JP5532775B2 - Communication system and retransmission buffer capacity measuring apparatus - Google Patents

Description

  The present invention relates to a communication system for recognizing the capacity of a retransmission buffer of an opposite device and a capacity of the retransmission buffer in a re-transmissible communication system having a retransmission buffer by using a link transmission line compliant with, for example, the PCI Express standard. It relates to a measuring device.

  In recent years, PCI Express, which is a third generation PC interface standard, has been adopted in communications such as communications between LSIs on PC boards, communications between PC boards, and communications between devices via a relatively short cable ( (Refer nonpatent literature 1.). The PC board includes a CPU, a root complex device that connects the CPU to the PCI express link, an endpoint device connected to the root complex device via the PCI express link, and a reference clock signal generation circuit. Is done. Here, the endpoint device is a semiconductor circuit such as a graphics card or a USB host controller. The PCI Express link is a dual simplex type link transmission line including at least one set of unidirectional differential transmission lines.

  In communication of data packets between computers, in order to maintain reliable data delivery, when a data packet from a transmission device is received without error, the reception device returns an acknowledgment to the transmission side. In such a communication system, for example, Patent Document 1 discloses that in packet communication between a transmission station and a reception station, the transmission station records the transmission time of the DT packet and is an acknowledgment packet corresponding to the packet. ) Comprising means for measuring the reception time of the packet, means for calculating a round-trip response time from the difference between the reception time of the ACK packet and the transmission time of the corresponding DT packet, means for measuring the reception interval of the ACK packet, and the response A communication system comprising a means for calculating an optimum window size based on the round trip time and the reception interval is disclosed.

  However, the conventional technique disclosed in Patent Document 1 optimizes the relationship between the size of a buffer for packet retransmission arranged in a transmission device and the transmission delay (transmission interval) of an acknowledgment from the reception device. It was not intended. In order to solve this problem, Japanese Patent Application Laid-Open No. 2004-228688 discloses a “transmission apparatus and reception” in order to provide a communication system capable of optimizing the size of the packet retransmission buffer and the transmission delay (interval) of the acknowledgment. A communication system in which a communication device is communicably connected, wherein the transmission device transmits a data packet to the reception device, and transmits a data packet transmitted from the transmission device to the reception device. A retransmission buffer held for retransmission, and the reception device receives a data packet from the transmission device and determines the validity of the data packet, and the validity determination unit On the basis of the determination result, a positive response indicating that the packet is approved or a negative response indicating that the packet is not approved An acknowledgment transmission unit for transmitting to the transmission device at intervals, and the transmission device further transmits the data packet from the transmission unit until receiving the acknowledgment from the reception device. Based on the delay time measurement unit that measures the delay time, the delay time measured by the delay time measurement unit, and the capacity of the retransmission buffer, whether or not the acknowledgment transmission interval at the acknowledgment transmission unit is appropriate is determined. And a transmission interval instruction unit for transmitting an instruction to change the transmission interval of the acknowledgment to the receiving device based on the determination result ”.

  However, although the communication system according to Patent Document 2 is easy to be circuitized, since it uses Vendor Specific DLLP (Data Link Layer Packet), the opposite device cannot be used unless it has the same function, and is versatile. There was a problem that there was no. In addition, in the case of continuous communication in which the packet length and continuity frequently change, there is a problem that the Vendor Specific DLLLP may interfere with communication as a useless packet.

  In the prior art according to Non-Patent Document 1, the capacity of the retransmission buffer is not defined because it varies depending on the mounting apparatus, and is not described regarding the retransmission buffer of the opposite device and its management. Also, as a supplement, when an ACK NAK latency timer (hereinafter referred to as AL timer) expires, an ACK packet is transmitted to the opposite device, and the device that received the ACK packet uses the ACK packet sequence number (for example, # 5) to retransmit the buffer. Open up to the corresponding part (# 5).

  PCI Express is a high-speed serial interface and an IO interface. Opposite devices (root complex for endpoints and vice versa) do not know which company is inserted into the device. For this reason, the retransmission buffer capacity of the opposite device is unknown, it is not known what maximum payload size is used for communication, and the retransmission buffer and retransmission buffer management unit may become a bottleneck in communication efficiency.

  In addition, noise may be superimposed in data communication, which may affect communication efficiency. If noise is superimposed, a communication error may occur and the capacity of the retransmission buffer or transmission buffer may become full. There was a problem that the communication efficiency was lowered.

  Furthermore, in the existing specification, the retransmission buffer capacity is released by the ACK from the opposite device. In the existing specification, ACK is transmitted when the AL timer expires, and the AL timer is defined by the lane width and the maximum payload size. For this reason, there is a problem that communication cannot be performed when the retransmission buffer of the opposite device is filled with data.

  Furthermore, since communication is performed in both directions, as shown below, when a long packet transfer occurs from the reception component before the AL timer expires, the transmission component is transmitted when the retransmission buffer of the transmission component becomes full. There is a problem that the packet transfer from is not performed and the communication efficiency is lowered. This will be described in detail below.

  FIG. 2 is a timing chart showing a first conventional example of a communication procedure between a transmission component (endpoint: EP) and a reception component (receive component: RC) in a communication system according to the prior art using PCI Express. It is a chart. In FIG. 2, when a packet is transferred from the transmission component, the retransmission buffer management unit of the opposite device indicates that an ACK packet is returned based on the expiration of the AL timer. Here, the packet is transferred from the transmission component to the reception component, and the sequence number (SEQ #) is returned as the last sequence number (SEQ # = 12) by combining three packets.

  FIG. 3 is a timing chart showing a second conventional example of a communication procedure between a transmission component (EP) and a reception component (RC) in a communication system according to the prior art using PCI Express. FIG. 3 shows that a NAK (Negative AcKnowledge) packet, which is a negative acknowledgment packet, is returned from the receiving component to the transmitting component during communication in which packets are transferred from the transmitting component to the receiving component. In addition, when the AL timer expires, it indicates that ACK packets are returned together.

