JP2615982B2 - Communication error recovery method and device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication error recovery method for a communication error occurring in communication between communication control apparatuses interconnected via a communication line, and an apparatus for realizing the method. It is about.

2. Description of the Related Art Domestic Digital Bus (D2B: Domestic Digital Bus) (IEC 84 (Secretaria
t) 86 1, 2 Draft-Domestic Digital Bus (D2
FIG. 2 shows the communication network configuration in B))). Each communication control unit is composed of a communication control unit and a slave status information unit. The communication control devices are connected to each other via a communication line 5.
The communication control unit transmits and receives a communication frame to and from the communication line 5. FIG. 3 shows a communication frame for transmission and reception. The communication frame includes a mode bit part, a master address part, a slave address part, a control field part, and a data field part with the start bit part at the head. The start bit part indicates the head of the communication frame.
The mode bit indicates the mode of the communication frame, and
mode0, mode1, and mode2 are defined. The transmission speed of the communication frame and the maximum number of transmission data bytes differ depending on each mode, and the communication control device that can receive the communication frame of the higher mode can receive the communication frame of the lower mode. For example, the communication control device that can receive up to mode 2 is mode
0, mode1 communication frames can be received. The master address section includes a master address and a parity bit. The master address indicates a source address of the communication frame, and the parity bit indicates a parity value of the master address. The slave address portion is composed of a slave address, a parity bit, and an ack bit, the slave address is a destination address of the communication frame, the parity bit is a parity value of the slave address, and the ack bit is a destination communication control device that has received the communication frame. Indicates an affirmative / negative (ACK / NACK) response. When the communication control unit in the destination communication control device receives the communication frame normally, the communication control unit acknowledges in the ACK bit part of each field (AC
K). The control field portion is composed of a control field, a parity bit, and an ack bit, the control field is an attribute of the communication frame, the parity bit is a parity value of the control field, and the ack bit is a communication control device that has received the communication frame. Indicates a positive / negative (ACK / NACK) response. The data field portion is composed of data, a Cont / EOD bit, and an ack bit. The data is data to be transmitted by the communication frame, and the Cont / EOD bit is whether the data byte of the data field portion is a continuation / last byte. The parity bit indicates the parity value of the data and the Cont / EOD bit, and the ack bit indicates the affirmative / negative (ACK / NA) returned by the destination communication control device that has received the communication frame.
CK) Indicates a response. FIG. 5 shows the attribute contents indicated by the control field. The control field is made up of 4-bit data, and is divided into those that perform a write operation and a read operation. The write operation indicates that data is written from a source communication control device (hereinafter referred to as a master) to a destination communication control device (hereinafter referred to as a slave). The read operation indicates that data of the slave is read from the master. Slave status reading indicates reading of slave status information which is state information of a unit in the slave, and data reading indicates reading of slave data. The reading of the lock address is used when the slave is locked by another master and when reading the unit address of the locking master. The locking operation will be described later. The writing of the memory address indicates that the memory address is written from the master to the slave. Command writing indicates that a command is written from the master to the slave, and data writing indicates that data is written from the master to the slave. Each CF (Control Field) specifies a lock operation. When no lock operation is performed, there is no lock, when lock is performed, lock is performed, and when lock operation is released, lock is released. Here, the lock operation will be described. FIG. 6 shows a communication sequence for the lock operation. The communication control device 11a performs frame transmission (a) (CF = command writing + lock) to the communication control device 11b. Upon receiving this frame, the communication control device 11b is locked with respect to the communication control device 11a. In this case, the communication control device 11b enters a state in which it does not receive a communication frame other than the communication control device 11a. Accordingly, at this time, if the communication control device 11c performs frame transmission (b) (CF = command writing + lock) to the communication control device 11b, the communication frame (b) is not received. The communication control device 11a transmits a frame to the communication control device 11b (c)
When (CF = command writing + unlocking) is performed, the communication control device 11b is unlocked, and when the communication control device 11c next performs frame transmission (d) to the communication control device 11b, this communication frame Can be received by the communication control device 11b. The slave status information stored in the slave status information section indicates the state of each communication control device, and the contents are shown in FIG. The slave transmission buffer status of b0 indicates that the slave transmission buffer status of the communication control device is empty / mot empty. The slave receive buffer status of b1 is em on the slave receive buffer status of the communication control device.
Indicates pty / not empty. The lock state of the unit b2 indicates whether the communication control device is locked by another communication control device. The implementation state of the memory address of b3 indicates whether the memory is implemented in the communication control device. The slave transmitter state of b4 indicates whether the slave side can transmit data. The mode state of b6 and b7 indicates the highest frame mode in which the communication control device can transmit and receive. In FIG. 2, when each communication control device communicates via the communication line 5, only a specific communication frame may be able to communicate depending on the state of the destination communication control device (slave), that is, the slave status state. If the slave was able to receive normally or if the data of the communication frame was receivable, affirmative (ACK) in each field part of the communication frame
Reply the response to the master. For example, if the slave address value of the communication frame received on the slave side does not match the unit address value of the communication control device, that is, if a communication frame not addressed to the automatic communication control device is received, a negative acknowledgment (NACK) is received in the address field portion. reply. Here, when a negative acknowledgment (NACK) is generated in each field of one communication frame and the communication does not end normally, it is called that a communication error has occurred. FIG. 7 shows an error occurrence condition on the slave side. here
It shows a NACK (negative acknowledgment) generator, its error factor, and the applied CF in the communication frame at that time. Timing errors 1), 4) and 10) show cases where an error has occurred in the reception timing at the time of frame reception. The higher mode 2) indicates a case where a communication frame in a mode higher than the mode that can be received by the slave is received. No slave / down
In the case of 3), the receiving operation is obviously impossible. locking
Error 5) occurs when a slave is locked and a master other than the locking master communicates. Slave receives buffer full6), 11),
In the case of transmission buffer empyu7), slave transmission unit disable
In the case of 8) and no memory 9), a communication error occurs when a communication frame having each CF value is received. In the communication network shown in FIG. 2, the procedure and function of how to recover from the communication error when the above-described communication error occurs are not specified, and the same communication frame is used when the communication error occurs. There was no other way but to resend.

