Apparatus and method for interprocessor communication

Abstract: In order to provide communication between two processors in a data processing unit, a target processor includes apparatus that can store data signal groups from a source processor. Having stored a data signal group from the source processor, the target processor notifies the source processor of the receipt of the data signal group. In response to the presence of the stored data signal group, the target processor executes a command identified by the transferred data signal group. The source processor at a preselected time, executes an instruction to determine if the command designated by the data signal group stored in the target processor has been executed. The commands specified by the transferred data signal groups can be executed under hardware control by the target processor in a relatively short time immediately following completion of the instruction in execution in the target processor at the time of the transfer of the data signal group. The interprocessor communication has only a minor impact on the performance of the source processor and the target processor because of the command implementation by apparatus.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to data processing systems and, more particularly, to the communication between components of the data processing system, the components each having signal processing capability. 2. Discussion of the Related Art As the complexity of the modern data processing systems has increased, the problems involved with the communication between processing components has similarly increased. However, the need for this interprocessor communication has expanded. In the multiprocessor and multiprogrammed data processing environment, the exchange of information or the sharing of processing activity among system components is frequently required and the coordination of these activities results in the requirement for a protocol to provide the information between the processors. As an example of interprocessor communication, reference is made to the published European patent application EP-A-154 551 which describes an apparatus for enabling a first processor to cause a second processor to effect a transfer of data between the processors in accordance with data transfer commands sent from the first processor to the second processor. While this reference deals with the transfer of data between a pair of processors it is not possible to have one processor controlled through the direct transfer of commands from another processor. In the European published patent application EP-A-167 454 a data processing system for controlling transfer of commands between a plurality of processors is disclosed including a single control unit which is connected to all the processors by separate information transfer lines instead of a common bus to which the different processors are coupled. The control unit selects the source processor generating a command transfer request signal and receives the target processor address from the source processor. Thus, the target processor and predetermined transfer information are determined in accordance with the selected source processor. The predetermined transfer information is transferred to the target processor via an information transfer path which is established between the source and target processor by the said control unit. In another example of interprocessor communication, a processor can have a content addressable memory associated therewith to facilitete address translation. In the multiprocessor system, the contents of the content addressable memory associated with each processor cannot be inconsistent. Inconsistencies can result in data processing system errors. When a first (source) processor performs a process that results in the change or invalidation of the contents of the content addressable memory associated with the first processor, then the contents of a content addressable memory of the second (target) processor equivalent to the changed or invalidated memory contents of the first processor must be similarly changed or invalidated. In order to provide this communication, the related art provides a potential target processor with storage apparatus, wherein a source processor can store signals indicative of the requirement for communication with the target processor by the source processor. The source processor stores signals representing the communication desired between the two processors in a predetermined location in main memory, typically referred to as the processor mailbox, and transfers signals to the storage apparatus in the target processor. The target processor, according to a prearranged protocol, reviews the storage apparatus, and when a signal is found in the storage apparatus, the target processor retrieves the contents of a location in its mailbox. The contents of the mailbox identify the activity that the source processor is requesting the target processor to perform. This procedure for interprocessor communication may have a significant impact on the performance. The target processor must first identify the presence of a a communication request, must stop the current processing activity and call upon a software procedure to retrieve the contents of the mailbox, interpret the contents of the stored request and perform the activity indicated by the mailbox file contents. In addition, the source processor may suspend other activity in order to determine whether the activity requested by the source processor has been performed. A need has therefore been felt for apparatus and method that would provide for interprocessor communication by minimizing the impact on system performance. Objects of the Invention It is therefore an object of the present invention to provide an improved data processing system. It is yet another object of the present invention to provide apparatus and method for communication between processing components of the data processing system. It is still another object of the present invention to permit execution of a command generated in a first processor by a second processor without intervention of a software program in the second processor. It is a still further object of the present invention to provide for interprocessor communication in a data processing system that reduces the impact of the communication on the performance of the data processing system. Summary of the Invention The aforementioned and other objects are accomplished, according to the present invention, by providing apparatus and method as set out in claims 1 and 6, respectively using a target processor that can receive and store a command transmitted by a source processor via a system bus. The source processor receives a signal from the target processor when the command is stored in the storage apparatus. When the command is stored in the apparatus of the target processor, a status signal is generated in the target processor. When the target processor completes execution of the current instruction, the status signal causes the command stored in the target processor to be executed. After execution of the command, the target processor continues the instruction sequence in progress at the time that the command was entered in the target processor apparatus. The transferred command, in the preferred embodiment, can result in two types of activity in the target processor. The first type of activity is a modification of control data stored in the target processor, i.e. modification of data relating to address translation. The second type of activity is the performance of a function requested by the source processor, i.e. execution of the request stored in the target processor mailbox. The source processor can examine the main memory location, altered as a result of the data command transmitted to the target processor, to ascertain that the command has been executed. These and other features of the present invention will become apparent upon reading of the following discussion along with the drawings. Brief Description of the Drawings Figure 1 is a block diagram of a data processing system capable of utilizing the present invention. Figure 2 is a block diagram of a processor of a data processing system illustrating components used in the implementation of the present invention according to the preferred embodiment. Figure 3 is a flow diagram illustrating the communication between processors according to the present invention. Figure 4 is a diagram illustrating the format of the data signal groups associated with the transferred command that are transferred between the source processor and the target processor on the address lines of the system bus. Figure 5a, 5b and 5c illustrate the format of data signal groups associated with the transferred command that are transferred on the data lines of the system bus. Figure 6 illustrates the organization of main memory locations associated with each processor that supports the operation of the present invention. Figure 7 is a diagram illustrating the execution of the transferred command in relation to other data processing system activity. Description of the Preferred Embodiment 1. Detailed Description of the Figures Referring now to Fig. 1, a data processing system capable of advantageously utilizing the present invention is shown. The data processing system includes at least two processors (illustrated by processor 10 and processor 11, a main memory unit 15, at least one peripheral interface units (illustrated by peripheral unit 12 and peripheral unit 13) and a system bus 19. In the data processing system illustrated in Figure 1, the main memory unit stores the data signal groups to be manipulated by the processors. During initialization of the system, The storage space on the main memory unit 15 is divided into a multiplicity of regions, each storing preidentified logic signals. In addition, the main memory unit has certain regions reserved for control data, the control data being accessible to the processors. The use of a common main memory unit for a plurality of processors is described as a "tightly coupled" system. Referring next to Figure 2, components of the processors relevant to the present invention are shown. The processor includes a system bus interface unit 21 that senses all the data (logic) signal groups applied to the system bus. The logic signals applied to the system bus include information designating the target component to which an associated data signal group is to be applied within the target processor. The system bus interface unit 21 includes the apparatus for identifying when signals applied to the system bus 19 are to be transmitted to the processor with which the interface unit is associated. The system bus interface unit 21 also includes apparatus for applying a signal, communicating to the source processor that the target processor has received the logic signals, on line 29 to the system bus 19. This signal is generally referred to as the "acknowledge" signal. The data signals from the source processor are stored in a storage apparatus 22. Associated with the storage apparatus 22 is a storage cell 24, such as a register cell, that causes a signal to be applied within the target processor indicating that a data signal group is stored in the storage apparatus 22. The applied signal further indicates to the target processor that signal group stored in the register 22 is a command. The signals in the storage apparatus 22 are applied to decode logic 24. The signal from storage cell 23 is applied to switch 27. The output signals from switch 27 are applied to the decode logic 24 and to the processor instruction register 25. Output signals from the decode logic 24 are applied to a content addressable memory 26 and to interrupt apparatus 28. The interrupt apparatus 28 applies signals to the system bus interface unit 21 and the decode logic 24 applies signals to the system interface unit 21. Referring once again to Figure 2, the processor is shown as having a content addressable memory included therein. In the preferred embodiment, each processor includes two content addressable memories, one content addressable memory associated with data segments and one content addressable memory associated with data pages. The content addressable memories are used to translate a symbolic address used by a program executing in a processor to a physical address designating a location in the main memory unit. An appropriate command in storage apparatus 22 can invalidate a selected location or all the locations in a content addressable memory. Referring next to Fig. 3, a flow diagram illustrating communication between two processors is shown. After the source processor identifies the requirement to communicate with the target processor in step 301, a software lock is set in the operating system to prevent simultaneous communication by two processors in step 302. The source processor, for selected interprocessor communication sequences, prepares and stores data files in a predetermined main memory unit location, i.e. the target processor mailbox, in step 303. In step 304, the source processor executes the interprocessor instruction, the instruction then transfers the command to the target processor in step 305. In step 305, the target processor acknowledges the receipt of the command after the transfer has taken place. If the acknowledge signal is not received, in step 307 the source processor once again attempts to transfer the data signal group to the target processor via step 305. When the transfer of the data signal group is successful, then the source processor continues with the current instruction sequence execution. This instruction sequence execution continues until a preselected activity and then performs the testing of the indicia in step 310. The target processor, after completion of the execution of the current instruction or instruction sequence, executes the command in step 308 identified by the transferred data signal group. In step 309, the target processor establishes an indicia available to the source processor indicating completion of the activity, i.e. execution of the transferred command. At a later period of time, the source processor tests, in step 310, the indicia set by the target processor to determine if the command designated by the transferred data signal group has been executed. Referring next to Fig. 4, the format of the portion of the command transferred from the source processor to the target processor on the address lines of the system bus is shown. The logic signal group is 16 bits in length. Bits 0 through 9 specify the identification number of the target processor. Bits 10 through 15 specify the function to be performed by the target processor. These functions include (0) flush the segment content addressable memory, (1) flush an entry in the segment content addressable memory, (2) flush the page content addressable memory, (3) set activity flag and place an entry in the interrupt queue and (4) flush an entry in the page content addressable memory. Referring to Figure 5a, 5b, and 5c, portions of the transferred command transferred over the data lines of the system bus is shown. For functions 0 and 2, wherein the entire contents of a content addressable memory are invalidated, no additional information is needed. When the function requested by the source processor is (1) or (4), i.e. flush an entry in the segment or page content addressable memory, then the format of the second data signal group is shown in Fig 5a and 5c respectively.. In Fig. 5a, data signal group, the bits in positions 2 through 11 specify the particular entry in the segment content addressable memory to be flushed. The data signals transferred in Fig. 5a and 5c are available to the source processor in software visible registers. In Fig. 5c, the designation of the particular page descriptor requires two signal groups, the page descriptor identified by positions 4 through 15 in the first signal group and positions 16 through 22 in the second data group. As shown in Fig. 5b, when the function code (3) is transferred, in the associated signal group transferred over the data lines of the system bus, bits 0 through 9 identify the source processor while bits 10 through 15 designate the interrupt level. The interface unit includes apparatus to interpret the function code to determine if the data lines have logic signals applied thereto that are relevant to the process identified by the function code. Referring next to Fig. 6, an organization of the memory locations in main memory associated with each processor supporting the present invention is shown. At the time of initialization of the system, the operating system allocates a group of memory locations 61 to a selected processor. The memory locations associated with each processor has allocated therein particular memory locations reserved for specified type data. In particular, a plurality of locations 62 are reserved for activity flags. Similarly, a plurality of locations in the group of main memory locations associated with each processor are reserved as the mail box and store messages and requests from other processors. Referring to Fig. 7, a diagram illustrating the operation of the present invention is shown. The target processor executes a series of instructions 71, i.e. by loading the instruction register. At some point, the source processor executes the interprocessor instruction and transfers command 72 to the target processor. The completion of the command transfer will typically occur during the execution of a current instruction. After the current instruction has been executed, the target processor will execute the command 73 stored in storage apparatus 22. The target processor will then execute the next instruction in the sequence. 