  FIG. 4 is a timing chart showing a third conventional example of a communication procedure between a transmission component (EP) and a reception component (RC) in a communication system according to the prior art using PCI Express. FIG. 4 shows that when a packet is transferred from the transmission component to the reception component, the packet transfer from the reception component to the transmission component is started before the AL timer of the reception component expires. By the time the ACK packet is returned from the reception component to the transmission component, the retransmission buffer of the transmission component is full, and communication of packet transfer from the transmission component to the reception component is stopped. In addition, since a long TLP (Transaction Layer Packet) transmission is started before the transmission of the ACK packet, the ACK packet cannot be returned.

  As described with reference to FIGS. 2 to 4, when a long packet transfer occurs from the receiving component before the AL timer expires, the packet transfer from the transmitting component is performed when the retransmission buffer of the transmitting component is full. Communication efficiency is reduced.

  An object of the present invention is to provide a communication system that solves the above-described problems, can detect the maximum capacity of the retransmission buffer of the opposite device, and can improve the communication efficiency as compared with the prior art. is there.

  Another object of the present invention is to solve the above-described problems and provide a retransmission buffer capacity measuring apparatus capable of detecting the maximum capacity of the retransmission buffer of the opposite device.

A communication system according to a first aspect of the present invention is a communication system in which a transmission device and a reception device are communicably connected,
The transmission device includes a packet transmission unit for transmitting a data packet to the reception device, a retransmission buffer for holding a data packet transmitted to the reception device for retransmission, and a data packet transmitted to the reception device. A retransmission buffer management unit for assigning a management number;
The receiving device receives the data packet from the transmitting device, and approves the packet based on a validity determination unit that determines the validity of the data packet and a determination result of the validity determination unit. An acknowledgment transmission unit that transmits an acknowledgment or a negative response that indicates a negative response to the transmission device at a predetermined interval, and a packet transmission unit that transmits a data packet to the transmission device.
When the above receiving apparatus that has received the data packet from the transmitting device, without a reception response is positive acknowledgment or negative acknowledgment in order to retransmission of the transmission device,
The transmitter retransmits a predetermined amount of data packets stored in the retransmission buffer of the transmitter after expiration of the retransmission timer of the transmitter;
The receiving apparatus receives a predetermined amount of data packets retransmitted from the transmitting apparatus, and estimates a capacity of the received predetermined amount of data packets as a maximum capacity of a retransmission buffer of the transmitting apparatus.

In the communication system, when retransmission is performed between the transmission device and the reception device, retransmission control is performed upon reception of a negative response or expiration of a retransmission timer,
The transmission device and the reception device determine a retransmission timer value according to the maximum payload size and the lane width of the connection destination at the time of communication initialization between the transmission device and the reception device,
The data packet transmitted by the receiving apparatus calculates a data size that can be theoretically transmitted before the retransmission timer expires, and performs packet transfer with a maximum payload size.

  Further, in the communication system, the receiving apparatus estimates a data storage state of the retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus, and accordingly Thus, the packet transfer is performed by changing the packet length of the packet transmitted from the receiving device or changing the data size.

  Further, in the communication system, the receiving apparatus estimates a data accumulation state of a retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus, and the retransmission When it is detected that a predetermined amount of data is stored in the buffer, the expiration time of the retransmission timer is shortened or a transmission request is made to the transmission apparatus.

  Still further, in the communication system, the receiving device estimates a data accumulation state of a retransmission buffer of the transmitting device based on a reception response transmitted from the receiving device and a size of packet data transmitted from the receiving device, and When it is detected that a full amount of data is stored in the retransmission buffer, the retransmission timer is forcibly expired or an acknowledgment is transmitted to the transmission apparatus.

  Still further, in the communication system, the receiving apparatus estimates a data storage state of a retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus, and the reception apparatus When a packet is transferred from the device to the transmitting device, a response transmission request signal is sent to release the retransmission buffer of the transmitting device according to the data accumulation status of the retransmission buffer of the transmitting device and the packet size to be transferred next It is characterized by that.

  In the communication system, the receiving apparatus estimates a maximum capacity of a retransmission buffer of the transmitting apparatus, and notifies an upper layer to transmit a data packet having a length corresponding to the maximum capacity.

  Furthermore, in the communication system, the receiving apparatus estimates the maximum capacity of the retransmission buffer of the transmitting apparatus, and in the communication system that implements flow control, in order to prevent misrecognition due to communication stop due to the influence of the reception buffer, In the initial sequence, the flow control reception buffer is released.

Furthermore, in the communication system, the above transmitting apparatus and the receiving apparatus when each having information of the maximum capacity of the retransmission server Ffa opposing device, and wherein the transmitting and receiving information of the maximum capacity of the retransmission buffer to each other.

  Still further, in the communication system, the operation of the transmission device and the reception device can be controlled from a higher-layer device or a facing device.

A retransmission buffer capacity measuring apparatus according to a second invention is a retransmission buffer capacity measuring apparatus for a receiving apparatus in a communication system in which a transmitting apparatus and a receiving apparatus are communicably connected.
The receiving device receives the data packet from the transmitting device, and approves the packet based on a validity determination unit that determines the validity of the data packet and a determination result of the validity determination unit. An acknowledgment transmission unit that transmits an acknowledgment or a negative response that indicates a negative response to the transmission device at a predetermined interval, and a packet transmission unit that transmits a data packet to the transmission device.
When the above receiving apparatus that has received the data packet from the transmitting device, without a reception response is positive acknowledgment or negative acknowledgment in order to retransmission of the transmission device,
The receiving apparatus receives a predetermined amount of data packets retransmitted from the transmitting apparatus, the data packet being stored in a retransmission buffer of the transmitting apparatus after expiration of a retransmission timer of the transmitting apparatus. The capacity of the received predetermined amount of data packets is estimated as the maximum capacity of the retransmission buffer of the transmitting apparatus.

In the retransmission buffer capacity measuring device, when performing retransmission at the receiving device, performing retransmission control upon reception of a negative response or expiration of a retransmission timer,
The receiving device determines a retransmission timer value according to a maximum payload size and a lane width of a connection destination at the time of communication initialization between the transmitting device and the receiving device,
The data packet transmitted by the receiving apparatus calculates a data size that can be theoretically transmitted before the retransmission timer expires, and performs packet transfer with a maximum payload size.

