Abstract: In order to provide communication between two processors in a data processing system, 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 interprocessor command or instruction 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.

Abstract: A multiprocessor computer system includes a number of processors, each processor having an interrupt mechanism and connecting in common to a system bus over which interrupt requests are communicated. When a processor accepts an interrupt request from another processor, it generates an acknowledge response on the system bus. If such processor contains a previous and pending interrupt request of an equal or higher priority level, it generates a not acknowledge response on the system bus and refuses the interrupt request. At the completion of servicing an interrupt request, each processor places on the system bus, an interrupt completed command including an address identifying such processor, a code designating a priority level to which it has switched and a code indicating that the processor has completing servicing an interrupt request.

Abstract: A bus interface priority network provides access to a system bus by a plurality of different types of requestors as a function of the types of transactions they are required to process. The network includes programmable circuit for identifying the type of requestor and selecting a delay for accessing the system bus on the basis of requestor type thereby eliminating the need to adjust timing to the slowest requestor.

Abstract: A multiprocessor computer system having a first processor having a first interrupt mechanism for generating interrupt requests, a second processor having a second interrupt mechanism, and a system bus for communicating interrupt requests from the first processor to the second processor. The second interrupt mechanism is responsive to an interrupt request by generating an acknowledge response on the system bus when the second processor accepts the interrupt request and generating a not acknowledge response on the system bus when the second processor contains a previous and pending interrupt request of higher level and refuses the interrupt request. The second interrupt mechanism is responsive to the completion of servicing of an interrupt request by the second processor by placing on the system bus an interrupt completed command, which includes an address identifying the second processor and a code indicating that the second processor has completing servicing an interrupt request.

Abstract: A data processing system includes a system management unit, a number of central subsystems, a main memory and a number of peripheral subsystems all coupled in common to a system bus. Any subsystem may generate a command which includes a first field specifying a destination subsystem, a second field specifying the operation the destination subsystem is to perform. If a response is required, the subsystem generating the initial command may specify a third subsystem for receiving the response command.

Abstract: A multiprocessor computer system includes first processors, second processors, a system management means for performing system management functions, including detecting pending power shut-downs and sending power shut-down messages addressed to each of the first processors warning of pending power shut-downs, and a system bus for communication between the first and second processors and the system management means, including the communication of pending power shut-down messages. The first processors include interrupt handling means responsive to pending power shut-down messages for executing power shut-down routines for placing the first processors into a known state before power termination, but the second processors inherently do not include a power shut-down capability.

Abstract: A data processing unit includes a number of tightly coupled central subsystems, a number of peripheral subsystems, a main memory and a system management facility all coupled in common to a system bus. The system management unit has top priority on the system bus and includes centralized resources which provide apparatus for indicating the status of power and temperature, booting the subsystems, testing the subsystems, timing central subsystem functions, and allowing local and remote maintenance access to the subsystems. The system management facility receives commands from the central subystem to read from and write into the timers as well as to read the status of the overall system. The system management facility generates special commands to the central subsystem to indicate when the timers have decremented to ZERO as well as special commands to aid in hardware and software debugging.

Abstract: A multiprocessor system includes a plurality of central subsystem (CSS) units, a plurality of memory units and input/output units which connect in common to a system bus for transferring requests between a pair of units on a priority basis defined by a distributed bus priority network included as part of the system bus. A private bus (P bus) connects all of the CSS units and memory units in common for high speed block data transfers. Each CSS unit includes input circuits which couple to the priority network for detecting when the system bus is in an idle state. P bus logic circuits couple to the P bus and generate a transfer request in response to a request from its CSS unit only when the P bus is detected to be in an idle state. The idle signals from both buses are used to generate a system bus request for P bus access only when both buses are in an idle state so as to eliminate the need to contend for system bus use.

Abstract: A multiprocessor system includes a plurality of identical central subsystem (CSS) units, a plurality of memory subsystem units and input/output units which connect in common to a system bus. Requests are transferred between a pair of units on a priority basis defined by a distributed bus priority network included as part of the system bus. Each CSS unit includes cycle stealer logic circuits which grant bus cycles on a round robin basis. The cycle stealer logic circuits are connected to receive high priority request signals from the network and refuse acceptance of a cycle granted to such CSS unit as a low priority requester thereby passing it along to a next lower priority CSS unit.

Abstract: Memory retry logic to improve the resilience of system memory operations with respect to system errors or faults which prevent a memory read operation from being completed on a first attempt by allowing the memory to retry the operation once. The memory retry logic detects the occurrence of an improper response from the system element requesting a memory read operation when attempting to initiate the system bus operation for reading the data from memory to the requesting element and, if an improper response indicating that the requesting element is not accepting the bus operation request is detected, stores the memory operation request and the requested data and retries the data transmission on the next available bus cycle. If the memory receives an improper response of a specified type during a bus operation of a memory burst, the memory will terminate the operation and proceed to the next requested operation.

Abstract: A means for ascertaining the health, or basic operational status, of a system unit. A "health check" provides an indication of either "yes", the system unit is operational, or "no", the system unit is either inoperative or there is a question as to whether the system is operational. The test is performed by requesting that the system unit perform a high priority "short" operation and noting the response provided to the request; the actual execution of the request is unimportant and it is the response of the unit under test to the receipt of the request for a bus operation that is the actual indicator of the status of the unit being tested. The requested operation is not directed at the unit whose operational status is to be determined, but instead at a bus interface unit which performs bus operations for the unit to be tested and whose responses to requests for bus operations are effected by the operational status of the unit that is to be tested.