However, in the above-mentioned conventional method, for example, when a communication error occurs due to the down of the partner slave, even if the communication frame is retransmitted, the operation is useless, and the transmission on the communication line is useless. There was a problem of reducing efficiency.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a communication error recovery method for effectively recovering such a problem and a device used for the method.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a communication control unit having a function of performing communication via a communication line as a communication control device, and a slave status information unit for storing slave status information. When a communication error occurs when an arbitrary communication control device A communicates with another communication control device B via the communication line using a device having a communication management unit for managing communication The communication manager A1 in the source communication controller A is the communication manager in the destination communication controller B.
The status of the communication control device B from the slave status information unit B3 in the communication control device B by a communication frame via the communication line and the communication control units A2 and B2 in the communication control devices A and B with respect to B1. The communication management unit A1 reads the slave status information indicated by the communication unit A1, and judges from the content of the read slave status information, performs a process corresponding to the content to the communication control unit A2, and recovers a communication error. Like that.

According to the present invention, for example, when the partner slave is down
If a communication error occurs due to communication, the status of the other slave is read out via the communication line and the other
By detecting that the frame is down, it is judged that it is useless even if the frame is retransmitted at that time, and the frame retransmission operation is stopped. Therefore, an effective error without reducing the transmission efficiency on the communication line You can recover.

