JPS6366462B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a priority control system, and particularly to a priority connection control system when a plurality of processing devices are connected via a common transmission path.

When multiple processing devices share the transmission path,
The use of transmission paths, for example, transmission requests, may conflict between processing devices.

Conventionally, a method disclosed in Japanese Patent Application Laid-Open No. 114804/1983 has been known as a method for resolving such conflicts. This method detects a packet collision and starts a timer, sets a random waiting time using a random number, and waits for each terminal device (hereinafter referred to as a "transmitting station" or simply "station").
The system attempts to average out the priorities of each transmitting station by randomizing the waiting time until transmission starts again. This system has a serious drawback in that when packets from multiple transmitting stations collide, all the transmitting stations have to wait a certain amount of time and then try transmitting again, resulting in extremely large loss time.

Figure 1 shows this situation. When packets from two transmitting stations A and B collide, station A receives t _A and station B receives t _B (where t _A < t _B) . .) is given a waiting time. After waiting time _tA , station A tries to transmit again, but station B is forced to wait for waiting time _tB . In this case, both stations must stand by during _tA , causing increased loss time.

Various attempts have been made to overcome this drawback, but the fact is that randomization using waiting time is one-dimensional, and time allocation using randomization requires a large amount of bit time in proportion to the number of transmitting stations. There were some shortcomings. in this regard,
This will be explained in more detail by giving an example.

Fig. 2 shows an example of this, in which packets transmitted from each transmitting station are divided into priority packets and non-priority packets, and priority packets (the number of priority levels is n) and non-priority packets (the number of priority levels are n). (The total number is m.) A waiting time is set for each. According to this method, the non-priority packets start transmitting after _to+r (1rm), and the probability in this case is r/m, which is averaged among the non-priority packets. On the other hand, transmission of priority packets will start after t _p (1 pn) according to a predetermined priority order. In this case, since the priority packets are prioritized, it is not possible for a plurality of transmitting stations to obtain an averaged transmission right between each priority level.

Figure 3 shows the case where multiple priority levels are set and a random waiting time is set for each priority level, and each priority packet has t _(p-1)n+r (m
is the number of packets within one priority level, and n is the number of priority levels. Also, transmission starts after 1pn, 1rm), and transmission rights are obtained that are averaged at each priority level, but there is a drawback that the overall waiting time is longer. In this case, for non-priority packets, t _on+q (however, 1
ql,l is the total number of non-priority packets. ), and the waiting time is even longer.

In addition, as another method, the applicant filed a patent application in 1973.
There is a method proposed in No. 26443. In this system, each transmitting station assigns its own address when transmitting, and the priority order is determined based on the bit structure of the address. This system has the disadvantage that in the event of contention, a transmitting station with an address with a high priority is always given priority, making it difficult to equalize the priorities.

A first object of the present invention is to provide a priority control method that eliminates the above-mentioned drawbacks of the conventional priority control method and makes it possible to give each processing device an averaged transmission right. A second object of the present invention is to provide a priority control system that makes it possible to always give priority transmission rights as needed. Furthermore, a third object of the present invention is to provide a priority control system that enables efficient use of transmission paths.

In order to achieve the above object, the priority control method of the present invention is applicable to each processing unit in a serial data transmission system in which a plurality of processing units are connected via a common transmission path and each processing unit transmits information in packet units. When the device sends out the packet, it adds a special pattern to the beginning of the packet, consisting of a pattern that specifies the priority of the set processing device and a pattern that is determined irregularly, and sends the packet to other processing devices. If a transmission conflict occurs between the competing processing devices, the processing device with the highest priority among the competing processing devices obtains the transmission right by combining the patterns specifying the priorities, and the competing processing devices When there are multiple processing devices with the same priority, any one of the processing devices with the same priority can obtain the transmission right by combining irregularly determined patterns. The feature is that the priorities of processing devices with the same priority are averaged.

Hereinafter, the present invention will be explained in detail based on the drawings.
FIG. 4 is an explanatory diagram showing the principle of the present invention. In the present invention, each of the plurality of transmitting stations (in this case, two stations are called station A and station B) has a unique priority pattern, and this pattern is positioned at the beginning of each packet and transmitted. Ru. Priority patterns are synthesized on the transmission line, and only the station that compares the signal on the transmission line with its own signal and detects a discrepancy immediately stops transmitting. Therefore, the remaining stations (stations with high priority, in this case A)
The station) no longer detects a mismatch during pattern transmission and can continue transmitting. The station that stopped transmitting midway (in this case, station B)
waits until a transmission line becomes available.

