JP2006054750A - Flow control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To aatain a flow control without using dedicated lines or occupying many bits in a packet header part. <P>SOLUTION: When information, indicating the state of a receiving buffer 108 in a receiving side unit 103 is transmitted to a transmitting side unit 102, a credit information attachment deciding part 111 judges whether information can be attached to packet data to be transmitted from the receiving side unit 103 to the transmission-side unit 102, and at the deciding of the possibility of attachment, a header correction part 110 attaches the information to a single bit of the header in the packet data and transmits the information to the transmission-side unit 102. Consequently the transmission-side unit 102 can obtain the information indicating the state of the receiving buffer 108 in the reception-side unit 102. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flow control method for performing flow control between transmitting and receiving apparatuses that transmit and receive packet data.

  Conventionally, a back pressure method, a credit method, or the like is used for flow control between transmitting and receiving apparatuses when transmitting and receiving packet data. The flow control is generally performed by controlling data transmission in the transmission side apparatus so that reception data does not overflow from a reception buffer provided in the reception side apparatus.

  In the back pressure method, when the amount of data stored in the reception buffer provided in the reception side device reaches a specified value, a transmission stop instruction signal is sent from the reception side device to the transmission side device and received. This is flow control in which an instruction signal for restarting transmission is transmitted after the amount of data stored in the buffer falls below a specified value.

  In the credit system, an adjacent credit counter (hereinafter referred to as NCC) that counts the number of blocks of transmission data is provided in the transmission side device, and NCC is incremented every time one block is transmitted. The receiving device also has its own credit counter (hereinafter referred to as SCC) that counts the number of received data blocks swept from the receiving buffer, and the SCC is incremented every time one block of data is swept from the receiving buffer. Is done.

  In the transmission side device, when the NCC reaches a certain threshold value, data transmission is stopped. In general, this threshold is defined by the size of the reception buffer.

  The SCC counter value of the receiving side device is notified to the transmitting side device as credit information, and the SCC counter value is then subtracted by the notified credit information value. In the transmission side apparatus, the value of the credit information notified from the NCC count value is subtracted, and in the transmission side apparatus, the state of the reception buffer of the reception side apparatus is grasped, so that appropriate flow control is performed.

  Here, paying attention to the credit information, in order to always perform flow control, it is necessary to always notify the credit information from the receiving device to the transmitting device.

  As one method for that purpose, there is a method in which a dedicated line dedicated to credit information is provided, and credit information is exchanged between the transmitting and receiving apparatuses using the dedicated line.

  As another method, there is a method of flowing credit-dedicated packet data on a data line.

Furthermore, a method of embedding credit information in normal transmission / reception data without providing a dedicated line or dedicated data is also considered (see, for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 09-233082 JP 2000-236351 A

  However, when a dedicated line dedicated to credit information is provided, there is a problem that hardware increases.

  In addition, when credit-dedicated packet data is sent over the data line, credit information can be transferred without affecting performance if normal data transfer is not performed, but normal transmission / reception data is continuous. In this case, there is a problem in that the performance deteriorates by interposing the packet data dedicated for credit between the normal transmission / reception data. On the other hand, if the packet data dedicated for credit is not inserted when normal transmission / reception data is continuous, the credit information cannot be transferred at all, so that the NCC reaches the threshold at the transmission side device, and the reception is received. Even though there is a margin in the reception buffer of the side device, data transmission from the transmission side device is stopped.

  Furthermore, when credit information is embedded in normal transmission / reception data, since the credit information cannot be embedded in the payload portion of the transmission / reception data packet, this credit is usually included in the header portion including information such as packet routing control. Although information is embedded, if many bits are spent on credit information, there is a problem that other functions are restricted.

  The present invention has been made in view of the problems of the conventional techniques as described above, and performs flow control without using a dedicated line or occupying multiple bits in the packet header section. An object is to provide a flow control method capable of

In order to achieve the above object, the present invention provides:
It comprises two devices that transmit and receive packet data on a data line, and the two devices have a reception buffer that temporarily holds packet data transmitted from the other device of the two devices, and the reception buffer A flow control method for notifying the other apparatus of the state of
Each of the two devices is
Information addition determination means for determining whether or not information indicating the state of the reception buffer can be added to packet data transmitted to the other of the two apparatuses;
And adding means for adding information indicating the state of the reception buffer to one bit of the header in the packet data to be transmitted to the other device when the information adding determination means determines that it is possible.

Each of the two devices is
A counter that increments the number of blocks of packet data swept from the receive buffer;
The adding means adds the count value in the counter to one bit of a header in packet data transmitted to the other device.

Each of the two devices is
Extraction means for extracting information indicating the notified state of the reception buffer from transmitted packet data;
A counter that increments the number of blocks of packet data transmitted to the other of the two devices, and decrements the number of blocks of packet data swept from the reception buffer based on the information extracted by the extraction means It is characterized by having.

When packet data is transmitted and received between two devices on a data line, the state of the reception buffer in the device that receives the packet data of the two devices becomes the packet data transmission side. A flow control method for notifying a device,
A process of determining whether or not information indicating a state of the reception buffer can be added to packet data transmitted from a device serving as a reception side of the packet data to a device serving as a transmission side of the packet data;
When it is determined that the information can be given, a process of giving information indicating the state of the reception buffer to one bit of the header in the packet data;
Processing for transmitting packet data to which information indicating the state of the reception buffer is added from a device serving as a reception side of the packet data to a device serving as a transmission side of the packet data.

A process of incrementing the number of blocks of the packet data swept from the reception buffer;
And a process of assigning the incremented number of blocks of packet data to one bit of a header in the packet data.

In addition, a process of extracting information indicating the notified state of the reception buffer from the transmitted packet data;
Increment the number of blocks of packet data transmitted from the device that is the transmission side of the packet data, and based on the extracted information indicating the state of the reception buffer, the number of blocks of packet data swept from the reception buffer And decrementing.

  In the present invention configured as described above, the number of blocks of the packet data swept from the reception buffer is counted by the counter in the device on the receiving side, and the device on the transmitting side is counted by the information addition judging means. It is determined whether or not the count value counted by the counter can be added to the packet data transmitted to the terminal as information indicating the state of the reception buffer. If it is determined by the information addition determination means, the information indicating the status of the reception buffer is added to the 1 bit of the header in the packet data transmitted to the device on the transmission side by the addition means, and the transmission is performed. The information indicating the state of the reception buffer is obtained by the transmission side apparatus.

  In this way, information indicating the state of the reception buffer is added to one bit of the header in the packet data transmitted from the device on the reception side to the device on the transmission side. Flow control can be performed without occupying multiple bits in the unit.

  As described above, the present invention comprises two devices that transmit and receive packet data on a data line, and the two devices receive temporarily hold packet data transmitted from the other device of the two devices. This is a flow control system that has a buffer and notifies the status of the reception buffer to the other device, and each of the two devices indicates the status of the reception buffer in packet data transmitted to the other device of the two devices. An information addition determination unit that determines whether information can be added, and a reception buffer state in one bit of a header in packet data transmitted to the other device when the information addition determination unit determines that the information can be added. And a granting means for giving the information to be shown, so it is not necessary to use a dedicated line or occupy many bits in the packet header part. It is possible to perform flow control.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of a flow control system of the present invention.

