packets to and from a communication partner device via A-PHY, and the communication unit receives an ACK signal from the communication partner device, and if the packet with the MC number indicated in the ACK signal is not present in a transmission buffer, transmits an ACK request signal to the communication partner device requesting the ACK signal indicating the latest MC number present in the reception buffer of the communication partner device.

[0008] A communication device according to a second aspect of the present disclosure includes a communication unit that transmits and receives packets to and from a communication partner device via A-PHY, and the communication unit receives an ACK request signal that requests an ACK signal indicating the latest MC number present in a receive buffer when the packet having the MC number indicated in the ACK signal sent to the communication partner device is not present in the transmit buffer of the communication partner device, and when the ACK request signal is received, transmits the ACK signal indicating the latest MC number present in the receive buffer to the communication partner device.

[0009] In a first aspect of the present disclosure, packets are sent and received between a communication partner device via A-PHY, an ACK signal is received from the communication partner device, and if the packet with the MC number indicated by the ACK signal is not present in the transmission buffer, an ACK request signal is sent to the communication partner device requesting the ACK signal indicating the latest MC number present in the reception buffer of the communication partner device.

[0010] In a second aspect of the present disclosure, packets are sent and received between a communication partner device via A-PHY, and an ACK request signal is received requesting the ACK signal indicating the latest MC number present in the receive buffer when the packet with the MC number indicated in the ACK signal sent to the communication partner device is not present in the transmit buffer of the communication partner device, and when the ACK request signal is received, the ACK signal indicating the latest MC number present in the receive buffer is sent to the communication partner device.

[0011] 1 is a diagram illustrating an overview of a communication system to which the technology according to the present disclosure can be applied. FIG. 1 is a diagram illustrating an example of the configuration of an A-packet. FIG. 2 is a diagram illustrating an example of the configuration of a source-sink according to an embodiment of the present disclosure. FIG. 3 is a flowchart illustrating behavior when a single retransmission request is received. FIG. 4 is a flowchart illustrating behavior when a gap retransmission request is received. FIG. 5 is a diagram illustrating an example of processing for a transmission buffer when a single retransmission request is received. FIG. 6 is a flowchart illustrating behavior when an ACK is received. FIG. 7 is a diagram illustrating an example of processing for a transmission buffer when an ACK is received. FIG. 8 is a diagram illustrating an example of processing for a transmission buffer when an ACK is received. FIG. 9 is a diagram illustrating behavior when an ACK is received according to the present disclosure. FIG. 10 is a diagram illustrating an example of a CN. FIG. 11 is a diagram illustrating an example of the configuration of an ACK and an ACK Req. FIG. 12 is a diagram illustrating loss of an error packet after receiving an ACK. FIG. 13 is a diagram illustrating avoidance of loss of an error packet after receiving an ACK.

[0012] Modes for carrying out the present disclosure (hereinafter referred to as embodiments) will be described below in the following order.

[0013] 1. Overview of communication system 2. Example of source-sink configuration 3. Conventional technology and its problems 4. Operation when ACK is received using the technology according to the present disclosure 5. Comparison between conventional technology and the technology according to the present disclosure 5-1. Example of operation in conventional technology (loss of error packet after receiving ACK) 5-2. Example of operation in technology according to the present disclosure (avoidance of loss of error packet) 6. Modification

[0014] 1. Overview of Communication System FIG. 1 is a diagram showing an example configuration of a communication system to which the technology according to the present disclosure can be applied.

[0015] The communication system 1 shown in FIG. 1 is composed of a communication device 10 and a communication device 20. The communication devices 10 and 20 exchange data via a communication path 30. In the communication system 1, data is transmitted between the communication devices 10 and 20 via an A-PHY network. A-PHY is a standard defined by the MIPI Alliance as a physical layer for in-vehicle SerDes. That is, the communication devices 10 and 20 transmit and receive packets to and from each other via A-PHY.

[0016] One of the communication devices 10 and 20 is configured as a communication device on the image sensor side mounted on an in-vehicle camera, and the other is configured as a communication device on the ECU (Electronic Control Unit) side, which is a computer that controls the vehicle.