The entire priority pattern may be one pattern, but it can be divided into an area for specifying the priority level (F-PR) and an area for randomly specifying the priority each time within a group of equal priority levels. (V-PR), it becomes possible to grant transmission rights with priority as necessary, which is the second object of the present invention. FIG. 5 is a diagram illustrating the processing situation when the priority levels are different between the A station and the B station, and FIG. 6 is a diagram explaining the processing situation when the priority levels are the same. In the following explanation, it is assumed that the signal "1" has priority among the signal "0" and the signal "1" in signal synthesis on the transmission path. When the priority levels are different as shown in FIG. 5, station B detects a discrepancy with the signal on the transmission line at the second bit of F-PR and stops transmitting the third and subsequent bits. Therefore, there is A on the transmission path.
The F-PR of the station is transmitted, and regardless of the content of the V-PR, the transmission of station A will always have priority over that of station B. As shown in Figure 6, if the priority level is the same for both stations A and B, in F-PR transmission, station A and station B
Since neither station detects a conflict with the transmission line data, the station continues to transmit V-PR. V-PR
Station B detects a discrepancy at the second bit and stops transmitting the third and subsequent bits. Therefore, station A is V-
PR does not detect any discrepancy and continues transmission.

In the unlikely event that the priority level is the same and the V-PR pattern is also the same, the priority will be determined by the difference in the source station address (SA in Figure 7) that is subsequently transmitted in the V-PR. .

FIG. 8 is a diagram showing the frame structure of a packet used in the transmission system of the present invention. In Figure 8, SYN is a synchronization signal, F-PR is a fixed priority signal, V-PR is a variable priority signal,
SA is the source station address signal, DA is the destination station address signal, CNT is the control flag, and CK
indicate check bit groups, respectively. F-
If the PR is unnecessary, it can be deleted.

FIG. 9 is a block diagram showing one embodiment of the present invention. When data is sent from the terminal device 1 to the output buffer 2, the output buffer 2 receives the special code pattern (corresponding to the above-mentioned V-PR) sent from the random pattern generation circuit 3 and the priority pattern generation circuit. 4 (the pattern for determining the predetermined priority given by F-PR
corresponds to ) with the transmitter logic stage 5
Each signal is subjected to processing such as parallel-to-serial conversion and sent to a transmission line 7 through a driver 6.

Also, signals from other stations input from the transmission line 7 through the receiver 8 are processed by the receiver logic stage 9, such as serial-to-parallel conversion, and only necessary data is sent to the input buffer 10 and input to the terminal device 1. Ru.

In a transmitting station configured in this way, when a packet collision occurs between the local station and another station, the priority pattern sent from the local station and the transmission path input via the receiver are The signal pattern is determined by the priority discrimination circuit 11.
If a difference is detected between the two bits, a signal is immediately issued to the transmitter logic stage 5 to stop the transmission of the own station. This causes the transmitter logic stage 5 to stop transmitting and the transmitting station enters a standby state. Further, the retry counting circuit 12 is counted up by the transmission stop signal. This count number is taken into consideration when setting a priority pattern (V-PR) that is set when starting a new transmission after waiting is over.

By randomly generating the priority pattern (V-PR) in the random pattern generation circuit 3 for each transmission, it becomes possible to better average the priorities of each transmitting station. Furthermore, when creating the priority pattern, it is also effective for averaging to weight each transmitting station based on the number of retries, etc., as described above.

As described above, according to the present invention, in a serial data transmission system in which a plurality of transmitting stations are connected via a common transmission path, each transmitting station adds a special code pattern for contesting the transmission path at the beginning of the transmitted signal. If there is a transmission conflict with another station, the priority is determined by combining the special code patterns, so the priority of transmission between each transmitting station is determined based on its importance. This method has many advantages, such as being able to perform better averaging and at the same time making efficient use of the transmission path.

[Brief explanation of drawings]

Figure 1 is a time chart showing the conventional method, Figures 2 and 3 are diagrams explaining waiting time, Figure 4 is a time chart showing the method of the present invention, and Figures 5 to 7 are operating conditions. FIG. 8 is a diagram showing the frame structure, and FIG. 9 is a block diagram. 1: Terminal device, 2: Output buffer, 3: Random pattern generation circuit, 4: Priority pattern generation circuit, 5: Transmitter logic stage, 6: Driver, 7: Transmission line, 8: Receiver, 9: Receiver logic Stage 10: Input buffer, 11: Priority discrimination circuit, 12: Retry counting circuit.

Claims (1)

[Claims] 1. In a serial data transmission system in which multiple processing devices are connected via a common transmission path and information is sent in packets between each processing device, when each processing device sends out the packet, the A special pattern for transmission route contention consisting of a pattern specifying the priority of a processing device and a pattern determined irregularly is added to the beginning, and if a transmission conflict occurs with another processing device, the above-mentioned By combining patterns specifying priorities, the processing device with the highest priority among the competing processing devices obtains the transmission right, and when there are multiple processing devices with the same priority among the competing processing devices. , by combining irregularly determined patterns, any one of the processing devices with the same priority obtains the transmission right, and the priorities of the processing devices with the same set priority are averaged. A priority control method characterized by: