METHOD FOR PROGRAM LOADING

Abstract: A system for loading a program in a distributed system including a plurality of information processing units (ll - l5) interconnected by a transmission system (l) comprises an information processing unit for preparing a program and sending the program to the transmission system, another information processing unit having means for receiving the program from the transmission system and storing the program in a memory in accordance with a content of the program, and means for retrieving a program based on program structural information, which program corresponds to the program structural information, and sending the retrieved program to the transmission system, and other information processing units each having means for sending the program structural infor­ mation to the transmission system and means for selecting a corresponding program from the transmission system and loading the selected program in the unit.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a distributed system comprising a plurality of information processing units interconnected by a data transmission system, and more particularly to a method for program loading by coordination of the distributed information processing units. DESCRIPTION OF THE PRIOR ART In a prior art distributed system, when a program is to be loaded to subsystems, a subsystem which developed the program functions as a master station who grasps a memory map of the subsystems to which the program is to be loaded and directly loads the program to them. In conventional communication systems, described in EP-A-0 036 172 for example, a master station transmits a program to a communication station using the address of that station. Accordingly, if the system configuration changes due to memory allocation or expansion or maintenance of the subsystems or stations, the memory or station addresses also change and it is impossible to load the program. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for program loading which permits loading of the latest version of a program to a started subsystem, without requiring a central management device, in a distributed system in which the system configuration changes with maintenance, failure or expansion and the program per se also gradually changes by function enhancement. In order to achieve the above object, the present invention provides a distributed system defined in claim 1, comprising a plurality of information processing units interconnected by a data transmission system, in which: a program is prepared in one of the information processing units and sent to the data transmission system; the program is received in a first information processing unit, a content thereof is checked, and the program is stored in a memory; program structural information of a second information processing unit is sent to the transmission system; based on this program structural information the corresponding program is retrieved and sent to the transmission system; and the corresponding program is selected from the transmission system and loaded to the second information processing unit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an overall configuration of a system; Fig. 2 shows a configuration of an information processing unit which serves as a subsystem; Fig. 3 shows a format of a message which flows on a transmission system; Fig. 4 shows transmission and reception status of the message; Fig. 5 shows a format of a message which uses a program as a data; Fig. 6 shows a format of a file when programs are stored depending on their contents; Fig. 7 shows a program structural information of the subsystem; Fig. 8 shows a format of a start message sent by a started subsystem; Fig. 9 shows transmission and reception status of the message; Fig. l0 shows a format of a start response message sent in response to the start message; and Fig. ll shows a process flow chart at the start of the subsystem. DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is now explained with reference to the accompanying drawings. Fig. l shows an overall configuration of a distributed processing system to which the present embodiment is applied. It comprises a loop transmission system l and a plurality of information processing units ll, l2, --- l5 connected thereto. As shown in Fig. 2, an i-th information processing unit li comprises a transmission system interface 40 which is an interface to a node control processor (NCP) 2 of the loop transmission system, a processor 50, a RAM 60 for storing programs and data of the processor, a ROM 70 which contains structural information of the information processing unit, and an interface to I/O devices such as a disk and terminals. A disk device 20 and a terminal device 30 may be connected to the I/O interface as shown in Fig. 4. The information processing units are interconnected through the transmission system l and there is no master-slave relation among the information processing units and they process asynchronously to each other. Fig. 3 shows a format of a message which flows through the transmission system l. In Fig. 3, numerals l0l and l07 denote flag areas which indicate the beginning and the end of the message, respectively, numeral l02 denotes an area in which a code (FC) indicating a content of a read data field (D) l05 of the message is set, numerals l03 and l04 denote areas for message controlling data SA and DN, and numeral l06 denotes an area for a frame check sequence (FCS). The transmission system reformats the data sent from the information processing unit li through the transmission system interface 40, into the message shown in Fig. 3 and sends it to the transmission line. The message sent to the transmission line circulates through the transmission line through the NCP's on the transmission line, and received by the transmitting NCP and erased thereby. On the other hand, each NCP detects the FC of the message received from the transmission line and compares it with an FC pre-registered in the NCP by the information processing unit. If the received FC matches with the registered FC, the FC and the data D in the received message are sent to the processor 50. If the received message is not the self-sent message, it is sent to the next NCP. In the present embodiment, the processor l5 of the information processing unit is used as a subsystem to which the program developing terminal 30 is connected, and the information processing unit l4 is used as a program editing subsystem which extracts as program from the data flowing through the transmission system, edits it and stores it in the disk. The program loading to the information processing unit l2 is explained below. The operation of the information processing unit l5 to which the program developing terminal 30 is connected (hereinafter it is called a program developing subsystem) is explained. When a new program is developed in the program developing terminal, an input datas FC (input FC), an output data FC(output FC) and a header indicating a program length are added to the program (which is relocatable), and they are sent to the loop transmission system through the I/O interface 80, processor 50 and transmission system interface. When the data is sent, the FC used to the message is a content code FC P which indicates that the content is a program. Even if the input/output FC of the program changes, the content code FC P does not change. Fig. 5 (a) shows a content (FC and a data field) of a message sent to the transmission system when the program developing subsystem develops a program P₁ having FC₁ as the input FC, FC₂ as the output FC and LP₁ as its length. In the present embodiment, the numbers of the input/output data of the programs are one, respectively. When the numbers of the input/output data are more than one, a plurality of input/output FC areas are prepared (Fig. 5 (b)). In sending the program, it is not necessary to know where the information processing unit to which the program is to be loaded is located in the system, but a new program, whenever it is developed, need only be sent to the transmission line. It is the subsystem having the program FC "FC P " registered in the NCP that reads in the program sent to the transmission system. The operation of the information processing unit l4 to which the disk device 20 is connected (hereinafter it is called a program editing subsystem) is now explained. In the NCP to which the program editing subsystem is connected, the FC P which indicates the program has been registered as the FC. Each time the program flows through the transmission system, the program editing subsystem reads it in and stores it on the disk 20. Fig. 6 shows a format of storage. Since the input/output FC is written in the header of the program, the program is stored by using the FC as a key. In the present embodiment, the numbers of the input/output data of the program are one, respectively, but the program is stored by using an input/output FC'S where the number of input/output data are plural as input keys. In Fig. 4, the program shown in Fig. 5 (a) is sent from the program developing subsystem and it is read in by the program editing subsystem and stored on the disk. In Fig. 6, the program just read in is stored on the disk. The operation of the information processing unti l2 to which the program is loaded is now explained. In the ROM 70 of the information processing unit l2, subsystem structural information (Fig. 8) indicating inout/output FC's of the program to be loaded to the RAM 60 in the unit has been written. The information processing unit l2, when it is powered on, sends a subsystem start message to the loop transmission system in accordance with a subsystem structural information (Fig. 7) stored in the ROM 70. Fig. 8 shows the subsystem start message. Since the subsystem structural information includes the input/output FC's for two programs, the number of programs (2) and the input/output FC's for the respective programs are added. The FC of the subsystem start information (FC start) is common to all imformation processing units which are started. The FC of the subsystem start information is registered in the NCP to which the program editing subsystem is connected. When the program editing subsystem receives the subsystem start information, it searches the disk by using the input/output FC attached to the data field as a key. If there is a program having a matching input/output FC, a subsystem start response message shown in Fig. l0 is prepared based on the matched program and its input/output FC, and it is sent to the loop transmission system. The format thereof is shown in Fig. l0. After the information processing unit l2 has sent the start message, it operates in accordance with a flow shown in Fig. ll. After it has sent the start message, it sets a timer and waits for a predetermined time until it receives a start response message (steps 503, 504). If time is out, it increments a start failure counter, and if the number of times of failure reaches three, it sends a start failure message (step 507). If it receives the start response message, it checks whether all of the programs having the input/output FC's designated by the subsystem structural information have been received, and if there is an error, it retries the starting. If it has received all programs having the input/output FC's necessary in its subsystem, it sequentially loads the programs from the start response message (step 5l0). After the loading, all input/output FC's of the loaded programs are registered in the NCP. This is illustrated in Fig. 9. In accordance with the present invention, a desired program can be loaded to a subsystem by the coordination of other subsystems without knowing the system configuration or the location of the program. Accordingly, the expandability and reliability of the program loading are improved. The program developing sybsystem sends the new program whenever it develops and the other subsystems store the latest program. When other subsystem starts, the latest program is sent in accordance with the program structural information. Thus, whenever the subsystem starts, the latest program is loaded to the subsystem. As to a revised version of the program, it is sent from the program developing subsystem to the transmission system and stored in other subsystem. Thereafter, the subsystem whose program should be revised is restarted.

Claims: A method of loading a program in a distributed processing system including a plurality of information processing units (11 to 15) interconnected by a transmission channel (1), comprising the following steps: retrieving a desired program (P₁, P₂) stored in a memory (20) of a first information processing unit (14); transmitting said program (P₁, P₂) retrieved from said memory (20); and loading the transmitted program in a memory (60) of a second information processing unit (12), characterized in that said first information processing unit (14) is any one of said plurality of information processing units (11 to 15) connected to said transmission channel (1), and that the retrieval and/or loading of the desired program (P₁, P₂) is made on the basis of an identifier (FC₂, FC₃, FC₇, FC₆) which is stored with the program (P₁, P₂) and is irrespective of address information. The method of claim 1, characterized in that said identifier (FC₂, Fc₃, FC₇, FC₆) is used to retrieve the desired program from said first information processing unit (14). The method of claim 1 or 2, characterized in that said identifier (FC₂, FC₃, FC₇, FC₆) is used to load said program (P₁, P₂) from said transmission channel (1) into said second information processing unit (12). The method of any one of claims 1 to 3, characterized in that said identifier (FC₂, FC₃, FC₇, FC₆) is an identifier of input and/or output data of the desired program. The method of any one of claims 1 to 4, characterized in that the following steps are carried out prior to the aforementioned steps: storing the program (P₁, P₂) and identifier (FC₂, FC₃, FC₇, FC₆) in the memory (20) of the first information processing unit (14); transmitting a message from an information processing unit (12) including the identifier (FC ST , FC₂, FC₃, FC₇, FC₆) referring to the program to be loaded into the second information processing unit (12). The method of claim 1, further comprising the steps of: generating a program (P₁) in any one (15) of the information processing units (11 to 15); transmitting said program (P₁) and its identifier (FC P ); receiving said program (P₁) and its identifier (FC P ) at the first information processing unit (14); checking the identifier (FC P ) of said program (P₁); selecting the program (P₁) having an identifier (FC P ) corresponding to a specific identifier (FC P ); storing the selected program (P₁) in a memory (20); and performing a processing which is requested for execution of said stored program (P₁). The method of claim 6, wherein said processing step includes a step for registering information including the identifier (FC P ) referring to said stored program (P₁).

Inventors: KASASHIMA, HIROKAZU, KAWANO, KATSUMI, KOIZUMI, MINORU, MORI, KINJI, NAKAI, KOZO, ORIMO, MASAYUKI, SUZUKI, YASUO
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: G06F9
IPC codes: G06F13, G06F9, G06F15