[0017] The communication device 10 includes a processing unit 11 and a communication unit 12. The processing unit 11 is composed of a chip that performs processing related to the Protocol Adaptation Layer (PAL), a CPU (Central Processing Unit) that controls the operation of each unit of the communication device 10, and the like. The communication unit 12 is composed of a chip that performs processing related to data transmission, and the like. The communication unit 12 performs processing related to A-PHY (mainly PHY layer processing). The processing unit 11 performs processing related to the upper layer that is the layer above A-PHY.

[0018] The communication device 20 includes a processing unit 21 and a communication unit 22. The processing unit 21 is composed of a chip that performs PAL-related processing, a CPU that controls the operation of each unit of the communication device 20, and the like. The communication unit 22 is composed of a chip that performs data transmission-related processing, and the like. The communication unit 22 performs A-PHY-related processing. The processing unit 21 performs processing related to the upper layer, which is the layer above A-PHY.

[0019] In the communication system 1, one of the communication devices 10 and 20 serves as a source and the other as a sink. Transmission from the source to the sink is called a downlink, and transmission from the sink to the source is called an uplink. The transmission speed (communication speed) differs between the downlink and the uplink, with the downlink being faster than the uplink.

[0020] Here, it is assumed that in the communication system 1, an A-packet is transmitted from the communication device 10 on the sink side to the communication device 20 on the source side by serial communication via the communication path 30.

[0021] The communication unit 12 transmits the A-packet generated by the processing unit 11. At this time, the communication unit 12 adds an MC (Message Counter) number to the A-packet to be transmitted. For example, the MC number is a value from 0 to 255, and a different number is added to each A-packet. For example, the starting value is 0, and the number is incremented for each A-packet, and when the value reaches 255, it returns to 0 (wraps around), so that the MC number can continue to be added.

[0022] FIG. 2 is a diagram showing an example of the configuration of an A-packet.

[0023] As shown in FIG. 2, an A-Packet is composed of an A-Packet Header, an A-Packet Payload, and an A-Packet Tail.

[0024] The A-packet header includes the following fields: an 8-bit Adaptation Descriptor, an 8-bit Service Descriptor, an 8-bit Placement Descriptor, an 8-bit PHY2, an 8-bit Target Address, an 8-bit PHY3, an 8-bit Payload Length, and an 8-bit PHY Header CRC.

[0025] When an A-packet is transmitted from the source-side communication device 20 to the sink-side communication device 10, the same processing is basically performed, except that the above-described processing on the sink side and source side is reversed.

[0026] 2. Example of Source-Sink Configuration FIG. 3 is a diagram illustrating an example of a source-sink configuration according to an embodiment of the present disclosure.

[0027] FIG. 3 shows an example of the configuration of a source 100 corresponding to the communication device on the image sensor side and a sink 200 corresponding to the communication device on the ECU side.

[0028] The source 100 is configured to include a CMOS (Complementary Metal Oxide Semiconductor) Image Sensor (CIS) 110 , an adaptation layer 120 , a data link layer 130 , and a PHY layer 140 .

[0029] The CIS 110 has a plurality of pixels and outputs pixel data obtained by photoelectric conversion. The adaptation layer 120 converts various data, such as the pixel data output by the CIS 110, into A-packets. As described above, MC numbers ranging from 0 to 255 are assigned in order to the A-packets. The data link layer 130 realizes data transmission with the sink 200 by providing functions and procedures for transmitting and receiving data via the PHY layer 140.

[0030] The PHY layer 140 corresponds to, for example, the communication unit 12 included in the communication device 10 in Fig. 1 and performs processing related to A-PHY. The PHY layer 140 is configured to include an RTS (Retransmission) 150 that performs processing related to retransmission, etc. The RTS 150 has a transmission buffer 151 (TX Buffer) that stores packets that have already been transmitted and packets that are scheduled to be transmitted.

[0031] On the other hand, the sink 200 is configured to include at least a PHY layer 210 .

[0032] The PHY layer 210 corresponds to, for example, the communication unit 22 included in the communication device 20 in FIG. 1 and performs processing related to A-PHY. The PHY layer 210 is configured to include an RTS 220 that performs processing related to retransmission, etc. The RTS 220 has a CRC check unit 221 that performs error detection using the CRC added to the A-packet from the source 100, and a receive buffer 222 (RX Buffer) that stores received packets. The packets stored in the receive buffer 222 are transferred to the subsequent data link layer (not shown), for example, in the order of their MC numbers.