  In this embodiment, as shown in FIG. 1, on a data line 101 through which packet data passes, a unit 102 serving as a transmission side device that transmits packet data, and a reception side that receives packet data transmitted from the unit 102 An NCC addition instruction that outputs an addition instruction for each number of flits that are blocks obtained by dividing the transmitted packet data when the packet data is transmitted. Unit 105, transmission unit 113 that outputs packet data output from NCC addition instruction unit 105 to unit 103, reception unit 114 that receives packet data transmitted from unit 103, and reception unit 114. NC that outputs a subtraction instruction based on the credit information given in the packet data A subtraction instruction unit 106 and an NCC control unit 104 that counts the number of transmission packet data frits based on the addition instruction output from the NCC addition instruction unit 105 or the subtraction instruction output from the NCC subtraction instruction unit 106 are provided. Yes. Also, in the unit 103, a reception buffer 108 that temporarily holds packet data transmitted from the unit 102 and received by the unit 103, and packet data that is swept when the packet data is swept from the reception buffer 108 SCC addition instruction unit 109 that outputs an addition instruction for each number of flits, and an SCC control unit that counts the number of flits of packet data swept from the reception buffer 108 based on the addition instruction output from the SCC addition instruction unit 109 107, a credit information addition determination unit 111 that determines whether the count value in the SCC control unit 107 can be added as credit information to the packet data passing through the data line 112, and a credit information addition determination unit 111 To add credit information to packet data A header correction unit 110 that corrects the header portion by adding credit information to the header portion of the packet data when it is determined that the header portion can be received, and the packet data whose header portion is corrected by the header correction unit 110 And a transmission unit 115 for transmitting packet data to the unit 102 from the unit 103.

  FIG. 2 is a diagram showing the configuration of the NCC control unit 104 shown in FIG.

  As shown in FIG. 2, the NCC control unit 104 shown in FIG. 1 transmits based on the NCC addition instruction output from the NCC addition instruction unit 105 and the NCC subtraction instruction output from the NCC subtraction instruction unit 106. A selection instruction unit 201 that determines whether to add or subtract the number of flits of packet data, a selector 202 whose output is controlled based on the determination result in the selection instruction unit 201, and an output value of the selector 202 The NCC 203 is a counter to be held, an adder 205 that increments the value of the NCC 203, and a subtracter 204 that decrements the value of the NCC 203.

  FIG. 3 is a diagram showing the configuration of the NCC subtraction instruction unit 106 shown in FIG.

  As shown in FIG. 3, the NCC subtraction instructing unit 106 shown in FIG. 1 stores the header part of packet data transmitted from the unit 103 and received by the receiving unit 114 in the unit 102 and the credit information in the header. A selection instruction unit 301 that determines whether or not the credit flit is valid, and a selector 302 that selects a flag indicating whether or not the credit flit is valid based on a determination result in the selection instruction unit 301. The credit frit valid flag 303 that holds the output of the selector 302, and the invalid frit mask unit 304 that masks invalid frit portions of the flits assigned with the valid flag by the credit frit valid flag 303.

  FIG. 4 is a diagram showing a configuration of the SCC control unit 107 shown in FIG.

  As illustrated in FIG. 4, the SCC control unit 107 illustrated in FIG. 1 receives a reception instruction based on the addition instruction output from the SCC addition instruction unit 109 and the credit subtraction instruction output from the credit information addition determination unit 111. A selection instruction unit 401 that determines whether to perform addition or subtraction of the number of flits of the packet data swept from the buffer 108, a selector 402 whose output is controlled based on the determination in the selection instruction unit 401, and a selector 402 SCC 406 that is a counter that holds the output value of SCC 406, an adder 403 that increments the value of SCC 406, and a subtractor 404 that subtracts the credit subtraction value output from credit information addition determination unit 111 from the value output from SCC 406. An adder 405 for further incrementing the value output from the subtractor 404; Are al configuration.

  FIG. 5 is a diagram for explaining the position of the credit information embedded in the packet data transmitted from the unit 103 to the unit 102 shown in FIG.

  As shown in FIG. 5, the packet data transmitted from the unit 103 shown in FIG. 1 to the unit 102 includes a header portion 501 and a data portion 502, and one bit other than the control information 503 is included in the header portion 501. Is stored as a credit information storage area CFLAG504. A packet having a header whose CFLAG 504 is 1 can be used as credit information, and the returned credit information can be extracted by counting the number of flits (packet length) of the packet. .

  The operation of the flow control system configured as described above will be described below.

  FIG. 6 is a diagram for explaining the operation of the flow control method shown in FIG. FIG. 6 shows an example in which packet data (packet 1-1) having a length of 4 flits and packet data (packets 1-2) having a length of 5 flits pass on the data line 101. .

  When the NCC addition instruction unit 105 detects a valid flit of the two packet data described above, first, an addition instruction is output to the NCC control unit 104. As this addition instruction, “1” is output as shown in the time slots T1, T2, T4, T5, T7 to T11.