  In the retransmission buffer capacity measuring apparatus, the receiving apparatus estimates a data accumulation state of the retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus. Accordingly, the packet transfer is performed by changing the packet length of the packet transmitted from the receiving apparatus or changing the data size.

  Further, in the retransmission buffer capacity measuring apparatus, the receiving apparatus estimates a data accumulation state of the retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus. Then, when it is detected that a predetermined amount of data is stored in the retransmission buffer, the expiration time of the retransmission timer is shortened or a transmission request is made to the transmission apparatus.

  Still further, in the retransmission buffer capacity measuring apparatus, the receiving apparatus determines the data storage status of the retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus. When estimating and detecting that a full amount of data is stored in the retransmission buffer, the retransmission apparatus is forcibly expired or an acknowledgment is transmitted to the transmission apparatus. .

  Still further, in the retransmission buffer capacity measuring apparatus, the receiving apparatus estimates a data accumulation state of the retransmission buffer of the transmitting apparatus based on a reception response transmitted from the receiving apparatus and a size of packet data transmitted from the receiving apparatus. When the packet is transferred from the receiving device to the transmitting device, a response transmission request is issued to release the retransmission buffer of the transmitting device according to the data accumulation status of the retransmission buffer of the transmitting device and the packet size to be transferred next. A signal is transmitted.

  In the retransmission buffer capacity measuring apparatus, the receiving apparatus estimates a maximum capacity of the retransmission buffer of the transmitting apparatus and notifies an upper layer to transmit a data packet having a length corresponding thereto. To do.

  Further, in the retransmission buffer capacity measuring apparatus, the receiving apparatus estimates a maximum capacity of the retransmission buffer of the transmitting apparatus, and in a communication system that implements flow control, erroneous recognition due to communication stoppage due to the influence of the reception buffer. In order to prevent this, the flow control reception buffer is released in the initial sequence.

Furthermore, in the measurement apparatus of the retransmission buffer capacity, it is the receiving device when having the information of the maximum capacity of the retransmission server Ffa opposing device, and wherein the transmitting and receiving information of the maximum capacity of the retransmission buffer to each other.

  Still further, in the retransmission buffer capacity measuring apparatus, the operation of the receiving apparatus is controllable from an upper layer apparatus or an opposing device.

  According to the communication system and the retransmission buffer capacity measuring apparatus according to the present invention, the maximum capacity of the retransmission buffer of the opposite device can be estimated. For example, an IO interface such as a PCI Express press can be connected to various devices. Depending on the connection, the communication usage such as the packet length changes. By estimating the maximum capacity of the retransmission buffer of the facing device, the communication efficiency can be improved as follows.

  In addition, in the configuration in which the transmitting device transmits a packet from the receiving device so that the transmitting device transmits the packet, and the receiving device does not return a response request, the transmitting device transmits the packet from the receiving device. Send the packet. The packet size is set to a packet size that can be theoretically transmitted before the retransmission timer expires. Since the initialization sequence that transmits as few packets as possible is started, the time of the initialization sequence can be shortened.

  Furthermore, the maximum capacity of the retransmission buffer of the opposite device is estimated, and an acknowledgment is sent from the reception device according to the data accumulation status, so that the communication efficiency due to the fact that the retransmission buffer of the transmission device is filled with data Can be prevented.

  Furthermore, it is judged from the data accumulation status of the retransmission buffer of the opposite device and the packet to be transferred next from the receiving component, and an acknowledgment is sent, but the data accumulation amount of the retransmission buffer of the opposite device exceeds a certain amount. However, the retransmission buffer may be filled while a long packet is transmitted from the receiving device, and packet communication transmitted from the transmitting device may stop. This can be avoided.

  In addition, it is possible to estimate the maximum capacity and data storage capacity of the retransmission buffer of the opposite device, and use this to transmit a packet having an optimal length to the upper layer. By this notification, transfer with an optimal packet size can be performed from the upper layer, so that communication efficiency can be improved, and this information can be notified to the device upper layer and the opposite device of the apparatus.

  Furthermore, in order to prevent communication from being stopped due to the influence of the reception buffer of the reception device, the reception buffer is opened. In addition, the initial sequence can be omitted by enabling both devices to notify the maximum capacity and data storage capacity of the retransmission buffer as a communication system. Further, the retransmission buffer recognition sequence of the opposite device can be executed or stopped by the upper layer or the opposite device.

It is a block diagram which shows the structure of the communication system using the PCI express which concerns on one Embodiment of this invention. 7 is a timing chart showing a first conventional example of a communication procedure between a transmission component (EP) 10 and a reception component (RC) 20 in a communication system according to the related art using PCI Express. 10 is a timing chart showing a second conventional example of a communication procedure between a transmission component (EP) 10 and a reception component (RC) 20 in a communication system according to the related art using PCI Express. 12 is a timing chart illustrating a third conventional example of a communication procedure between a transmission component (EP) 10 and a reception component (RC) 20 in a communication system according to the related art using PCI Express. FIG. 2 is a timing chart illustrating a first embodiment of a communication procedure between a transmission component (EP) 10 and a reception component (RC) 20 in the communication system of FIG. 1. 2 is a timing chart showing a communication procedure for recognizing the capacity of a retransmission buffer 13 of an opposite device in the communication system of FIG. 2 is a timing chart showing a communication procedure of a first management method of a TLP size in the communication system of FIG. 1. 3 is a timing chart showing a communication procedure of a second management method of the TLP size in the communication system of FIG. 1. 2 is a flowchart showing a process of recognizing the maximum capacity of a retransmission buffer and managing the size of a TLP in the communication system of FIG. 3 is a flowchart showing a TLP size management process by a received packet management unit 22 of the communication system of FIG. 1.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each following embodiment, the same code | symbol is attached | subjected about the same component.

  FIG. 1 is a block diagram showing a configuration of a communication system using a PCI express according to an embodiment of the present invention. In the present embodiment, a communication system using a PCI express will be described below. Here, the PCI Express is a serial bus that is upwardly compatible with the PCI bus, and has a wide data bandwidth of up to 32 lanes at a maximum of 2.5 Gbps per lane.