[0033] In the source 100 and sink 200 configured in this manner, the source 100 transmits original packets to the sink 200 as appropriate. In response, the sink 200 transmits a single retransmission request, a gap retransmission request, or an ACK signal to the source 100 depending on the result of error detection by the CRC check unit 221. When the source 100 receives a single retransmission request or a gap retransmission request from the sink 200, it transmits a packet (retransmission packet) corresponding to the retransmission request to the sink 200. Although a detailed description will be omitted, a single retransmission request is a retransmission request for a packet with one MC number, and a gap retransmission request is a retransmission request for packets with at least one or more consecutive MC numbers.

[0034] 3. Prior Art and Its Issues (Retransmission Request) The source 100 and the sink 200 store transmitted / received packets in the transmission buffer 151 and the reception buffer 222, respectively, in preparation for retransmission of packets containing errors (hereinafter referred to as error packets).

[0035] The A-PHY standard stipulates that if source 100 receives a retransmission request indicating an MC number that does not exist in transmission buffer 151, the retransmission request will be rejected so that there is no discrepancy in the MC numbers of packets held in transmission buffer 151 and reception buffer 222.

[0036] FIG. 4 is a flow chart illustrating the behavior of source 100 upon receiving a single retransmission request.

[0037] When the PHY layer 140 of the source 100 (the communication unit 12 of the communication device 10) receives a single retransmission request from the sink 200 in step S11, it determines in step S12 whether a packet with the MC number (hereinafter referred to as "this MC") indicated in the single retransmission request exists in the TX Buffer (transmission buffer 151).

[0038] If the packet of this MC exists in the TX Buffer, the process proceeds to step S13 , where the PHY layer 140 of the source 100 retransmits the packet of this MC held in the TX Buffer to the sink 200 .

[0039] On the other hand, if the packet of this MC does not exist in the TX Buffer, the process proceeds to step S14, where the PHY layer 140 of the source 100 rejects the single retransmission request from the sink 200.

[0040] FIG. 5 is a flowchart illustrating the behavior of the source 100 when it receives a gap retransmission request.

[0041] When the PHY layer 140 of the source 100 (the communication unit 12 of the communication device 10) receives a gap retransmission request from the sink 200 in step S21, it determines in step S22 whether or not a packet with the most recent MC number (hereinafter referred to as Post Gap MC) among the MC numbers indicated in the gap retransmission request exists in the TX Buffer (transmission buffer 151).

[0042] If a packet with a Post Gap MC exists in the TX Buffer, the process proceeds to step S23, where the PHY layer 140 of the source 100 determines whether a packet with the oldest MC number (hereinafter referred to as the Last Matched MC) among the MC numbers indicated in the gap retransmission request exists in the TX Buffer (transmission buffer 151).

[0043] If the packet of the Last Matched MC exists in the TX Buffer, the process proceeds to step S24, and the PHY layer 140 of the source 100 retransmits the packets from (Last Matched MC+1) to (Post Gap MC-1) stored in the TX Buffer to the sink 200.

[0044] On the other hand, if the Post Gap MC packet does not exist in the TX Buffer, or if the Last Matched MC packet does not exist in the TX Buffer, the process proceeds to step S25, and the PHY layer 140 of the source 100 rejects the gap retransmission request from the sink 200.

[0045] In addition, if the Post Gap MC packet exists in the TX Buffer but the Last Matched MC packet does not exist in the TX Buffer, the packets held in the TX Buffer from (Last Matched MC+1) onwards may be retransmitted to the sink 200.

[0046] As described above, conventionally, in the A-PHY standard, the source 100 has the function of determining the processing to be performed in response to a retransmission request indicating an MC number that does not exist in the TX buffer, i.e., an unintended retransmission request.

[0047] For example, as shown in Fig. 6, it is assumed that packets with MC numbers 2 to 5 (hereinafter referred to as MC=2-5, etc.) are held in the TX Buffer (transmission buffer 151). In this case, a single retransmission request indicating MC=2-5 is accepted and MC=2-5 is retransmitted, while a single retransmission request indicating any other MC number is ignored.