2. Operation of the Preferred Embodiment In the present invention, interprocessor commands that can be executed by apparatus (hardware) are chosen. In addition, the interprocessor commands are chosen so that if the apparatus for non-software execution is not available, the apparatus can be added without excessive additional design complexity and without unacceptable additional apparatus. The content addressable memory location invalidation and a portion of an interrupt command are two interprocessor commands implemented in the preferred embodiment, however other commands can be similarly processed by the present invention. The present invention permits a greater independence of operation between the processors. This independence is achieved by selecting certain activity for use with the present invention. In particular, the preferred embodiment involves two types of interprocessor communication. In the first type of communication, the source processor informs the target processor that a certain address identified by the contents of a content addressable memory is no longer valid. The command transferred to the target processor then invalidates the address(es) designated by the source processor in the content addressable memory. In the second type of communication, the source processor requires that the target processor gain access to data signal groups in the processor mailbox, for example, to execute a routine or program under the control of the source processor. In this communication, the source processor transfers the request to the target processor mailbox for use by the target processor. The command transferred to the target processor in this second type of communication indicates the type of activity, i.e. the data groups in the main memory to be used by the target processor, and the priority level of the activity requested by the source processor. The designation of the priority level provides for an orderly execution of activity by the target processor and eliminates inappropriate interruption of activity by a lower level process. In either type of communication, apparatus has been added to the processors so the transferred command can be executed by the target processor without software intervention. The presence of a signal in the storage cell 23 prevents the instruction register from executing the next instruction until the command stored in storage apparatus 22 has been executed. appropriate decoding apparatus has been added to the processors so that a content addressable memory can have either a selected or the entire contents invalidated. With respect to the command related to the request stored in the processor mail box, the interrupt apparatus 28 tests the priority of the currently executing program against the priority of the request in the mailbox while simultaneous loading appropriate activity flags and priority designation in the main memory location group associated with the target processor. When the request priority is higher than the currently executing program, then a full interrupt is executed by the processor and the request in the mailbox will be executed next by the processor. If the priority of the request is lower than the priority of the currently executing program, then the currently executing program will continue in execution. When the source processor originally transfers the data signal group, the receipt of the "acknowledge" signal permits the source processor to execute other instructions. According to the prior art, the operation of the source processor would be interrupted until confirmation that the requested operation was completed. In the current invention, the source processor is free to execute other instructions after the identification of the "acknowledge" signal. The source processor does examine the contents of selected locations in the main memory to insure that the requested operation has in fact taken place. But this examination can take place after other processing by the source processor, permitting more independent operation. After execution of the invalidation of the contents of a location or locations in a content addressable memory, the command provides that an appropriate activity flag be set in a predefined location in main memory in order that the source processor can insure that the command has been executed. With respect to the command related to the processor interrupt, the command requires that activity flags, processor identification numbers and priority levels be stored in selected predefined main memory locations. The source processor can interrogate those locations to determine in the command has been executed, so no independent signal need be set in the main memory to indicate completion of this command. It will be clear that the apparatus added to implement the command transferred by the interprocessor instruction can be used by any processor in execution of internal activity, i.e. invalidating content addressable memory contents. Although the invention has been described in relation to the communication between processors, it will be clear that in the modern data processing systems many system components are being designed with logic signal manipulation capability. The technique described can be used for improved communication between any of the system components with appropriate processing capability.