  First, a function provided in the data link layer defined in the PCI Express standard to guarantee the validity of TLP transmitted / received between links will be described with reference to FIG. FIG. 1 is a diagram for explaining a TLP approval procedure using a retransmission buffer 13 and an ACK DLLP (Data Link Layer Packet). In FIG. 1, a transmission component 10 is connected to a reception component 20 via a predetermined wired link bus. It is connected. The transmission component 10 includes a packet reception unit 11 and a packet transmission unit 12 having a retransmission buffer 13. The reception component 20 includes a packet transmission unit 21 having an acknowledgment transmission unit 21a, a reception packet management unit 22 having a sequence number management unit 22a, a validity judgment unit 23, a retransmission buffer status management unit 24, an AL An AL timer management unit 25 having a timer 25t and a response transmission control unit 26 having a sequence number management unit 26a are provided.

  In the communication system configured as described above, a plurality of TLPs are transmitted from the transmission component 10 to the reception component 20, where a predetermined sequence number is assigned to the TLP, and the transmitted TLP is a retransmission buffer. 13 is recorded. The reception packet management unit 22 of the reception component 20 receives a plurality of TLPs, and the sequence numbers are recorded and managed by the sequence number management unit 22a. Next, in the conventional example, the validity determination unit 23 determines the validity of the received TLP as will be described in detail later, and transmits the packet to the packet transmission unit 21 so as to return an ACK packet from the packet transmission unit 21. However, this embodiment is particularly characterized in that the following processing unit is provided.

(1) Retransmission buffer status management unit 24: Recognizes, stores and manages the maximum capacity of the retransmission buffer 13 of the opposite device (transmission component 10) and the currently accumulated data storage capacity by a method described in detail later. The information is transmitted to the response transmission control unit 26 or the upper layer. In addition, although the opposing device of the receiving component 20 is the transmitting component 10, the opposing device of the transmitting component 10 is the receiving component 20, and so on.
(2) AL timer management unit 25 having an AL timer 25t: The AL timer 25t is configured to expire when a plurality of predetermined TLPs whose validity has been confirmed is received, and a response transmission control unit indicates that the timer has expired. 26.
(3) Response transmission control unit 26: a sequence number management unit 26a that stores and manages a sequence number of TLP transmission from the reception component 20, and the retransmission buffer status management unit 24 sets the retransmission buffer 13 of the opposite device to a predetermined value. When it is determined that a certain amount of data is stored, or when the response transmission control unit 26 recognizes the length of the next TLP to be transmitted and exceeds a predetermined threshold length, an ACK transmission request signal Is generated and output to the confirmation response transmission unit 21a, the confirmation response transmission unit 21a controls to generate an ACK packet and transmit it from the packet transmission unit 21 to the transmission component 10.

  When the transmitting component 10 receives the ACK DLLLP from the receiving component 20 and knows that the TLP has been approved, the transmitting component 10 deletes the TLP from the retransmission buffer 13 as approved.

  In the present embodiment, a sequence number and LCRC (Link Cyclic Redundancy Check) are used on the TLP in order to realize the function of guaranteeing the validity of the TLP transmitted / received between the links. The sequence number is a 12-bit ID indicating a serial number and a unique value for the past 4096 TLPs, and is generated when transmitting the TLP from the transmission component 10. Using the continuity, the receiving component 20 can determine the validity of whether there is no TLP reception omission or the like. On the other hand, LCRC is a 32-bit CRC (Cyclic Redundancy Check). The LCRC is generated when transmitting the TLP from the transmitting component 10, and the receiving component 20 can detect an error by comparing with the CRC calculated by the receiving component 20 itself. As described above, the data link layer of the receiving component 20 determines the validity of the TLP based on whether the sequence number and the LCRC are correct. At this time, when the data link layer of the receiving component 20 receives a valid TLP, it sends back an ACK DLLLP (affirmative DLLP), and when it receives an invalid TLP, it sends back a NAK DLLP (negative DLLLP).

  The data link layer of the transmission component 10 once holds the transmitted TLP in the retransmission buffer, and deletes the approved TLP from the retransmission buffer 12 when notified by the ACK DLLLP. Further, when it is notified by NAK DLLP that at least one TLP is unapproved, all TLPs after the unapproved TLP remaining in the retransmission buffer 12 are retransmitted to the reception component 20. However, the ACK DLLLP indicating the approval does not necessarily need to be transmitted every time the receiving component 20 receives one TLP, and the sequence number indicated by the sequence number indicated by sending the last approved TLP sequence number on the ACK DLLLP Up to TLP can be approved at the same time. This has the effect of suppressing the number of ACK DLLLP transmissions and suppressing the decrease in bandwidth due to the transmission of ACK DLLLP. The transmission delay of the ACK DLLLP is not strictly defined in the standard, only a rough guideline is shown, and it depends on the implementation.

  As described above, in the present embodiment, a packet for transmitting a packet from the reception component 20 is transmitted to the transmission component 10. In response, packet transmission from the transmission component 10 to the reception component 20 is performed. In the packet transfer, it is assumed that the receiving component 20 does not return a response. Based on information from the reception packet management unit 22 and the validity judgment unit 23 of the reception component 20, the retransmission buffer status management unit 24 stores the maximum capacity of the retransmission buffer 13 of the transmission component 10 and the current capacity as will be described in detail later. Estimate and recognize the data storage capacity.

  FIG. 5 is a timing chart showing Example 1 of a communication procedure between the transmission component (EP) 10 and the reception component (RC) 20 in the communication system of FIG. In the state of FIG. 4, the presence of the retransmission buffer 13 of the opposite device and the maximum capacity (that is, the buffer size) of the retransmission buffer 13 are recognized, and the length of the packet to be transferred next from the reception component 20 to the transmission component 10 is recognized. , Generating a response transmission request signal so as to return an ACK packet. That is, before transmission of an ACK packet for which the AL timer 25t has not expired, there may be a case where an ACK packet cannot be returned because transmission of a long TLP exceeding a predetermined threshold length has started. 24, when it is determined that a predetermined amount of data is stored in the retransmission buffer 13, an ACK transmission request signal is generated and output to the acknowledgment transmission unit 21a to forcibly transmit the ACK packet to the transmission component 10. To do. Further, the response transmission control unit 26 recognizes the length of the next TLP to be transmitted, and when it recognizes that a TLP exceeding a predetermined threshold length is transmitted, generates an ACK transmission request signal. The ACK packet is forcibly transmitted to the transmission component 10 by outputting to the acknowledgment transmission unit 21a. As a result, the ACK packet is received by the transmission component 10, the data in the retransmission buffer 13 is deleted, and the normal state can be restored.