[0048] (ACK Signal) When the sink 200 receives a packet from the source 100 normally, it can notify the source 100 that there is no need to retransmit that packet by using an ACK signal indicating the MC number of that packet.

[0049] FIG. 7 is a flowchart illustrating the behavior of the source 100 when it receives an ACK.

[0050] When the PHY layer 140 of the source 100 (the communication unit 12 of the communication device 10) receives an ACK signal from the sink 200 in step S31, it releases packets before the MC number (this MC) indicated in the ACK signal from the TX Buffer (transmission buffer 151) in step S32.

[0051] Here, the A-PHY standard does not specify the timing of issuing an ACK signal in the sink 200, so the source 100 can receive an ACK signal indicating any MC number at any timing. Furthermore, the source 100 does not have the function to select the processing to be performed for an ACK signal indicating an MC number that does not exist in the TX buffer, i.e., an unintended ACK signal.

[0052] For example, as shown in Fig. 8, when packets with MC numbers 2 to 5 (MC=2-5) are held in the TX Buffer (transmission buffer 151), when an ACK signal indicating MC=4 is received, packets up to MC=4, i.e., MC=2-4, are released. Similarly, as shown in Fig. 9, when an ACK signal indicating MC=2 is received, packets up to MC=2, i.e., only MC=2, are released.

[0053] On the other hand, as shown in Fig. 10, when an ACK signal indicating MC=6 is received, depending on the implementation, it is possible to either not release any packets held in the TX buffer or to release all packets held in the TX buffer.Also, as shown in Fig. 11, when an ACK signal indicating MC=1 is received, depending on the implementation, it is possible to either not release any packets held in the TX buffer or to release all packets held in the TX buffer.

[0054] If the source 100 receives an unintended ACK signal in this way, there is a risk that a discrepancy will occur between the MC numbers of packets held in the TX buffer and the RX buffer. In this case, the state in which the discrepancy in the MC numbers occurs will continue until an ACK signal indicating the MC number held in the TX buffer is received, or until both the TX buffer and the RX buffer are reset due to a link down between the source 100 and the sink 200 or sleep between the source 100 and the sink 200.

[0055] <4. Operation when ACK is received using the technology according to the present disclosure> In the technology according to the present disclosure, in response to an unintended ACK signal as described above, the source 100 determines whether a packet with the MC number indicated in the ACK signal is present in the TX Buffer, and determines whether to accept or reject the ACK signal.

[0056] The behavior of the source 100 to which the technology according to the present disclosure is applied when receiving an ACK will be described with reference to the flowchart of FIG.

[0057] When the PHY layer 140 of the source 100 (the communication unit 12 of the communication device 10) receives an ACK signal from the sink 200 in step S101, it determines in step S102 whether a packet with the MC number (this MC) indicated in the ACK signal exists in the TX Buffer (transmission buffer 151).

[0058] If the packet of this MC exists in the TX Buffer, the process proceeds to step S103, where the PHY layer 140 of the source 100 releases the packet before this MC indicated by the ACK signal from the TX Buffer.

[0059] On the other hand, if the packet of this MC does not exist in the TX Buffer, the process proceeds to step S104 , where the PHY layer 140 of the source 100 discards the ACK signal from the sink 200 .

[0060] Furthermore, in step S105, the PHY layer 140 of the source 100 issues an ACK request signal (ACK Req) requesting an ACK signal indicating the latest MC number present in the RX buffer (receiving buffer 222) of the sink 200, and transmits it to the sink 200.

[0061] In the A-PHY standard, each request or packet is transmitted by successively transmitting a control mark (CM) and control nibbles (CN) as control data. Conventionally, the CN of the A-PHY standard defines an ACK (Ack Indication) that indicates a positive response in the uplink (from the sink to the source). In the technology disclosed herein, a positive response request in the downlink (from the source to the sink) is newly defined in the CN.

[0062] FIG. 13 is a diagram showing an example of a newly defined CN.

[0063] 13, Null, PS (Packet Start), PE (Packet End), RRS (Ret. Req. Start), RE (Req. End), GRS (Gap Req. Start), RTR (Re-Train Req.), CMR (sCMax Req.), and INT (Interrupt) / PC (Packet Continue) are CNs defined in the conventional method. In the technology disclosed herein, as shown in FIG. 13, ACK Req (Ack Indication Request) is newly defined as the CN of code 1010 in addition to the previously defined ACK (Ack Indication).