  Then, in the selection instruction unit 201 in the NCC control unit 104, an instruction to output the value output from the adder 205 is given to the selector 202.

  FIG. 7 is a diagram showing selection logic in the selection instruction unit 201 shown in FIG.

  As shown in FIG. 7, in the selection instruction unit 201, when only the addition instruction from the NCC addition instruction unit 105 is given, an instruction to output the value output from the adder 205 is given to the selector 202. When only the subtraction instruction from the NCC subtraction instruction unit 106 is given, an instruction to output the value output from the subtractor 204 is given to the selector 202. Further, when the addition instruction from the NCC addition instruction unit 105 and the subtraction instruction from the NCC subtraction instruction unit 106 are given, or when neither the addition instruction nor the subtraction instruction is given, the value output from the NCC 203 Is output to the selector 202.

  In the time slots T1, T2, T4, T5, and T7 to T11, since the NCC addition instruction is “1”, the value of the NCC 203 is incremented by the adder 205 and held in the NCC 203. The values at that time are shown in time slots T2 to T12.

  Next, the packet 1-1 and the packet 1-2 are transmitted from the transmission unit 113 in the unit 102, received by the reception buffer 108 in the unit 103, and temporarily held. When the packet 1-1 and the packet 1-2 temporarily held in the reception buffer 108 are swept from the reception buffer 108, the SCC addition instruction unit 109 determines that the effective flits of the packet 1-1 and the packet 1-2 are When each is detected, an addition instruction is output to the SCC control unit 107. As this addition instruction, “1” is output as shown in time slots T5, T6, and T9 to T15 of FIG.

  Then, in the selection instruction unit 401 in the SCC control unit 107, an instruction to output the value output from the adder 403 is given to the selector 402.

  FIG. 8 is a diagram showing selection logic in the selection instruction unit 401 shown in FIG.

  As shown in FIG. 8, in the selection instruction unit 401, when only the addition instruction from the SCC addition instruction unit 109 is given, an instruction to output the value output from the adder 403 is given to the selector 402. When only the subtraction instruction from the credit information addition determination unit 111 is given, an instruction to output the value output from the subtractor 404 is given to the selector 402. When the addition instruction from the SCC addition instruction unit 109 and the subtraction instruction from the credit information addition determination unit 111 are given, the selector 402 is given an instruction to output the value output from the adder 405. When neither the addition instruction from the SCC addition instruction unit 109 nor the subtraction instruction from the credit information addition determination unit 111 is given, an instruction to output the value output from the SCC 406 is given to the selector 402.

  The value output from the selector 402 in this way is held in the SCC 406.

  Here, it is necessary to notify the credit information in the unit 103 to the unit 102 which is the transmission side device. Time slots T1 to T12 show examples in which packet data of 9 flits (packet 2-1) and packet data of 3 flits (packet 2-2) pass on the data line 112.

  FIG. 9 is a diagram showing the selection logic of the credit information addition determination unit 111 shown in FIG. The packet length information is embedded in the control information 503 shown in FIG.

  As shown in FIG. 9, in the credit information addition determination unit 111 that determines whether credit information can be added to packet data passing through the data line 112, the credit information is the total number of flits (packet length) in the packet. Therefore, if the packet length of the packet data reaching the credit information addition determination unit 111 is compared with the value held in the SCC 406 and the packet length is larger than the value held in the SCC 406, the SCC control A credit subtraction instruction is not output to the unit 107. That is, no credit information is given to the packet. In this case, “0” is output to the selection instruction unit 401.

  On the other hand, when the packet length is equal to or smaller than the value held in SCC 406, a credit subtraction instruction is output from credit information addition determination unit 111 to SCC control unit 107. That is, credit information is given to the packet. In this case, “1” is output to the selection instruction unit 401.

  The credit information addition determination unit 111 detects that the packet length of the packet 2-2 is 9 flits in the time slot T1. Since the value held in the SCC 406 at that time is “0”, credit information is not given based on the selection logic of the credit information grant judging unit 111 shown in FIG. No subtraction instruction is output.

  When the packet 2-2 reaches the credit information addition determination unit 111 in the time slot T10 and the packet length is detected to be 3 flits, the value held in the SCC 406 at that time is “3”. The credit information addition determination unit 111 outputs a credit subtraction instruction and a credit subtraction value “3” to the SCC control unit 107.

  When the credit subtraction instruction output from the credit information addition determination unit 111 is received by the SCC control unit 107, the selection instruction unit 401 in the SCC control unit 107 causes the selector 402 to input the selection logic shown in FIG. On the other hand, an instruction to output the value output from the subtractor 404 to the SCC 406 is given.

  In the subtractor 404, “3” that is the credit subtraction value output from the credit information addition determination unit 111 is subtracted from “3” that is the value held in the SCC 406 of the time slot T10 to become “0”. However, since the SCC addition instruction is given from the SCC addition instruction unit 109 at the same time, “1” is added to “0” in the adder 405, and the result “1” is sent to the selector 402. Is output from the selector 402 to the SCC 406 (time slot T11).

  Since the SCC addition instruction unit 109 further receives the packet 1-2, the SCC addition instruction is issued (time slots T11 to T15), and the value held in the SCC 406 is incremented (time slots T12 to T16). .

  The packet 2-1 determined by the credit information addition determining unit 111 that credit information cannot be assigned based on the selection logic shown in FIG. 9 is input to the header correcting unit 110 and “0” is input to the CFLAG 504 in the packet header unit 501. ”Is set, and the packet 2-2 determined that credit information can be added is input to the header correction unit 110,“ 1 ”is set to the CFLAG 504 in the packet header unit 501, and the transmission unit 115 transmits the unit 102. (Time slots T1, T10).

  The packet 2-1 and the packet 2-2 transmitted from the transmission unit 115 in the unit 103 are respectively received by the reception unit 114 in the unit 102, and the packet 2-1 and the packet received by the reception unit 114 are received. 2-2 is output from the reception unit 114 to the NCC subtraction instruction unit 106. When the selection instruction unit 301 in the NCC subtraction instruction unit 106 receives the packet 2-1, the header unit 501 is identified, and it is detected that “0” is referenced with reference to the area of the CFLAG 504. The

  FIG. 10 is a diagram showing selection logic in the selection instruction unit 301 shown in FIG.

  In the selection instruction unit 301, when the header unit 501 is identified and the area of the CFLAG 504 is detected to be “0”, an instruction to output “0” to the credit flit valid flag 303 is sent to the selector 302. Given.

  When the selection instruction unit 301 recognizes something other than the header part 501, the selection instruction unit 301 instructs the selector 302 to output the value of the credit frit valid flag 303, that is, “0” to the credit frit valid flag 303. Given to.

  Similarly, when the packet 2-2 is received in the selection instruction unit 301, the header unit 501 is identified, the CFLAG 504 is detected as “1” by referring to the area of the CFLAG 504, and the credit flit is detected. An instruction to output “1” to the valid flag 303 is given from the selection instruction unit 301 to the selector 302.

  When the selection instruction unit 301 recognizes something other than the header part 501, the selection instruction unit 301 instructs the selector 302 to output the value of the credit frit valid flag 303, that is, “1” to the credit frit valid flag 303. Given to.

  In the credit flit valid flag 303, the output value of the selector 302 is set and output to the invalid flit mask unit 304. In the invalid flit mask unit 304, masking is performed for portions that are not valid flits. Therefore, only the effective flit is given as an NCC subtraction instruction from the NCC subtraction instruction unit 106 to the NCC control unit 104, and during the time slots T15 to T17, the subtraction instruction given from the NCC subtraction instruction unit 106 in the selection instruction unit 201 Accordingly, the selector 202 gives an instruction to output the value output from the subtracter 204. As a result, the value held in the NCC 203 is subtracted by the credit information transmitted from the unit 103.

  If there is no packet to be transmitted in the unit 103, a credit information-dedicated packet describing the value of the SCC is transmitted to the unit 102 at that time, and the NCC 203 of the unit 102 subtracts the number of transmission packet data frits. A method is also conceivable.