  FIG. 6 is a timing chart showing a communication procedure for recognizing the capacity of the retransmission buffer 13 of the opposite device in the communication system of FIG. In FIG. 6, first, the receiving component 20 transmits a packet transmission request signal to the transmitting component 10 (step S1). In contrast, the transmitting component 10 transmits a TLP to the receiving component 20 (step S2). ). In the example of FIG. 6, the receiving component 20 has received TLPs up to sequence number # 1, and has managed and recognized the retransmission buffer status management unit 24. When the transmission component 10 completes the transfer up to TLP (SEQ # = 4) with respect to the reception component 20 (step S3), the reception component 20 manages and recognizes that fact (step S4). At this time, the retransmission buffer status management unit 24 has not recognized the maximum capacity of the retransmission buffer 13 of the transmission component 10 that is the opposite device, and has confirmed that data up to TLP (SEQ # = 4) has been received. (Step S5). In this case, the retransmission buffer status management unit 24 requests the response transmission control unit 26 not to transmit an ACK packet (step S5). As a result, the retransmission timer of the transmission component 10 expires (step S6), and the transmission component 10 retransmits the TLP (SEQ # = 0 to 4) (step S7). As a result, the retransmission buffer status management unit 24 has received TLP (SEQ # = 0 to 4) so far and retransmission has been performed, so that the maximum capacity of the retransmission buffer 13 is the five sequences as shown in FIG. The data storage capacity corresponding to the TLP of the number can be estimated and detected.

  FIG. 7 is a timing chart showing a communication procedure of the first management method of the TLP size in the communication system of FIG. Assume that the maximum capacities of retransmission buffers of devices facing each other are recognized from each other by the method shown in FIG. In FIG. 7, when the transmitting component 10 is transferring TLP (SEQ # = 3) to the receiving component 20 (step S11), when a predetermined time T1 has elapsed, the AL timer 25t expires and an acknowledgment response is transmitted. The unit 21a transmits ACK (SEQ # = 0) to the transmission component 10 (step S12). In this state, the sequence number management unit 22a recognizes that it is TLP (SEQ # = 2), and the sequence number management unit 26a recognizes that it is ACK (SEQ # = 0). Here, when the retransmission buffer status management unit 24 determines that the accumulated data storage capacity of the retransmission buffer 13 exceeds the maximum capacity (a certain amount) of the retransmission buffer 13 of the opposite device (step S13), an ACK transmission request signal is sent. Generated and output to the confirmation response transmitter 21a via the response transmission controller 26a (step S14). At this time, the retransmission buffer status management unit 24 updates the data storage status of the retransmission buffer 13 that it manages to TLP (SEQ # = 3) (step S15), and the sequence number management unit 26a receives ACK (SEQ # = 2), the acknowledgment transmission unit 21a transmits ACK (SEQ # = 2) to the transmission component 10 (step S16).

  As described above, according to the first TLP management method of FIG. 7, the sequence number obtained by subtracting the sequence number in which the ACK packet is returned from the received TLP sequence number and the corresponding TLP size are received. It can be managed in the component 20.

  FIG. 8 is a timing chart showing a communication procedure of the second management method of the TLP size in the communication system of FIG. In FIG. 8, while the transmitting component 10 is transferring TLP (SEQ # = 3) to the receiving component 20 (step S21), the retransmission buffer status management unit 24 has received up to TLP (SEQ # = 2). Recognize. Here, when the receiving component 20 is transmitting a TLP to the transmitting component 10 (step S22), the data storage capacity of the retransmission buffer 13 recognized by the retransmission buffer status management unit 24 is a predetermined threshold value. When it is detected that (constant amount) is reached (step S23), or when the response transmission control unit 26a determines that the TLP data length is full (step S24), an ACK response transmission request signal is generated. In response to this, the confirmation response transmission unit 21a transmits ACK (SEQ # = 2) (step S25). Thereby, the data in the retransmission buffer 13 of the transmission component 10 is deleted, and the reception component 20 can transmit the next TLP to the transmission component 10 (step S26).

  FIG. 9 is a flowchart showing processing for recognizing the maximum capacity of the retransmission buffer 13 and managing the TLP size in the communication system of FIG. 9 and 10 are subroutines in the main routine related to the operation of the apparatus.

  In step S31 of FIG. 9, the maximum capacity of the retransmission buffers 13 of one or the other component is notified, and in step S32, it is determined whether or not the maximum capacity of the retransmission buffer 13 is implemented by a register or the like. While the process proceeds to step S33, the process proceeds to step S41 when NO. In step S33, the maximum capacity of the retransmission buffer 13 of the opposite device is confirmed by a packet (TLP, DLLP), and the sequence number of TLP received in step S34, the sequence number that transmitted ACKNAK, and the size of the TLP are stored. To estimate the data storage capacity of the retransmission buffer 13 (see FIG. 7). In step S35, it is determined whether or not the data storage capacity of the retransmission buffer 13 of the opposite device exceeds a threshold value. If YES, the process proceeds to step S36. If NO, the process proceeds to step S37. In step S36, ACK is transmitted from the receiving component 20, the AL timer 25t expires (see FIG. 8), and the process returns to the original main routine. On the other hand, after the AL timer 25t expires in step S37, ACK is transmitted and the process returns to the original main routine.