[0064] FIG. 14 is a diagram showing an example of the structure of an ACK and an ACK Req.

[0065] 14A shows an example of the structure of an ACK packet transmitted as an ACK signal. In the CN of the ACK packet, CN1 is ignored, and CN2 is set to ACK indicating a positive response. The byte data following the CN consists of an MC number used to release the packet in the TX buffer and a CRC (Cyclic Redundancy Check) used for error checking.

[0066] 14B shows an example of the structure of an ACK Req packet transmitted as an ACK request signal. In the CN of the ACK Req packet, CN1 is set to Null, and CN2 is set to ACK Req, which indicates an acknowledgement request. The byte data d1 following CN may be empty data, or may be composed of, for example, an MC number indicating a packet to be released in the TX Buffer.

[0067] As described above, the ACK Req indicating an acknowledgment request is newly defined without changing the format of the conventional A-PHY standard, thereby reducing the impact of increased circuitry.

[0068] When the PHY layer 210 of the sink 200 (the communication unit 22 of the communication device 20) receives an ACK request signal (ACK Req), it transmits an ACK signal indicating the latest MC number present in the RX Buffer at that time to the source 100. At this time, packets with an MC number earlier than the latest one are released from the RX Buffer.

[0069] On the other hand, when the PHY layer 140 of the source 100 (the communication unit 12 of the communication device 10) receives an ACK signal indicating the latest MC number from the sink 200, it releases packets with an MC number earlier than the latest one from the TX buffer.

[0070] According to the above process, even if an unintended ACK signal is received, the source 100 issues and transmits an ACK request signal to the sink 200, which causes packets before the MC number indicated by the ACK Req to be released in both the TX buffer and the RX buffer. This makes it possible to resolve any discrepancies between the transmission buffer and the reception buffer.

[0071] 5. Comparison Between the Prior Art and the Technology According to the Present Disclosure In the following, the prior art and the technology according to the present disclosure will be compared using specific operation examples.

[0072] (5-1. Example of Operation in Conventional Technology (Loss of Error Packet After Receiving ACK)) FIG. 15 is a diagram illustrating the loss of an error packet after receiving ACK, as an example of source-sink operation in conventional technology.

[0073] 15, the left side shows the behavior of the TX (source 100), which is the operation of the PHY layer 140 and the state of the TX Buffer (transmit buffer 151) at timings P11 to P17. The right side shows the behavior of the RX (sink 200), which is the operation of the PHY layer 210 and the state of the RX Buffer (receive buffer 222) at timings P21 to P27.

[0074] First, at timing P11, the PHY layer 140 has completed transmission of MC=0-18 (packets with MC numbers 0 to 18), and the TX Buffer holds the transmitted MC=0-18. Meanwhile, at timing P21, the PHY layer 210 has completed reception of MC=0-18, and the RX Buffer holds the transmitted MC=0-18.

[0075] At timing P12, the PHY layer 140 releases MC=0 from the TX buffer because the fixed time, Max RTS Delay, has elapsed. In this way, the TX (source 100) releases packets that have been held in the TX buffer for the fixed time (Max RTS Delay), as well as packets with the MC number indicated in the received ACK signal.

[0076] On the other hand, at timing P22, the PHY layer 210 still holds MC=0 in the RX buffer because the conditions for releasing an MC (packet) from the RX buffer are different from those for the TX buffer. Conditions for releasing an MC from the RX buffer include when the oldest MC in the RX buffer is transferred to the data link layer, when an ACK signal is issued, or when a significant jump in the MC number occurs.

[0077] That is, at timing P23, the PHY layer 210 issues an ACK signal for MC=0 (hereinafter referred to as ACK MC=0, etc.), thereby releasing MC=0 from the RX buffer. In this way, the RX (sink 200) can issue an ACK signal for any MC at any timing.

[0078] On the other hand, at timing P13, the PHY layer 140 receives an ACK MC=0 without an MC=0 in the TX buffer. In this way, the TX (source 100) can receive an ACK signal for an MC that does not exist in the TX buffer. In this case, the PHY layer 140 releases packets before MC=0 from the TX buffer.