Claims: Data processing system of the type in which a plurality of processors (10, 11) are coupled to a system bus (19) for interprocessor communication of signal groups along said bus wherein a source processor executes an interprocessor instruction and transfers the ensuing command (72) to a target processor, such processor comprising an interface unit (21) for receiving from external and for storing command signal groups, said processor comprising a first execution apparatus (25, 26) for the processing of data signal groups in response to instruction signal groups which are the native commands of said processor, and further characterised by: a second execution apparatus (22, 23, 24, 27, 28) coupled to a portion of said first execution apparatus (25, 26) and responsive to said command signal group stored in said interface unit (21) for performing an operation on said coupled portion of said first execution apparatus, said operation being determined by said command signal group, said second execution apparatus enabling pre-processing of said command and generation of a signal to inform said processor that a command signal group has been received from external and stored in said interface unit, said enabling and generation occurring while said first execution apparatus is concurrently processing data signal groups. Data processing system according to claim 1, wherein each processor can function as source processor as well as target processor in that each processor of said plurality of processors is characterized by comprising said first execution apparatus, said interface unit and said second execution apparatus. Data processing system according to claim 2, wherein the provision of the said two execution apparatuses enables the source processor which is in the interprocessor command sending mode to continue its instruction execution and the target processor to complete execution of the current instruction (71) before execution of the command (73) which is stored (22) in said second execution apparatus commences (Fig. 7). Data processing system according to claim 3, characterized in that the said processor comprises means for applying completion indicia to said system bus indicating to the source processor completion of execution of the transferred command by said target processor. Data processing system according to claim 2, characterized in that the interface unit of said processor applies a suspend signal (72) to said first execution apparatus of the target processor to cause said first execution apparatus to suspend execution of the native commands (71) until said predetermined operation (73) performed by said second execution apparatus has been completed, whereby operation of said first execution apparatus is suspended only after completion of the native command (71) currently being executed by said first execution apparatus (Fig. 7). Method for use in a data processing system of the type in which a plurality of processors (10, 11) are coupled to a system bus (19) for permitting a source processor to control the operation of a target processor which executes a series of instructions (71), and wherein the source processor executes an interprocessor instruction (72) whereupon a command is transferred (step 305) to the target processor, characterized by the following combination of sequential steps: identifying each of a plurality of pre-established conditions in said source processor and generating a command signal group in said source processor in response to each one of said pre-established conditions, said command signal group being determined by said one pre-established condition; applying said command signal group to said system bus (19) and retrieving said command signal group from said system bus (19) by said target processor; storing said command signal group in an interface unit (21) of said target processor and thereby enabling in a second execution apparatus (22, 23, 24, 27, 28), coupled between the interface unit and a selected portion of a first execution apparatus (25, 26) of said target processor, the pre-processing of said command signal group and the generation of a signal to inform said processor that a command signal group has been stored in said interface unit, while said first execution apparatus is concurrently processing data signal groups; suspending the processing of instructions (71) of said first execution apparatus in response to said command signal group after completion of execution of the current instruction; performing a predetermined operation (73) on said selected portion of a first execution apparatus (25, 26) of said target processor in response to said pre-processed command signal group; and the source processor which is in the interprocessor command sending mode, continuing with the current instruction execution. Method according to claim 6, characterized in that said command signal group is accompanied by an address signal group which identifies said target processor and that retrieval of said command signal group from said system bus (19) by said target processor is in response to said address signal group. Method according to claim 6, characterized in that the said source processor continues with the current instruction execution upon receipt of an acknowledgement signal from the target processor which indicates successful transfer of said command signal group from the source to the target processor. Method according to claim 8, characterized in that the said source processor continues with the current instruction execution until a predetermined activity state and then performs the testing of indicia (step 310) established (in step 309) by the target processor and made available to the source processor for putting the source processor into said activity state, said indicia indicating completion of the execution of the transferred command by the target processor.

Inventors: BARLOW GEORGE J, GEYER JAMES B, MORGANTI VICTOR M, PRANGE PATRICK E, BARLOW, GEORGE J., GEYER, JAMES B., MORGANTI, VICTOR M., PRANGE, PATRICK E.
Applicants: BULL HN INFORMATION SYST, BULL HN INFORMATION SYSTEMS INC.
Application year: 1987
Main classification: G06F15
IPC codes: G06F15