  In this embodiment, the case where packet data is transmitted from the unit 102 to the unit 103 has been described as an example. However, the units 102 and 103 include the same components, and the unit 103 to the unit 102 It is conceivable to transmit packet data. In this case, the same processing as described above is performed.

It is a block diagram which shows one Embodiment of the flow control system of this invention. It is a figure which shows the structure of the NCC control part 104 shown in FIG. It is a figure which shows the structure of the NCC subtraction instruction | indication part 106 shown in FIG. It is a figure which shows the structure of the SCC control part 107 shown in FIG. It is a figure for demonstrating the position of the credit information embedded in the packet data transmitted to the unit 102 from the unit 103 shown in FIG. It is a figure for demonstrating operation | movement of the flow control system shown in FIG. It is a figure which shows the selection logic in the selection instruction | indication part 201 shown in FIG. It is a figure which shows the selection logic in the selection instruction | indication part 401 shown in FIG. It is a figure which shows the selection logic of the credit information provision determination part 111 shown in FIG. It is a figure which shows the selection logic in the selection instruction | indication part 301 shown in FIG.

Explanation of symbols

101, 112 Data line 102, 103 Unit 104 NCC control unit 105 NCC addition instruction unit 106 NCC subtraction instruction unit 107 SCC control unit 108 Reception buffer 109 SCC addition instruction unit 110 Header modification unit 111 Credit information addition determination unit 113, 115 Transmission unit 114 Receiving unit 201, 301, 401 Selection instruction unit 202, 302, 402 Selector 203 NCC
204, 404 Subtractor 205 403, 405 Adder 303 Credit frit valid flag 304 Invalid flit mask section 406 SCC
501 Header part 502 Data part 503 Control information 504 CFLAG

Claims (6)

It comprises two devices that transmit and receive packet data on a data line, and the two devices have a reception buffer that temporarily holds packet data transmitted from the other device of the two devices, and the reception buffer A flow control method for notifying the other apparatus of the state of
Each of the two devices is
Information addition determination means for determining whether or not information indicating the state of the reception buffer can be added to packet data transmitted to the other of the two apparatuses;
A flow control method comprising: an adding unit that adds information indicating a state of the reception buffer to one bit of a header in packet data to be transmitted to the other device when it is determined to be possible by the information addition determining unit. The flow control method according to claim 1,
Each of the two devices is
A counter that increments the number of blocks in which the packet data swept from the reception buffer is divided into a plurality of blocks;
The assigning means assigns the count value in the counter to one bit of a header in packet data transmitted to the other device. In the flow control system according to claim 1 or claim 2,
Each of the two devices is
Extraction means for extracting information indicating the notified state of the reception buffer from transmitted packet data;
A counter that increments the number of blocks of packet data transmitted to the other of the two devices, and decrements the number of blocks of packet data swept from the reception buffer based on the information extracted by the extraction means A flow control system characterized by comprising: When packet data is transmitted and received between two devices on a data line, the state of the reception buffer in the device that receives the packet data of the two devices is changed to the device that is the packet data transmission side. A flow control method for notification,
A process of determining whether or not information indicating a state of the reception buffer can be added to packet data transmitted from a device serving as a reception side of the packet data to a device serving as a transmission side of the packet data;
When it is determined that the information can be given, a process of giving information indicating the state of the reception buffer to one bit of the header in the packet data;
And a process of transmitting packet data to which information indicating the state of the reception buffer is added from a device serving as a reception side of the packet data to a device serving as a transmission side of the packet data. The flow control method according to claim 4,
A process of incrementing the number of blocks of the packet data swept from the reception buffer;
And a process of assigning the incremented number of blocks of packet data to one bit of a header in the packet data. In the flow control method according to claim 4 or 5,
A process of extracting information indicating the status of the notified reception buffer from the transmitted packet data;
Increment the number of blocks of packet data transmitted from the device that is the transmission side of the packet data, and based on the extracted information indicating the state of the reception buffer, the number of blocks of packet data swept from the reception buffer And a process of decrementing the flow.

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