[0079] However, because the value of the 8-bit MC number (MC[7:0]) wraps around to 0 after 255, it is not possible to determine whether a packet is new or old based on the magnitude of the value. Furthermore, the A-PHY standard does not prescribe the TX's discretion to ignore unintended ACK signals. Therefore, depending on the implementation, all MCs up to "non-existent MC = 0" may be released from the TX buffer. As a result, receiving an unintended ACK signal can cause a discrepancy between the MCs held in the TX buffer and the RX buffer.

[0080] Here, it is assumed that after MC=19 is transmitted to the RX (sink 200) and stored in the TX buffer at timing P13, all MCs (MC=1-19) are released from the TX buffer due to the unintended reception of an ACK signal. After that, at timing P14, the PHY layer 140 continues packet transmission from MC=20.

[0081] Meanwhile, at timing P24, the PHY layer 210 detects an error for MC=19 and issues a retransmission request. In response to this retransmission request, at timing P15, the PHY layer 140 rejects the retransmission request for MC=19 as an unintended request because MC=19 is not present in the TX buffer. At this time, a packet with MC=21 is transmitted to the RX (sink 200) and stored in the TX buffer. Subsequent MCs are transmitted and stored in the same manner.

[0082] At timing P25, the PHY layer 210 issues an additional retransmission request because MC=19 was not retransmitted. Here, a packet with MC=20 is received and stored in the RX buffer. Subsequent MCs are similarly received and stored. In response to this retransmission request, at timing P16, the PHY layer 140 rejects the retransmission request for MC=19 as an unintended request because MC=19 is not present in the TX buffer.

[0083] At timing P26, the PHY layer 210 issues an additional retransmission request because MC=19 is not retransmitted. In response to this retransmission request, at timing P17, the PHY layer 140 rejects the retransmission request for MC=19 as an unintended request because MC=19 does not exist in the TX buffer.

[0084] In this way, the issuance and reception of retransmission requests for MCs that will ultimately not be retransmitted are repeated.

[0085] Here, between the source 100 and the sink 200, not only packets are transmitted from the source 100 to the sink 200, but also packets are transmitted from the sink 200 to the source 100 as appropriate. However, since a retransmission request has the highest packet transmission priority, repeated retransmission requests from the sink 200 to the source 100 restrict the transmission rate of original packets and retransmission packets from the sink 200.

[0086] At timing P27, since a retransmission request for the same MC can be issued a maximum of three times, the PHY layer 210 will not issue any more retransmission requests for MC=19. Furthermore, since MC=19 will not be retransmitted, the error packet (MC=19) will be lost.

[0087] (5-2. Example of Operation in Technology According to the Present Disclosure (Avoiding Loss of Error Packets)) FIG. 16 is a diagram illustrating an example of source-sink operation in the technology according to the present disclosure, which illustrates avoiding loss of error packets after receiving an ACK.

[0088] As in Fig. 15, the left side of Fig. 16 shows the behavior of TX (source 100), which is the operation of the PHY layer 140 and the state of the TX Buffer (transmit buffer 151) at timings P111 to P115. The right side of Fig. 16 shows the behavior of RX (sink 200), which is the operation of the PHY layer 210 and the state of the RX Buffer (receive buffer 222) at timings P121 to P126.

[0089] First, at timing P111, the PHY layer 140 has completed transmission of MC=0-18, and the TX Buffer holds the transmitted MC=0-18. Meanwhile, at timing P121, the PHY layer 210 has completed reception of MC=0-18, and the RX Buffer holds the transmitted MC=0-18.

[0090] At timing P112, the PHY layer 140 releases MC=0 from the TX buffer because a certain time, Max RTS Delay, has elapsed.

[0091] On the other hand, at timing P122, the PHY layer 210 still holds MC=0 in the RX buffer because the MC (packet) release conditions from the RX buffer are different from those of the TX buffer.

[0092] That is, at timing P123, the PHY layer 210 issues an ACK MC=0, thereby releasing the MC=0 from the RX Buffer. Here again, the RX (sink 200) can issue an ACK signal for any MC at any timing.