Abstract: A method and apparatus for resetting memory state when power is applied to the system. The memory has memory elements, a refresh clock and a refresh counter for counting refresh cycles and providing refresh signals to the memory elements, the memory elements and refresh means being connected from the power system and from a battery back-up means. A state detection means is connected from the refresh counter for detecting a change in state of the refresh counter to a state equivalent to the reset state of the refresh counter and asserting a state change signal. A means responsive to the state change signal and to the occurrence of the reset signal provides a memory controller reset signal, so that the memory controller reset signal occurs in synchronization with the change of state of the refresh counter to a state equivalent to the refresh counter reset state.

Abstract: The pipelined central processing system (CSS) units of a multiprocessor system are tightly coupled to connect in common to a system bus for sharing main memory and input/output controllers/devices. The CSS includes several circuit boards for the different VLSI circuit chip pipelined stages and associated control circuits in addition to the bus interface unit (BIU) circuits. Each board includes one or more unusual event (UEV) detector circuits for signaling when the behavior of a stage is abnormal. The UEV fault signals from each board are collected by the BIU board. When a UEV fault is detected, the BIU board circuits prevent any further communications with the system bus and broadcasts the UEV fault signal to the other boards causing the different pipelined stages to emulate the completion of the instructions within the pipeline thereby flushing it. It is thereafter placed in a nonpipelined mode.

Abstract: A multiprocessor system includes a plurality of identical central subsystem (CSS) units, a plurality of memory and input/output (I/O) subsystem units which connect in common to an asynchronous bus system. Each CSS subsystem unit includes a cancel command mechanism for enabling each such unit to effectively withdraw from the asynchronous bus or switch the state of a resource such as a memory or I/O lock mechanism included in such subsystem without otherwise disturbing the state of such subsystems.

Abstract: A multiprocessor system includes a system management facility (SMF) unit, a plurality of central subsystem (CSS) units, a plurality of memory subsystem units and first and second pluralities of input/output units which connect in common to a system bus. Requests are transferred between a pair of units on a distributed bus priority network included as part of the system bus on the basis of the unit's physical position on the bus relative to one end of the bus. The SMF unit positioned at the high priority end of the bus includes fast recovery bus request logic circuits which connect to the high priority request line of the priority network. Each of the CSS units positioned after the SMF unit on either side of the memory subsystems includes bus request logic circuits which connect only to the low priority request line. The memory subsystems each include bus request logic circuits which connect to both the high and low priority request lines for accepting and granting cycles from higher and lower priority units.

Abstract: A plurality of units which are coupled to transfer requests, transfer data over an asynchronous bus network during allocated bus transfer cycles. The network has a tie-breaking bus priority network which is distributed to a common interface portion of each of the plurality of units and grants bus cycles and resolves simultaneous requests on a priority basis. At least one unit includes bus saturation detection apparatus included within its common interface portion for monitoring bus activity over established intervals of time. The detection of the occurrence of at least one available cycle over the given interval of time signals that the bus network is not in a saturated state. When the indicator specifies that the bus network is saturated, the unit throttles down its operation by increasing the amount of time between issuing data requests. Throttling continues until the bus is no longer being saturated.

Abstract: A multiprocessor data processing system includes a processing unit which, together with other processing units, including input/output units, connects in common to an asynchronous bus network for sharing a main memory. At least one processing unit includes a synchronous private write through cache memory system which includes a main directory and data store in addition to a bus watcher and a duplicate directory. The bus watcher connects to the asynchronous bus network and captures all main memory requests while the duplicate directory maintains a copy of the cache unit's main directory. Independently and autonomously synchronously operated tie-breaker circuits apply requests to the main and duplicate directories. When tie-breaker circuits detect conditions relating to a request which could result in cache incoherency, it initiates uninterrupted sequences of cycles within the corresponding cache main or duplicate directory to complete the processing of that same request.

Abstract: A synchronizing apparatus couples two independently operated bus systems, each bus system capable of generating asynchronous control signals for controlling the states of all of the units within the entire system. The apparatus includes a pair of synchronizer storage elements, each connected to receive, store, and transmit an asynchronous control signal from one of the bus systems to the other bus system. The synchronizer elements are connected to receive a set of complementary clocking signals from a timing source. Both synchronizer elements are interconnected so that by decoding the internal states of such elements only one of the control signals will be transmitted when both synchronizer elements simultaneously receive control signals from both buses thereby ensuring reliable operation throughout the entire system.

Abstract: A central subsystem of a data processing system includes a writable control store which is loaded with firmware to control the central subsystem operations. The central subsystem logic is responsive to a sequence of commands from a system management facility to load the control store and verify that the control store firmware is loaded correctly.

Abstract: A data processing system includes a plurality of units including a bus interface unit (BIU), each of which couple in common to different positions along an asynchronous common system bus. The BIU couples to a plurality of local units which connect to a high speed local bus. The asynchronous common system bus includes a distributed tie-breaking network which consists of a plurality of like priority network sections. The BIU includes a priority resolver which incorporates the priority network section having the highest priority access to the asynchronous bus. The priority resolver includes a local priority resolver circuit for resolving priorities between local requestors within a minimum amount of time. The priority network section and local priority resolver circuit are interconnected so that the signal generated by the network section request circuits to request use of the asynchronous bus is applied to the local priority resolver circuit and to the common bus at the same time.