  In step S41, the receiving component 20 sends a packet (for example, a large amount of MRd) to the transmitting component 10 to cause the transmitting component 10 to retransmit, so that the receiving component 20 enters a sequence in which no ACK packet is returned. In step S42, the receiving component 20 determines whether there is no NAK packet, that is, whether or not a communication error occurs. If YES, the process proceeds to step S45. If NO, the process proceeds to step S43. In step S43, a NAK packet is transmitted. In step S44, it is determined whether the NAK packet has been transmitted a plurality of times. If NO, the process returns to step S41. If YES, the process returns to the original main routine. In step S45, the maximum capacity of the retransmission buffer 13 of the opposite device is measured, and then in step S46, the TLP data payload length is changed to increase the accuracy. The receiving component 20 sends a packet (for example, MRd) to the transmitting component 10 and causes the transmitting component 10 to retransmit, so that the receiving component 20 enters a sequence in which no ACK packet is returned. In step S47, the receiving component 20 determines whether there is no NAK packet, that is, whether or not a communication error occurs. If YES, the process proceeds to step S50. If NO, the process proceeds to step S48. In step S48, a NAK packet is transmitted. In step S49, it is determined whether the NAK packet has been transmitted a plurality of times. If NO, the process returns to step S46. If YES, the process returns to the original main routine. In step S50, the maximum capacity of the retransmission buffer 13 of the opposite device is measured. In step S51, the maximum capacity of the retransmission buffer 13 of the opposite device is recognized, and the process proceeds to step S34.

  That is, steps S41 to S51 show an automatic maximum capacity recognition (detection) method of the retransmission buffer 13 of the opposite device. In the modified example, as shown in step S38, the process may jump from step S45 to step S51.

  In the processing of FIG. 9 configured as described above, when the transmission component 10 and the reception component 20 manage the retransmission buffer 13 of the opposite device, respectively, the maximum of the retransmission buffer 13 of the opposite device is used using packet communication. Check the capacity information. When the maximum capacity of the retransmission buffer 13 of the opposite device cannot be recognized, the following method for checking the transmission buffer of the opposite device is used. In order to cause the transmission component 10 to transmit a packet from the reception component 20, the packet is transmitted, and the reception component 20 does not return an ACK packet. The transmission component 10 enters the initial sequence of packet transmission from the reception component 20 because the transmission status of the reception component 20 and the communication from the transmission component 10 are stopped, and communication occurred during the initial sequence. It is configured to escape the situation. The initial sequence may be automatically entered, and may be configured to be controllable from an upper layer or a counter device.

  In this embodiment, since the PCI Express implementation is implemented, a retransmission timer is implemented, and retransmission is performed when the timer expires. As a result, the transmission component 10 causes retransmission. Therefore, in order for the transmission component 10 to transmit a packet from the reception component 20, with respect to the packet transmission, an amount of packet requests that can be theoretically transferred is transmitted using the retransmission function by the retransmission timer. Judged from the returned packet. When data smaller than the requested data amount is received by the receiving component 20 and retransmitted, the packet length is changed and the packet is transferred again from the transmitting component 10 to determine the maximum capacity of the retransmission buffer 13.

In the above configuration, the in normal communication, recognizing the maximum capacity of the retransmission server Ffa 13 of a facing device (i.e. size), and grasping the data storage state of the counter device of retransmission Babbua 13 transmits satisfies a certain amount Also, the transmission from the reception component 20 is determined, and the ACK packet is transmitted. Further, by recognizing the maximum capacity of the retransmission buffer 13 of the opposite device and notifying the higher layer, when performing packet communication from the reception component 20 to the transmission component 10, transfer with an optimum packet size is possible. Using these, communication efficiency can be improved.

  FIG. 10 is a flowchart showing a TLP size management process by the received packet management unit 22 of the communication system of FIG.

  In FIG. 10, TLP is transmitted from the receiving component 20 to the transmitting component 10 in step S61, and the size of the TLP received by the receiving component 20 from the transmitting component 10 is detected in step S62. In step S63, whether transfer is possible or not based on the data capacity calculated from the retransmission timer value and the theoretically transferable rate (the required time can be calculated by dividing the data capacity by the rate. If it is smaller than the value, transfer is possible.) Is determined. If YES, the process proceeds to step S64, and if NO, the process proceeds to step S66. In step S64, it is determined that the maximum capacity of the retransmission buffer 13 of the transmission component 10 is sufficiently large, packet communication is performed in a normal state, and the process returns to the original main routine.

  In step S66, the TLP size received by the reception component 20 is transmitted to the transmission component 10 by shortening the length of the TLP by a predetermined length, and whether or not the prescribed data amount is received by the reception component 20 in step S67. If NO, the process returns to step S66 while if YES, the process proceeds to step S68. In step S68, the recognition of the retransmission buffer 13 proceeds to step S69, and otherwise the process proceeds to step S70. In step S69, since the reception component 20 recognizes the size (maximum capacity) of the retransmission buffer 13 of the transmission component 10 and the reception component 20 can recognize the data storage state of the retransmission buffer 13, an ACK packet is received according to the threshold value. Therefore, the retransmission buffer 13 can be used optimally. In step S70, the maximum capacity of the retransmission buffer 13 is set in the register, and the recommended length for transmission / reception of data packets during transmission / reception can be determined. Is possible.

  As described above, in the processing of FIG. 10, when the information of the retransmission buffer 13 can be transmitted to each other by each device, the information notification method of the retransmission buffer 13 of the opposite device in FIG. 9 is simply realized by packet communication. As shown in FIG. 9, the communication efficiency can be improved.

  In the above embodiment, when estimating the maximum capacity of the retransmission buffer 13 of the opposite device, in the communication system that implements flow control, in order to prevent erroneous recognition due to the suspension of communication due to the influence of the reception buffer, The flow control reception buffer may be opened.

Further, in the above embodiment, the receiving component 20 may estimate the maximum capacity of the retransmission buffer 13 and notify the upper layer to transmit a data packet having a length corresponding to the maximum capacity. Further, when each transmission component 10 and the receiving component 20 has information of the maximum capacity of the retransmission server Ffa 13 of the opposing device, it may send and receive information of the maximum capacity of the retransmission buffer to each other. Still further, each of the transmission component 10 and the reception component 20 may be configured such that their operations can be controlled from a higher-layer apparatus or an opposing device.

  Further, the maximum capacity of the retransmission buffer 13 may be estimated when evaluating the operation of the transmission component 10, for example, reception in a communication system in which the transmission component 10 and the reception component 20 are connected to be communicable. A retransmission buffer capacity measuring device for the component 20 may be configured.

  As described above, according to the present embodiment, the maximum capacity of the retransmission buffer of the opposite device can be estimated. For example, an IO interface such as a PCI Express may connect to various devices. Depending on the connection, the usage status of communication such as packet length changes. By estimating the maximum capacity of the retransmission buffer of the facing device, the communication efficiency can be improved as follows.

  In addition, in order to cause the transmission component 10 to transmit a packet from the reception component 20 and transmit the packet, and the reception component 20 does not return a response request, the transmission component 10 causes the transmission component 10 to transmit a packet. Send the packet. The packet size is set to a packet size that can be theoretically transmitted before the retransmission timer expires. Since the initialization sequence that transmits as few packets as possible is started, the time of the initialization sequence can be shortened.

  Furthermore, the maximum capacity of the retransmission buffer of the opposite device is estimated, and an acknowledgment is sent from the receiving device according to the data accumulation status, so that the retransmission efficiency of the transmission component 10 is filled with data. Can be prevented.

  Furthermore, it is judged from the data accumulation status of the retransmission buffer of the opposite device and the packet to be transferred next from the receiving component, and an acknowledgment is sent, but the data accumulation amount of the retransmission buffer of the opposite device exceeds a certain amount. However, while the long packet is transmitted from the reception component 20, the retransmission buffer is filled, and packet communication transmitted from the transmission component 10 may be stopped. This can be avoided.

  In addition, it is possible to estimate the maximum capacity and data storage capacity of the retransmission buffer of the opposite device, and use this to transmit a packet having an optimal length to the upper layer. By this notification, transfer with an optimal packet size can be performed from the upper layer, so that communication efficiency can be improved, and this information can be notified to the device upper layer and the opposite device of the apparatus.

  Furthermore, in order to prevent communication from being stopped due to the influence of the reception buffer of the reception component 20, the reception buffer is opened. In addition, the initial sequence can be omitted by enabling both devices to notify the maximum capacity and data storage capacity of the retransmission buffer as a communication system. Further, the retransmission buffer recognition sequence of the opposite device can be executed or stopped by the upper layer or the opposite device.

As described above in detail, according to the communication system according to the present invention and the retransmission buffer capacity measuring device, in the communication system in which the transmission device and the reception device are connected to be communicable, the transmission device transmits a data packet. A packet transmitting unit for transmitting to the receiving device; a retransmission buffer for holding a data packet transmitted to the receiving device for retransmission; and a retransmission buffer managing unit for assigning a management number to a data packet transmitted to the receiving device The receiving device receives a data packet from the transmitting device and determines the validity of the data packet, and the packet is based on the determination result of the validity determining unit. An acknowledgment transmission unit that transmits an acknowledgment or negative acknowledgment indicating approval to the transmitter at predetermined intervals, and data And a packet transmitter for transmitting packet to the transmission apparatus, the above-mentioned receiving apparatus when receiving the data packet from the transmitting device is the acknowledgment or negative acknowledgment in order to retransmission of the transmission device Without transmitting a reception response, the transmitting apparatus retransmits a predetermined amount of data packets stored in the retransmission buffer of the transmitting apparatus after the retransmission timer of the transmitting apparatus expires, and the receiving apparatus is retransmitted from the transmitting apparatus. The predetermined amount of data packets are received, and the capacity of the received predetermined amount of data packets is estimated as the maximum capacity of the retransmission buffer of the transmitting apparatus. Therefore, it is possible to estimate the maximum capacity of the retransmission buffer of the opposite device. For example, an IO interface such as PCI Express may connect to various devices. Depending on the connection, the packet length, etc. Communication usage will change. By estimating the maximum capacity of the retransmission buffer of the face-to-face device, communication efficiency can be improved.

10 ... Sending component,
11: Packet receiver,
12 ... Packet transmission unit,
20 ... receiving component,
21 ... Packet transmission unit,
21a ... confirmation response transmission unit,
22: Received packet management unit 22,
22a ... Sequence number management unit,
23 ... the legitimacy judging section,
24 ... retransmission buffer status management unit,
25 ... AL timer management department,
25t ... AL timer,
26 ... Response transmission control unit,
26a: Sequence number management unit 26a.

Japanese Patent Laid-Open No. 2001-111618. JP 2007-180611 A.

"PCI Express Base Specification Revision 2.0", Peripheral Component Interconnect-Special Interest Group (PCI-SIG), December 2006. Nobutaka Arai et al., “Revised new edition of PCI Express introductory course, Gen2 augmentation”, published by Telephone Shimbun Co., Ltd., pages 86-103, issued on June 20, 2008.

Claims (20)

In a communication system in which a transmission device and a reception device are communicably connected,
The transmission device includes a packet transmission unit for transmitting a data packet to the reception device, a retransmission buffer for holding a data packet transmitted to the reception device for retransmission, and a data packet transmitted to the reception device. A retransmission buffer management unit for assigning a management number;
The receiving device receives the data packet from the transmitting device, and approves the packet based on a validity determination unit that determines the validity of the data packet and a determination result of the validity determination unit. An acknowledgment transmission unit that transmits an acknowledgment or a negative response that indicates a negative response to the transmission device at a predetermined interval, and a packet transmission unit that transmits a data packet to the transmission device.
When the above receiving apparatus that has received the data packet from the transmitting device, without a reception response is positive acknowledgment or negative acknowledgment in order to retransmission of the transmission device,
The transmitter retransmits a predetermined amount of data packets stored in the retransmission buffer of the transmitter after expiration of the retransmission timer of the transmitter;
The receiving apparatus receives a predetermined amount of data packets retransmitted from the transmitting apparatus, and estimates a capacity of the received predetermined amount of data packets as a maximum capacity of a retransmission buffer of the transmitting apparatus. system. When retransmission is performed between the transmission device and the reception device, retransmission control is performed upon reception of a negative response or expiration of a retransmission timer,
The transmission device and the reception device determine a retransmission timer value according to the maximum payload size and the lane width of the connection destination at the time of communication initialization between the transmission device and the reception device,
2. The communication system according to claim 1, wherein the data packet transmitted by the receiving apparatus calculates a data size that can be theoretically transmitted before expiration of a retransmission timer and performs packet transfer with a maximum payload size.   The receiving apparatus estimates the data storage status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and transmits the data from the receiving apparatus accordingly. 3. The communication system according to claim 2, wherein packet transfer is performed by changing a packet length of a packet to be changed or changing a data size. The receiving device estimates the data storage status of the retransmission buffer of the transmitting device based on the reception response sent from the receiving device and the size of the packet data sent from the receiving device,
4. The transmission apparatus according to claim 2, wherein when it is detected that a predetermined amount of data is stored in the retransmission buffer, an expiration time of a retransmission timer is shortened or a transmission request is made to the transmission apparatus. The communication system described.   The receiving apparatus estimates the data accumulation status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and the amount of data in the retransmission buffer is full. 4. The communication system according to claim 2, wherein, when it is detected that a message is stored, a retransmission timer is forcibly expired or an acknowledgment is transmitted to the transmission device. 5.   The receiving apparatus estimates the data accumulation status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and transfers the packet from the receiving apparatus to the transmitting apparatus. 3. When performing, a response transmission request signal is transmitted to release the retransmission buffer of the transmission device according to a data accumulation state of the retransmission buffer of the transmission device and a packet size to be transferred next. Or the communication system of 3 description.   4. The communication system according to claim 2, wherein the receiving device estimates a maximum capacity of a retransmission buffer of the transmitting device and notifies an upper layer to transmit a data packet having a length corresponding to the maximum capacity.   The receiving apparatus estimates the maximum capacity of the retransmission buffer of the transmitting apparatus, and in a communication system that implements flow control, in order to prevent misrecognition due to the suspension of communication due to the influence of the receiving buffer, 8. The communication system according to claim 1, wherein the reception buffer is opened. When having information of the maximum capacity of the retransmission server Ffa of each said transmitting apparatus and the receiving apparatus facing devices, any of the claims 1 to 8, wherein the transmitting and receiving information of the maximum capacity of the retransmission buffer to each other The communication system as described in any one.   10. The communication system according to claim 1, wherein operations of the transmission device and the reception device can be controlled from a higher-layer device or an opposing device. In a measuring apparatus for retransmission buffer capacity for a receiving apparatus in a communication system in which a transmitting apparatus and a receiving apparatus are communicably connected,
The receiving device receives the data packet from the transmitting device, and approves the packet based on a validity determination unit that determines the validity of the data packet and a determination result of the validity determination unit. An acknowledgment transmission unit that transmits an acknowledgment or a negative response that indicates a negative response to the transmission device at a predetermined interval, and a packet transmission unit that transmits a data packet to the transmission device.
When the above receiving apparatus that has received the data packet from the transmitting device, without a reception response is positive acknowledgment or negative acknowledgment in order to retransmission of the transmission device,
The receiving apparatus receives a predetermined amount of data packets retransmitted from the transmitting apparatus, the data packet being stored in a retransmission buffer of the transmitting apparatus after expiration of a retransmission timer of the transmitting apparatus. An apparatus for measuring a retransmission buffer capacity, wherein the capacity of the received predetermined amount of data packets is estimated as a maximum capacity of a retransmission buffer of the transmission apparatus. When performing retransmission at the above receiver, perform retransmission control upon receipt of negative response or expiration of retransmission timer,
The receiving device determines a retransmission timer value according to a maximum payload size and a lane width of a connection destination at the time of communication initialization between the transmitting device and the receiving device,
12. The retransmission buffer capacity according to claim 11, wherein the data packet transmitted by the receiving apparatus calculates a data size that can be theoretically transmitted before expiration of a retransmission timer and performs packet transfer with a maximum payload size. Measuring device.   The receiving apparatus estimates the data storage status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and transmits the data from the receiving apparatus accordingly. 13. The retransmission buffer capacity measuring apparatus according to claim 12, wherein packet transfer is performed by changing a packet length of a packet to be transmitted or changing a data size.   The receiving apparatus estimates the data accumulation status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and a predetermined amount of data is stored in the retransmission buffer. 14. The retransmission buffer capacity measuring device according to claim 12 or 13, wherein when the storage is detected, the expiration time of a retransmission timer is shortened or a transmission request is made to the transmission device.   The receiving apparatus estimates the data accumulation status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and the amount of data in the retransmission buffer is full. 14. The retransmission buffer capacity measurement according to claim 12 or 13, wherein a retransmission timer is forcibly expired or an acknowledgment is transmitted to the transmission apparatus when it is detected that the message is stored. apparatus.   The receiving apparatus estimates the data accumulation status of the retransmission buffer of the transmitting apparatus based on the reception response transmitted from the receiving apparatus and the size of the packet data transmitted from the receiving apparatus, and transfers the packet from the receiving apparatus to the transmitting apparatus. 13. When performing, a response transmission request signal is transmitted to release the retransmission buffer of the transmission device according to a data accumulation state of the retransmission buffer of the transmission device and a packet size to be transferred next. Or the retransmission buffer capacity measuring device according to 13.   14. The retransmission buffer capacity according to claim 12 or 13, wherein the receiving apparatus estimates a maximum capacity of a retransmission buffer of the transmitting apparatus and notifies an upper layer to transmit a data packet having a length corresponding thereto. Measuring device.   The receiving apparatus estimates the maximum capacity of the retransmission buffer of the transmitting apparatus, and in a communication system that implements flow control, in order to prevent misrecognition due to the suspension of communication due to the influence of the receiving buffer, in the initial sequence, the flow control The retransmission buffer capacity measuring apparatus according to claim 11, wherein the reception buffer is opened. When the above receiving apparatus having the information of the maximum capacity of the retransmission server Ffa opposing device, according to any one of claims 11 to 18, characterized in that transmitting and receiving information of the maximum capacity of the retransmission buffer to each other For measuring retransmission buffer capacity.   The retransmission buffer capacity measuring apparatus according to any one of claims 11 to 19, wherein the operation of the receiving apparatus can be controlled from a higher layer apparatus or an opposing device.

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