[0093] On the other hand, at timing P113, the PHY layer 140 receives an ACK MC=0 when there is no MC=0 in the TX buffer. At this time, the PHY layer 140 discards the ACK signal for the MC that does not exist in the TX buffer. Furthermore, the PHY layer 140 issues an ACK Req requesting an ACK signal indicating the latest MC number present in the RX buffer of the RX (sink 200) and transmits it to the RX.

[0094] It is assumed here that after ACK Req is transmitted to RX at timing P113, MC=19 is transmitted to RX and stored in the TX Buffer.

[0095] At timing P124, the PHY layer 210 receives an ACK Req from the TX and issues an ACK MC=18, thereby releasing packets with MC=18 and earlier (MC=1-18) from the RX Buffer. That is, the PHY layer 210 issues an ACK signal for the latest MC that can be issued. Then, at timing P114, the PHY layer 140 receives an ACK MC=18 and releases packets with MC=18 and earlier (MC=1-18) from the TX Buffer. This makes it possible to resolve any discrepancies between the TX Buffer and the RX Buffer. At this time, a packet with MC=20 is transmitted to the RX and stored in the TX Buffer. Subsequent MCs are transmitted and stored in the same manner.

[0096] Also, at timing P124, the PHY layer 210 detects an error in MC=19 received after the ACK Req and issues a retransmission request. In response to this retransmission request, at timing P115, the PHY layer 140 retransmits MC=19 stored in the TX Buffer to the RX.

[0097] In the RX, after receiving the packet with MC=20 at timing P125, the retransmitted packet with MC=19 is received at timing P126.

[0098] As described above, according to the technology disclosed herein, it is possible to avoid the loss of error packets.

[0099] Furthermore, the technology disclosed herein can avoid repeated issuance and reception of retransmission requests to MCs that will ultimately not be retransmitted, and can also avoid rate-limiting the transmission of original packets and retransmission packets from the sink 200.

[0100] 6. Modifications The current A-PHY standard does not provide a mechanism for the TX (source 100) to actively release packets from the TX buffer. As described above, the condition for releasing a packet from the TX buffer is the passage of Max RTS Delay or the reception of an ACK signal. Furthermore, if the capacity of the TX buffer has reached Max Size, the TX will not fetch new packets from the data link layer.

[0101] In contrast to this, in the technology disclosed herein, the PHY layer 140 of the TX (source 100) may transmit an ACK Req to the RX (sink 200) before burst transmitting packets. This allows the capacity of the TX Buffer to be reduced in advance, and prevents the capacity of the TX Buffer from reaching its Max Size.

[0102] Alternatively, the PHY layer 140 of the TX (source 100) may transmit an ACK Req to the RX (sink 200) after transmitting a burst of packets. This allows the capacity of the TX Buffer to be reduced even after the burst transmission, and prevents the capacity of the TX Buffer from reaching the Max Size.

[0103] Furthermore, the PHY layer 140 of the TX (source 100) may periodically transmit an ACK Req to the RX (sink 200), thereby periodically reducing the capacity of the TX Buffer and preventing the capacity of the TX Buffer from reaching its Max Size.

[0104] In this specification, a system refers to a collection of multiple components (devices, modules (components), etc.), regardless of whether all of the components are contained in the same housing. Therefore, multiple devices housed in separate housings and connected via a network, and a single device housed in a single housing with multiple modules, are both systems.

[0105] Furthermore, the embodiments to which the technology according to the present disclosure is applied are not limited to the above-described embodiments, and various modifications are possible within the scope that does not deviate from the gist of the technology according to the present disclosure.