Embodiment FIG. 1 shows the configuration of a communication network according to an embodiment of the present invention. In FIG. 1, reference numerals 1a, 1b, and 1c denote communication control devices connected to each other via a communication line 5, and reference numerals 2a, 2b, and 2c denote communication with communication control units of other communication control devices via the communication line 5. The communication control unit, 3a, 3b, 3c performs error recovery processing management when a communication error occurs, and the communication management unit, 4a, 4b, which transmits and receives a communication frame to and from the communication control unit as necessary.
Reference numeral 4c denotes a slave status information section that manages slave status information that is state information of each communication control device.
The error recovery processing sequence performed by the communication
Figures (a), (b), (c), (d), and (e) show. This will be described with reference to the drawings. Fig. 8 (a)
First, a frame is transmitted. It determines whether this transmission was successful, and if it was successful,
Next, it is determined whether or not there is untransmitted data. If data to be transmitted still remains, the untransmitted data is transmitted, and confirmation and transmission of the untransmitted data are repeated up to three times. 3
If all the data can be transmitted in the retransmission operations, the process exits with return information of "normal termination".
However, if all data has not been transmitted even after performing the retransmission operation three times, the process exits with return information of "timing error". When it is determined that the transmission has failed in the first determination of the transmission result, the slave status is read out to the partner slave next. If reading the slave status fails, determine whether the transmission failure was due to a NACK in the address field. If so, lower the mode. Otherwise, check the slave status up to three times in the same mode. The reading and the determination of the transmission result are repeated. If the transmission is not successful in the three retransmissions, one of the retransmission frames
If any ACK bit occurs in the address field, the process exits with return information of "timing error". However, one ACK for all retransmission frames
If no bit is generated, the process exits with return information of "no slave / down". If the slave status reading is successful, the process continues to FIG. 8 (b). From the slave status read in FIG. 8 (b), the mode of the frame that can be received by the slave and the mode of the transmitted transmission frame are compared to determine whether the mode of the transmission frame is appropriate. Mode1 for slaves that can only receive communication frames up to
If you try to send a frame, lower the mode.
Next, when CF = RD + lk or RD + ulk of the transmission frame, it is first determined from the content of the slave status information read earlier whether or not the slave transmitter is disablu, and if so, the “slave transmitter disabl”
The process exits with return information "e". Next, the slave transmission buffer is empty based on the contents of the slave status information.
Then, the process exits with return information “slave transmission buffer empty”. If not, it is further determined from the slave status information whether or not the partner slave is in the locked state.
It continues to figure (d). If the other slave is in the locked state, first, a read of a lock address indicating the address value of the master locking the other slave is transmitted via the communication circuit. If the reading of the lock address fails, the read frame is transmitted up to three times at maximum, and if all fail, the process exits with the return information of the "timing error". If the read of the lock address is successful, the read lock address is compared with its own unit address, and if they match, the process follows the process of FIG. 8D. If they do not match, the process is performed together with the "locking error" return information. Exit. If CF = RD + lk or RD + ulk of the transmission frame, the process continues to FIG. 8 (c). In the case of CF = WD + lk, WD + ulk, WC + lk, WC + ulk of the transmission frame in FIG. 8 (c), it is determined from the previously read slave status information whether or not the reception buffer of the slave is full. If so, the process goes out of the shoulder with the return information of "reception buffer full". If the partner slave is locked from the slave status information, the lock address is read from the partner slave and retransmitted up to three times until the transmission succeeds. If the transmission is not successful even after three retransmissions, the process exits with the return information of "timing error". If the reading of the lock address is successful, the read lock address is compared with the own unit address, and if they do not match, the process exits with the "locking error" return information. If they match, the process of FIG. 8 (e) is continued. If the transmission frame CF is not WD + lk, WD + ulk, WC + lk, or WC + ulk, the processing continues to the processing in FIG. In FIG. 8 (d), if CF = WMA + lk of the transmission frame, the slave reception buffer reads fu from the slave status information read earlier.
ll, and if so, “Receive buffer full
The process exits with the return information of l ". If the slave is locked from the slave status information, the lock address is read from the slave and retransmitted up to three times until the transmission succeeds. If the lock address is not successfully transmitted, the process exits with the return information of “timing error.” If the lock address is successfully read, the read lock address is compared with the unit address, and if not, the “locking error” is detected. If it matches, it is further determined from the slave status information whether or not the partner slave has a memory. If there is a memory, the process continues to FIG. 8 (e). The process exits with the return information of "no memory". CF of transmission frame = WMA + l
If it is not k, the process continues to the process in FIG. In the process of FIG. 8 (e), the frame is transmitted first, and if the transmission fails, retransmission is performed up to three times. If the transmission is not successful after three retransmissions, the process exits with the return information of "timing error". If the transmission is successful, it is determined whether or not there is untransmitted data, and if so, the untransmitted data is retransmitted up to three times. If there is still untransmitted data after three retransmissions, the process exits with return information of “timing error”. If all data has been transmitted, the process ends with return information of “normal end”.

Effects of the Invention As described above, according to the present invention, when a communication error occurs, an effective error recovery can be performed without lowering the transmission efficiency on the communication line, which is extremely practical in practice.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a communication system to which the error recovery procedure of the present invention is applied, FIG. 2 is a block diagram showing one example of a conventional communication system, and FIG. 3 is shown on a communication line. FIG. 1 is a configuration diagram showing one embodiment of a communication frame format to be used.
FIG. 4 is a block diagram showing one embodiment of the contents of the slave status information, FIG. 5 is a block diagram showing one embodiment of the contents of the control field of the communication frame, and FIG. 6 is a clock operation between the communication control devices. FIG. 7 is an explanatory view showing one embodiment of the present invention, and FIG.
FIG. 14 is an explanatory diagram showing one embodiment of a communication error occurrence condition, and FIG.
FIG. 1 is a configuration diagram showing one embodiment of a master processing sequence in the error recovery procedure of the present invention. 1a, 1b, 1c: communication control device, 2a, 2b, 2c: communication control unit, 3a, 3b, 3c: communication management unit, 4a, 4b, 4c: slave status information unit, 5: communication line .

Claims (2)

(57) [Claims] 1. A communication control device comprising: a communication control unit having a function of performing communication via a communication line; a slave status information unit for storing slave status information; and a communication management unit for managing communication. In a communication network connected to individual communication lines, if a communication error occurs when an arbitrary communication control device A communicates with another communication control device B via the communication line, a communication of a transmission source is performed. The communication management unit A1 in the control device A communicates the communication line and the communication control devices to the communication management unit B1 in the communication control device B of the receiving destination.
The communication control unit A reads the slave status information indicating the state of the communication control device B from the slave status information unit B3 in the communication control device B by a communication frame via the communication control units A2 and B2 in the communication control unit A. A1 is a communication error recovery method characterized by determining from the content of the read slave status information, performing a process corresponding to the content to the communication control unit A2, and recovering a communication error. 2. A communication control unit having a function of performing communication via a communication line, a slave status information unit for storing slave status information, and a communication management unit for managing communication. When communication is performed via a line and the communication fails, the communication management unit transmits slave status information from the slave status information unit in the destination communication control device to the communication line and each communication control unit of the communication source and the destination. A communication control unit for performing a process corresponding to the content of the slave status information to the communication control unit to recover a communication error.