[0106] Furthermore, the present disclosure may have the following configurations. (1) A communication method including a communication device transmitting and receiving packets to a communication partner device via A-PHY, receiving an ACK signal from the communication partner device, and, if the packet having the MC number indicated in the ACK signal is not present in a transmission buffer, transmitting an ACK request signal to the communication partner device requesting the ACK signal indicating the most recent MC number present in the reception buffer of the communication partner device. (2) The communication method described in (1), in which, if the packet having the MC number indicated in the ACK signal is not present in the transmission buffer, the ACK signal is rejected and the ACK request signal is transmitted to the communication partner device. (3) The communication method described in (2), in which, if the packet having the MC number indicated in the ACK signal is present in the transmission buffer, the packet having the MC number previous to the MC number is released from the transmission buffer. (4) The communication method described in (3), in which, if the communication partner device receives the ACK request signal, the communication device transmits the ACK signal indicating the most recent MC number present in the reception buffer. (5) The communication method according to (4), in which the communication device, when receiving the ACK signal indicating the latest MC number, releases the packets with the latest MC number or earlier from the transmission buffer. (6) The communication method according to any of (1) to (5), in which the ACK request signal is specified by CN (Control Nibbles) of an A-packet. (7) The communication method according to any of (1) to (6), in which the ACK request signal is further transmitted to the communication partner device before or after burst transmitting the packets. (8) The communication method according to any of (1) to (7), in which the ACK request signal is further transmitted to the communication partner device at regular intervals.(9) A communication device comprising: a communication unit that transmits and receives packets to and from a communication partner device via A-PHY, the communication unit receiving an ACK signal from the communication partner device, and, if the packet having the MC number indicated in the ACK signal is not present in a transmit buffer, transmitting an ACK request signal to the communication partner device requesting the ACK signal indicating the latest MC number present in the receive buffer of the communication partner device. (10) A communication device comprising: a communication unit that transmits and receives packets to and from a communication partner device via A-PHY, the communication unit receiving an ACK request signal that requests the ACK signal indicating the latest MC number present in the receive buffer, the ACK request signal being transmitted if the packet having the MC number indicated in the ACK signal transmitted to the communication partner device is not present in the transmit buffer of the communication partner device, and, if the ACK request signal is received, transmitting the ACK signal indicating the latest MC number present in the receive buffer to the communication partner device.

[0107] REFERENCE SIGNS LIST 1 communication system, 10 communication device, 11 processing unit, 12 communication unit, 20 communication device, 21 processing unit, 22 communication unit, 30 communication path, 100 source, 110 CIS, 120 adaptation layer, 130 data link layer, 140 PHY layer, 150 RTS, 151 transmission buffer, 200 sink, 210 PHY layer, 220 RTS, 221 CRC check unit, 222 reception buffer

Claims

1. A communication method comprising: a communication device that transmits and receives packets to and from a communication partner device via A-PHY; receiving an ACK signal from the communication partner device; and, if the packet with the MC number indicated in the ACK signal is not present in the transmission buffer, transmitting an ACK request signal to the communication partner device requesting the ACK signal indicating the most recent MC number present in the reception buffer of the communication partner device.

2. The communication method according to claim 1, wherein if the packet having the MC number indicated by the ACK signal is not present in the transmission buffer, the ACK signal is rejected and the ACK request signal is transmitted to the communication partner device.

3. The communication method according to claim 2, wherein, if the packet with the MC number indicated by the ACK signal exists in the transmission buffer, the packets with the MC number before the MC number are released from the transmission buffer.

4. The communication method according to claim 3, wherein the communication partner device, when receiving the ACK request signal, transmits the ACK signal indicating the latest MC number present in the receiving buffer to the communication device.

5. The communication method according to claim 4, wherein the communication device, when receiving the ACK signal indicating the latest MC number, releases the packets with an MC number earlier than the latest MC number from the transmission buffer.

6. The communication method according to claim 1, wherein the ACK request signal is defined by the CN (Control Nibbles) of an A-packet.

7. The communication method according to claim 1, further comprising transmitting the ACK request signal to the communication partner device before or after burst transmitting the packets.

8. The communication method according to claim 1, further comprising transmitting the ACK request signal to the communication partner device at regular intervals.

9. A communication device comprising a communication unit that transmits and receives packets to and from a communication partner device via A-PHY, wherein the communication unit receives an ACK signal from the communication partner device, and if the packet with the MC number indicated by the ACK signal is not present in the transmission buffer, transmits an ACK request signal to the communication partner device requesting the ACK signal indicating the most recent MC number present in the reception buffer of the communication partner device.

10. A communication device comprising a communication unit that transmits and receives packets to and from a communication partner device via A-PHY, wherein the communication unit receives an ACK request signal that requests an ACK signal indicating the most recent MC number present in a receive buffer when the packet with the MC number indicated in the ACK signal sent to the communication partner device does not exist in the send buffer of the communication partner device, and when the ACK request signal is received, transmits the ACK signal indicating the most recent MC number present in the receive buffer to the communication partner device.

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